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Interspecific competition of fall armyworm Spodoptera frugiperda (J.E. Smith) parasitoids, Chelonus insularis (Cresson), Cotesia marginiventris (Cresson) and Microplitis manilae Ashmead (Hymenoptera: Braconidae)

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Title:
Interspecific competition of fall armyworm Spodoptera frugiperda (J.E. Smith) parasitoids, Chelonus insularis (Cresson), Cotesia marginiventris (Cresson) and Microplitis manilae Ashmead (Hymenoptera: Braconidae)
Alternate title:
Spodoptera frugiperda
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Rajapakse, Rohan Harshalal Sarathchandra
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xi, 147 leaves : ill. ; 28 cm.

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Armyworms ( jstor )
Eggs ( jstor )
Female animals ( jstor )
Instars ( jstor )
Larvae ( jstor )
Oviposition ( jstor )
Parasite hosts ( jstor )
Parasitism ( jstor )
Parasitoids ( jstor )
Species ( jstor )
Dissertations, Academic -- Entomology and Nematology -- UF
Entomology and Nematology thesis Ph. D
Fall armyworm -- Biological control ( lcsh )
Miami metropolitan area ( local )
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bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

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Thesis:
Thesis (Ph. D.)--University of Florida, 1985.
Bibliography:
Includes bibliographical references (leaves 134-145).
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Also available online.
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Typescript.
General Note:
Vita.
Statement of Responsibility:
by Rohan Harshalal Sarathchandra Rajapakse.

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INTERSPECIFIC COMPETITION OF FALL ARMYWORM
SPODOPTERA FRUGIPERDA (J.E. SMITH) PARASITOIDS,
CHELONUS INSULARIS (CRESSON), COTESIA MARGINIVENTRIS
(TCRESSNT)ATTD MICROPLITIS MANTAE ASHMEAD
(HYMENOPTERA: BRACONIDAE)









By

ROHAN HARSHALAL SARATHCHANDRA RAJAPAKSE









A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY





UNIVERSITY OF FLORIDA

1985











ACKNOWLEDGEMENTS



I am grateful to Dr. Van H. Waddill, chairman of my

supervisory committee, for his advice, encouragement and

guidance throughout the experimental work and preparation

of this dissertation. I am also indebted to him for

providing me financial support to pursue my studies at the

Department of Entomology and Nematology, University of

Florida.

I would like to express special thanks to Dr. Tom R.

Ashley co-chairman of supervisory committee, for inspira-

tion and guidance and in preparation of this dissertation,

and for generously providing facilities and materials at

USDA Laboratory. His warm friendship and understanding is

greatly appreciated.

I am also indebted to Drs. John Strayer and Daniel

Roberts for their interest and contributions as members of

my supervisory committee, and giving invaluable encourage-

ment when it was dearly needed. There are special thanks

for Dr. Stratton H. Kerr and Dr. Andrew Duncan for their

invaluable advice and suggestions.

I wish to express my gratitude to all the personnel

from both USDA Insect Attractants Laboratory at

Gainesville and TREC at Homestead who have helped me in

numerous ways in conducting my experiments. Special

thanks also go to Pamela Wilkening, Polly Hall and Delaine

Miller of USDA, Insect Attractants Lab.

ii











My heartfelt thanks and affection go to JoAnne White

for her encouragement and assistance and to Patricia Davis

for the assistance in typing this dissertation.













































iii











TABLE OF CONTENTS


Page

ACKNOWLEDGEMENTS........................................ ii

LIST OF TABLES........................................... vii

LIST OF FIGURES......................................... viii

ABSTRACT ................................................. x

INTRODUCTION............................................. 1

LITERATURE REVIEW........................................ 5

The Fall Armyworm, Spodoptera frugiperda
(J.E. Smith)..................... 5
Seasonal Distribution ............ 5
Life History ..................... 6
Economic Status.................. 8
Natural Mortality................ 9
Management Strategies............ 13
The Larval Endoparasitoid Cotesia
marginiventris Cresson........... 14
rTgi Tn and Distribution.......... 14
Description...................... 15
Life Cycle...................... 17
The Egg-Larval parasitoid Chelonus
insularis Cresson................ 19
Origin and Distribution.......... 19
Description...................... 20
Life Cycle ....................... 21
The Larval Endoparasitoid Microplitis
manilae Ashmead.................. .23
escripTtion and Distribution..... 23
Interspecific Competition ................. 25

BIOLOGY AND HOST ACCEPTANCE OF MICROPLITIS
MANILAE (HYMENOPTERA: BRACONIDAE) RAISED ON FALL
ARMYWORM LARVAE......................................... 34

Introduction.............................. 34
Materials and Methods...................... 35
Age group Acceptance.............. 36
Developmental Rates.............. 36
Adult Longevity.................. 37
Time of Host exposure............ 37
Results and Discussion.................... 37



iv












INTERSPECIFIC COMPETITION BETWEEN PARASITOIDS OF THE FALL
ARMYWORM SPODOPTERA FRUGIPERDA ....................... 44

Introduction ............................... 44
Materials and Methods....................... 45
Results and Discussion ................... 50

EFFECT OF HOST AGE, PARASITOID AGE AND CHANGE OF
TEMPERATURE ON INTERSPECIFIC COMPETITION BETWEEN CHELONUS
INSULARIS, COTESIA MARGINIVENTRIS AND MICROPLITIS MANI-FA
IN FALL ARMYWORM.......................................... 67

Introduction................................ 67
Materials and Methods....................... 68
Experiment 1--Host Age............ 70
Experiment 2--C. marginiventris
Age ..... .......... 70
Experiment 3--Temperature
Effects ............. 70
Experiment 4--Dissection of
Multiparasitized
Hosts ............... 71
Results and Discussion...................... 72

INTERSPECIFIC COMPETITION BETWEEN FALL ARMYWORM
PARASITOIDS CHELONUS INSULARIS, AND COTESIA MARGINIVENTRIS
INSIDE FIELD CAGES AND PLOTS............................. .90

Introduction ............................... 90
Materials and Methods...................... 92
Host and Parasitoid Colony
Maintenence ............ 92
Experimental Procedures for Host
Parasitization......... 93
Experiment l--Host Density......... 96
Experiment 2--Field Cage.......... 103
Experiment 3--Field Plot.......... 117
Results and Discussion ..................... 120

GENERAL SUMMARY AND DISCUSSION............................. 130

REFERENCES ............................................... 134

BIOGRAPHICAL SKETCH ...................................... 146









v










LIST OF TABLES


Table Page


1. Percentage parasitization by M. manilae of fall army-
worm larvae............................................ 38

2. Developmental periods ( + SE) and progeny sex ratios
for M. manilae in fall armyworm larvae ................. 40

3. Percentage parasitization of second age group fall army-
worm larvae exposed to M. manilae for various amount
of time................................................. 42

4. Mean percentages for emergence of Chelonus insularis
(C.i.), Microplitis manilae (M.m.), Cotesia margini-
ventris (C.m.) and adut all armyworm (FAW), and
percentages of FAW larvae failing to mature because
they refused to feed on the diet, died from unknown
causes or failed to pupate ............................. 53

5. Mean percentages for emergence of Chelonus insularis
(C.i.), Cotesia marginiventris (C.m.7, Microplitis
manilae (M.m.) and adult fall armyworm (FAW) and mean
percentages of FAW larvae failing to mature because they
refused to feed on the diet or failed to pupate........ 55

6. Mean number and percentage of larval encounters, exami-
nations, oviposition probes and apparent ovipositional
successes by Cotesia marginiventris and Microplitis
manilae in faTT armyworm larvae exposed and not exposed
as eggs to Chelonus insularis.......................... 57

7. Mean percentages for numbers of encounters, examinations
and apparent ovipositions by C. marginiventris and
M. manilae during 2 host exposure periods separated by
FTfferent numbers of days .............................. 58

8. Mean percentages at different host ages for emergence of
Chelonus insularis (C.i.), Cotesia marginiventris (C.m.),
and adult fall armyworm (FAW) and percentage mortality of
FAW larvae due to (a) refusal to feed on the diet and
(2) death from unknown causes .......................... 73

9. Mean percentages for emergence of Chelonus insularis
(C.i.), Cotesia marginiventris (C.m.), and adult faTl
armyworm (FAW) and percent mortality FAW larvae due to
(1) refused to feed on the diet and (2) died from
unknown causes, when age of C.m. was changed........... 76



vi











10. Mean percentage (+ SE) at several constant tempera
tures for emergence of Chelonus insularis (C.i.),
Cotesia marginiventris (TC.mT and adult FAW and percen-
tages of FAW larvae failing to mature because they
(1) refused to feed on diet and died, (2) died from
unknown causes (3) still larvae at end of test and
(4) escaped from cup ................................. 82

11. Mean (+ SE) emergence periods (days) at several con-
stant Temperatures for Cotesia marginiventris (C.m.) and
Chelonus insularis (C.i.) and adult FAW, and percentages
for FAW larvae failing to mature because they (1)
refused to feed on the diet and died and (2) still
larvae at end of test................................. 84

12. Fate of the larval parasitoids C. marginiventris (C.m.)
and M. manilae (M.m.) in competition with the egg-larval
parasiTtoif C.insularis as determined by dissection of
fall armyworm (FAW) T arvae............................ 88

13. Mean (+ SE) for superparasitized FAW, longevity of
adult T. marginiventris in days and percent survival
of hosT-larvae at 7 FAW densities ................... ..100

14. Sex ratio (+ SE) (9 :6 ) for C. marginiventris (C.m.)
and C. insuTaris (C.i.) from FAW larvae parasitized
insid a field cage ................................... 116

15. Mean percentage of small (0.2 0.7 mm), medium
(0.8 1.2 mm), and large (1.3 2.4 mm) head capsule
widths from FAW larvae collected from undersurface,
uppersurface, ground, between stalk and leaf sheath
and stalk in corn ..................................... 124

16. Fall armyworm feeding damage to different regions of
corn in plots where C. insularis (C.i.) and C. margini-
ventris (C.m.) were releease .............. ........... 125










vii











LIST OF FIGURES


Figure Page


1. Mean percentage emergence of C. insularis (C.i.), M.
manilae (M.m.) and C. marginiventris (C.m.) from fT1l
armyworm larvae exposed to multiple parasitizations.... 52

2. Behavioral ethogram of the host finding and oviposi-
tional sequence of C. marginiventris females on fall
armyworm larvae already parasitized--by the egg-larval
parasitoid C. insularis. (Solid arrows indicate
invariable pathways and dashed arrows represent alter-
nate pathways) ......................................... 61

3. Percentage parasitization by C. marginiventris of fall
armyworm larvae already exposed as eggs to C. insularis.
Larvae were randomly placed on four plant species held
in wire cages within a greenhouse....................... 65

4. Progeny sex ratios for C. marginiventris from differ-
ent aged C. marginiventrTs (C.m.) emerging from fall
armyworm Tlrvae parasitized as eggs by C. insularis
(C.i .)................................................. 79

5. Progeny sex ratios for C. insularis (C.i.) from differ-
ent aged C. marginiventris (C.m.) emerging from fall
armyworm Tarvae parasitized as eggs by C. insularis .... 81

6. Percentage emergence of C. marginiventris and C. insularis
from fall armyworm (FAW)-Tarvae, parasitized as eggs By
C. insularis. FAW larvae were exposed at different ages
to C. marginiventris and then held at 19, 22, 25, or
28r~for development. .................................. 86

7. Mean progeny production by C. marginiventris at 7 host
densities from eggs previously parasitized by C.
insularis .............................................. 98

8. Mean progeny production by C. insularis at 7 host den-
sities and parasitized agai'n by C. marginiventris...... 102

9. Sex ratio of C. marginiventris from 7 host densities... 105

10. Sex ratio of C. insularis from 7 host densities........ 107





viii











11. Percentage parasitization by C. insularis and C. margini-
ventris from FAW larvae recov'ered inside from TTeTl
cage during 3 test periods. Vertical bars within a
test period from left to right indicate treatments
1, 2, and 3 paper sections............................... 109

12. Mean percentage parasitized FAW instars in treatments
1, 2, and 3 paper sections inside field cage............. 112

13. Mean percentage of FAW larvae that became a) adults, b)
starved and died c) died from unknown reasons in
treatments 1, 2, and 3 paper sections inside field
cage ........... .......... ........................... .. 115

14. Percentage parasitization for principle parasitoid
species recovered from FAW larvae from (US) upper
surface of whorl, (LS) lower surface of whorl,
(GR) ground, (SH) between stalks and leaf sheath,
(ST) stalk and (WH) control in corn ...................... 119

15. Sex ratios for C. marginiventris and C. insularis
recovered from T7W larvae from (US) upper surface of
whorl, (LS) lower surface of whorl, (GR) ground, (SH)
between stalks and leaf sheath, (ST) stalk and (WH)
control in corn ......................................... 122

16. Illustration to exhibit the placement of egg contain-
ing paper sections in different regions of corn

US Upper surface of upper whorl
LS Lower surface of upper whorl
GR Ground
SH In between stalk and sheath
ST Stalk
WH Whorl region ......................................... 129















ix














Abstract of Dissertation Presented to the
Graduate School of the University of Florida
in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy



INTERSPECIFIC COMPETITION OF FALL ARMYWORM
SPODOPTERA FRUGIPERDA (J.E. SMITH) PARASITOIDS,
CHELONUS INSULARIS (CRESSON), COTESIA
MARGINTVINTIS (CRSSON) AND MICROPLTTIS
MANILAE ASHMEAD (HYMENOPTERA: BRACONIDAE)

By

Rohan Harshalal Sarathchandra Rajapakse

August, 1985

Chairman: Dr. Van H. Waddill
Co-Chairman: Dr. Thomas R. Ashley
Major Department: Entomology and Nematology


Interspecific competition within fall armyworm (FAW),

Spodoptera Frugiperda (J.E. Smith), larvae by the larval

parasitoids Cotesia (=Apanteles) marginiventris Cresson

and Microplitis manilae Ashmead and the egg-larval

parasitoid Chelonus insularis Cresson was studied.

Experiments conducted with 4 larval age groups (1,

24-48h; 2, 49-72 h; 3, 73-96 h; 4, 97-130 h) of the fall

armyworm revealed that the first 2 age groups were most

suitable for the development of M. manilae. The develop-

mental period of M. manilae ranged between 13-18 days.

Highest parasitization was observed for M. manilae when 2

females were exposed to 20 hosts for 30 min at 26+1"C.



x











Cotesia marginiventris was a superior competitior

relative to C. insularis and C. insularis was superior to

M. manilae. Subsequent parasitization by either C.

marginiventris or M. manilae or larvae exposed to C.

insularis as eggs did not result in additive host mortal-

ity. Microplitis manilae females changed their behavior

significantly by displaying a reduction of approximately

50% in host examinations, 45% in ovipositor probes, and

55% in apparent ovipositions when C. insularis parasitized

larvae were presented. Cotesia marginiventris displayed a

greater number on contacts, examinations and ovipositional

attacks in larvae 3 and 6 days after initial

parasitization by M. manilae.

The maximum reproductive potential for C. margini-

ventris was achieved in hosts 36 to 48 hours old and at a

temperature of 25"C. The optimum parasitoid age for C.

marginiventris during the host exposure period was 48 to

96 hours. Egg to adult developmental times at 25C, were

17 and 26 days for C. marginiventris and C. insularis,

respectively. In multiple parasitized larvae C. margini-

ventris appeared to physically attack and destroy the

larvae of C. insularis. C. insularis was the predominant

species that emerged from field cage but C. marginiventris

was a better competitor at host densities above 120

eggs/larvae. The damage to upper leaves was significantly

greater in non-parasitoid release plots than in parasitoid

released plots.

xi















INTRODUCTION

Chemical insect pest control has become a contro-

versial management strategy for several reasons. Insect

pests have frequently become resistant to pesticides, and

the costs of developing and registering a new insecticide

have risen sharply. There is also concern about the

effects of pesticides upon human health and the environ-

ment. This combination of circumstances has prompted

entomologists to seek alternative control strategies lead-

ing to the development of sophisticated techniques involv-

ing a wide array interdisciplinary approach that have been

termed "integrated pest management". Along with the

development of strategies such as breeding resistant plant

varieties and the use of pheromones to disrupt communica-

tions, there has been a resurgence of interest in the use

of entomophages.

Huffaker and Messenger (1976) defined biological con-

trol as the action of predators, parasites, and pathogens

which maintains host densities at levels lower than would

occur in the absence of these natural enemies. Despite

the many successes obtained through the introduction and

release of a pest's natural enemies, this classical

biological control strategy has not always provided the

desired degree of pest control. In this strategy of

biological control, natural enemies are deliberately

1





2





imported to control introduced or native pests. General

guidelines for locating, selecting and introducing agents

for biological control have been discussed (Huffaker and

Messenger 1976). Efforts should begin with a careful

study of the life cycle of the target pest. If it appears

that exotic competitors may be beneficial then foreign

exploration should first begin in areas environmentally

similar to the intended area of releases. Species that

are candidates for introduction must be evaluated care-

fully to insure that they are indeed beneficial and that

they themselves will not become pests.

Interspecific competition among natural enemies of a

given host can be of a great importance in biological

control. In classical biological control, the potential

for interspecific competition exists when more than one

species of natural enemy is released into the environment

and utilizes the same host. Regarding such multiple

species introductions, it has been suggested that such

interpecific competition could possibly lead to a decline

in the population regulation of the host (Watt 1965)

although others have refuted this idea (Huffaker et al.

1971). In endemic host enemy associations, interspecific

competition appears to play a crucial role in structuring

the parasitoid guild (Force 1974) and probably influences

the entire natural enemy complex as well. Generally, the

outcome of the competition is physiologically determined






3




within the host. Thus, researchers may be unable to

predict the outcome unless they can identify and duplicate

the relevant elements of the pest's physiology under

experimental conditions.

The parasitoid guild of Spodoptera frugiperda (J.E.

Smith), the fall armyworm (FAW), provides a relevant host

parasitoid association for assessing host and natural

enemy relationships. The FAW is a sporadic and

occasionally severe crop pest in the Southeastern United

States where this species is known to be able to survive

in winter (Luginbill 1928), though survival further north

is thought possible only during exceptionally mild winters

(Snow and Copeland 1969). In years of high population

density, FAW larvae may cause over $300 million in damage

(Mitchell 1979). Fifty three species of parasitoid

species have been recovered from FAW larvae (Ashley 1979)

and are responsible for significant reductions in FAW

larval populations (Ashley et al. 1982). The principal

parasitoids of the FAW either attack its eggs or the early

instars and thus provide suitable models for the study of

parasitoid interrelationships, especially with regard to

interspecific competition between the egg-larval and

larval parasitoids.

The following research was conceived to assess and

investigate the competitive abilities between the parasi-

toid larvae of Chelonus insularis Cresson, Cotesia






4




(Apanteles) marginiventris Cresson, and Microplitis

manilae Ashmead. The objectives of the study were to (1)

study the biology of M. manilae an imported larval

parasitoid of Spodoptera spp in Thailand, (2) investigate

interspecific competition between larvae of the

parasitoids C. insularis, C. marginiventris, and M.

manilae, (3) examine the effects of host and parasitoid

age, and temperature on the outcome of interspecific

competition, and (4) study the functional response of C.

marginiventris when exposed to different densities of FAW

larvae previously parasitized by C. insularis.














LITERATURE REVIEW

The Fall Armyworm, Spodoptera frugiperda (J.E. Smith)



The fall armyworm (FAW), Spodoptera frugiperda (J. E.

Smith), (Lepidoptera:Noctuidae) inflicts damage on a large

number of agricultural crops, especially those belonging

to the family Graminae, in the Southeastern and Central

United States (Luginbill 1928) and Central America

(Andrews 1980). Corn (Zea mays L.), Sorghum (Sorghum

bicolor (L.) Moench) and Bermudagrass (Cynodon dactylon

(L) Pers.) are the favored agricultural hosts for the FAW

(Sparks 1979). Economic damage to other crops, including

alfalfa, peanuts, rice and soybean, has also been

documented (Navas 1974, Morrill 1973, Pitre 1979). Tietz

(1972) lists 68 genera of plants, many of which are weed

species, that are attacked by the FAW.



Seasonal Distribution

Unlike most other insects in the temperate region,

the FAW has no mechanism for diapause. Thus, the species

overwinters commonly in South Florida and Texas, where

temperatures do not destroy it and where hosts are

continually available (Luginbill 1928). In mild winters

it is also found in Louisiana and Arizona (Snow and

Copeland 1969). During the spring and summer the FAW

5






6




disperses again throughout the eastern and central United

States, and, in some years, into Southern Canada

(Luginbill 1928). This migration is assisted by weather

fronts (Sparks 1979). Several hypotheses have been

advanced to explain the seasonal distribution of damaging

populations of FAW (Rabb and Stinner 1978; Walker 1980;

Barfield et al. 1980). Walker (1980) presented 3 models

to account for seasonal distribution patterns. Diffusion

and freeze-back and return flight (Walker 1980), "pied

piper" effect similar to diffusion and freeze back (Rabb

and Stinner 1978) and a model on seasonal distribution

patterns as combinations of short and long range

movements, as well as periodic overwintering in as yet

undiscovered habitats (Barfield et al. 1980) explained

this aspect.



Life History

The life cycle of the FAW has been described by

Luginbill (1928), Vickery (1929), Sparks (1979) and Keller

(1980). The adults are nocturnal and at dusk initiate

flying near host plants that are suitable for feeding,

oviposition, and mating. Mitchell et al. (1974) showed

that peak activity of adults occurred 6 hrs after sunset

and another small peak occurred approximately 3 hrs later.

Oviposition may occur on host plants where as many as





7




several hundred eggs may be laid in a mass and covered

with scales. Total oviposition by a female may exceed

2000 eggs over a period of up to 23 days (Luginbill 1928).

As larvae hatch from the eggs, they eat their egg shells

(Morrill and Green 1973), and as a result of negative

phototactic and geotactic behaviors, the first instars

move into the whorls of corn and sorghum (Pitre 1979).

The larvae feed preferentially on the developing leaves

and at high densities will eat the mature leaves, tassels,

ears, and the inner portions of the stalk (Luginbill 1928,

Morrill and Green 1973). Development proceeds through 6,

sometimes 7, and rarely 8 instars (Keller 1980). Tempera-

ture, larval nutrition, and probably egg nutrition were

factors affecting instar number in FAW (Keller 1980).

Mature larvae drop to the ground and pupate in the soil

within a chamber located 2 to 8 cm below the surface

(Luginbill 1928). Pupation depends upon soil texture,

moisture, and temperature (Sparks 1979). Pupae have been

found on plant parts during severe outbreaks (Burkhardt

1953). After eclosion, the adults find their way to the

soil surface, locate a plant or other object on which to

cling, and inflate their wings (Sparks 1979). There is

also evidence that different host plants (Roberts 1965,

Pencoe and Martin 1981) and different temperatures affect

the biology of FAW (Barfield et al. 1978).





8





Roberts (1965) reported that the larval diet can affect

the duration of larval period, pupal size, adult

longevity, fecundity, and egg viability.



Economic Status

In some years FAW larval densities are low and not

economically important while in other years high densities

inflict serious economic losses (Sparks 1979). The FAW

was recorded as an injurious pest in Georgia in 1797, and

in Florida in 1856 (Sparks 1979).

Damaging populations of FAW appear to occur

irregularly (Barfield et al. 1980). FAW infestation

levels are unpredictable (Barfield et al. 1980) and

conditions conductive to outbreaks are not well

understood (Keller 1980).

The FAW causes damage to corn by feeding on the

developing leaves within the whorl. In areas with severe

infestations the tassels, ears, mature leaves and stalks

are also consumed (Painter 1955). Defoliation ranges from

skeletonization of leaves by early larval instars to

complete leaf consumption by large larvae. Annual losses

due to larval feeding are estimated to be between $300 to

500 million in the United States (Mitchell 1979). Larval

food consumption has been studied by Luginbill (1928) and

Barfield et al. (1980).






9




Natural Mortality

Various abiotic and biotic agents act as mortality

agents of FAW populations in the field. Physical environ-

ment and natural mortality factors may act singly or in

combination to determine the annual distribution pattern

and densities of FAW populations (Barfield et al. 1980).

Among abiotic environmental factors, temperature appears

to be an important limiting factor (Barfield et al. 1980).

Low temperature may be the most important factor limiting

the winter survival of FAW (Luginbill 1928, Wood et al.

1979). Andrews (1980) reported that torrential daily

rains for several days result in drowning of small larvae

or washing them out of the whorls in corn in Central

America.

Cannibalism among larvae is an important factor

limiting population densities (Luginbill 1928). Mortality

attributable to cannibalism and intraspecific competition

is positively correlated with larval density (Wiseman and

McMillian 1969). Olive (1955) reported that first instar

larvae may destroy adjacent unhatched eggs while in the

process of devouring their own egg shells. Ashley (Pers.

Comm. 1985) studied the factors influencing cannibalism in

FAW and showed that the larval density in combination with

the amount of eatable surfae area affected cannibalism

more significantly than did the amount of non-eatable

surface area, diet volume, or photoperiod.







10



Natural mortality inflicted on FAW larvae by natural

enemies (parasitoids, predators and pathogens) in both

agricultural and wild host plant communities is believed

to play a substantial role in density regulation (Barfield

et al. 1980). Ashley (1979) presented detailed informa-

tion about the classification and distribution of the FAW

parasitoids and noted that 53 species from 43 genera and

10 families have been reared from FAW larvae. Among them

18 species occur in North America; 21 species occur in

Central and South America; and 14 species are common to

all three regions (Ashley 1979). Parasitoid species

attacking FAW vary between different agroecosystems. For

example, in a study by Ashley et al. (1980) in late

planted field corn, 8 species of parasitoids, representing

the families Braconidae, Ichneumonidae, Eulophidae and

Tachinidae, were collected from FAW larvae feeding on corn

and surrounding broadleaf signal grass. Chelonus texanus

Cresson caused the highest mortality followed by Meterous

autographae Musebeck and Euplectrus platyhypenae Howard.

Nickle (1976) reported that 7 species caused parasitiza-

tion of FAW larvae on peanuts and Apanteles marginiventris

Cresson., M. autographae and Ophion spp were responsible

for highest mortality. Ashley et al. (1983) in another

study on parasitization of FAW larvae on volunteer corn,

Bermudagrass (Cynondon dactylon (L)) and paragrass





11




(Brachiarie mutica (L)) reported that C. insularis Cresson

was the principal parasitoid on corn and C. insularis and

A. marginiventris were the major parasitoids on

Bermudagrass while M. autographae parasitized the highest

proportion of hosts in paragrass, reflecting a host plant

preference. The native parasitoids C. insularis and A.

marginiventris were the primary species attacking FAW

larvae in South Florida and they destroyed 63% of each of

the first instars; M. autographae and Rogas laphygmae

Viereck, as well as several tachinids and a group of

unidentified ichnuemonids, accounted for the rest of FAW

larval mortality (Ashley et al. 1982). Tingle et al.

(1978) reported that parasitoid populations attacking the

FAW on alternate host plants of, in or near crop fields

may be important sources of parasitoids that subsequently

attack FAW larvae in corn. Waddill et al. (1985) dis-

cussed the seasonal abundance of FAW parasitoids, C.

insularis, Temelucha spp. R. laphygmae, and C. margini-

ventris in southern Florida. Mitchell et al. (1984)

reported that FAW pheremone components had no significant

effect on the level of FAW parasitization by C. insularis

and Temelucha difficulis Basch. The successful rearing of

a pupal parasite Diapetimorpha introita of FAW in the

laboratory has also been documented (Pair et al. 1985).

Predators and pathogens are among other natural

enemies found to play a less consistent role in regulation






12




of FAW populations. Agnello (1978) compiled a list of 10

species of Hymenoptera (8 vespids and 2 sphecids) and 6

Hemiptera (3 reduviids, 1 pentatomid, 1 nabid and 1

anthocorid), 12 Coleoptera (9 carabids, 2 cicindellids and

1 coccinellid) a mammal (skunk), 3 amphibians (2 Bufo spp

and 1 Hyla spp) and a variety (13 species) of birds as

predators of FAW. An earwig, Doru spp inhabits whorls of

corn and sorghum and found to feed readily on small and

medium sized FAW larvae (Andrews 1980).

The FAW is reported to be susceptible to at least 16

species of entomogenous pathogens which includes viruses,

fungi, protozoa, nematodes and 2 strains of the bacterium

Bacillus thuringiensis Berliner (Gardner and Fuxa 1980).

Many of these occur naturally in FAW populations. A "poly

hedrosis" presumably nuclear polyhedrosis virus (NPV) was

reported as early as 1915 (Chapman and Glaser 1915) and a

granulosis virus has also been identified from FAW larvae

collected from sorghum (Steinhaus 1957). Fungi also are

natural mortality factors in FAW populations. Three

species have been reported and include Entomophthora

sphaerosperma Fresenius (Charles 1941), Nomuraea rileyi

(Farlow) Sampsom (Luginbill 1928) and Empusa spp

(Luginbill 1928). The natural occurrence of a nematode

Hexamermis spp in FAW larvae was reported from Venezuela

(Gnagliumi 1962). The only protozoan reported to occur






13




naturally in FAW is Nosema laphygmae Weiser, a microspori-

dium from Colombia (Weiser 1959).



Management Strategies

The major management strategies reported to control

FAW are insecticides (Young 1980), cultural control

(Luginbill 1928) and host plant resistance (Wiseman et al.

1979). Young (1980) suggested the use of irrigation water

as a carrier for insecticides, thereby supplying the

volume of liquid needed to penetrate all of the plant

sites, where FAW feed. Application of granular insecti-

cides directly to the whorl has been a common practice in

Central America (Andrews 1980).

The importance of mechanical and cultural control of

FAW was first reported by Luginbill (1928). Black light

traps and pheremone baited cylindrical electric grid traps

have been used to monitor seasonal populations of FAW in

Louisiana and Florida (Mitchell 1979). However, dispos-

able sticky traps baited with pheromone (z)-9-dodecen-l-ol

acetate have been used extensively in surveys in Georgia

and Florida. These traps were found to be most effective

in capturing FAW males when positioned approximately 1 m

above ground and near around preferred hosts (Mitchell

1979).

Wisemann and Davis (1979) showed the importance of

resistant plant varieties in managing FAW populations.





14




The resistance of corn variety "Antigua 2 D" to FAW has

already been documented (Wiseman et al. 1973). Resistant

varieties in sorghum, peanuts, Bermudagrass, rice, and

millet have also been reported (Davis 1980).

Considering the important factors regulating FAW

populations, action thresholds (AT) for grain sorghum have

been developed (Martin et al. 1980). These action

thresholds are estimated to be 10% of seedling sorghum

possessing egg masses after flowering. However there is a

lack of information in many areas which makes it

difficult to derive dynamic AT and population models

representing the dynamics and host interactions of the

FAW.

The Larval Endoparasitoid Cotesia (=Apanteles)
marginiventris Cresson


Origin and Distribution

Cotesia (=Apanteles) marginiventris is one of the

most freqently recovered parasitoids from field collected

FAW larvae. This parasitoid was originally described from

Cuba, and is native to the West Indies (Muesebeck 1921).

It has been previously classified as Microgaster margini-

ventris Cresson (1865), Apanteles grenadensis Ashmead

(1900), A. laphygmae Ashmead (1901), Apanteles (Protapan-

teles) harnedi Viereck (1912) and most recently Cotesia

marginiventris Cresson (Marsh 1978). It appears to have a

wide distribution within the United States, especially in





15





the southern states viz. Arkansas, Florida, Georgia,

Louisiana, Mississippi, Tennessee, North Carolina and

South Carolina (Wilson 1933, Mueller and Kunnalacca 1979,

Marsh 1978). Some 16 hosts of C. marginiventris have been

reported (Miller 1977) and all are noctuids. No crop

preference is shown by this parasitoid when attacking

Trichoplusia ni (Hbn.) on various food plants in

Mississippi (Boling and Pitre 1970).



Description

The egg and laral instars are described by Boling and

Pitre (1970), and the adults by Muesebeck (1921). The egg

is hymenepteriform, cylindrical with rounded ends. The

caudal end is slightly curved, and has a short peduncle.

The egg is 0.017 mm at the broad end, 0.088 mm in length

at oviposition and the peduncle is 0.0005 mm long (Boling

and Pitre 1970). The egg is found free in the hemocoel of

the host larvae. Up to 7 eggs have been found in a single

host when the host larva was exposed to several female

parasitoids. However, superparasitization does not

necessarily lead to multiple cocoon formation. Normally

only 1 egg is found per host (Boling and Pitre 1970). The

first instar larva is white and caudate and is usually

found in the posterior part of the host's body. First

instar larvae are never found attached to the host. The





16




larva has a caudal appendage which is a modification of

the last abdominal segment into a fleshy organ and a

caudal vesicle that increases in size with longevity.

Allen and Smith (1958) reported some species of Apanteles

as being cannibalistic in the first instar; but no

cannibalism has been observed in C. marginiventris (Boling

and Pitre 1970). The second instar is vesiculated with a

prominent anal vesicle and the body becomes more robust.

Allen and Smith (1958) suggested that the second instar

may actually be two instars. The third instar is

hymenopteriform with no anal vesicle. This larva tapers

anteriorly and is creamy white at first, turning light

brown upon emerging from the host (Boling and Pitre 1970).

The molt to the third instar happens just prior to

parasitoid emergence, which generally occurs at approxi-

mately the 4th abodminal segment in the dorsolateral area

of the host. The parasitoid initially constructs a one

sided crescent-shaped cocoon and after its body has become

seated, the larva closes the open side of the cocoon. The

cocoon is small (3mm long), ovoid, firm, smooth and com-

posed of white silk surrounded by some looser threads.

The pupa is exarate and enters pupation approximately 24

hrs after formation of cocoon. Adults can be identified

using the keys of Marsh (1971) (to genus) and Muesebeck

(1921) (to species). The black adult is about 2-5 mm

long, has yellow legs and is recognizable by the





17




sculpturing on the abdomen and hind coxa, and the color

and length of the hind tibial spurs (Marsh 1978).



Life Cycle

Cotesia marginiventris is an arrhenotokus larval

endoparasitoid of several lepidopteran pests. Female

parasitoids mate and oviposit within several minutes after

emerging from the pupal case but are more aggressive when

held for 24 hrs prior to host exposure (Boling and Pitre

1970). Mating occurs with the male approaching the female

from the rear, tapping her with his antennae and then

mounting on her for approximately half a second. Both

sexes mate many times and freely with other individuals.

Females often mate after having initiated egg laying

(Boling and Pitre 1970).

The egg is laid in early instar hosts. According to

Vickery (1929) first instars are parasitized before they

disperse and Kunnalaca and Mueller (1979) reported that

first instars are preferred. According to Boling and

Pitre (1970), C. marginiventris perfers to oviposit in 2

day old larva of T. ni rather than in 1 day or 3 day old

larvae of the same species. Later host instars are less

preferred becase host larvae usually jerk violently and

this movement interfers with oviposition (Kunnalaca and

Mueller 1979). In general parasitization increases with





18




increased exposure time. Kunnalaca and Mueller (1979)

reported that oviposition was accomplished quickly with a

single ovipositor thrust and this occurred primarily

during day light hours. Multiple oviposition was common

especially when few hosts were offered to a parasite

(Boling and Pitre 1970). Total fecundity ranged from 30

to 110 eggs per female (Kunnalaca and Mueller 1979).

Time required for the development of C. marginiven-

tris from oviposition to cocoon formation ranged from 6 to

11 days at 30C (Boling and Pitre 1970, Kunnalaca and

Mueller 1979). Boling and Pitre (1970) reported the

optimum time for development as 7 days in T. ni and

Pseudoplasia includens (Walker) and 6 days in Heliothes

virescens (F.) within 24 hours after existing host larva.

Kunnalaca and Mueller (1979) reported an optimum develop-

mental time of 8 days in Plathypena scabra (F). At 300C

and 25C, development times from cocoon to adult ranged

from 3-5 days and 4-7 days, respectively (Kunnalaca and

Mueller 1979). The sex ratio (1.5:1) favored males at

both 30C and 250C (Kunnalaca and Mueller 1979). Mean

longevity of adults at 30C and 25C was 5.6+2.5 and

9.1+4.2 days, respectively and females lived longer than

males at both temperatures (Kunnalaca and Mueller 1979).

Parasitization by C. marginiventris resulted in

growth retardation of the host (Danks et al. 1979).





19





Ashley (1983) reported that parasitization of FAW larvae

by C. marginiventris reduced maximum larval weights by

97%, compared to 6th instar nonparasitized larvae. C.

marginiventris destroyed its host when the host reached

the 4th instar. Hosts parasitized by C. marginiventris

gained the least amount of weight, produced the least

amount of frass, and had shortest life expectancies and

the smallest head capsule widths compared to other

parasitoids (Ashley 1983).

Loke et al. (1983) has described the behavioral

sequence for host finding and oviposition for C.

marginiventris on corn plants artifically damaged by 2nd

instar larvae of the FAW and reported that highest

parasitization rates occurred among 2nd instar larvae

collected from leaf surfaces. Bioassay responses in C.

marginiventris females to materials derived from FAW

larvae were most intense for frass and somewhat less

intense for larval and pupal cuticle materials, scales,

exuviae and silk (Loke and Ashley 1984).

The Egg-larval Parasitoid Chelonus insularis Cresson

Origin and Distribution
Chelonus insularis Cresson is one of the key

parasitoids regulating FAW populations in South Florida

(Ashley et al. 1982). It has been previously classified






20



as C. texanus Cresson (1872), C. texanoides Viereck

(1905), C_ exogyrus Viereck (1905) and C. bipustulatus

Viereck (1911) (Marsh 1978). C. insularis is distributed

throughout in North, Central and, South America, and the

West Indies and has been introduced into Hawaii and South

Africa (Marsh 1978).



Description

The eggs of C. insularis are white, and cylindrical,

and appear comma like in shape. They are slightly arcuate

with both ends rounded, one being larger than the other

(Glogoza 1980). The first instar larva has a prominent

square head with easily distinguishable dark, pointed,

mandibles and 7 body segments tapering from the thorax to

the abdomen (Glogoza 1980). The larva floats in the host

hemolymph. The second stage larva is cylindrical with a

tapered head. The body of the third stage is also

cylindrical and the head which is relatively narrow tapers

in the front. C. insularis causes its host to burrow in

the earth when the host reaches the 4th instar and to form

a pupation cell. After completing this cell the parasi-

toid larva consumes the entire contents of the host and

then pupates. The larva spins a cocoon by using a silky

secretion and this cocoon is cylindrical with almost flat

ends. Ashley (1983) found that of those FAW larvae






21




parasitized by C. insularis, 41% died in the 4th instar

and 59% died in the 5th instar. An emerging adult tears

the silky cocoon with its mandibles and escapes through

the opening. The body length of the adult is 4.5-5.0 mm

and description of adults is found in Marsh (1978).



Life Cycle

The female parasitoids can begin to lay eggs even if

they have not mated. The antennae are used to locate the

host, the female then lands on the eggs, positions

herself, and then injects her eggs directly into the host

egg. The female may lay continously for about an hour if

left undisturbed. Superparasitism is common in the genus

Chelonus (Broodryk 1969) and was observed in C. insularis

when parasitizing H. virescens (F.) eggs (Ables and Vinson

1981). Ables and Vinson (1981) reported that C. insularis

appeared to examine host eggs internally as well as

externally and was able to detect previously parasitized

hosts. The average time of development from oviposition

to adult is about 26 days for males and 28 days for

females. Rechav (1978) found similar results for other

Chelonus spp. Greatest fecundity was obtained at 30C

(Glogoza 1980). Survival was highest at low temperatures

and the greatest percentage of eggs was parasitized at

35"C (Glogoza 1980). Male biased sex ratios occurred at





22





20 and 40'C while at 35"C a 1:1 ratio was obtained

(Glogoza 1980).

C. insularis can develop in many hosts. Besides S.

frugiperda, it is also able to develop in Heliothes

armigera (Hubner), Spodoptera exigua (Hbn), Ephestia

sericaria (Scott) (Bianchi 1944). Marsh (1978) reported

that hosts for North America include Ephestia elutella,

(Hbn), Feltia subterranea (F), Heliothes zea (Boddie),

Loxostege sticticalis, (L.) Peridroma saucia (Hbn),

Spodoptera eridania (Ramer), Spodoptera ornithogalli

(Guenee), Spodoptera praefica Grote, and T. ni.

Parasitization of FAW by C. insularis reduced host

FAW larval weights by 70% and only 28% of the larvae

parsitized by C. insularis lived past the 9th day and

these larvae displayed an unusual increase in weight prior

to destruction by the parasitoid (Ashley 1983).

Ashley et al. (1982) found that the native parasitoid

C. insularis was the primary species attacking FAW in

South Florida and it emerged from 71% of the parasitized

larvae. C. insularis caused the highest mortality of FAW

larvae collected from corn and broadleaf signalgrass

(Ashley et al. 1980). Ashley et al. (1983) reported that

C. insularis parasitized 44% of all FAW larvae collected

from volunteer corn, Bermudagrass and paragrass and





23





regardless of the host plant, C. insularis had a parasiti-

zation rate 4 times greater than other competing parasi-

toids. Substantially higher percent parasitization was

obtained for corn than on other hosts (Ashley et al.

1983). Ashley et al. (1982) reported that C. insularis

parasitized the greatest proportion of FAW larvae having

head capsule widths of 0.3 mm. Chelonus insularis was not

recovered from larvae having head capsule widths greater

than 1.8 mm. This very clearly showed that C. insularis

is primarily an egg parasitoid with preference to early

instars to lay eggs. Mitchell et al. (1984) reported that

two FAW pheremone components (Z9DDA and Z9TDA) had no

significant effect on the level of FAW parasitization by

its principal parasite C. insularis. The sex ratio for C.

insularis shifted from approximately 1:1 (Female:male)

during spring to approximately 1:4 during the summer

months but the reduced proportion of females during summer

did not lower parasitization levels by C. insularis.



The Larval Endoparasitoid Microplitis manilae

Description and Distribution

Microplitis manilae (Ashm) is reported as an

important larval parasitoid of Spodoptera spp in Thailand

(Shepard, Pers. Comm 1982). This parasitoid is not





24





indigenous to the United States, and was imported from

Thailand through the USDA, Stoneville Research

Quarantine Facility, Mississippi.

No taxonomic or distribution literature was located

for M. manilae. The length of antennae in males is longer

than for the female. However, Marsh (1978) described a

closely related spp M. melianae Viereck. An unsuccessful

attempt was made to establish M. manilae in the FAW

overwintering range in South Florida (Ashley, Pers.

Comm. 1983).

The adults are ready to oviposit soon after emer-

gence. They will oviposit in FAW larvae for a period of

16-17 days. Different species of Microplitis attack the

early larval instars of their hosts (Altahtawy et al.

1976). The female deposits an egg through the integumant

of host larva into the hemolymph. The egg is elongated,

oval and translucent white in color. The first instar is

caudate with a relatively large head and the second instar

is vesiculate and creamy white. After the parasitoid

larva molts into the third instar, it emerges from the

host (FAW) and spins a cocoon. Although the host remains

alive after the parasitoid emerges, the host does not

develop further and stops feeding. The parasitoid larva

exits the host and pupates outside. A single parasitoid

normally develops from each host even after





25





superparasitism. However, development of two parasitoids

per host occurred more frequently when larger hosts were

provided. Biology of M. demolitor imported from

Queesland, Australia has been described by Shepard et al.

(1983).


Interspecific Competition

By definition competition occurs when two or more

organisms interfere with or inhibit one another (Pianka

1970). Smith (1929) defined "multiple parasitism" to

designate the type of parasitization in which the same

individual host insect is inhabited simultaneously by the

young of two or more different species of primary parasi-

toids. Fisher (1961) reported that this type of multi-

parasitism resulted in competition between the parasi-

toids. The occurrence of this type of multiparasitism

depends primarily upon the oviposition behavior of the two

parasitoids in response to hosts that are already parasi-

tized. In general, parasitoids require a host organism

for egg deposition and the development of immature stages.

Typically, the progeny of one or neither parasitoid will

survive when individuals of different species parasitize a

single host organism (Salt 1961). Therefore interspecific

competition between parasitoids for hosts may be a vital

component influencing guild composition (Zwolfer 1970).

Interspecific competition among parasitiods may even






26




result in the competitive exclusion of certain species

(Debach and Sundby 1963).

In many cases of interspecific competition, one

species has an intrinsic superiority over its opponent and

invariably destroys it, by the use of its mandibles

(Pemberton and Willard 1918, Simmonds 1953) or by an

unspecified means of physiological suppresion (Muesebeck

1918, Fisher 1961, Salt 1961).

More commonly there is no intrinsic superiority on

the part of either parasitoid, and free competition occurs

between them, the victor completing its development and

the loser dying, either as an egg or a young larva.

Several suggestions have been made in the literature as to

the possible mechanism of competition between such soli-

tary endoparasitic species. In the first place, the older

parasitoid is presumed to survive by eliminating the

younger through starvation (Fiske and Thompson 1909) thus

emphasizing the importance of time of oviposition as the

determining factor in competition. Secondly, cases of

direct physical attack by one parasitoid on another using

the mandibles for fighting has been recorded (Simmonds

1953). In these cases neither competitor has an intrinsic

advantage over the other and the result of competition is

apparently decided by the time of oviposition. The third

suggestion is that one parasitoid eliminated the other by

physiological suppression, either by conditioning the

hemolymph of the host so that it becomes unsuitable for





27




the development of any successor (Van den Bosch and

Haramoto 1953, Johnson 1959) or by the postulated

secretion of a toxic substance which kills the opponent

(Thompson and Parker 1930).

Competitive exclusion by previously introduced

parasitoids has been viewed as one of the factors that

explains the failure of introduced natural enemies in

classical biological control to become established (Ehler

and Hall 1982). The competitive exclusion hypothesis has

been subject of considerable debate in the literature.

Turnbull (1967) favored the competitive exclusion hypo-

thesis while Van den Bosch (1968) rejected it. However,

Ehler and Hall (1982) presented empirical evidence in

support of competitive exclusion and stated that this

could possibly lead to the extinction of an effective

natural enemy. In fact, Force (1974) showed that a very

effective natural enemy may in fact be an inferior com-

petitior. Thus Ehler and Hall (1982) suggested that (1)

simultaneous release of several species of natural enemies

should be avoided due to interspecific competition between

them that may lead to a lower establishment rate and (2)

extra care should be taken in establishing species where

incumbent species of natural enemies exist. However Moon

(1980) reported that while the principle of competitive

exclusion may be simple and attractive, it may not

adequately apply to the heterogenous real world.





28




In classical biological control, the potential for

interspecific competition exists when more than one

species of natural enemy is released into the environment.

Regarding such multiple species introduction, it has been

suggested that such interspecific competition could

possibly lead to a decline in population regulation of the

host (Turnbull and Chant 1961, Watt 1965) although others

have refuted this as a general phenomenon (Huffaker et al.

1971). Empirical evidence generally supports multiple

species introductions (Ehler 1978). However, such

evidence comes largely from successes involving multiple

species releases without regard to instances where such

releases did not yield total success (Ehler 1977). Miller

(1977) suggested the possiblity that intrinsically

superior competitors which exhibit a relatively low repro-

ductive capacity would displace or interfere with

intrinsically inferior competitors which exhibit a rela-

tively high reproductive capacity. There is a concern

that such competition would result in decreased parasiti-

zation rates. A computer simulation by Watt (1965) and a

greenhouse study by Force (1970) suggested that such a

reduction in the proportion of parasitization is

possible.

Other things being equal, intrinsically superior

species imported in biological control programs probably

become established more easily than intrinsically inferior





29




ones. Examples of intrinsically superior parasitoids that

have achieved such a role are two braconids, Opiun

oophilus Full. (Bess and Haramoto 1958) and Macrocentrus

ancylivorus Rohw. (Boyce and Dustan 1958). On the other

hand, an intrinsically inferior species may achieve a

higher level of parasitization in the field than its

rivals if it is extrinsically superior to them. For

example, Spalangia cameroni Perk., an intrinsically

inferior species, parasitized more house fly pupae than

all other species combined because the females were able

to penetrate more deeply into areas containing hosts

(Mourier and Hannine 1969). Obviously, an intrinsic

superiority of one parasitoid over another may result in

the waste of some parasitoids, but this effect, as pointed

out by Smith (1929), is likely to be an insignificant

factor in the comparative field efficiencies of two

competing forms.



Case Studies

The superiority of Metaphycus inteolus (Timberlake)

over Microterys flavus Howard inside the host (Coccus

hesperidium) in the field was contrary to the pattern of

dominance of both species when they competed within the

host (Bartlett and Ball 1964). Arther et al. (1964)

showed interactions between a braconid, rjCilus obscurator

(Nees), and an ischneumonid, Temelucha interruptor, inside





30





the pine shoot moth, Rhyaciona buoliana Schiff. They

reported that T. interruptor attacked more host larvae that

had been previously parasitized by 0. obscurator than

unparasitized hosts. Vinson (1972) reported that in

interspecific competition between larval parasitoids

Cardiochiles ngriceps Viereck and Campoletis perdistinctus

(Viereck) on tobacco budworm, H. virescens, that C.

perdistinctus had a slight advantage over C. nigriceps when

oviposition by the 2 species occurred at about the same

time. Part of the reason for the advantage by C. perdis-

tinctus may be more rapid growth rate of its larvae and a

shorter egg development period. When the competitors were

of similar age, one was eliminated through physical combat.

When one competitor is 1 or 2 days older it was able to

destroy several eggs of the younger competitor. However

when older parasitoid is 4 days old the younger larvae is

eliminated through physiological suppression (Vinson et al.

1972). Such suppressed larvae failed to grow and were

inactive although they may be alive. When one of the

tobacco budworm parasitoids was old or it eliminated the

younger competitor by physiological suppression (Vinson

1972). Fisher (1961) also presented evidence of physiologi-

cal suppression of younger larvae by the older competitor

through the reduction of oxygen available to the younger

larva. Wylie (1972) reported that only one parasitoid






31




species survived in interspecific competition among the

pupal parasitoids Nasonia vitripennis (Walk)., Muscidi-

fura zaraptor K. & L. and Splangia cameroni Perk. Nasonia

vitripennis and M. zaraptor were both intrinsically

superior to S. cameroni if the attacks on the hosts by

their females preceded, were simultaneous with, or

followed by up to 48 hrs those by females of S. cameroni.

Nasonia vitripennis was intrinsically superior to M.

zaraptor if its attacked preceded that by M. zaraptor by

at least 24 hrs. The success of N. vitripennis when

competing with S. cameroni was due to differences in rates

of egg and larval development and of host utilization by

the two species. In a similar study by Wallner et al.

(1982), larval parasitoids Apanteles melanoscelus

Ratzburg. and Rogas lymantriae (L.) inside the host

Lymantria dispar (L.) both attacked the previously

parasitized larvae but the parasitoid attacking the host

first was more successful.

The studies on multiparasitism between the internal

larval parasitoids of Rhyacionia buoliana Schiff. revealed

that interspecific competition took place between the

first instar larvae through direct physical attack

(Schroder 1974). However there are instances where these

internal parasitoids have coexisted within the host larva

and this provides a good example of a system of







32



"counter-balanced competition" (Zwolfer 1970). In such

systems, the competitive inferiority of a parasitoid

species in multiple parasitism is compensated for by a

superiority in other attributes such as searching

efficiency and synchronization with the host's life cycle

(Schroder 1974).

Weseloh (1983) reported that neither of the

parasitoids A. melanoscelus nor Compsilura concinnata

(Meigan) destroyed each other inside the host Lymantria

dispar and both emerged from about 11% of the hosts.

These results showed that both parasitoids appeared to be

remarkably tolerant of each other in the same host and

this probably happened because they fill different niches

and so do not compete with each other within the host.

The larval parasitoids Campoletis sonorensis

(Carlson) and Microplitis croceipes Cresson are intrinsi-

cally superior to C. insularis and physically attacked

the latter inside the host, H. virescens (Vinson and

Iwantsch 1980). In a similar study, Miller (1977)

reported that C. insularis larvae competing with A.

marginiventris inside Spodoptera praefica (Brote) were

dwarfed and nearly killed due to competition. A second

experiment involving C. insularis and Hyposoter exigue

(Vierek) yielded a similar result where H. exigue was a

superior intrinsic competitor relative to C. insularis and

C. marginiventris.





33





In a study on impact of native parasitoids on FAW in

Southern Florida, Ashley et al. (1982) described a mirror

image pattern of parasitization between C. insularis and

Temelucha spp collected from the FAW larvae. This

increase-decrease and decrease-increase pattern between

these two parasitoids may be indicative of interspecific

competition between these parasitoids (Ashley et al.

1982). Mitchell et al. (1984) reported the effect of two

FAW pheremone components (Z9DDA and Z9TDA) upon population

dynamics of its larval parasites and found that C.

insularis was the predominant species followed by T.

difficilis whose parasitization rate of FAW larvae was

initially high and then remained relatively constant for

the remainder of the experimental period. The explanation

for this type of parasitization pattern was that C.

insularis was a better internal competitor than T.

difficilis (Mitchell et al. 1984).















BIOLOGY AND HOST ACCEPTANCE OF MICROPLITIS MANILAE
(HYMENOPTERA:BRACONIDAE) RAISED ON FALL
ARMYWORM LARVAE


Introduction

The fall armyworm (FAW), Spodoptera frugiperda (J.E.

Smith), is a major pest of corn and Bermudagrass in the

southeastern United States (Luginbill 1928) and may extend

its range as far north as the Canadian border during the

summer and fall months (Snow and Copeland 1969). However,

since this pest has no mechanism for diapause or

overwintering its populations are restricted to portions

of south Florida and Texas during the winter months

(Luginbill 1928). Average estimates of annual crop losses

caused by the FAW exceed $300 million (Mitchell 1979).

Therefore, reducing the density of overwintering FAW

populations may result in a significant decrease in the

amount of damage done by this pest.

Microplitis manilae (Ashmead) is a parasitoid of

Spodoptera spp. in Thailand from where it was imported

into the United States. Even though the FAW does not

occur in Thailand, M. manilae develops successfully in

larvae of the FAW under laboratory conditions (Shepard,

personal comm. 1982). The biologies and distributions of




34






35



some members of this genus are known (Hafez 1951, Putter

and Thewke 1970). Lewis (1970) describes the life history

of M. croceipes (Cresson) for Heliothis spp. and reports

that the parasitoid prefers 1st and 2nd instars as hosts.

No research dats could be found that document the life

cycle and host age acceptance of M. manilae developing

within FAW larvae, nor has this parasitoid been reported

as a natural enemy of FAW anywhere within its range

(Ashley 1979).

The objectives of our research are to gain relevant

information about the biology and host age acceptance of

M. manilae when reared on FAW larvae. This information

may prove useful in mass production of this parasitoid for

inoculative or perhaps inundative releases should M.

manilae eventually demonstrate the potential of becoming a

significant mortality agent of FAW populations.



Materials and Methods

Female parasitoids were 24 hrs old and has been

exposed to males since female eclosion. Each replicate

consisted of exposing FAW larvae (number varied according

to experiment) to 6 female parasitoids in a plastic

container (7 x 10 cm diam) with 2 screened vents (1.5 x

3.0 cm) and having honey streaked on the underside of the






36




lid. During host exposure, FAW larvae fed on cubes (3

cm3) of pinto bean diet (Leppa et al. 1979) after which

the larvae were transferred individually to 30-ml plastic

cups that contained pinto bean diet where they remained

until their fate was determined. FAW larvae were kept as

23+2"C, 70+2% RH and under a 14:10 LD photoperiod. These

larvae were divided into 4 groups depending on their age:

1, 24-48 hrs; 2, 49-72 hrs, 3, 73-96 hrs; and 4, 97-130

hrs. Hosts older than 130 hrs were excluded because M.

manilae females would not accept them as hosts. The

laboratory rearing method for M. manilae consisted of

exposing parasitoids to approximately 50 FAW larvae which

were 48-72 hrs old for 3-5 hrs.

Age group acceptance--Depending on host availability

4-6 replicates of 3-4 FAW larvae of the same age group

were presented to two female M. manilae for 30 min. on the

same day. Data from 4 consecutive days comprosed a single

test and tests were replicated 4 different times.

Developmental rates--Microplitis manilae were exposed

for 24 hrs to hosts in the four age groups. Parasitoid

developmental times were determined from oviposition to

pupation and from pupation to adult emergence. Progeny

sex ratios were recorded for each age group.






37



Adult longevity--Freshly eclosed parasitoids were

exposed to hosts under continuous light at 26+1C and

longevity was recorded for 2 groups: (1) the females

(n=41) and males (n-57) were separated into different

cages and (2) both sexes were kept together and allowed to

mate for 2 hrs and then to oviposit for 24 hrs inside a

plastic container with 20 FAW larvae. After the host

exposure period, larvae were removed and adult parasitoids

were retained in the plastic containers.

Time of host exposure--In order to determine optimal

host exposure time, 2 female M. manilae were exposed to 20

hosts from the 2nd age group for 15, 30, 45 and 60 min.

and then removed. Four replicates were run.


Results and Discussion

Parasitoids displayed the highest host acceptance for

1st and 2nd age group larvae and a lesser acceptance for

3rd age group larvae (Table 1). Highest parasitization

rates occurred most frequently in 2nd age group larvae.

Significantly fewer 4th age group larvae were parasitized

compared to larvae of other groups, and there were several

occurrences of significant differences in host acceptance

between 2nd and 3rd age group larvae. Similar results

have been reported for other members of this genus (Hafez

1951, Lewis 1970). Putter and Thewke (1969) showed that










38












Table 1. Percent parasitization by M. manilae of fall
armyworm larvae



Age Test numbersa/

group

(hrs) 1 2 3 4





1 (24-48) 24.5 a 26.7 a 26.7 a 13.2 a

2 (49-72) 28.3 a 30.1 a 27.8 a 11.4 a

3 (73-96) 22.5 a 20.7 b 19.5 b 12.3 a

4 (97-130) 6.9 b 5.2 c 6.8 c 3.5 b

Total 369 418 521 279



apercentages followed by the same letter in the same column
are not significantly different by Duncan's Multiple Range
Test (P = 0.05).






39




M. feltiae preferred 1st to 3rd instar larvae (1st to 3rd

age groups) of its host Agrotis ipsilon (Hufnagel) and

Harcourt (1960) demonstrated a similar instar preference

for M. plutellae Muesebeck and its host the diamond back

moth Plutella maculipennis (Curtis). In contrast, Shepard

et al. (1983) reported that M. demolitor (Wilkinson)

preferred 3rd or 4th instar larvae of Heliothis spp.

However, larvae of this size displayed a vigorous defense

response and often damaged or destroyed the parasitoid.

We observed also that when M. manilae females attempted to

oviposit in 4th age group larvae that these larvae

aggressively attempted to thwart the ovipositional attempt

by swinging their heads and thoraxes from side to side in

an attempt to bite the parasitoid.

The larval and pupal developmental times for M.

manilae were similar for age groups 1-3 (Table 2). Egg to

pupa and pupa to adult developmental times for M. manilae

parasitizing 4th age age group hosts increased by approxi-

mately 2 days. Significantly more male progeny were pro-

duced from the 1st age group in contrast to the 2nd group

from which more female progeny emerged. No significant

differences were present in the sex ratios of progeny from

3rd or 4th age group larvae. The highest and lowest pro-

portions of female progeny were observed for age groups 2

and 4, respectively. Bryan et al. (1969) showed that the







40













Table 2. Developmental periods (X + S.E.) and progeny
sex ratios for M. manilae in fall armyworm larvae



Developmental period (days)
Age

group Sex ratio (%)a
Hosts Egg- Pupa-
(hrs) exposed pupa adult Total Males Females


1 (24-48) 106 10 + 2.3 4 + 0.7 14 + 3.0 62.5---*--37.5

2 (49-72) 127 10 + 2.9 3 + 0.9 13 + 3.8 42.9---*--57.1

3 (73-96) 93 10 + 2.1 4 + 1.1 15 + 3.2 46.8--ns--53.2

4 (97-130) 43 12 + 1.9 6 + 1.7 18 + 3.6 46.7--ns--55.3


aAsterisk indicates significance at the 5% level by Student's
t-test.








41


sex ratio of emerging progency of M. croceipes was

approximately 1:1 when reared at 25C. Only a single M.

manilae emerged per host larvae irrespective of the age

group parasitized. Bryan et al. (1969) reported an

occasional emergency of 2 M. croceipes adults from a

single Heliothis spp. larvae. Emerging M. manilae larvae

appeared to perfer a dry surface on which to pupate and

would frequently form cocoons on the underside of the lid

rather than on the moist diet surface.

Male and female longevity was about 6-7 days. Mating

increased female longevity to approximately 10 days. An

increase of approximately 10% in parasitization was

observed when the host exposure period for M. manilae

females was increased from 15 to 30 min. (Table 3). Host

exposure periods longer than 30 min. did not increase

significantly the parasitization rate.

Biological knowledge about this parasitoid is

necessary in any attempt to establish M. manilae as an

additional mortality agent in the overwintering range of

FAW. Ashley et al. (1982) showed that the native para-

sites destroyed approximately 63% of each of the 1st 4

instars and parasitization rates followed closely the

increase or decrease in FAW larval populations. Parasiti-

zation rates of 3.5-30.1% by M. manilae in FAW larvae were






42















Table 3. Percent parasitization of second age group fall
armyworm larvae exposed to M. manilae for various amounts of
time


Host (% Parasitization)
exposure (min) No. containers a (X + S.E.)


15 8 13.0 + 3.7 a

30 11 22.0 + 3.1 b

45 13 26.0 + 1.7 b

60 9 24.5 + 1.6 b


a Two female parasitoids and 20 larvae/container.

b Means followd by the same letter are not significantly
different (P<0.05) by Duncan's Multiple Range Test.







43




observed in the laboratory. The results of our research

will be used to rear M. manilae and to support efforts to

establish this parasitoid in the overwintering range of

FAW.















INTERSPECIFIC COMPETITION BETWEEN PARASITOIDS OF
THE FALL ARMYWORM


Introduction

The fall armyworm (FAW), Spodoptera frugiperda is a

serious pest of many graminaceous crops throughout the

southeastern United States. Average estimates of annual

crop losses exceed $300 million (Mitchell 1979). Since

overwintering occurs only in the southern portions of

Florida and Texas (Lunginbill 1928), increasing FAW mor-

tality within this range may lower the numbers of adults

participating in this pest's northward migration each

spring. Fifty-three species of parasitoids have been

reared from field collected larvae (Ashley 1979).

Knowledge of parasitoid interrelationships within FAW

larval populations will increase our understanding of the

factors that affects the dynamics of this pest, as well as

contribute the biological control efforts. In endemic

host enemy associations, interspecific competition appears

to play a crucial role in structuring the parasitoid guild

(Force 1974), and may influence the entire natural enemy

complex as well. Parasitoids of the FAW provide a







44






45




relevant model for the study of interspecific competition

within the host larva because of similarities in their

life cycles. Ashley et al. (1982) supports the concept of

interspecific competition during parasitiod development by

demonstrating the presence of a dependent density pattern

in percent parasitization between Chelonus insularis

Cresson and Temelucha difficilis Dasch.

The present study assesses interspecific competition

between two species of larval parasitoids, Microplitis

manilae (Ashm.) and Cotesia (=Apanteles) marginiventris

Cresson, and an egg-larval parasitoid C. insularis. It

also describes the host finding and ovipositional sequence

for C. marginiventris for hosts already parasitized by C.

insularis. In addition data are presented on host

acceptance of M. manilae and C. marginiventris of larvae

already parasitized by C. insularis.



Materials and Methods

Host eggs or larvae were obtained from a FAW colony

maintained at 23-25'C, 74-78% RH and under a 14:10 LD

photoperiod. Moth oviposition occurred on paper towels, a

portion of which were subsequently cut into sections each

having 50-60 eggs. All hosts utilized in an experiment came

from the same egg mass to help ensure host uniformity. In all

experiments, except the fourth, these paper sections were





46






placed in a plexiglas cage (25 cm3) and exposed to two

female C. insularis (24-48 hrs old) for 24 hrs. Each mass

was observed to verify that a C. insularis female had

parasitized the eggs. Masses attacked by two or more

females and eggs close to the edge of the paper section

that were not parasitized were destroyed. The larval

parasitoids emerged in plexiglass cages (25 cm3) kept at

26 + 10C, 60-70% RH and under a 14:10 LD photoperiod with

a fluorescent light intensity of 800 ft-c. Female

parasitoids were held in these cages along with males for

a minimum of 48 hrs. Unless otherwise indicated, female

parasitoids were between 2 to 4 days old. Host exposure

for the larval parasitoids lasted 24 hrs and was

accomplished by placing parasitoids, FAW larvae, and 1.5

cm cube of FAW diet (Leppla et al. 1979) into a 50-ml

container (7 x 10 cm diam) with two air vents (1.5 x 3.0

cm) located near the top on opposite sides. Parasitoids

were supplied with honey and water after adult eclosion

and during the ovipositional period. Following host

exposure, FAW larvae were placed individually into 30-ml

plastic cups that contained approximately 15 ml of diet.

These cups were held in a growth chamber at 25 + 1C,

77-80% RH and under a 14:10 LD photoperiod.

Experiment 1. Ninety FAW exposed previously to C.

insularis as eggs were divided into three equal groups.





47





Larvae in group one, were not exposed to C. marginiventris

or M. manilae and served to measure parasitization by C.

insularis. Remaining larvae were exposed as second

instars (48 hrs old) to C. marginiventris (group two) or

to M. manilae (group three). Treatments were replicated

nine times. The percent successful parasitization and the

fate of non-parasitized larvae were recorded.

Experiment 2. Twenty second-instar larvae exposed

previously to C. insularis as eggs were exposed to either

M. manilae or C. marginiventris in the plastic containers.

Ten replicates were made. In the control treatment,

larvae were exposed to either C. marginiventris or M.

manilae without prior parasitization by C. insularis.

Experiment 3. Fall armyworm larvae exposed as eggs

to C. insularis and unexposed larvae were kept in separate

plastic containers until the larvae were 3 days old. The

ten exposed and ten unexposed larvae were transferred to

new plastic containers. Two females of either C margini-

ventris or M. manilae were introduced into a container for

30 min and the number of encounters, antennal examina-

tions, ovipositor probes with and without cuticle contact

were recorded. An encounter was defined as the arresting

of random locomotion that resulted from sensing the FAW

larva. An examination occurred when antennal palpation of

the larvae by the parasitoid was observed. A probe was





48





observed. A probe was recorded when the parasitoid

thrusted its ovipositor toward the larval cuticle.

Finally, an apparent oviposition took place when the

parasitoid mounted the host and inserted its ovipositor.

Three replicates for each parasitoid species and larval

combination were examined. Further replication was not

possible because of the loss of the M. manilae colony.

Experiment 4. Eight host larvae derived from one of

the following four groups were placed in a glass petri

dish (15 x 100 mm diam): (1) initially parasitized by C.

marginiventris and subsequently exposed to M. manilae; (2)

initially not exposed to parasitoids and subsequently

exposed to M. manilae; (3) initially parasitized by M.

manilae and subsequently exposed to C. marginiventris; and

(4) initially not exposed to parasitoids and subsequently

to C. marginiventris.

As hosts were attacked they were removed and replaced

with fresh larva. Non-parasitized larvae served as a

control. The number of host encounters, examinations and

apparent ovipositions were recorded. Five replicates for

each species combination were run starting on the same day

hosts were parasitized and then repeated 3 and 6 days

later.

Experiment 5. The host finding behavior of C.

marginiventris was investigated using 4-week-old corn,

sorghum, Bermudagrass (Cynondon dactylon (L.)), and itch





49





grass. These plants were grown in pots (14.5 x 15 cm

diam) containing a mixture of sand, perlite and peat moss

(1:2:2 ratio, respectively). Supplementary nutrients were

supplied with fertilizer (8-8-8 plus trace elements). FAW

larvae exposed previously to C. insularis were allowed to

become second instars. Plants were placed in wire cages

(40 cm3) in a greenhouse at 26-28C, 70-75% RH and 14:

10 LD photoperiod. Thirty larvae were placed randomly on

the plant leaves. After 24 hrs, a female was introduced

into the cage and her host finding behavior observed.

Forty females were observed in sequence, their responses

recorded and synthesized subsequently into common

behavioral patterns.

Parasitization by C. margniventris on FAW larvae

also was measured on all four host plants. Thirty,

second-instar larvae already parasitized by C. insularis

were placed randomly into the plants. After 24 hrs of

host larval feeding, two female C. marginiventris were

introduced. The host larva were removed at 20-, 40-, 60-,

and 80-min intervals. Three replicates for each time

interval and plant species were made. Larvae were removed

from the plants and placed in 30-ml cups to determine

parasitization rates.







50




Results and Discussion

Experiment 1. Results of interspecific competition

demonstrated that C. insularis was significantly more

competitive than M. manilae (Fig. 1.) However, when C.

marginiventris replaced M. manilae within the host larva,

then C. marginiventris emerged more frequently than C.

insularis. The combined parasitization rates for the

three treatments ranged from 73-78%, which demonstrated

that multiple parasitization did not seem to affect FAW

larval mortality. FAW larvae parasitized by any two of

the three parasitoid species only produced a single

parasitoid, which suggests the destruction of one

parasitoid larva by another. Salt (1961) and Vinson and

Ables (1980) reported that when multiple parasitism

occurred, all but one species was usually eliminated

through physical attack, physiological suppression, or

both. In a few instances, especially with gregarios

parasitoids, some individualy of both species may survive

(Miller 1982, Weseloh 1983).

Substantial differences were not present between the

three parasitoid treatments for (1) larvae that success-

fully pupated and emerged as adults, (2) larvae that

starved because they did not feed on the diet, (3) larvae

that died from unknown causes and (4) larvae that fed on

the diet but did not pupate (Table 4). Rejection of the





























FIG. 1. Mean percentage emergence of C. insularis (Ci),
M. manilae (Mm), and C. marginiventrisTCm) from fall
armyworm larvae expose< to multip le parasitization.



















80 80
Occi
C 70- 3 Mm 70
0 BCm
F-
S60- -60
(T
S50- -50
LL
O
S40- -40

S30- -30

w 20- -20

J 10- = 10

0o o
- 0'1 0
Ci & Cm Ci&Mm Ci-only
TREATMENT







53

















Table 4. Mean percentages for emergence of Chelonus insularis
(Ci), Microplitis manilae (Mm), Cotesia marginiventris (Ci) and adult
FAW, and percent ages f Tor FAW larvae failing to mature because they
refused to feed on the diet, for dying from unknown causes, and for
failing to pupatea



Parasitoid emergence Refused Unknown Did not
Treatment Mm Cm Ci FAW diet causes pupateb

Ci x Mi 13.7a 64.3a 7.0a 3.9a 5.8a 5.4a

Ci x Cm 46.0b 27.4b 8.7a 4.0a 7.7a 6.5a

Ci only 74.4a 7.3a 4.3a 7.7a 5.9a


aTreatments replicated nine times with 30 larvae/treatment. Means
in the same column followed by the same letter were not significantly
different by Duncan's Multiple Range Test (P = 0.05). This means for
Mm (Column 2) and for Cm (Column 3) were compared using students
t-test.
bHad not pupated by the time nonparasitized larvae had emerged.





54





larval diet may be one of the sources of artificial

selection encountered when an insect population is placed

under laboratory colonization (Boller and Chambers 1977).

However, reasons for those larvae that fed on the diet but

did not pupate or molt during the allocated period were

not properly understood. Beckage (1982) observed Manduca

sexta (L.) larvae parasitized by Apanteles smerrintie

Riley often molted to larval-pupal intermediates even when

parasitoids failed to emerge.

Experiment 2. The proportions of C. marginiventris

and M. manilae adults that emerged from parasitized and

non-parasitized hosts were not different significantly

(Table 5). Cotesia marginiventris parasitized signifi-

cantly more hosts then M. manilae. Larvae that were not

parasitized by either parasitoid and emerged as FAW adults

displayed significant differences in all four treatments.

These data support the results of experiment 3, where M.

manilae females altered their ovipositional behavior

toward hosts already parasitized by C. insularis. Cotesia

marginiventris did not appear to discriminate against

hosts parasitized previously by C. insularis as there were

no significant differences between C. insularis x C.

marginiventris and C. marginiventris only treatments.

Vinson and Iwantsch (1980) did not discriminate against C.

insularis parasitized tobacco budworm hosts and neither

did M. croceipes.






55














Table 5. Mean percentage emergence for Cotesia marginiventris
(Cm) and Microplitis manilae (Mm) from FAW larvae exposed and not
exposed as eggs to Chelonus insularis (Ci) and percents for emergence
of FAW adults, larvae dying because they refused to eat the diet, and
larvae not pupating.



Mean emergence Refused Did not
Treatment Ci Cm Mm FAW diet pupateb


Ci x Cm 32.5 56.5 5.0 0.0 0.0

Cm only 52.5 30.0* 4.3 6.3

Ci x Mm 48.0 37.5 13.0 0.0 0.5

Mm only 44.5* 28.5* 11.5 16.5*


aTreatments replicated nine times with 20 larvae/treatment. Data
analyzed by Student's t-test (* =significantly different at the 5%
level).

Comparisons only made between treatments 1 ant 2, and 3, and 4. The
means for Ci in treatments 1 and 2 were not compared statistically.





56




Experiment 3. The behavior of M. manilae females

were altered significantly when exposed to hosts para-

sitized previously by C. insularis (Table 6). This

altered behavior occurred in three categories; examina-

tions, probes, and apparent oviposition. A similar

behavioral pattern was not found for C. marginiventris.

This indicated that C. marginiventris either cannot

discern the presence of C. insularis in the host or that

the presence of C. insularis does not inhibit oviposition.

Vinson and Ables (1980) reported that tobacco budworm

larvae parasitized previously by C. insularis also were

acceptable to larval parasitoids Microplitis croceipes

Cresson and Campoletis sonorensis Carlson as ovipositional

sites.

Experiment 4. The number of encounters, examina-

tions, and apparent ovipositions for the two larval para-

sitoids were not significantly different regardless of the

parasitization sequence or the number of days between host

exposure periods (Table 7). Initially, M. manilae made

greater numbers of encounters in C. marginiventris para-

sitized larvae than in non-parasitized larvae. There was

a trend for M. manilae to be more active with respect to

encounters, examinations and ovipositions on hosts para-

sitized by C. marginiventris compared to non-parasitized

hosts. Cotesia marginiventris was more active also on

hosts parasitized previously by M. manilae than on






57







Table 6. Mean and percents for encounters, examinations,
oviposition probes and apparent ovipositional success by Cotesia
marginiventris and Microplitis manilae in fall armyworm larvae
exposed and not exposed as eggs tfo helonus insularis.



Meana

Exposure to
C. insularis Encounters Examinations Probes Ovipositions


Microplitis manilae

Exposed 8.4 2.0 2.2 1.2

(60.8) (14.4) (15.9) (8.7)
Not Exposed 8.8 3.8* 4.2* 2.6*

(45.5) (19.6) (21.7) (13.4)

Cotesia marginiventris

Exposed 12.8 5.8 2.6 2.8

(54.3) (22.4) (11.2) (12.1)
Not exposed 14.2 5.8 2.9 2.9

(55.04) (22.5) (11.2) (11.2)


aStudent's t-test analyzed at a = 0.05 level. Percents are in
parentheses-and are based upon the total number of behavioral
observations (encounters + exams + probes + oviposition).






58







Table 7. Mean for numbers of encounters, examinations and
apparent ovipositions by Cotesia marginiventris (Cm) and Micro-
plitis manilae (Mm) during two host exposure periods separated by
different numbers of days.




Second host exposure meansa
Days between
Host exposure host exposure Examina- Apparent
Fir st Second period Encounters tions oviposition



Cm Mm 0 13.2 7.8 6.8

None Mm 11.8 6.9 5.6


3 10.8 4.2 3.6

9.6 5.4 3.0


6 10.6 8.8 4.6

9.8 8.0 4.0


Mm Cm 0 11.4 8.8 6.6

None Cm 9.6 7.8 6.0

3 15.6 9.6 5.6

14.4 8.8 5.2


6 16.8 6.9 7.8

17.4 6.8 7.0

- - -- - -
aNone of the number pairs were significantly different by
Student's t-test.






59




non-parasitized hosts. M. manilae had greater

ovipositional contacts with the hosts that contained C.

marginiventris larvae than C. marginiventris with host

that contained M. manilae larvae on the first day of host

exposure. This trend reversed itself on days 3 and 6.

Experiment 5. The host finding and behavioral

sequence for oviposition of C. marginiventris on FAW

larvae already parasitized by C. insularis on corn,

sorghum, Bermudagrass and itch grass consisted on nine

basic components (Fig. 2). During the sequence, preening

occurred at several different steps. A typical pattern

involved the following:

1. Random movement--The parasitoid female flew and

walked randomly inside the cage or on the plant leaves.

The upper portion of the leaf was preferred. The female

held her antennae close and parallel to the substrate, or

folded them back under her body.

2. Antennal palpation--The female started antennal

palpation of the surrounding leaves and on the substrate.

She held her antennae nearly parallel to the substrate and

lowered her flagella slightly and raised them back to the

horizontal position. This movement of the flagella

frequently lasted for 5 to 25 sec. The under surface of

the leaf was palpated more frequently.





























FIG. 2. Behavioral ethogram of the host finding and ovi-
positional sequence of C. marginiventris females on fall
armyworm larvae already parasitized by the egg-larval
parasitoid C. insularis. (Solid arrows indicate invari-
able pathways and dashed arrows represent alternate
pathways.)























!-(4)
S(3) Chemotaxis Larval
h, ,~, Contact A
A/
-\ \

(2) Antennal \ /
Palpation Mounting (5)

/ \
N- i
IN \ /

Random
Movement < ----- -> Preening Insertion (6)






(9) Resting V.
Oviposition (7)


SPo st
P o- /
k,-" -' /
-


(9) Resting I..
Oviposition (7)


Antennal _._-. Oviposition (8)
Palpation '
|^






62




3. Chemotaxis--The parasitoid became oriented and

walked rapidly toward the site where FAW larvae feeding on

the leaves. She vibrated her wings frequently and moved

her body in a manner that indicated excitement.

4. Larval contact--Locomotion was arrested and

antennal palpation of the host began with the apical

portions of both antennae.

5. Mounting--The parasitoid jumped quickly onto the

host, usually near the posterior portion.

6. Insertion--Stinging was performed immediately

after the process of mounting. The wings were extended

during the process.

7. Oviposition--This occurred immediately after

insertion and the parasitoid moved away quickly from the

host.

8. Postoviposition--The parasitoid restarted

antennal palpation of the substrate. The female began an

integrated sequence of abdominal bending and metathoracic

leg extension. Preening always occurred.

9. Resting--The parasitoid was motionless.

Loke et al. (1983) described the behavioral sequence

of C. marginiventris on FAW damaged corn plants with an

ethogram that consisted of 13 defined steps and divided

the pattern of host finding behavior for C. marginiventris

on non-parazitized FAW larvae into four phases:






63




non-searching movement, searching, oviposition, and

resting. Analysis of our ethogram and that of Loke et al.

(1983) showed that the elimination of certain steps in our

ethogram are of particular interest because chemical cues

from the earlier oviposition by C. insularis may have

altered the behavioral pattern of the female C. margini-

ventris after ovipositing in an already parasitized FAW

larvae.

The percent parasitization by C. marginiventris

showed more than a two-fold increase in corn compared to

sorghum and more than a four-fold increase over Bermuda-

grass and itch grass (Fig. 3). Sixty percent of the

larvae were parasitized by C. marginiventris in corn after

an 80-min host exposure period. There was no increase in

parasitization for Bermudagrass and itch grass after 20

min. Ashley et al. (1983) found that parasitization rates

for C. insularis and Temelucha spp. were substantially

higher in corn than in Bermudagrass and paragrass Brachi-

arie mutica (L.). Cotesia marginiventris parasitized the

highest proportion of hosts in Bermudagrass and paragrass.

The differences in parasitization rates between these

parasitoids may reflect a host plant preference (Ashley et

al. 1983).

In our study, M. manilae apparently failed to compete

successfully within the host larva when this larva contain





























FIG. 3. Percentage parasitization by C. marginiventris of
fall armyworm larvae already exposed as eggs to C.
insularis. Larvae were randomly placed on four pTant
specie-d held in wire cages within a greenhouse.





















80

*---* Corn
*...... Sorghum
---- Bermudagross
z 60- Itch grass
O 60 -
0


N

S40-
CO ,



'/ ................
N 20- *.*

0 -* - --*- -


20 40 60 80

TIME (min)





66






a developing C. insularis. The possibility also existed

that M. manilae recognized a previously parasitized host

and failed to oviposit. Larvae parasitized as eggs by C.

insularis caused a significant reduction in the number of

host contacts, examinations, and apparent oviposition by

M. manilae. Cotesia marginiventris oviposited in both C.

insularis parasitized and nonparasitized larvae and was

superior internal competitor compared to C. insularis.

Exposing FAW larvae that have been parasitized as eggs by

C. insularis to C. marginiventris or M. manilae did not

result in additional larval mortality. If this same

situation exists under field conditions, then C. insularis

may be the key regulator of FAW larval populations.















EFFECT OF HOST AGE, PARASITOID AGE AND CHANGE OF
TEMPERATURE ON INTERSPECIFIC COMPETITION BETWEEN
CHELONUS INSULARIS CRESSON, COTESIA MARGINIVENTRIS
-CRESSONADEMICROPLITIS MANILAE ASHMEAD
IN FALL ARMYWOORM


Introduction

The fall armyworm (FAW), Spodoptera frugiperda occurs

year-round in the tropical and subtropical areas of the

western hemisphere, where it feeds on corn, sorghum,

Bermudagrass and other members of the family Graminae.

Damaging populations of FAW occur irregularly, and

conditions conducive to outbreaks are not well understood

(Barfield 1980). Estimated losses attributed to FAW

reached $300 million in the southeastern United States

during 1977, one of the most severe outbreak years (Sparks

1979).

A very diverse complex of natural enemies, especially

parasitoids, attack the larval stages of FAW (Ashley

1979). The potential for interspecific competition exists

between these parasitoids because more than one species

attacks the same instar. Pemberton and Willard (1918)

suggested that competition between parasitoids may prevent

them from regulating their hosts effectively.







67






68




Ashley et al. (1982) reported the presence of a mirror

image pattern with respect to percent parasitization of

FAW larvae by the larval parasitoids, Chelonus insularis

Cresson and Temelucha difficilis Dasch. and suggested

that interspecific competition may have cuased this

pattern.

Factors such as host age and environmental tempera-

ture affect the outcome of interspecific competition and

evaluation of these factors should be of primary concern

before initiating parasitoid release programs against a

common host. A literature search provided no information

on the effect of host age and temperature on competition

among FAW parasitiods. Therefore, we selected the larval

parasitoids Microplitis manilae Ashmed. Cotesia

(Apanteles) marginiventris Cresson and the egg-larval

parasitoid C. insularis for our investigations. These two

parasitoids are among the principal natural enemies

regulating FAW populations in southern Florida (Ashley et

al. 1983). The specific objectives of our study were to

determine the effects of host age, temperature and the age

of C. marginiventris on interspecific competition.



Materials and Methods

Parasitoids were kept in plexiglass cages (50 x 50 x

24 cms) at 26 C,60-65% RH and under a 14:10 LD photoperiod





69





regime with a fluorescent light intensity of 800 ft-c and

were supplied with honey and water. Adults of C. margini-

ventris and C. insularis came from laboratory colonies

established from FAW larval collections made from corn at

Hastings and Homestead, Florida, respectively (Ashley

1983). Unless otherwise noted, parasitoids were 24-48 hrs

old when used. The FAW host eggs were obtained from

female moths maintained in a growth chamber set at

26-27"C, 70-75% RH and with a 14:10 LD photo regime. Host

eggs were seperated using the technique of Gross et al.

(1981). All eggs utilized in the experiments came from

the same egg mass to help insure host uniformity. A grid

was drawn on filter paper and individual eggs were placed

in the center of each square. In all experiments FAW eggs

were exposed initially to two female C. insularis inside a

circular plastic container (7 x 10 cm diam) with 2

screened vents (1.5 x 3.0 cm) and containing 4 cubes

(1.5 cm) of FAW diet (Leppla et al. 1979). Eggs attcked

by two or more females and unparasitized eggs were de-

stroyed. The grids were then cut into squares and sus-

pended in a plastic container like those used for oviposi-

tion by C. insularis until egg hatch. These containers

were kept inside an environmentally controlled cabinet set

at 27C, 70% RH, with a 14:10 LD photophase. When the FAW

larvae were 48 hrs old (all were second instars) they were





70




exposed to two female C. marginiventris for 24 hrs inside

a plastic container which was similar to the one used for

C. insularis. The host larvae were then placed inside 30

ml plastic cups containing approximately 15 ml of diet.

These cups were sealed with paper lids and placed inside

the cabinet. The larvae remained in these cups and their

fate recorded. The control treatment for experiments 1

and 2 consisted of larvae exposed only to C. margini-

ventris.

Experiment 1--Host Age

Forty second instar FAW larvae (head capsule width

0.4-0.5 mm) were transferred to an ovipositional unit at

12, 24, 36, 48, 60, 72, and 84 hrs of age and exposed to

two female C. marginiventris for 24 hrs. Each age was

replicated seven times.

Experiment 2--C. marginiventris Age

Cotesia marginiventris cocoons were held for adult

sclosion and mating inside a plastic container similar to

the one used for C. insularis oviposition. When C.

marginiventris parasitoids were 24, 48, 72, 96, and 108

hrs old, two females were exposed for 24 hrs with 40

second instar FAW larvae. Treatments were replicated

seven times.

Experiment 3--Temperature Effects

Thirty second instar FAW larvae were exposed to two

female C. marginiventris for 24 hrs. These experiments






71




were conducted in plastic containers like those used for

oviposition by C. insularis. After exposure to C.

marginiventris, larvae were placed individually in 30 ml

plastic cups and held at the following temperatures 19,

22, 25, 28 and 31C and RH 75-78% with a 14:10 LD photo-

phase. Each treatment was replicated seven times. A

control treatment was run at 26C with host larvae exposed

only to C. insularis. The cups were checked three times a

week and larval fate recorded.

In a second portion of this experiment larvae emerg-

ing from eggs parasitized by C. insularis were exposed to

C. marginiventris when reaching the following host ages

(hrs) 6-10, 12-18, 24-30, 36-42 and 48-54. After exposure

to C. marginiventris, larvae were individually placed into

30 ml cups and held at the temperatures cited above.

Treatments were replicated six times. The control

treatment was held at 26*C and the RH ranged between

70-75%.

Experiment 4--Dissection of Multiparasitized Hosts

Host exposure to C. insularis followed by exposure to

C. marginiventris or M. manilae were performed as pre-

viously described. The C. insularis C. marginiventris

parasitized larvae were then placed inside a plastic

container for 3, 5, 7 or 9 days. The C. insularis M.

manilae parasitized larvae were similarly held for






72




3, 6, 8, or 10 days. Twenty to thirty host larvae were

dissected at the end of each time period to determine the

condition of the competing parasitoids. In the nine day

treatment, C. marginiventris larvae had emerged before

dissections were done. However, since the host was still

alive it was dissected to determine the fate of the

immature C. insularis. The descriptions of Boling and

Pitre 1970) and Glogoza (1980) were used to recognize

larvae of C. marginiventris and C. insularis,

respectively.



Results and Discussion

Thirty six hr old FAW larvae produced the highest

proportion of C. marginiventris and lowest proportion of

C. insularis (Table 8). Emergence of C_ marginiventris

showed significant differences between 60 and 72 hrs and

24 and 36 hrs but there were not significant differences

between 12 and 24 hrs, and 72 and 84 hrs. There was not

significant difference in emergence of C. marginiventris

from hosts 36 hrs old and the control. Loke and Ashley

(1984) reported that highest rate of parasitization by C.

marginiventris of FAW occurred in 48 hr old larvae (second

instars). Kunnalaca and Mueller (1979) and Boling and

Pitre 1970) stated that females of C. marginiventris

produced the most progeny from 2 and 3 day old hosts.

Larvae less than 24 hrs did not produce as many








73










Table 8. Mean percentages at different host ages for
emergence of Chelonus insuaris (C.i.) Cotesia marginiventris
(C.m.) and adult fall armyworm and percent mortality of FAW
larvae due to (1) refused to feed on the diet, and (2) died
from unknown causes.a/



Percent FAW mortality
Host age b/ Parasitoid emergence Refused diet Unknown
(hrs) C.i. C.m. FAW and diet causes


12 25.5a 20.7a 45.2a 7.4a l.la

24 30.4a 15.7a 35.0b 12.2a 6.7ab

36 17.6a 44.2b 20.3c 13.2a 4.8ab

48 18.8a 40.1bc 16.2cd 17.4a 7.5ab

60 31.7a 32.9c 14.3cd 14.la 6.9ab

72 52.7b 17.6a 14.8cd 11.7a 3.lab

84 45.9b 15.2a 10.6d 18.7a 9.6b

Control 45.2b 25.6b 15.8a 8.5b



a/ Treatments were replicated 7 times with 40 larvae per
treatment. Means followed by same letter for a given column
are not significantly different by Duncans Multiple Range
Test. (P = 0.05).







74



C. marginiventris as larvae between 36 and 48 hrs.

Chelonus insularis emerged more successfully than C.

marginiventris from larvae 12 and 24, and 72 and 84 hrs

old. Emergence of C. insularis in early and latter ages

of the host was expected because in most cases of multi-

parasitism the first species that attacked the host was

more successful than the second species (Doutt and De Bach

1964). The emergence pattern of C. insularis showed

significant differences between larvae 60 and 72 hrs old.

This difference was probably a function of the larger

larvae becoming less suitable for parasitization by C.

marginiventris. The percentage of non-parasitized larvae

that became adults was greater except at 48 and 84 hrs

than those that died from unknown causes or starved to

death. There was a steady decrease in the percent larvae

that became FAW adults as host age increased. Substanti-

ally more larvae died refusing to eat the diet and died

than from unknown causes. No significant differences were

found between host ages for larvae dying from refusing to

feed. This rejection of larval diet may be a source of

artificial selection encountered when an insect population

is placed under laboratory colonization (Boller and

Chambers 1977). Ashley et al. (1982) reported that a

definite proportion of the FAW larval population refused

to feed on the artificial diet and that diet rejection was

not restricted to the early instars. Significant






75




differences were observed for larvae dying from unknown

causes between 12 and 24 hrs and 72 and 84 hrs of age.

Experiment 2--C. marginiventris Age

C. marginiventris adults which were 48 to 96 hrs old

produced more parasitoids than did those 24 or 108 hrs old

(Table 9). There were no significant differences in emer-

gence of C. insularis at 24 and 108 hrs suggesting that C.

marginiventris was either too young or too old to start

egg laying. There were no significant differences between

the control and 48, 72 and 96 hrs which indicated that the

presence of a C. insularis larva inside the host did not

reduce oviposition by C. marginiventris. Mean parasitiza-

tion for all ages illustrated that C. insularis had a

higher parasitization level (45%) than C. marginiventris

(41%). Wallner (1982) reported that when two parasitoids

attack the same host the parasitoid ovipositing in the

host first was more successful. Significant differences

were observed for emergence of C. insularis at all the

ages studied. However, highest emergence for C. insularis

occured at 24 and 108 hrs.

Deaths due to unknown causes ranged from approxi-

mately 2.00 to 7.5 percent with the most mortality occur-

ing in the 108 hr treatment and control. A substantially

high proportion of larvae refused to eat the diet in 96,

108 hrs and control treatments.






76











Table 9. Mean percentages for emergence of Chelonus
insularis (C.i.), Cotesia marginiventris (C.m.) and adult FAW
and percent mortalTtyfoT FAW larvae due to (1) refused to feed
on the diet, (2) dietd from unknown causes, when age of C.m.
was changed a/



Percent FAW mortality
C.m. age b/ Parasitoid emregence Refused diet Unknown
(hrs) C.1. C.m. FAW and diet causes


24 58.5a 33.6a 2.9a 2.9a 2.0a

48 39.3b 52.5b 2.la 3.2a 2.9ab

72 42.4bc 47.4b 1.4a 4.9ab 3.9ab

96 30.6b 48.7b 2.la 13.7c 5.4ab

108 54.5a 21.Oc 5.9a 11.Obc 7.7b

Control 55.0b 9.9a 14.8c 10.lb



a/ Treatments were replicated 7 times with 40 larvae per
treatment. Means followed by same letter for a given column
are not significantly different by Duncans Multiple Range
Test. (P = 0.05).






77




Male progeny were always in greater abundance in C.

marginiventris regardless of parental age (Fig 4). Boling

and Pitre (1970) reported that mated C. marginiventris

generally produced with a sex ratio of 1:1. However, only

the 72 hr age group came close to this ratio. A very high

percentage of female C. insularis emerged in 96 hrs (Fig

5) and a very large percent of males emerged from the 108

hr group. Sex ratios in hymenopterous parasitoids may be

affected by suitable host abundance (Rechav 1978);

however, the reason for the abrupt change of sex ratio of

C. insularis in the 96 and 108 hr treatments was not

properly understood. Mitchell et al. (1984) reported a

significant shift in the sex ratio of C. insularis towards

males in the field between April and October.

Experiment 3--Temperature effects

Cotesia marginiventris emerged most successfully at

25C and it appeared that temperature affected the outcome

of competition (Table 10). Significant differences be-

tween emergence rates were present for C. marginiventris

at all temperatures except 28 and 31C. There were no

significant differences at 22, 25, 31 and 28C for C.

insularis but significantly more emerged at 28 than at

25'C. Less emergence was observed for both parasitoids at

low temperatures while optimum temperatures for C.

marginiventris and C. insularis were 25 and 31C,





























FIG. 4. Progeny sex ratios for C. marginiventris from
different aged C. marginiventris"TC.m.) emergi ng from fall
armyworm larvae parasitized as eggs by C. insularis.














100
1 Females
S90-
u 9 Males
Z 80
LU
(D
MC 70
LU
w 60
F--
2 50
W

U 40
AL
0. 30-
Z

10
0
24 48 72 96 108

AGE OF C.marginiventris (hrs)






























FIG. 5. Progeny sex ratios for C. insularis (C.i.) from
different aged C. marginiventris"TC.m.) emerging from fall
armyworm larvae parasitized as eggs by C. insularis.














100
90- Females
0 90
L Males
Z 80-
LUJ
(D
nr 70
LUJ
L 60

z 50

)0 40
LLU
0- 30

< 20-
LlU
10

0 24 48 72 96 108

AGE OF C.insularis (hrs)








C1


Table 10. Mean percentages (+ SE) when reared at several constant temperatures for emer-
gence of Chelonus insularis (C.i.T, Cotesia marginiventris (C.m.) and adult fall armyworm and
percentages For FAW arvae failing to mature because they (1) refused to feed on diet and died,
(2) died from unknown causes, (3) still larvae at end of test, and (4) escaped from cup a/



Percent
Temperature Parasitoid emergence Refused diet Unknown Still
(C) T.T. C.m. FAW and died causes alive Escaped

19 10.3+1.5a 8.5+2.0a 8.2+1.9a 26.9+2.0a 15.5+3.4a 30.5+3.0a 3.3+1.4a

22 12.6+2.1a 18.6+1.9b 16.1+1.8a 34.4+2.7b 3.9+1.2b 14.2+3.2b 2.3+1.2a

25 13.6+2.6a 61.0+3.6c 15.5+3.9a 3.9+1.1d 6.0+1.8b 0.0+0.Oc 1.9+1.2ab

28 34.4+2.0b 32.8+3.0d 15.2+1.4a 9.3+1.7c 7.8+1.4b 0.5+4.9c 1.8+1.2ab

31 38.9+1.8b 29.8+3.3d 14.9+3.0a 9.6+0.9c 6.8+1.5b O.0+0.Oc 1.5+1.0a

Control 35.5+1.4b 17.6+1.0a 10.3+0.8c 10.7+1.0b 1.5+1.1c 15.0+1.7c


a/ Treatments were replicated 7 times with 30 larvae/treatment. Means followed by same
letter for a given column was not significantly different by Duncans Multiple Range Test.
(P = 0.05).







83



respectively. Temperature did not affect emergence of FAW

adults. A significant number of larvae were found to be

alive at 19 and 22C. There was a significant difference

for larvae which died for unknown reasons at 19C and the

remaining temperatures.

The time required for development of C. marginiven-

tris from oviposition to emergence as adults ranged from

12-20 days and declined as temperature increased (Table

11). The longest emergence period for both parasitoids

occured at 190C. Kunnalaca and Mueller (1979) reported

the development time for C. marginiventris decreased

between 25 and 30C. The range of time required for C.

insularis from oviposition to adult emergence was from 26

to 35 days. Significant differences were observed between

19 and 22C for all parameters measured. An abnormally

high number of larvae was unable to pupate at 19C and

development of the FAW was slower at the lower

temperatures. Keller (1980) reported similar results.

Cotesia marginiventris emerged more successfully than

C. insularis when hosts were 12-18 hrs old at 19, 22, and

25C (Fig 6). Chelonus insularis was more successful at

host ages of 36-42 and 48-54 hrs under all temperatures

indicating that C. marginiventris either did not prefer

older hosts or was unable to develop in them successfully.

Cotesia marginiventris was more successful with hosts at






84










Table 11. Mean (+ SE) emergence periods (days) when reared at
several constant temperatures for Cotesia marginiventris (C.m.) and
Chelonus insularis (C.i.) and adult faTT armyworm and percentages for
FAW Iarvae failing to mature because they (1) refused to feed on the
diet and died, (2) still larvae at end of test. a/

------ --;--~- ------ ---;-------- - -"-- U-I- IU

Percent
Temperature b/ Parasitoid emergence Refused diet Still
(C) 7T -. C.m. A- and died alive



19 35.5+1.1a 20.1+1.2a 40.6+1.3a 3.5+1.0a 60.3+1.1a

22 30.3+1.6b 18.6+1.1b 34.5+1.1b 6.9+1.5b 30.3+1.7b

25 26.3+1.5b 17.3+2.1b 28.9+2.1c 1.5+1.7b O.OOc

28 27.5+1.9b 12.5+12.5b 19.5+1.3d 2.7+1.7b O.OOc

--I- U' I "-~"-~"-~~- `- ~-Y~IU" Y- ------ ~-----

a/ Treatments were replicated 7 times with 30 larvae/ treatment. Means
followed by same letter for a given column are not significantly
different by Duncans Multiple Range Test. (P = 0.05).






















FIG. 6. Percentage emergence of C. marginiventris and C. insularis from fall
armyworm (FAW) larvae, parasitizeTdon eggs by C. 7 nsulaTTs. F ~ rvae were
exposed at different ages to C. marginiventris and then held at 19, 22, 25, 05
28C for development.


























S0-

LO
.













N
ci)
OD








0 0A
E00





co (10 n t ro C'J

SGIOiISVJVd AO 39N393ii3 %






87




24-30 hrs old at 22 and 25C than was C. insularis. In.

general, C. marginiventris emerged from a higher propor-

tion of younger hosts than did C. insularis. Hosts older

than 36 hrs produced more C. insularis regardless of

temperature. Two possible explanations for this are as

follows: (1) C. marginiventris was a better competitor in

younger hosts and (2) either oviposition or successful

competition was reduced in older hosts larvae containing a

developing C. insularis.

Experiment 4--Dissection of Multiparasitised Hosts

Dissections of multiparasitized larvae showed no evi-

dence of physical attack between parasitoids during the

first 5 days of host development (Table 12). However 7

days after parasitition, 5 C. insularis larvae had visible

melanized scars, while those of C. marginiventris were

unscared suggesting that C. marginiventris physically

attacked larvae of C. insularis. Vinson and Ables(1980)

reported that larvae of C. insularis had visible evidence

of physical attack after 3 days in hosts parasitized by

the larval parasitoid Campoleis sonorensis (Carlson). Six

days after parasitization by M. manilae, 5 dead M.

manilae larvae were found in the hosts. This number of

dead larvae was higher at 8 and 10 days although there was

no visible evidence of physical attack. Vinson and

Iwantsch (1980) reported that M. croceipes mutilated the





88






Table 12. Fate of larval parasitoid C. marginiventris (C.m.) and M. manilae
(M.m.) in competition with the egg larval and parasitoid C. insularis as determined by
dissection of fall armyworm (FAW).


Fate of
No. of FAW After exposure to C. marginiventris
Competitor larvae 2nd parasitoid Fate of or
species dissected when dissected C. insularis M. manilae



C.m. 26 3 23 larvae 21 eggs
3 no larvae 5 no larvae

26 5 22 larvae 19 larvae
4 no larvae 7 no larvae

20 7 5 injured larvae 4 injured larvae
15 larvae 16 larvae

23 9 /c 3 larvae/a

M.m. 30 3 28 larvae 26 egge
2 no larvae 3 shriveled egge
1 no egg

23 6 20 larvae 5 dead larvae
3 no larvae 12 healthy larvae
6 no larvae

20 8 20 larvae 7 dead
10 healthy larvae
3 no larvae

23 10 10 larvae 10 dead larvae/b
13 no larvae 2 no larvae


/a Most of C. marginivenris have formed cocoons.

/b Some larvae emerging from host to form cocoon outside.

/c C. insularis larvae were not found.






89




C. insularis larvae by physical attack and killed them in

5 days.

In summary, C. marginiventris reproduced most suc-

cessfully in 36 hr old FAW larvae. C. marginiventris

adults which were 48 to 96 hrs old produced the greatest

number of parasitoids. C. insularis and C. marginiventris

developed optimally at 31 and 25C. Cotesia marginiven-

tris physically attacked developing C. insularis larva

inside the host. Dead M. manilae larvae were found in

hosts multiparasitized by C. insularis and M. manilae but

the cause of the death was unknown.




Full Text
33
In a study on impact of native parsito ids on FAW in
Southern Florida, Ashley et al (1982) described a mirror
image pattern of parasitization between C. insularis and
Terne!ucha spp collected from the FAW larvae. This
increase-decrease and deer ease-increase pattern between
these two parasitoids may be indicative of interspecific
competition between these parasitoids (Ashley et al .
1982). Mitchell et al ( 1984) reported the effect of two
FAW pheremone components (Z9D0A and Z9TDA) upon population
dynamics of its larval parasites and found that C.
insu1aris was the predominant species followed by T.
difficilis whose par as itization rate of FAW larvae was
initially high and then remained relatively constant for
the remainder of the experimental period. The explanation
for this type of parasitization pattern was that C.
insu1 aris was a better internal competitor than T.
difficilis (Mitchell et al. 1984).


126
were observed on May 8th, 12th, and June 17th in terms of
damage to upper leaves in parasitoid release and non
release plots. Damage to lower leaves also showed
significant differences between these two plots on June
17th. The damage to stalks were negligible in both plots.
Keller (1980) reported that mature leaves are a qualita
tively better food source for FAW than developing leaves.
However, FAW larvae appar to prefer developing leaves
under field conditions (Morrill and Greene 1973). Since
feeding on mature leaves exposes FAW larvae to natural
enemies and climatic changes, concealed feeding in whorls
may have survival advantage. This trend was observed on
all observatio dates except June 9, July 15, in
non-parasitoid release plots and June 9th, in parasitoid
released plots.
Cotesia marginiventris and insularis produced the
most progeny at a host density of 64 eggs/larvae per cup.
Longevity of marginiventris was greatest at a host
density of 8 larvae/cup. Chelonus insularis had an
emergence of 60% in field cages but C_^ marg i n i ventr i s was
a better competitor at host densities above 2 egg massses
per paper section. Seventy percent of all hosts in the
first instars were parasitized. Chelonus insular is
emerged 72% and 58.5% of the time from parasitized larvae
on the lower and upper surfaced of corn leaves,
respectively.


Cotesia marginiventris was a superior competitior
relative to i n s u 1 a r i s and C^_ i nsu 1 ar i s was superior to
M. man i 1ae. Subsequent par as itization by either C.
marginiventris or M man i 1ae or larvae exposed to C.
insu1 aris as eggs did not result in additive host mortal
ity. Mic r o p1 itis man i 1ae females changed their behavior
significantly by displaying a reduction of approximately
50% in host examinations, 45% in ovipositor probes, and
55% in apparent ovipositions when C in s u1aris parasitized
larvae were presented. Cotesia marginiventris displayed a
greater number on contacts, examinations and ovi pos itional
attacks in larvae 3 and 6 days after initial
par as itization by m an i 1ae .
The maximum reproductive potential for C. margini
ventris was achieved in hosts 36 to 48 hours old and at a
temperature of 25C. The optimum parasitoid age for C.
marginiventris during the host exposure period was 48 to
96 hours. Egg to adult developmental times at 25C, were
17 and 26 days for marginiventris and C^_ i n su 1 ar i s,
respectively. In multiple parasitized larvae C, margini-
ventris appeared to physically attack and destroy the
larvae of in s u1 a ris C insularis was the predominant
species that emerged from field cage but marginiventris
was a better competitor at host densities above 120
eggs/larvae. The damage to upper leaves was significantly
greater in non-parasitoid release plots than in parasitoid
released plots.
xi


INTERSPECIFIC COMPETITION BETWEEN PARASITOIDS OF
THE FALL ARMYWORM
Introduction
The fall armyworm (FAW), Spodoptera frugiperda is a
serious pest of many graminaceous crops throughout the
southeastern United States. Average estimates of annual
crop losses exceed $300 million (Mitchell 1979). Since
overwintering occurs only in the southern portions of
Florida and Texas (Lunginbil1 1928), increasing FAW mor
tality within this range may lower the numbers of adults
participating in this pest's northward migration each
spring. Fifty-three species of parsito ids have been
reared from field collected larvae (Ashley 1979).
Knowledge of parsito id interrelationships within FAW
larval populations will increase our understanding of the
factors that affects the dynamics of this pest, as well as
contribute the biological control efforts. In endemic
host enemy associations, interspecific competition appears
to play a crucial role in structuring the parasitoid guild
(Force 1974), and may influence the entire natural enemy
complex as well. Parasitoids of the FAW provide a
44


20
as texanus Cresson (1872), texanoides Viereck
(1905), exogyrus Viereck (1905) and bipustulatus
Viereck (1911) (Marsh 1978). C. insular is is distributed
throughout in North, Central and, South America, and the
West Indies and has been introduced into Hawaii and South
Africa (Marsh 1978).
Description
The eggs of C. insular is are white, and cylindrical,
and appear comma like in shape. They are slightly arcuate
with both ends rounded, one being larger than the other
(Glogoza 1980). The first instar larva has a prominent
square head with easily distinguishable dark, pointed,
mandibles and 7 body segments tapering from the thorax to
the abdomen (Glogoza 1980). The larva floats in the host
hemolymph. The second stage larva is cylindrical with a
tapered head. The body of the third stage is also
cylindrical and the head which is relatively narrow tapers
in the front. C. insularis causes its host to burrow in
the earth when the host reaches the 4th instar and to form
a pupation cell. After completing this cell the parasi-
toid larva consumes the entire contents of the host and
then pupates. The larva spins a cocoon by using a silky
secretion and this cocoon is cylindrical with almost flat
ends. Ashley (1983) found that of those FAW larvae


22
20 and 40C while at 35C a 1:1 ratio was obtained
(G1ogoza 1980).
C insularis can develop in many hosts. Besides S.
frugiperda, it is also able to develop in He1 iothes
armigera ( H u b n e r) Spodoptera exigua (Hbn ) Ephestia
sericaria (Scott) (Bianchi 1944). Marsh (1978) reported
that hosts for North America include Ephestia elutella,
(Hbn), Felt i a subterrnea (F), He!iothes zea (Boddie),
Loxostege sticticalis (L.) Per idroma s aucia (Hbn),
Spodopter a e rid a nia (Ramer), Spodoptera ornithogalli
(Guenee), Spodopter a pr aef i ca Grote, and T^_ n i .
P ar as i t i z at i on of FAW by i n s u 1 a r i s reduced host
FAW larval weights by 70% and only 28% of the larvae
parsitized by in s u 1 a r i s lived past the 9th day and
these larvae displayed an unusual increase in weight prior
to destruction by the parasitoid (Ashley 1983).
Ashley et al. (1982) found that the native parasitoid
C. insularis was the primary species attacking FAW in
South Florida and it emerged from 71% of the parasitized
larvae. C. insu1aris caused the highest mortality of FAW
larvae collected from corn and broadleaf signalgrass
(Ashley et al. 1980). Ashley et al (1983) reported that
C. insularis parasitized 44% of all FAW larvae collected
from volunteer corn, Bermudagrass and paragrass and


18
increased exposure time. Kunnalaca and Mueller (1979)
reported that oviposition was accomplished quickly with a
single ovipositor thrust and this occurred primarily
during day light hours. Multiple oviposition was common
especially when few hosts were offered to a parasite
(Boling and Pitre 1970). Total fecundity ranged from 30
to 110 eggs per female (Kunnalaca and Mueller 1979).
Time required for the development of C. marginiven-
tr i s from oviposition to cocoon formation ranged from 6 to
11 days at 30C (Boling and Pitre 1970, Kunnalaca and
Mueller 1979). Boling and Pitre (1970) reported the
optimum time for development as 7 days in T^ n_i_ and
Pseudoplasia includens (Walker) and 6 days in Heliothes
virescens (F.) within 24 hours after existing host larva.
Kunnalaca and Mueller (1979) reported an optimum develop
mental time of 8 days in Plathypena scabra (F). At 30C
and 25C, development times from cocoon to adult ranged
from 3-5 days and 4-7 days, respectively (Kunnalaca and
Mueller 1979). The sex ratio (1.5:1) favored males at
both 30C and 25C (Kunnalaca and Mueller 1979). Mean
longevity of adults at 30C and 25C was 5.6 + 2.. 5 and
9.1M.2 days, respectively and females lived longer than
males at both temperatures (Kunnalaca and Mueller 1979).
Paras itization by marginiventris resulted in
growth retardation of the host (Danks et al 1979 ).


FIG. 2. Behavioral ethogram of the host finding and ovi-
positional sequence of marginiventris females on fall
armyworm larvae already parasitized by the egg-larval
parasitoid C. insularis. (Solid arrows indicate invari
able pathways and dashed arrows represent alternate
pathways.)


75
differences were observed for larvae dying from unknown
causes between 12 and 24 hrs and 72 and 84 hrs of age.
Experiment 2--C. marginiventris Age
C. marginiventris adults which were 48 to 96 hrs old
produced more parasitoids than did those 24 or 108 hrs old
(Table 9). There were no significant differences in emer
gence of C^_ i n s u 1 a r i s at 24 and 108 hrs suggesting that C .
marginiventris was either too young or too old to start
egg laying. There were no significant differences between
the control and 48, 72 and 96 hrs which indicated that the
presence of a insu1 aris larva inside the host did not
reduce oviposition by margin iventris. Mean parasitiza-
tion for all ages illustrated that C. insularis had a
higher paras itization level (45%) than C. marginiventris
(41%). Wallner (1982) reported that when two parasitoids
attack the same host the parasitoid ovipositing in the
host first was more successful. Significant differences
were observed for emergence of i n s u 1 a r i s at all the
ages studied. However, highest emergence for C. insularis
occured at 24 and 108 hrs.
Deaths due to unknown causes ranged from approxi
mately 2.00 to 7.5 percent with the most mortality occur -
ing in the 108 hr treatment and control. A substantially
high proportion of larvae refused to eat the diet in 96,
108 hrs and control treatments.


56
Experiment 3. The behavior of mani 1 ae females
were altered significantly when exposed to hosts para
sitized previously by insu1 aris (Table 6). This
altered behavior occurred in three categories; examina
tions, probes, and apparent oviposit ion. A similar
behavioral pattern was not found for marginiventris.
This indicated that marginiventris either cannot
discern the presence of insu1 aris in the host or that
the presence of insularis does not inhibit oviposition.
Vinson and Abies (1980) reported that tobacco budworm
larvae parasitized previously by insu 1aris also were
acceptable to larval parasitoids Microplitis croceipes
Cresson and Campoletis sonorensis Carlson as ovipositional
sites.
Experiment 4. The number of encounters, examina
tions, and apparent ovipositions for the two larval para
sitoids were not significantly different regardless of the
parasitization sequence or the number of days between host
exposure periods (Table 7). Initially, M_^ man i 1 ae made
greater numbers of encounters in marginiventris para
sitized larvae than in non-parasitized larvae. There was
a trend for man i 1 ae to be more active with respect to
encounters, examinations and ovipositions on hosts para
sitized by C_^ marginiventris compared to non-par as i ti zed
hosts. Cotesia marginiventris was more active also on
hosts parasitized previously by M. manilae than on


99
superparasitism at high densities (Table 13). The longev
ity of emerging m a r gi niv e n t ris was greater at lower
densities than at higher densities. Substantially more
larvae were found dead at higher than at lower parasitoid
densities, probably due to cannibalism. (Ashley, Pers.
Comm. 1985).
A similar trend of progeny production was observed
for C. insularis (Fig 8). The 64 larvae/cup treatment had
produced the highest number of progeny. The number of
progeny were related to the parasitoid density. As the
number of larvae per treatment was increased a consequent
increase in progeny production was observed. This is a
well recognized characteristic of many parasitic
hymenoptera (Legner 1969). C. insularis was more success
ful in progeny production than margin i ventris at higher
densities. A number of events may have been responsible
for the apparent success of C. insularis. The females
spent less time examining eggs before ovipositing at the
higher density. Also the female insularis oviposited
more eggs at higher host density than at lower density.
C. marginiventris may have detected hosts previously
parasitized by C. insularis by some external stimuli and
reduced oviposition. C. insularis received unparasitized
eggs for oviposition. The reduction of oviposition by C.
marginiventris may have helped for developing C. insularis
larvae to emerge without a competition.


131
showed that interspecific competition occurred between
exotic and indigenous FAW natural enemies. My data and
that of Ashley et al. (1982) and Mitchell et al. (1984)
indicated that is is difficult to establish additional
natural enemy species in the overwintering range of FAW in
South Florida, because of the dominance of C. insu 1aris.
Host age preference, developmental period and longe
vity of NL man i 1 ae, a larval parasitoid of Spodopter a spp,
imported from Thailand, were studied. First (24-48) and
second (49-72 hrs) age group of FAW larvae found to be
most suitable for parasitoid propagation. The develop
mental period ranged from 13-18 days. Male and female
longevity was about 6-7 days. Paras itization rates of
3.5-30.1% by M^ mani1ae in FAW larvae were observed. This
biological information will be useful in the event that M.
man i 1ae is reared for inundative or inoculative releases
in overwintering range of FAW.
Competition within FAW larvae by C. marginiventris,
M. man i 1 ae and i nsul ar i s revealed that C_^ marg i n i ven -
tris was a superior competitor compared to C. insularis
but i n s u 1 a r i s was superior to ^ man i 1 ae. Subsequent
par as i t i zat i on by either marginiventris or man i 1 ae
of larvae exposed to insu1 aris as eggs did not
result in additive host mortality. Description and
analysis of host finding behavior by C. marginiventris in
FAW larvae previously parasitized by C. insularis showed


40
Table 2. Developmental periods (X +_ S.E.) and progeny
sex ratios for M. man i 1ae in fall armyworm larvae
Developmental
period
(days)
Age
group
Sex ratio (%)a
( hr s)
Hosts
exposed
Egg-
pupa
Pupa-
ad u 11
Total
Males
Femal es
1 (24-48)
106
10 + 2.3
4 + 0.7
14 + 3.0
62.5-
--*--37.5
2 (49-72)
127
10 + 2.9
3 + 0.9
13 + 3.8
42.9-
--*--57.1
3 (73-96)
93
10 + 2.1
4 + 1.1
15 + 3.2
46.8-
-ns--53.2
4 (97-130)
43
12 + 1.9
6 + 1.7
18 + 3.6
46.7-
-ns--55.3
aAsterisk indicates significance at the 5% level by Student's
t-test.


3
within the host. Thus, researchers may be unable to
predict the outcome unless they can identify and duplicate
the relevant elements of the pest's physiology under
experimental conditions.
The parsito id guild of Spodoptera frugiperda (J.E.
Smith), the fall armyworm (FAW), provides a relevant host
parasitoid association for assessing host and natural
enemy relationships. The FAW is a sporadic and
occasionally severe crop pest in the Southeastern United
States where this species is known to be able to survive
in winter (Luginbill 1928), though survival further north
is thought possible only during exceptionally mild winters
(Snow and Copeland 1969). In years of high population
density, FAW larvae may cause over $300 million in damage
(Mitchell 1979). Fifty three species of par asitoid
species have been recovered from FAW larvae (Ashley 1979)
and are responsible for significant reductions in FAW
larval populations (Ashley et al. 1982). The principal
parasitoids of the FAW either attack its eggs or the early
instars and thus provide suitable models for the study of
parasitoid interrelationships, especially with regard to
interspecific competition between the egg-larval and
larval parasitoids.
The following research was conceived to assess and
investigate the competitive abilities between the parasi
toid larvae of Chelonus insu1 aris Cresson, Cotesia


4
(Apante 1 es) marginiventris Cresson, and Microp1 itis
man i 1ae Ashmead. The objectives of the study were to (1)
study the biology of man i 1 ae an imported larval
parasitoid of Spodoptera spp in Thailand, (2) investigate
interspecific competition between larvae of the
parasitoids i nsul ar i s, C marginiventris, and M.
man i 1ae, (3) examine the effects of host and parasitoid
age, and temperature on the outcome of interspecific
competition, and (4) study the functional response of C.
marginiventris when exposed to different densities of FAW
larvae previously parasitized by C. insularis.


80
§ C, marqiniventris males
I C, marqiniventris females
ED C. insularis males
M C. insularis females
cn
Q
70
O
\
CO
60
<
cr
<
50
Q_
1
40
LJ
O
30
cr
LU
CL
20
10
US LS GR SH
WH
LOCATION ON PLANT


MEAN NUMBER OF ADULTS
FAW LARVAL DENSITY


10
Natural mortality inflicted on FAW larvae by natural
enemies (parasitoids, predators and pathogens) in both
agricultural and wild host plant comm uni ties is believed
to play a substantial role in density regulation (Barfield
et al. 1980). Ashley (1979) presented detailed informa
tion about the classification and distribution of the FAW
parasitoids and noted that 53 species from 43 genera and
10 families have been reared from FAW larvae. Among them
18 species occur in North America; 21 species occur in
Central and South America; and 14 species are common to
all three regions (Ashley 1979). Parasitoid species
attacking FAW vary between different agroecosystems. For
example, in a study by Ashley et al. (1980) in late
planted field corn, 8 species of parasitoids, representing
the families Braconidae, Ichneumonidae, Eulophidae and
Tachinidae, were collected from FAW larvae feeding on corn
and surrounding broadleaf signal grass. Chelonus texanus
Cresson caused the highest mortality followed by Meterous
autographae Musebeck and Euplectrus piatyhypenae Howard.
Nickle (1976) reported that 7 species caused parasitiza-
tion of FAW larvae on peanuts and Apanteles marginiventris
Cresson., M. autographae and 0phion spp were responsible
for highest mortality. Ashley et al. (1983) in another
study on par as itization of FAW larvae on volunteer corn,
Bermudagrass (Cynondon dactylon (L)) and paragrass


49
grass. These plants were grown in pots (14.5 x 15 cm
diam) containing a mixture of sand, perlite and peat moss
(1:2:2 ratio, respectively). Supplementary nutrients were
supplied with fertilizer (8-8-8 plus trace elements). FAW
larvae exposed previously to insu1 aris were allowed to
become second instars. Plants were placed in wire cages
(40 cm3) in a greenhouse at 26-28C, 70-75% RH and 14:
10 LD photoperiod. Thirty larvae were placed randomly on
the plant leaves. After 24 hrs, a female was introduced
into the cage and her host finding behavior observed.
Forty females were observed in sequence, their responses
recorded and synthesized subsequently into common
behavioral patterns.
Parasiti zation by C_^ margi ni ventr i s on FAW larvae
also was measured on all four host plants. Thirty,
second-instar larvae already parasitized by C in su 1aris
were placed randomly into the plants. After 24 hrs of
host larval feeding, two female _C^_ margi ni ventr i s were
introduced. The host larva were removed at 20-, 40-, 60-,
and 80-min intervals. Three replicates for each time
interval and plant species were made. Larvae were removed
from the plants and placed in 30-ml cups to determine
parasitization rates.


74
C. marginiventris as larvae between 36 and 48 hrs.
Chelonus insular is emerged more successfully than C.
marginiventris from larvae 12 and 24, and 72 and 84 hrs
old. Emergence of insu1 aris in early and latter ages
of the host was expected because in most cases of multi
parasitism the first species that attacked the host was
more successful than the second species (Doutt and De Bach
1964). The emergence pattern of i nsul ar i s showed
significant differences between larvae 60 and 72 hrs old.
This difference was probably a function of the larger
larvae becoming less suitable for par as itization by C.
marginiventris. The percentage of non-parasitized larvae
that became adults was greater except at 48 and 84 hrs
than those that died from unknown causes or starved to
death. There was a steady decrease in the percent larvae
that became FAW adults as host age increased. Substanti
ally more larvae died refusing to eat the diet and died
than from unknown causes. No significant differences were
found between host ages for larvae dying from refusing to
feed. This rejection of larval diet may be a source of
artificial selection encountered when an insect population
is placed under laboratory colonization (Boiler and
Chambers 1977). Ashley et al. (1982) reported that a
definite proportion of the FAW larval population refused
to feed on the artificial diet and that diet rejection was
not restricted to the early instars. Significant


BIOLOGY AND HOST ACCEPTANCE OF MICROPLITIS MAN I LAE
(HYMENOPTERA:BRACONIDAE ) RAISED ON FALL
ARMYWORM LARVAE
Introduction
The fall armyworm (FAW), Spodoptera frugiperda (J.E.
Smith), is a major pest of corn and Bermudagrass in the
southeastern United States (Luginbill 1928) and may extend
its range as far north as the Canadian border during the
summer and fall months (Snow and Copeland 1969). However,
since this pest has no mechanism for diapause or
overwintering its populations are restricted to portions
of south Florida and Texas during the winter months
(Luginbill 1928). Average estimates of annual crop losses
caused by the FAW exceed $300 million (Mitchell 1979).
Therefore, reducing the density of overwintering FAW
populations may result in a significant decrease in the
amount of damage done by this pest.
Mic r o p1 itis man i 1ae (Ashmead) is a parasitoid of
Spodoptera spp. in Thailand from where it was imported
into the United States. Even though the FAW does not
occur in Thailand, M. manilae develops successfully in
larvae of the FAW under laboratory conditions (Shepard,
personal comm. 1982). The biologies and distributions of
34


12
of FAW populations. Agnello (1978) compiled a list of 10
species of Hymenoptera (8 vespids and 2 sphecids) and 6
Hemiptera (3 reduviids, 1 pentatomid, 1 nabid and 1
anthocorid), 12 Coleptera (9 carabids, 2 cicindellids and
1 coccinellid) a mammal (skunk), 3 amphibians (2 Bufo spp
and 1 Hyla spp) and a variety (13 species) of birds as
predators of FAW. An earwig, Doru spp inhabits whorls of
corn and sorghum and found to feed readily on small and
medium sized FAW larvae (Andrews 1980).
The FAW is reported to be susceptible to at least 16
species of entomogenous pathogens which includes viruses,
fungi, protozoa, nematodes and 2 strains of the bacterium
Bacillus thuringiensis Berliner (Gardner and Fuxa 1980).
Many of these occur naturally in FAW populations. A "poly
hedrosis" presumably nuclear polyhedrosis virus (NPV) was
reported as early as 1915 (Chapman and Glaser 1915) and a
granulosis virus has also been identified from FAW larvae
collected from sorghum (Steinhaus 1957). Fungi also are
natural mortality factors in FAW populations. Three
species have been reported and include Entomophthora
sphaerosperma Fresenius (Charles 1941), Nomuraea rileyi
(Farlow) Sampsom (Luginbill 1928) and Empusa spp
(Luginbill 1928). The natural occurrence of a nematode
Hexamermis spp in FAW larvae was reported from Venezuela
(Gnagliumi 1962). The only protozoan reported to occur


132
that this behavior consisted of 9 basic steps. These
results supported the conclusion of Loke and Ashley (1984)
that host finding behavior of marginiventris is
influenced by chemicals from both plant and host. The
percentage par as itization by marginiventris showed more
than two fold increase in corn when compared to the
increase in sorghum, Bermudagrass, and itch grass. M.
man i 1ae females significantly altered their behavior when
hosts had already been parasitized by C in s u1aris .
C. insu1aris was the major parasitoid when FAW eggs
were glued to upper surfaces of corn leaves (58.5%) lower
surfaces (71%) and between stalks and leaf sheaths
(40.5%). A higher percentage of marginiventris emerged
from the treatments in the ground (15.5%) or the stalks
(35.5%). Significant differences were observed with
respect to damage to upper leaves in whorls of corn in
parasitoid release plots than non parasitoid release plots
and this was related to the impact of parasitoids on FAW
larvae.
Additional work is needed in several areas and new
avenues for research opened up as a result of information
gathered from studies reported here. The superiority of
one parasitoid over another in multiple parasitization
results in the waste of some parasitoids. How this
affects the comparative field efficiencies of all 3
parasitoids studied, as well as the population dynamics of


14
The resistance of corn variety "Antigua 2 D" to FAW has
already been documented (Wiseman et al. 1973). Resistant
varieties in sorghum, peanuts, Bermudagrass, rice, and
millet have also been reported (Davis 1980).
Considering the important factors regulating FAW
populations, action thresholds (AT) for grain sorghum have
been developed (Martin et al. 1980). These action
thresholds are estimated to be 10% of seedling sorghum
possessing egg masses after flowering. However there is a
lack of information in many areas which makes it
difficult to derive dynamic AT and population models
representing the dynamics and host interactions of the
FAW.
The Larval Endoparasitoid Cotesia (=Apanteles)
marginiventris Cresson
Origin and Distribution
Cotesia (=Apanteles) marginiventris is one of the
most freqently recovered parasitoids from field collected
FAW larvae. This parasitoid was originally described from
Cuba, and is native to the West Indies (Muesebeck 1921).
It has been previously classified as Microgaster margini
ventris Cresson (1865), Apante!es grenadensis Ashmead
(1900), A. laphygmae Ashmead (1901), Apante!es (Protapan-
teles) harnedi Viereck (1912) and most recently Cotesia
marginiventris Cresson (Marsh 1978). It appears to have a
wide distribution within the United States, especially in


135
Ashley, T. R., C. S. Barfield, V. H. Waddill, and E. R.
Mitchell. 1983. Paras itization of fall armyworm
larvae on volunteer corn Bermudagrass, and paragrass.
Fla. Entomol 66 : ( 2 ): 267-71.
Ashley, T. R., V. H. Waddill, E. R. Mitchell and J. Rye.
1982. Impact of native parasites on the fall armyworm,
Spodoptera frugiperda, (Lepi doptera:Noctuidae) in
South Florida and release of exotic parasites Eiphosoma
vitticole (Hymenoptera:Ichuemonidae) Environ. Ent.
TT7~8 ST- -J7.
Barfield, C. S., E. R. Mitchell, and S. L. Poe. 1978. A
temperature dependent model for fall armyworm
development. Ann. Entomol. Soc. Amer. 71: 70-4.
Barfield, C. S., J. L. Stimac and M. A. Keller. 1980.
State of the art for predicting damaging infestations
of fall armyworm. Fla. Entomol. 63: (4): 364-73.
Barlett, B. R. and J. C. Ball. 1964. The development
biologies of two encyrtid parasites of Coceos
hesperidurn and their intrinsic competition. Ann. Ent.
Soc. Amer. 57: 496-503.
Beckage, N. E. 1982. Incomplete host development induced
by parasitism of Manduca sexta larvae by Apanteles
smerinthi Ann. Entorno. Soc. Amer. 75 : 24-27 .
Bess, H. A. and F. H. Haramoto. 1958. Biological control
of the oriental fruit fly in Hawaii. Proc. 10th Int.
Congr. Entomol. 4: 835-40.
Bianchi, F. A. 1944. The recent introduction of armyworm
parasites from Texas. Hawaii Plant Rec. 48(3) 203-12.
Boling, J.C. and H. N. Pitre. 1970. Life history of
Apanteles marginiventris with descriptions of immature
stages. Kans. Entomol Soc. 43: 465-70 .
Boiler, E. G., and D. L. Chambers. 1977. Quality aspects
of mass reared insects, pp. 219-236. In: R. L.
Ridgeway and S. E. Vinson (eds.), Biological Control by
Augmentation of Natural Enemies. Plenum Press, New
York.


BIOGRAPHICAL SKETCH
Rohan Harshalal Sarathchandra Rajapakse is the only
son of Mr. and Mr. Don Wilson Rajapakse of Wellawatte,
Colombo, Sri Lanka. Rohan Rajapakse received his primary
and secondary education at Isipathana Maha Vidyalaya,
Colombo. He entered the Faculty of Agriculture of the
University of Peradeniya in 1972, and graduated with
second class honors in 1976. He then worked briefly as an
assistant lecturer and joined the Post Graduate Institute
of Agriculture (PGIA), University of Peradeniya, in 1977.
Between the years 1976 and 1977, he also worked as a
research assisant in entomology in Sri Lanka Cashew
Corporation. He received his masters degree in entomology
from PGIA, University of Peradeniya, in 1978, and joined
the permanent staff of the Faculty of Agriculture,
University of Ruhuna as an assistant lecturer in 1978. He
taught entomology and plant pathology for undergraduate
students at the University of Ruhuna until 1981. He
arrived in Gainesville, Florida, in December of 1981, to
pursue his studies leading to Ph.D. degree at the
Department of Entomology and Nematology at the University
of Florida.
146


62
3. Chemotaxis--The parasitoid became oriented and
walked rapidly toward the site where FAW larvae feeding on
the leaves. She vibrated her wings frequently and moved
her body in a manner that indicated excitement.
4. Larval contact--Locomotion was arrested and
antennal palpation of the host began with the apical
portions of both antennae.
5. Mounting--The parasitoid jumped quickly onto the
host, usually near the posterior portion.
6. Insertion--Stinging was performed immediately
after the process of mounting. The wings were extended
during the process.
7. Ovi pos ition--This occurred immediately after
insertion and the parasitoid moved away quickly from the
host.
8. Postoviposition--The parasitoid restarted
antennal palpation of the substrate. The female began an
integrated sequence of abdominal bending and metathoracic
leg extension. Preening always occurred.
9. Resting--The parasitoid was motionless.
Loke et al. (1983) described the behavioral sequence
of _C^ marginiventris on FAW damaged corn plants with an
ethogram that consisted of 13 defined steps and divided
the pattern of host finding behavior for marginiventris
on non-par azi ti zed FAW larvae into four phases:


136
Boyce, H. R. and G. G. Dustan. 1958. Prominent features
of parasitism of twig-intesting larvae of the oriental
fruit moth Grapholitha molesta (Busck) (Lepidoptera:
01ethreutidUeT in OnFarTo^ Canada. Proc. 10th Int.
Congr. Entomol 4: 493-96 .
Broodryk, S. W. 1969. The biology of Che!onus
curvimaculatus Cameron. (Hymenoptera:Eraconidae) J.
Entomol. Soc. South Africa. 32(1): 169-89.
Bryan, D. E., C. G. Jakson, and R. Patana. 1969.
Laboratory studies on Microplitis croceipes, a braconid
parasite of Heliothes spp. J. Econ. Ent. 62: 1141-44.
Burkhart, C. C. 1953. Feeding and pupating habits of the
fall armyworm in corn. J. Econ. Entomol. 45: 1035-7.
Chapm an, J. W. and R. W. Glaser. 1915. A preliminary
list of insects which have wilt, with a comparative
study of their polyhedra. J. Econ. Entomol. 8:140-9.
Charles, V. K. 1941. A preliminary list of the
entomogenous fungi of North America. USDA, Bur. Ent.
Plant Quar. Insect Pest Bull. 21: 707-85.
Charnov, E. L. and J. Bull. 1977. When is sex
environmentally determined. Nature. 266: 828-30.
Danks, H. W. R. L. Rabb, and D. S. Southern. 1979.
Biology of insect parasites of Heliothes larvae in
North Carolina. J. Georgia. EntomoT Soc. 14(1):
31-7.
Davis, F. M. 1980. Fall armyworm plant resistance
programs. Fla. Entomol. 15: 277-82.
De Bach, P. and Sundby, R. A. 1963. Competitive
displacement between ecological homologues. Hi lgardi a
34(5): 105-66.
Doutt, R. L. and P. De Bach. 1964. Some biological
control concepts and questions in biological control of
insect pests and weeds. P. De Bach and E. Schlinger
(Eds.). Re inhold, New York, pp 124.
Ehler, L. E. 1977 Paras itization of cabbage looper in
California cotton. Environ. Entomol. 6(6): 783-4.


88
Table 12. Fate of larval parasitoid C. marginiventris (C.m.) and M. manilae
(M.m.) in competition with the egg larval and parasitoid C. insularis as determined by
dissection of fall armyworm (FAW).
Competitor
species
No. of FAW
larvae
dissected
After exposure to
2nd parasitoid
when dissected
Fate of
C. insularis
Fate of
marginiventris
or
M. manilae
C.m.
26
3
23 larvae
3 no larvae
21 eggs
5 no larvae
26
5
22 larvae
4 no larvae
19 larvae
7 no larvae
20
7
5 injured larvae
15 larvae
4 injured larvae
16 larvae
23
9
/c
3 larvae^3
M.m.
30
3
28 larvae
2 no larvae
26 egge
3 shriveled egge
1 no egg
23
6
20 larvae
3 no larvae
5 dead larvae
12 healthy larvae
6 no larvae
20
8
20 larvae
7 dead
10 healthy larvae
3 no larvae
23
10
10 larvae
13 no larvae
10 dead larvae^
2 no larvae
/a Most of
C. marginivenris
have formed cocoons.
/b Some larvae emerging from host to form cocoon outside,
/c C. insularis larvae were not found.


13
naturally in FAW is Nosema laphygmae Weiser, a microspori-
diurn from Colombia (Weiser 1959).
Management Strategies
The major management strategies reported to control
FAW are insecticides (Young 1980), cultural control
(Luginbill 1928) and host plant resistance (Wiseman et al.
1979). Young (1980) suggested the use of irrigation water
as a carrier for insecticides, thereby supplying the
volume of liquid needed to penetrate all of the plant
sites, where FAW feed. Application of granular insecti
cides directly to the whorl has been a common practice in
Central America (Andrews 1980).
The importance of mechanical and cultural control of
FAW was first reported by Luginbill (1928). Black light
traps and pheremone baited cylindrical electric grid traps
have been used to monitor seasonal populations of FAW in
Louisiana and Florida (Mitchell 1979). However, dispos
able sticky traps baited with pheromone (z)-9-dodecen-l-o 1
acetate have been used extensively in surveys in Georgia
and Florida. These traps were found to be most effective
in capturing FAW males when positioned approximately 1 m
above ground and near around preferred hosts (Mitchell
1979 ) .
Wisemann and Davis (1979) showed the importance of
resistant plant varieties in managing FAW populations.


32
"counter-balanced competition" (Zwolfer 1970). In such
systems, the competitive inferiority of a parasitoid
species in multiple parasitism is compensated for by a
superiority in other attributes such as searching
efficiency and synchronization with the host's life cycle
(Schroder 1974).
Weseloh (1983) reported that neither of the
parasitoids A^_ mel anoscel us nor Compsi 1 ura concinnata
(Meigan) destroyed each other inside the host Lymantria
dispar and both emerged from about 11% of the hosts.
These results showed that both parasitoids appeared to be
remarkably tolerant of each other in the same host and
this probably happened because they fill different niches
and so do not compete with each other within the host.
The larval parasitoids Campoletis sonorensis
(Carlson) and Microplitis croceipes Cresson are intrinsi
cally superior to C in s u1 a ris and physically attacked
the latter inside the host, virescens (Vinson and
Iwantsch 1980). In a similar study, Miller (1977)
reported that C. insularis larvae competing with A .
marginiventris inside Spodoptera praefica (Brote) were
dwarfed and nearly killed due to competition. A second
experiment involving C in s u1 a ris and Hypo soter exigue
(Vierek) yielded a similar result where ex i que was a
superior intrinsic competitor relative to C. insularis and
C. marginiventris.


25
superparasitism. However, development of two parsito ids
per host occurred more frequently when larger hosts were
provided. Biology of M_;_ demo 1 i tor imported from
Queesland, Australia has been described by Shepard et al.
(1983) .
Interspecific Competition
By definition competition occurs when two or more
organisms interfere with or inhibit one another (Pianka
1970). Smith (1929) defined "multiple parasitism" to
designate the type of parasitization in which the same
individual host insect is inhabited simultaneously by the
young of two or more different species of primary parasi-
toids. Fisher (1961) reported that this type of multi
parasitism resulted in competition between the parsi
to ids. The occurrence of this type of multi parasitism
depends primarily upon the oviposit ion behavior of the two
parasitoids in response to hosts that are already parasi
tized. In general, parasitoids require a host organism
for egg deposition and the development of immature stages.
Typically, the progeny of one or neither parasitoid will
survive when individuals of different species parasitize a
single host organism (Salt 1961). Therefore interspecific
competition between parasitoids for hosts may be a vital
component influencing guild composition (Zwolfer 1970).
Interspecific competition among parasitiods may even



PAGE 1

INTERSPECIFIC COMPETITION OF FALL ARMYWORM SPODOPTERA FRUGIPERDA (J.E. SMITH) PARASITOIDS, CHELONUS INSULARIS (CRESSON), COTESIA MARG I N I V ENTR I S (TREASON)" "A"N"D MICROPLITIS MA'NTL'AE ASHMEAD (HYMENOPTERA: BRACONIDAE ) By ROHAN HARSHALAL SARATHCHANDRA RAJAPAKSE A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1985

PAGE 2

ACKNOWLEDGEMENTS I am grateful to Dr. Van H. W add i 1 1 chairman of my supervisory committee, for his advice, encouragement and guidance throughout the experimental work and preparation of this dissertation. I am also indebted to him for providing me financial support to pursue my studies at the Department of Entomology and Nematology, University of Florida. I would like to express special thanks to Dr. Tom R. Ashley co-chairman of supervisory committee, for inspiration and guidance and in preparation of this dissertation, and for generously providing facilities and materials at USDA Laboratory. His warm friendship and understanding is greatly appreciated. I am also indebted to Drs. John Strayer and Daniel Roberts for their interest and contributions as members of my supervisory committee, and giving invaluable encouragement when it was dearly needed. There are special thanks for Dr. Stratton H. Kerr and Dr. Andrew Duncan for their invaluable advice and suggestions. I wish to express my gratitude to all the personnel from both USDA Insect Attractants Laboratory at Gainesville and TREC at Homestead who have helped me in numerous ways in conducting my experiments. Special thanks also go to Pamela Wilkening, Polly Hall and Delaine Miller of USDA, Insect Attractants Lab. i i

PAGE 3

My heartfelt thanks and affection go to JoAnne White for her encouragement and assistance and to Patricia Davis for the assistance in typing this dissertation. i i i

PAGE 4

TABLE OF CONTENTS Page ACKNOWLEDGEMENTS ii LIST OF TABLES vii LIST OF FIGURES viii ABSTRACT x INTRODUCTION 1 LITERATURE REVIEW 5 The Fall Armyworm, Spodoptera frugiperda (J.E. Smith).... 5 Seasonal Distribution 5 Life History 6 Economic Status 8 Natural Mortality 9 Management Strategies 13 The Larval Endopar as i toi d Cotes i a marg i n i ventr i s Cresson 14 TjrTgTn and Distribution 14 Description 15 Life Cycle 17 The Egg-Larval parasitoid Chel onus i nsul ar i s Cresson 19 Origin and Distribution 19 Description 20 Life Cycle 21 The Larval E ndo par as i to i d Mi cropl i t is man i 1 ae Ashmead 23 Description and Distribution 23 Interspecific Competition 25 BIOLOGY AND HOST ACCEPTANCE OF MICROPLITIS MAN I LAE (HYMENOPTERA: BRACONIDAE') RAISED" 0~N FALL ARMYWORM LARVAE 34 Introduction 34 Materials and Methods 35 Age group Acceptance 36 Developmental Rates 36 Adult Longevity 37 Time of Host exposure 37 Results and Discussion 37 i v

PAGE 5

INTERSPECIFIC COMPETITION BETWEEN PARASITOIDS OF THE FALL ARMYWORM SPODOPTERA FRUGIPERDA 44 Introduction 44 Materials and Methods 45 Results and Discussion 50 EFFECT OF HOST AGE, PARASITOID AGE AND CHANGE OF TEMPERATURE ON INTERSPECIFIC COMPETITION BETWEEN CHELONUS INSULARIS COTESIA MARG I N I V E NTR I S AND MICROPLITIS MaNIlAE IN FALL ARMYWORM.. 67 Introduction 67 Materials and Methods 68 Experiment l--Host Age 70 Experiment 2--C. margin i ventri s "A~ge 70 Experiment 3--Temper ature Effects 70 Experiment 4--Dissection of Mul tiparasi ti zed Hosts 71 Results and Discussion 72 INTERSPECIFIC COMPETITION BETWEEN FALL ARMYWORM PARASITOIDS CHELONUS INSULARIS AND COTESIA MARG I N I V ENTR I S INSIDE FIELD CAGES AND PLOTS 90 Introduction 90 Materials and Methods 92 Host and Parasitoid Colony Maintenence 92 Experimental Procedures for Host Parasiti zation 93 Experiment l--Host Density 96 Experiment 2--Field Cage 103 Experiment 3--Field Plot 117 Results and Discussion 120 GENERAL SUMMARY AND DISCUSSION 130 REFERENCES 134 BIOGRAPHICAL SKETCH 146 v

PAGE 6

LIST OF TABLES Table Page 1. Percentage par as i t i z at i on by M. manilae of fall armyworm larvae 38 2. Developmental periods (x + SE) and progeny sex ratios for M. manilae in fall armyworm larvae 40 3. Percentage par as i t i zat i on of second age group fall armyworm larvae exposed to man i 1 ae for various amount of time 42 4. Mean percentages for emergence of Chelonus insular is ( C. i ) Mi crop! it is mani 1 ae ( M m ) Cotesia margi ni ventris (Cm.) a'nd" "adult fall armyworm (FaW)7 ancl percentages of FAW larvae failing to mature because they refused to feed on the diet, died from unknown causes or failed to pupate 53 5. Mean percentages for emergence of Chel onus i nsul ar i s (C.i.) Cotesia marginiventri s (Cm.), Mi cropl i ti s manilae (M.m.) and adult fall armyworm ( FAW ) and mean percent ages of FAW larvae failing to mature because they refused to feed on the diet or failed to pupate 55 6. Mean number and percentage of larval encounters, examinations, oviposition probes and apparent ov i pos i t i on al successes by Cotesia margin i ventris and M i c r o p 1 i t i s manilae in faTT armyworm 1 ar v ae exposed and noli exposed as eggs to Chel onus i nsul ar i s 57 7. Mean percentages for numbers of encounters, examinations and apparent ovipositions by C_ margin i ventris and M man i 1 ae during 2 host exposure periods separated by (TTfferent numbers of days 58 8. Mean percentages at different host ages for emergence of Chelonus i n s u 1 a r i s ( C i ) Cotesia marginiventris (Cm.), and adult fall armyworm (FAF) and percentage mortality of FAW larvae due to (a) refusal to feed on the diet and (2) death from unknown causes 73 9. Mean percentages for emergence of Chelonus i nsul ar i s ( C i ) C o t e s i a marginiventris ( C .m ) and" adult fall armyworm (PAW) arT3 percent mortal i ty FAW larvae due to (1) refused to feed on the diet and (2) died from unknown causes, when age of Cm. was changed 76 vi

PAGE 7

10. Mean percentage (+_ SE) at several constant tempera tures for emergence of Chelonus insular is (C.i.), Cotesi a marg in i ventr is ( C .m ) and adult FAW and percentages of F" A W larvae : failing to mature because they (1) refused to feed on diet and died, (2) died from unknown causes (3) still larvae at end of test and (4) escaped from cup 82 11. Mean (+ SE) emergence periods (days) at several constant temperatures for Cotesia marg i n i ventr i s (Cm.) and Chelonus insular is (C.i.) and adult FAW, and percentages for FAW larvae failing to mature because they (1) refused to feed on the diet and died and (2) still larvae at end of test 84 12. Fate of the larval parasitoids C. marg i n i ventr i s (Cm.) and M. mani 1 ae (M.m.) in competition with the egg-larval parasTtoid C/ insular is as determined by dissection of fall armyworm ( FAW ) 1 ar v ae 88 13. Mean (+ SE) for super par as i t i zed FAW, longevity of adult C marg i n i ventr i s in days and percent survival of hosTHarvae at 1 FAW densities 100 14. Sex ratio (+ SE) (<}:#) for mar g i n i ventr i s (Cm.) and C_ i nsuTar i s (C.i.) from FAW larvae parasit i zed inside a field cage 116 15. Mean percentage of small (0.2 0.7 mm), medium (0.8 1.2 mm), and large (1.3 2.4 mm) head capsule widths from FAW larvae collected from undersurf ace, upper surf ace ground, between stalk and leaf sheath and stalk in corn 124 16. Fall armyworm feeding damage to different regions of corn in plots where C_ insul ari s (C.i.) and C marg i n i ventris (Cm.) were rel eased ... 125 vii

PAGE 8

LIST OF FIGURES Figure Page 1. Mean percentage emergence of i nsul ar i s (C.i.), M. mani 1 ae (M.m.) and margi n i yentri s (Cm.) from faTl armyworm larvae exposed to multiple parasitizations.... 52 2. Behavioral ethogram of the host finding and ovipositional sequence of marg i ni yentr i s females on fall armyworm larvae already par as i t i zed" "by the egg-larval parasitoid C. insularis (Solid arrows indicate invariable pathways and dashed arrows represent alternate pathways ) 61 3. Percentage par as i t i zat i on by C. mar g i n i ventr i s of fall armyworm larvae already exposed as eggs to C. insularis Larvae were randomly placed on four plant spec i es held in wire cages within a greenhouse 65 4. Progeny sex ratios for C. mar gin i i ventr i s from different aged C. marg i n i ventrTs (C.m.) emer g i ng from fall armyworm Tar v ae par asTt i z"e~d as eggs by i nsul ar i s (Ci.) 79 5. Progeny sex ratios for C i nsul ar i s (C.i.) from different aged C. m a r g i n i v e n t r i s ( C m ) emerging from fall armyworm Tarvae parasitized as eggs by insul ari s ... 81 6. Percentage emergence of C. marg i n i ventr i s and C. insularis from fall armyworm ( FAW)^"arv ae parasi ti zed as eggs by i nsul ar i s FAW larvae were exposed at different ages to C m a r gTn i v e n t r i s and then held at 19 22 25, or 28r~for development 86 7. Mean progeny production by marginiventris at 7 host densities from eggs previously parasitized by C i nsul ari s 98 8. Mean progeny production by insularis at 7 host densities and parasitized again by C. margi n i ventr i s 102 9. Sex ratio of mar gin i ventr is from 7 host densities... 105 10. Sex ratio of C. insularis from 7 host densities 107 viii

PAGE 9

11. Percentage par as i t i zat i on by C. insular is and C. margi ni ventr i s from F AW larvae recovered inside from TTeld cage during 3 test periods. Vertical bars within a test period from left to right indicate treatments 1, 2, and 3 paper sections 109 12. Mean percentage parasitized F AW instars in treatments 1, 2, and 3 paper sections inside field cage H2 13. Mean percentage of FAW larvae that became a) adults, b) starved and died c) died from unknown reasons in treatments 1, 2, and 3 paper sections inside field cage 14. Percentage parasiti zation for principle parasitoid species recovered from FAW larvae from (US) upper surface of whorl, (LS) lower surface of whorl, (GR) ground, (SH) between stalks and leaf sheath, (ST) stalk and (WH) control in corn 119 15. Sex ratios for C. margi ni ventr i s and C. insular is recovered from T"A"W larvae from (US) upper surface of whorl, (LS) lower surface of whorl, (GR) ground, (SH) between stalks and leaf sheath, (ST) stalk and (WH) control in corn 122 16. Illustration to exhibit the placement of egg containing paper sections in different regions of corn US Upper surface of upper whorl LS Lower surface of upper whorl GR Ground SH In between stalk and sheath ST Stalk WH Whorl region A ix

PAGE 10

Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy INTERSPECIFIC COMPETITION OF FALL ARMYWORM SPODOPTERA FRUGIPERDA (J.E. SMITH) PARASITOIDS, CHELONUS INSULARIS (CRESSON), COTESIA MAR G I'N I'VYnTRTS (CKTSSON) AND MICROPLI 1'IS MANlLAE ASHMEAD ( HYMENOPTERA: BRACONIDAE ) By Rohan Harshalal Sar athchandra Rajapakse August, 1985 Chairman: Dr. Van H. Waddill Co-Chairman: Dr. Thomas R. Ashley Major Department: Entomology and Nematology Interspecific competition within fall armyworm (FAW), Spodoptera Frugiperda (J.E. Smith), larvae by the larval parasitoids C o t e s i a ( = Apantel es ) marg i n i ventr i s Cress on and M i c r o p 1 i t i s man i 1 ae Ashmead and the egg-larval parasitoid Chel onus i nsul ar i s Cresson was studied. Experiments conducted with 4 larval age groups (1, 24-48h; 2, 49-72 h; 3, 73-96 h; 4, 97-130 h) of the fall armyworm revealed that the first 2 age groups were most suitable for the development of J^. man i 1 ae The developmental period of M^ m a n i 1 a e ranged between 13-18 days. Highest par as i t i zat i on was observed for M_^ man i 1 ae when 2 females were exposed to 20 hosts for 30 min at 26+lC. x

PAGE 11

Cotesia marginiventris was a superior competitior relative to i nsul ar i s and i nsul ar i s was superior to M mani 1 ae Subsequent parasi ti zation by either C margin i ventr i s or M man i 1 ae or larvae exposed to C i nsu 1 ar i s as eggs did not result in additive host mortality. Microplitis manilae females changed their behavior significantly by displaying a reduction of approximately 50% in host examinations, 45% in ovipositor probes, and 55% in apparent ovipositions when C. insular is parasitized larvae were presented. Cotesia marginiventris displayed a greater number on contacts, examinations and ov i pos i t i on al attacks in larvae 3 and 6 days after initial parasiti zation by manilae The maximum reproductive potential for C. margini ventris was achieved in hosts 36 to 48 hours old and at a temperature of 25C. The optimum parasitoid age for C marginiventris during the host exposure period was 48 to 96 hours. Egg to adult developmental times at 25C, were 17 and 26 days for marginiventris and i nsul ar i s respectively. In multiple parasitized larvae C. margini ventris appeared to physically attack and destroy the larvae of i nsul ar i s C i nsul ar i s was the predominant species that emerged from field cage but marginiventris was a better competitor at host densities above 120 eggs/larvae. The damage to upper leaves was significantly greater in non-parasitoid release plots than in parasitoid released plots. xi

PAGE 12

INTRODUCTION Chemical insect pest control has become a controversial management strategy for several reasons. Insect pests have frequently become resistant to pesticides, and the costs of developing and registering a new insecticide have risen sharply. There is also concern about the effects of pesticides upon human health and the environment. This combination of circumstances has prompted entomologists to seek alternative control strategies leading to the development of sophisticated techniques involving a wide array interdisciplinary approach that have been termed "integrated pest management". Along with the development of strategies such as breeding resistant plant varieties and the use of pheromones to disrupt communications, there has been a resurgence of interest in the use of entomoph ages Huffaker and Messenger (1976) defined biological control as the action of predators, parasites, and pathogens which maintains host densities at levels lower than would occur in the absence of these natural enemies. Despite the many successes obtained through the introduction and release of a pest's natural enemies, this classical biological control strategy has not always provided the desired degree of pest control. In this strategy of biological control, natural enemies are deliberately 1

PAGE 13

2 imported to control introduced or native pests. General guidelines for locating, selecting and introducing agents for biological control have been discussed (Huffaker and Messenger 1976). Efforts should begin with a careful study of the life cycle of the target pest. If it appears that exotic competitors may be beneficial then foreign exploration should first begin in areas environmentally similar to the intended area of releases. Species that are candidates for introduction must be evaluated carefully to insure that they are indeed beneficial and that they themselves will not become pests. Interspecific competition among natural enemies of a given host can be of a great importance in biological control. In classical biological control, the potential for interspecific competition exists when more than one species of natural enemy is released into the environment and utilizes the same host. Regarding such multiple species introductions, it has been suggested that such interpecific competition could possibly lead to a decline in the population regulation of the host (Watt 1965) although others have refuted this idea (Huffaker et al 1971). In endemic host enemy associations, interspecific competition appears to play a crucial role in structuring the parasitoid guild (Force 1974) and probably influences the entire natural enemy complex as well. Generally, the outcome of the competition is physiologically determined

PAGE 14

3 within the host. Thus, researchers may be unable to predict the outcome unless they can identify and duplicate the relevant elements of the pest's physiology under experimental conditions. The parasitoid guild of Spodopter a f rugi perda (J.E. Smith), the fall armyworm (FAW), provides a relevant host parasitoid association for assessing host and natural enemy relationships. The FAW is a sporadic and occasionally severe crop pest in the Southeastern United States where this species is known to be able to survive in winter (Luginbill 1928), though survival further north is thought possible only during exceptionally mild winters (Snow and Copeland 1969). In years of high population density, FAW larvae may cause over $300 million in damage (Mitchell 1979). Fifty three species of parasitoid species have been recovered from FAW larvae (Ashley 1979) and are responsible for significant reductions in FAW larval populations (Ashley et al 1982 ). The principal parasitoids of the FAW either attack its eggs or the early instars and thus provide suitable models for the study of parasitoid interrelationships, especially with regard to interspecific competition between the egg-larval and larval parasitoids. The following research was conceived to assess and investigate the competitive abilities between the parasitoid larvae of Chel onus insularis Cresson, Cotesi a

PAGE 15

4 ( Apanteles ) marg i n i ventr i s Cresson, and Mi crop! i ti s mani 1 ae Ashmead. The objectives of the study were to (1) study the biology of M. manilae an imported larval parasitoid of Spodopter a spp in Thailand, (2) investigate interspecific competition between larvae of the parasitoids insul ari s C marg i n i ventr i s and M. mani 1 ae (3) examine the effects of host and parasitoid age, and temperature on the outcome of interspecific competition, and (4) study the functional response of C marg i n i ventr is when exposed to different densities of FAW larvae previously parasitized by C i nsul ar i s

PAGE 16

LITERATURE REVIEW The Fall Armyworm, Spodoptera frugiperda (J.E. Smith) The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), (Lepidoptera: Noctuidae) inflicts damage on a large number of agricultural crops, especially those belonging to the family Graminae, in the Southeastern and Central United States (Luginbill 1928) and Central America (Andrews 1980). Corn ( Zea mays L ) Sorghum ( Sorghum bi col or (L.) Moench) and Bermudagrass ( Cynodon dactylon (L) Pers.) are the favored agricultural hosts for the FAW (Sparks 1979). Economic damage to other crops, including alfalfa, peanuts, rice and soybean, has also been documented (Navas 1974, Morrill 1973, Pitre 1979). Tietz (1972) lists 68 genera of plants, many of which are weed species, that are attacked by the FAW. Seasonal Distribution Unlike most other insects in the temperate region, the FAW has no mechanism for diapause. Thus, the species overwinters commonly in South Florida and Texas, where temperatures do not destroy it and where hosts are continually available (Luginbill 1928). In mild winters it is also found in Louisiana and Arizona (Snow and Copeland 1969). During the spring and summer the FAW 5

PAGE 17

6 disperses again throughout the eastern and central United States, and, in some years, into Southern Canada (Luginbill 1928). This migration is assisted by weather fronts (Sparks 1979). Several hypotheses have been advanced to explain the seasonal distribution of damaging populations of F AW (Rabb and Stinner 1978; Walker 1980; Barfield et al 1980). Walker (1980) presented 3 models to account for seasonal distribution patterns. Diffusion and freeze-back and return flight (Walker 1980), "pied piper" effect similar to diffusion and freeze back (Rabb and Stinner 1978) and a model on seasonal distribution patterns as combinations of short and long range movements, as well as periodic overwintering in as yet undiscovered habitats (Barfield et al 1980) explained this aspect. Life History The life cycle of the FAW has been described by Luginbill (1928), Vickery (1929), Sparks (1979) and Keller (1980). The adults are nocturnal and at dusk initiate flying near host plants that are suitable for feeding, oviposition, and mating. Mitchell et al ( 1974 ) showed that peak activity of adults occurred 6 hrs after sunset and another small peak occurred approximately 3 hrs later. Oviposition may occur on host plants where as many as

PAGE 18

7 several hundred eggs may be laid in a mass and covered with scales. Total oviposition by a female may exceed 2000 eggs over a period of up to 23 days (Luginbill 1928). As larvae hatch from the eggs, they eat their egg shells (Morrill and Green 1973), and as a result of negative phototactic and geotactic behaviors, the first instars move into the whorls of corn and sorghum (Pitre 1979). The larvae feed preferentially on the developing leaves and at high densities will eat the mature leaves, tassels, ears, and the inner portions of the stalk (Luginbill 1928, Morrill and Green 1973). Development proceeds through 6, sometimes 7, and rarely 8 instars (Keller 1980). Temperature, larval nutrition, and probably egg nutrition were factors affecting instar number in FAW (Keller 1980). Mature larvae drop to the ground and pupate in the soil within a chamber located 2 to 8 cm below the surface (Luginbill 1928). Pupation depends upon soil texture, moisture, and temperature (Sparks 1979). Pupae have been found on plant parts during severe outbreaks (Burkhardt 1953). After eclosion, the adults find their way to the soil surface, locate a plant or other object on which to cling, and inflate their wings (Sparks 1979). There is also evidence that different host plants (Roberts 1965, Pencoe and Martin 1981) and different temperatures affect the biology of FAW (Barfield et al 1978 ).

PAGE 19

8 Roberts (1965) reported that the larval diet can affect the duration of larval period, pupal size, adult longevity, fecundity, and egg viability. Economic Status In some years FAW larval densities are low and not economically important while in other years high densities inflict serious economic losses (Sparks 1979). The FAW was recorded as an injurious pest in Georgia in 1797, and in Florida in 1856 (Sparks 1979). Damaging populations of FAW appear to occur irregularly (Barfield et al 1980). FAW infestation levels are unpredictable (Barfield et al 1980) and conditions conductive to outbreaks are not well understood (Keller 1980). The FAW causes damage to corn by feeding on the developing leaves within the whorl. In areas with severe infestations the tassels, ears, mature leaves and stalks are also consumed (Painter 1955). Defoliation ranges from skeletonization of leaves by early larval instars to complete leaf consumption by large larvae. Annual losses due to larval feeding are estimated to be between $300 to 500 million in the United States (Mitchell 1979). Larval food consumption has been studied by Luginbill (1928) and Barfield et al (1980)

PAGE 20

9 Natural Mortality Various abiotic and biotic agents act as mortality agents of F AW populations in the field. Physical environment and natural mortality factors may act singly or in combination to determine the annual distribution pattern and densities of FAW populations (Barfield et al 1980). Among abiotic environmental factors, temperature appears to be an important limiting factor (Barfield et al 1980). Low temperature may be the most important factor limiting the winter survival of FAW (Luginbill 1928, Wood et al 1979). Andrews (1980) reported that torrential daily rains for several days result in drowning of small larvae or washing them out of the whorls in corn in Central Amer i c a Cannibalism among larvae is an important factor limiting population densities (Luginbill 1928). Mortality attributable to cannibalism and i ntr aspec i f i c competition is positively correlated with larval density (Wiseman and McMillian 1969). Olive (1955) reported that first instar larvae may destroy adjacent unhatched eggs while in the process of devouring their own egg shells. Ashley (Pers. Comm. 1985) studied the factors influencing cannibalism in FAW and showed that the larval density in combination with the amount of eatable surfae area affected cannibalism more significantly than did the amount of non-eatable surface area, diet volume, or photoperiod.

PAGE 21

10 Natural mortality inflicted on FAW larvae by natural enemies ( parasi toids, predators and pathogens) in both agricultural and wild host plant communities is believed to play a substantial role in density regulation (Barfield et al 1980). Ashley (1979) presented detailed information about the classification and distribution of the FAW parasitoids and noted that 53 species from 43 genera and 10 families have been reared from FAW larvae. Among them 18 species occur in North America; 21 species occur in Central and South America; and 14 species are common to all three regions (Ashley 1979). Parasitoid species attacking FAW vary between different agroecosystems For example, in a study by Ashley et al (1980) in late planted field corn, 8 species of parasitoids, representing the families Braconidae, Ichneumoni dae, Eulophidae and Tachinidae, were collected from FAW larvae feeding on corn and surrounding broadleaf signal grass. Chelonus texanus Cresson caused the highest mortality followed by M e t e r o u s autographae Musebeck and Eupl ectr us pi atyhypen ae Howard. Nickle (1976) reported that 7 species caused parasitization of FAW larvae on peanuts and Apantel es mar g i n i ventr i s Cresson., M. autographae and Oph i on spp were responsible for highest mortality. Ashley et al (1983) in another study on par as i t i z at i on of FAW larvae on volunteer corn, Bermudagrass ( Cynondon dactylon ( L ) ) and paragrass

PAGE 22

11 ( Brae hi arie m u t i c a ( L ) ) reported that i nsul ar i s Cresson was the principal parasitoid on corn and C._ insular is and A. marg i n i ventr i s were the major parasitoids on Bermud agr ass while M. autographae parasitized the highest proportion of hosts in paragrass, reflecting a host plant preference. The native parasitoids C. insul ari s and A marg i n i ventr i s were the primary species attacking FAW larvae in South Florida and they destroyed 63% of each of the first instars; M. autographae and Rogas 1 aphygmae Viereck, as well as several tachinids and a group of unidentified ichnuemoni ds accounted for the rest of FAW larval mortality (Ashley et al 1982). Tingle et al (1978) reported that parasitoid populations attacking the FAW on alternate host plants of, in or near crop fields may be important sources of parasitoids that subsequently attack FAW larvae in corn. Waddill et al (1985) discussed the seasonal abundance of FAW parasitoids, C i nsul ari s Temel ucha spp. 1 aphygmae and mar gin i ventr i s in southern Florida. Mitchell et al ( 1984) reported that FAW pheremone components had no significant effect on the level of FAW parasi ti zati on by C. insul ari s and "[em el u c h a d i f f i c u 1 i s Basch. The successful rearing of a pupal parasite Pi apetimorpha i n t r o i t a of FAW in the laboratory has also been documented (Pair et al 1985). Predators and pathogens are among other natural enemies found to play a less consistent role in regulation

PAGE 23

12 of FAW populations. Agnello (1978) compiled a list of 10 species of Hymenopter a (8 vespids and 2 sphecids) and 6 Hemiptera (3 reduviids, 1 pentatomid, 1 nabid and 1 anthocorid), 12 Coleoptera (9 carabids, 2 cicindellids and 1 coccinellid) a mammal (skunk), 3 amphibians (2 Buf o spp and 1 Hyl a spp) and a variety (13 species) of birds as predators of FAW. An earwig, Doru spp inhabits whorls of corn and sorghum and found to feed readily on small and medium sized FAW larvae (Andrews 1980). The FAW is reported to be susceptible to at least 16 species of entomogenous pathogens which includes viruses, fungi, protozoa, nematodes and 2 strains of the bacterium Bacillus thur i ngi ensi s Berliner (Gardner and Fuxa 1980). Many of these occur naturally in FAW populations. A "poly hedrosis" presumably nuclear polyhedrosis virus (NPV) was reported as early as 1915 (Chapman and Glaser 1915) and a granulosis virus has also been identified from FAW larvae collected from sorghum (Steinhaus 1957). Fungi also are natural mortality factors in FAW populations. Three species have been reported and include Entomophthor a sphaerosperma Fresenius (Charles 1941), Nomuraea rileyi (Farlow) Sampsom (Luginbill 1928) and Empusa spp (Luginbill 1928). The natural occurrence of a nematode Hexamermi s spp in FAW larvae was reported from Venezuela (Gnagliumi 1962). The only protozoan reported to occur

PAGE 24

13 naturally in FAW is Nosema laphygmae Weiser, a microsporidium from Colombia (Weiser 1959). Management Strategies The major management strategies reported to control FAW are insecticides (Young 1980), cultural control (Luginbill 1928) and host plant resistance (Wiseman et al 1979). Young (1980) suggested the use of irrigation water as a carrier for insecticides, thereby supplying the volume of liquid needed to penetrate all of the plant sites, where FAW feed. Application of granular insecticides directly to the whorl has been a common practice in Central America (Andrews 1980). The importance of mechanical and cultural control of FAW was first reported by Luginbill (1928). Black light traps and pheremone baited cylindrical electric grid traps have been used to monitor seasonal populations of FAW in Louisiana and Florida (Mitchell 1979). However, disposable sticky traps baited with pheromone ( z)-9-dodecen-l-ol acetate have been used extensively in surveys in Georgia and Florida. These traps were found to be most effective in capturing FAW males when positioned approximately 1 m above ground and near around preferred hosts (Mitchell 1979 ) Wisemann and Davis (1979) showed the importance of resistant plant varieties in managing FAW populations.

PAGE 25

14 The resistance of corn variety "Antigua 2 D" to FAW has already been documented (Wiseman et al 1973). Resistant varieties in sorghum, peanuts, Bermudagr ass rice, and millet have also been reported (Davis 1980). Considering the important factors regulating FAW populations, action thresholds (AT) for grain sorghum have been developed (Martin et al 1980). These action thresholds are estimated to be 10% of seedling sorghum possessing egg masses after flowering. However there is a lack of information in many areas which makes it difficult to derive dynamic AT and population models representing the dynamics and host interactions of the FAW. The Larval Endoparasi toi d Cotesi a ( =Apantel es ) marg i n i ventr i s Cresso*rT~ Origin and Distribution Cotes i a ( = Apantel es ) mar g i n i ventr i s is one of the most freqently recovered parasitoids from field collected FAW larvae. This parasitoid was originally described from Cuba, and is native to the West Indies (Muesebeck 1921). It has been previously classified as Microgaster margini ventr i s Cresson (1865), Apantel es grenadensis Ashmead (1900), A. laphygmae Ashmead (1901), Apantel es ( Protapan tel es ) harned i Viereck (1912) and most recently Cotesi a marg i n i ventr i s Cresson (Marsh 1978). It appears to have a wide distribution within the United States, especially in

PAGE 26

15 the southern states viz. Arkansas, Florida, Georgia, Louisiana, Mississippi, Tennessee, North Carolina and South Carolina (Wilson 1933, Mueller and Kunnalacca 1979, Marsh 1978). Some 16 hosts of C^ mar g i n i ventr i s have been reported (Miller 1977) and all are noctuids. No crop preference is shown by this parasitoid when attacking Trichoplusia ni_ (Hbn.) on various food plants in Mississippi (Boling and Pitre 1970). Description The egg and laral instars are described by Boling and Pitre (1970), and the adults by Muesebeck (1921). The egg is hymenepter i f orm cylindrical with rounded ends. The caudal end is slightly curved, and has a short peduncle. The egg is 0.017 mm at the broad end, 0.088 mm in length at oviposition and the peduncle is 0.0005 mm long (Boling and Pitre 1970). The egg is found free in the hemocoel of the host larvae. Up to 7 eggs have been found in a single host when the host larva was exposed to several female parasitoids. However, s u per par as i t i zat i on does not necessarily lead to multiple cocoon formation. Normally only 1 egg is found per host (Boling and Pitre 1970). The first instar larva is white and caudate and is usually found in the posterior part of the host's body. First instar larvae are never found attached to the host. The

PAGE 27

16 larva has a caudal appendage which is a modification of the last abdominal segment into a fleshy organ and a caudal vesicle that increases in size with longevity. Allen and Smith (1958) reported some species of Apantel es as being cannibalistic in the first instar; but no cannibalism has been observed in C. mar g i n i ventr i s (Boling and Pitre 1970). The second instar is vesiculated with a prominent anal vesicle and the body becomes more robust. Allen and Smith (1958) suggested that the second instar may actually be two instars. The third instar is hymenopter i f orm with no anal vesicle. This larva tapers anteriorly and is creamy white at first, turning light brown upon emerging from the host (Boling and Pitre 1970). The molt to the third instar happens just prior to parasitoid emergence, which generally occurs at approximately the 4th abodminal segment in the dorsolateral area of the host. The parasitoid initially constructs a one sided crescent-shaped cocoon and after its body has become seated, the larva closes the open side of the cocoon. The cocoon is small (3mm long), ovoid, firm, smooth and composed of white silk surrounded by some looser threads. The pupa is exarate and enters pupation approximately 24 hrs after formation of cocoon. Adults can be identified using the keys of Marsh (1971) (to genus) and Muesebeck (1921) (to species). The black adult is about 2-5 mm long, has yellow legs and is recognizable by the

PAGE 28

17 sculpturing on the abdomen and hind coxa, and the color and length of the hind tibial spurs (Marsh 1978). Life Cycle Cotes i a mar gin i ventr i s is an arr henotokus larval endoparasitoid of several lepidopteran pests. Female parasitoids mate and oviposit within several minutes after emerging from the pupal case but are more aggressive when held for 24 hrs prior to host exposure (Boling and Pitre 1970). Mating occurs with the male approaching the female from the rear, tapping her with his antennae and then mounting on her for approximately half a second. Both sexes mate many times and freely with other individuals. Females often mate after having initiated egg laying (Bol ing and Pitre 1970) The egg is laid in early instar hosts. According to Vickery (1929) first instars are parasitized before they disperse and Kunnalaca and Mueller (1979) reported that first instars are preferred. According to Boling and Pitre ( 1970), C. mar g i n i ventr i s p er f ers to oviposit in 2 day old larva of L_ n_i_ rather than in 1 day or 3 day old larvae of the same species. Later host instars are less preferred becase host larvae usually jerk violently and this movement interfers with oviposition (Kunnalaca and Mueller 1979). In general parasiti zation increases with

PAGE 29

increased exposure time. Kunnalaca and Mueller (1979) reported that oviposition was accomplished quickly with single ovipositor thrust and this occurred primarily during day light hours. Multiple oviposition was common especially when few hosts were offered to a parasite (Boling and Pitre 1970). Total fecundity ranged from 30 to 110 eggs per female (Kunnalaca and Mueller 1979). Time required for the development of C. margin iven tr i s from oviposition to cocoon formation ranged from 6 11 days at 30C (Boling and Pitre 1970, Kunnalaca and Mueller 1979). Boling and Pitre (1970) reported the optimum time for development as 7 days in T^ n_i_ and Pseudoplasia includens (Walker) and 6 days in He! i othes v i r esc en s (F.) within 24 hours after existing host larva Kunnalaca and Mueller (1979) reported an optimum develop mental time of 8 days in Plathypena scabra (F). At 30C and 25C, development times from cocoon to adult ranged from 3-5 days and 4-7 days, respectively (Kunnalaca and Mueller 1979). The sex ratio (1.5:1) favored males at both 30C and 25C (Kunnalaca and Mueller 1979). Mean longevity of adults at 30C and 25C was 5 6 + 2 5 and 9.1+4.2 days, respectively and females lived longer than males at both temperatures (Kunnalaca and Mueller 1979). Par as i t i zat i on by margi n i ventr i s resulted in growth retardation of the host (Danks et al 1979).

PAGE 30

19 Ashley ( 1983) reported that par as i t i zat i on of FAW larvae by marginiventris reduced maximum larval weights by 97%, compared to 6th instar non par as i t i zed larvae. C mar gin i ventr i s destroyed its host when the host reached the 4th instar. Hosts parasitized by C. marginiventris gained the least amount of weight, produced the least amount of frass, and had shortest life expectancies and the smallest head capsule widths compared to other parasitoids (Ashley 1983). Loke et al (1983) has described the behavioral sequence for host finding and oviposition for C mar g i n i ventr is on corn plants artifically damaged by 2nd instar larvae of the FAW and reported that highest parasiti zation rates occurred among 2nd instar larvae collected from leaf surfaces. Bioassay responses in C marg i n i ventr i s females to materials derived from FAW larvae were most intense for frass and somewhat less intense for larval and pupal cuticle materials, scales, exuviae and silk (Loke and Ashley 1984). The Egg-larval P ar as i to i d C he 1 on us insularis Cresson Origi n and Distribution Chel onus i nsul ar i s Cresson is one of the key parasitoids regulating FAW populations in South Florida (Ashley et al 1982). It has been previously classified

PAGE 31

20 as texanus Cresson ( 1872 ), texanoi des Viereck (1905), Cj_ exogyrus Viereck (1905) and bi pustul atus Viereck (1911) (Marsh 1978). C. insular is is distributed throughout in North, Central and, South America, and the West Indies and has been introduced into Hawaii and South Africa (Marsh 1978). Description The eggs of C i nsul ar i s are white, and cylindrical, and appear comma like in shape. They are slightly arcuate with both ends rounded, one being larger than the other (Glogoza 1980). The first instar larva has a prominent square head with easily distinguishable dark, pointed, mandibles and 7 body segments tapering from the thorax to the abdomen (Glogoza 1980). The larva floats in the host hemolymph. The second stage larva is cylindrical with a tapered head. The body of the third stage is also cylindrical and the head which is relatively narrow tapers in the front. C i nsul ar i s causes its host to burrow in the earth when the host reaches the 4th instar and to form a pupation cell. After completing this cell the parasitoid larva consumes the entire contents of the host and then pupates. The larva spins a cocoon by using a silky secretion and this cocoon is cylindrical with almost flat ends. Ashley (1983) found that of those FAW larvae

PAGE 32

21 parasitized by C i nsul ar i s 41% died in the 4th instar and 59% died in the 5th instar. An emerging adult tears the silky cocoon with its mandibles and escapes through the opening. The body length of the adult is 4.5-5.0 mm and description of adults is found in Marsh (1978). Life Cycle The female parasitoids can begin to lay eggs even if they have not mated. The antennae are used to locate the host, the female then lands on the eggs, positions herself, and then injects her eggs directly into the host egg. The female may lay continously for about an hour if left undisturbed. Superparasiti sm is common in the genus Chel onus (Broodryk 1969 ) and was observed in C. insular is when parasitizing v i rescens (F.) eggs (Abies and Vinson 1981). Abies and Vinson (1981) reported that C. insular is appeared to examine host eggs internally as well as externally and was able to detect previously parasitized hosts. The average time of development from oviposition to adult is about 26 days for males and 28 days for females. Rechav (1978) found similar results for other Chel onus spp. Greatest fecundity was obtained at 30C (Glogoza 1980). Survival was highest at low temperatures and the greatest percentage of eggs was parasitized at 35C (Glogoza 1980). Male biased sex ratios occurred at

PAGE 33

22 20 and 40C while at 35C a 1:1 ratio was obtained (Glogoza 1980). C. i nsul ar i s can develop in many hosts. Besides S f mgi perda it is also able to develop in Hel i othes artni gera (Hubner), Spodoptera exigua (Hbn), Ephesti a sericari a (Scott) (Bianchi 1944). Marsh (1978) reported that hosts for North America include Ephesti a elutella, (Hbn), Feltia subterranea (F), Hel iothes zea (Boddie), Loxostege sticticalis (L.) Peridroma saucia (Hbn), Spodoptera eridania (Ramer), Spodoptera ornithogalli (Guenee), Spodoptera pr aef i c a Grote, and rn_. Parasiti zation of F AW by C. insular is reduced host FAW larval weights by 70% and only 28% of the larvae parsitized by C i nsul ar i s lived past the 9th day and these larvae displayed an unusual increase in weight prior to destruction by the parasitoid (Ashley 1983). Ashley et al (1982) found that the native parasitoid C. insular is was the primary species attacking FAW in South Florida and it emerged from 71% of the parasitized larvae. C. insular is caused the highest mortality of FAW larvae collected from corn and broadleaf signalgrass (Ashley et al 1980). Ashley et al (1983) reported that C. insular is parasitized 44% of all FAW larvae collected from volunteer corn, Bermudagrass and paragrass and

PAGE 34

23 regardless of the host plant, C. insular is had a parasitization rate 4 times greater than other competing parasitoids. Substantially higher percent parasiti zation was obtained for corn than on other hosts (Ashley et al 1983). Ashley et al (1982 ) reported that C. insular is parasitized the greatest proportion of FAW larvae having head capsule widths of 0.3 mm. Che 1 onus insular is was not recovered from larvae having head capsule widths greater than 1.8 mm. This very clearly showed that C. insular is is primarily an egg parasitoid with preference to early instars to lay eggs. Mitchell et al (1984) reported that two FAW pheremone components ( Z90DA and Z9TDA) had no significant effect on the level of FAW parasi ti zati on by its principal parasite C. insularis The sex ratio for C i nsul ar i s shifted from approximately 1:1 ( Femal e :mal e) during spring to approximately 1:4 during the summer months but the reduced proportion of females during summer did not lower par as i t i z at i on levels by C. insularis The Larval Endoparasitoid Microplitis manilae Description and Distribution M i c r o p 1 i t i s manilae (Ashm) is reported as an important larval parasitoid of Spodopter a spp in Thailand (Shepard, Pers. Comm 1982). This parasitoid is not

PAGE 35

24 indigenous to the United States, and was imported from Thailand through the USDA, Stoneville Research Quarantine Facility, Mississippi. No taxonomic or distribution literature was located for M^ man i 1 ae The length of antennae in males is longer than for the female. However, Marsh (1978) described a closely related spp M. melianae Viereck. An unsuccessful attempt was made to establish mani 1 ae in the F AW overwintering range in South Florida (Ashley, Pers. Comm. 1983). The adults are ready to oviposit soon after emergence. They will oviposit in F AW larvae for a period of 16-17 days. Different species of Microplitis attack the early larval instars of their hosts (Altahtawy et al 1976). The female deposits an egg through the integumant of host larva into the hemolymph. The egg is elongated, oval and translucent white in color. The first instar is caudate with a relatively large head and the second instar is vesiculate and creamy white. After the parasitoid larva molts into the third instar, it emerges from the host (FAW) and spins a cocoon. Although the host remains alive after the parasitoid emerges, the host does not develop further and stops feeding. The parasitoid larva exits the host and pupates outside. A single parasitoid normally develops from each host even after

PAGE 36

25 superparasitism. However, development of two parasitoids per host occurred more frequently when larger hosts were provided. Biology of M. demolitor imported from Queesland, Australia has been described by Shepard et al (1983) Interspecific Competition By definition competition occurs when two or more organisms interfere with or inhibit one another (Pianka 1970). Smith (1929) defined "multiple parasitism" to designate the type of parasiti zation in which the same individual host insect is inhabited simultaneously by the young of two or more different species of primary parasitoids. Fisher (1961) reported that this type of multiparasitism resulted in competition between the parasitoids. The occurrence of this type of mul ti parasi ti sm depends primarily upon the oviposition behavior of the two parasitoids in response to hosts that are already parasitized. In general, parasitoids require a host organism for egg deposition and the development of immature stages. Typically, the progeny of one or neither parasitoid will survive when individuals of different species parasitize a single host organism (Salt 1961). Therefore interspecific competition between parasitoids for hosts may be a vital component influencing guild composition (Zwolfer 1970). Interspecific competition among parasitiods may even

PAGE 37

26 result in the competitive exclusion of certain species (Debach and Sundby 1963). In many cases of interspecific competition, one species has an intrinsic superiority over its opponent and invariably destroys it, by the use of its mandibles (Pemberton and Willard 1918, Simmonds 1953) or by an unspecified means of physiological suppresion (Muesebeck 1918, Fisher 1961, Salt 1961). More commonly there is no intrinsic superiority on the part of either parasitoid, and free competition occurs between them, the victor completing its development and the loser dying, either as an egg or a young larva. Several suggestions have been made in the literature as to the possible mechanism of competition between such solitary endopar as i t i c species. In the first place, the older parasitoid is presumed to survive by eliminating the younger through starvation (Fiske and Thompson 1909) thus emphasizing the importance of time of oviposition as the determining factor in competition. Secondly, cases of direct physical attack by one parasitoid on another using the mandibles for fighting has been recorded (Simmonds 1953). In these cases neither competitor has an intrinsic advantage over the other and the result of competition is apparently decided by the time of oviposition. The third suggestion is that one parasitoid eliminated the other by physiological suppression, either by conditioning the hemolymph of the host so that it becomes unsuitable for

PAGE 38

27 the development of any successor (Van den Bosch and Haramoto 1953, Johnson 1959) or by the postulated secretion of a toxic substance which kills the opponent (Thompson and Parker 1930). Competitive exclusion by previously introduced parasitoids has been viewed as one of the factors that explains the failure of introduced natural enemies in classical biological control to become established (Ehler and Hall 1982). The competitive exclusion hypothesis has been subject of considerable debate in the literature. Turnbull (1967) favored the competitive exclusion hypothesis while Van den Bosch (1968) rejected it. However, Ehler and Hall (1982) presented empirical evidence in support of competitive exclusion and stated that this could possibly lead to the extinction of an effective natural enemy. In fact, Force (1974) showed that a very effective natural enemy may in fact be an inferior competitior. Thus Ehler and Hall (1982) suggested that (1) simultaneous release of several species of natural enemies should be avoided due to interspecific competition between them that may lead to a lower establishment rate and (2) extra care should be taken in establishing species where incumbent species of natural enemies exist. However Moon (1980) reported that while the principle of competitive exclusion may be simple and attractive, it may not adequately apply to the heterogenous real world.

PAGE 39

28 In classical biological control, the potential for interspecific competition exists when more than one species of natural enemy is released into the environment. Regarding such multiple species introduction, it has been suggested that such interspecific competition could possibly lead to a decline in population regulation of the host (Turnbull and Chant 1961, Watt 1965) although others have refuted this as a general phenomenon (Huffaker et al 1971). Empirical evidence generally supports multiple species introductions (Ehler 1978). However, such evidence comes largely from successes involving multiple species releases without regard to instances where such releases did not yield total success (Ehler 1977). Miller (1977) suggested the possiblity that intrinsically superior competitors which exhibit a relatively low reproductive capacity would displace or interfere with intrinsically inferior competitors which exhibit a relatively high reproductive capacity. There is a concern that such competition would result in decreased parasitization rates. A computer simulation by Watt (1965) and a greenhouse study by Force (1970) suggested that such a reduction in the proportion of par as i t i zat i on is possible. Other things being equal, intrinsically superior species imported in biological control programs probably become established more easily than intrinsically inferior

PAGE 40

29 ones. Examples of intrinsically superior parasitoids that have achieved such a role are two braconids, 0 p i un oophi 1 us Full. (Bess and Haramoto 1958) and Macrocentrus ancyl i vorus Rohw. (Boyce and Dustan 1958). On the other hand, an intrinsically inferior species may achieve a higher level of par as i t i z at i on in the field than its rivals if it is ex tr i n s i c al 1 y superior to them. For example, Spalangia cameroni Perk., an intrinsically inferior species, parasitized more house fly pupae than all other species combined because the females were able to penetrate more deeply into areas containing hosts (Mourier and Hannine 1969). Obviously, an intrinsic superiority of one parasitoid over another may result in the waste of some parasitoids, but this effect, as pointed out by Smith (1929), is likely to be an insignificant factor in the comparative field efficiencies of two competing forms. Case Studies The superiority of Metaphycus inteolus (Timberlake) over Mi croterys f 1 avus Howard inside the host ( Coccus h e s p e r i d i urn ) in the field was contrary to the pattern of dominance of both species when they competed within the host (Bartlett and Ball 1964). Arther et al (1964) showed interactions between a braconid, Orgi 1 us obscur ator (Nees), and an i schneumoni d Temelucha interruptor inside

PAGE 41

30 the pine shoot moth, Rhyaciona buoliana Schiff. They reported that T. interruptor attacked more host larvae that had been previously parasitized by 0^ obscur ator than unparasi ti zed hosts. Vinson (1972) reported that in interspecific competition between larval parasitoids Cardiochiles nigriceps Viereck and Campoletis perd i st i nctus (Viereck) on tobacco budworm, H. virescens that C perdi sti nctus had a slight advantage over ni gri ceps when oviposition by the 2 species occurred at about the same time. Part of the reason for the advantage by perdi s t i nctus may be more rapid growth rate of its larvae and a shorter egg development period. When the competitors were of similar age, one was eliminated through physical combat. When one competitor is 1 or 2 days older it was able to destroy several eggs of the younger competitor. However when older parasitoid is 4 days old the younger larvae is eliminated through physiological suppression (Vinson et al 1972). Such suppressed larvae failed to grow and were inactive although they may be alive. When one of the tobacco budworm parasitoids was old or it eliminated the younger competitor by physiological suppression (Vinson 1972). Fisher (1961) also presented evidence of physiological suppression of younger larvae by the older competitor through the reduction of oxygen available to the younger larva. Wylie (1972) reported that only one parasitoid

PAGE 42

31 species survived in interspecific competition among the pupal parasitoids N ason i a v i t r i p e n n i s (Walk)., Muse i d i fur a zar aptor K. & L. and S p 1 a n g i a c amer on i Perk. N ason i a vitr i penni s and M. zaraptor were both intrinsically superior to S. cameroni if the attacks on the hosts by their females preceded, were simultaneous with, or followed by up to 48 hrs those by females of cameron i N a s o n i a v i t r i p e n n i s was intrinsically superior to zaraptor if its attacked preceded that by zaraptor by at least 24 hrs. The success of v i t r i p e n n i s when competing with S. cameroni was due to differences in rates of egg and larval development and of host utilization by the two species. In a similar study by Wallner et al (1982), larval parasitoids Apanteles melanoscelus Ratzburg. and Rogas lymantriae (L.) inside the host Lymantria dispar (L.) both attacked the previously parasitized larvae but the parasitoid attacking the host first was more successful. The studies on mul t i par as i t i sm between the internal larval parasitoids of Rhyac i on i a b u o 1 i a n a Schiff. revealed that interspecific competition took place between the first instar larvae through direct physical attack (Schroder 1974). However there are instances where these internal parasitoids have coexisted within the host larva and this provides a good example of a system of

PAGE 43

32 "counter-balanced competition" (Zwolfer 1970). In such systems, the competitive inferiority of a parasitoid species in multiple parasitism is compensated for by a superiority in other attributes such as searching efficiency and synchronization with the host's life cycle (Schroder 1974). Weseloh (1983) reported that neither of the parasitoids mel anoscel us nor Compsi 1 ura conci nnata (Meigan) destroyed each other inside the host Lymantr i a d i s p a r and both emerged from about 11% of the hosts. These results showed that both parasitoids appeared to be remarkably tolerant of each other in the same host and this probably happened because they fill different niches and so do not compete with each other within the host. The larval parasitoids Campoletis sonorensis (Carlson) and Microplitis croceipes Cresson are intrinsically superior to i nsul ar i s and physically attacked the latter inside the host, HL virescens (Vinson and Iwantsch 1980). In a similar study, Miller (1977) reported that C i nsul ar i s larvae competing with A marg i n i ventr i s inside Spodopter a praef i ca (Brote) were dwarfed and nearly killed due to competition. A second experiment involving i nsul ar i s and Hypo sote r e x i g u e (Vierek) yielded a similar result where ex i que was a superior intrinsic competitor relative to C i n su 1 ar i s and C marginiventris

PAGE 44

33 In a study on impact of native parasitoids on FAW in Southern Florida, Ashley et al (1982) described a mirror image pattern of parasi ti zati on between C. insular is and Temel ucha spp collected from the FAW larvae. This increase-decrease and deer easei ncrease pattern between these two parasitoids may be indicative of interspecific competition between these parasitoids (Ashley et al 1982). Mitchell et al (1984) reported the effect of two FAW pheremone components (Z9DDA and Z9TDA) upon population dynamics of its larval parasites and found that C insul ari s was the predominant species followed by T ._ d i f f i c i 1 i s whose parasiti zation rate of FAW larvae was initially high and then remained relatively constant for the remainder of the experimental period. The explanation for this type of par as i t i zat i on pattern was that C i n s u 1 a r i s was a better internal competitor than T difficilis (Mitchell et al 1984).

PAGE 45

BIOLOGY AND HOST ACCEPTANCE OF MICROPLITIS MAN I LAE (HYMENOPTERA:BRACONIDAE) RAISED ON FALL ARMYWORM LARVAE Introduction The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is a major pest of corn and Bermudagrass in the southeastern United States (Luginbill 1928) and may extend its range as far north as the Canadian border during the summer and fall months (Snow and Copeland 1969). However, since this pest has no mechanism for diapause or overwintering its populations are restricted to portions of south Florida and Texas during the winter months (Luginbill 1928). Average estimates of annual crop losses caused by the FAW exceed $300 million (Mitchell 1979). Therefore, reducing the density of overwintering FAW populations may result in a significant decrease in the amount of damage done by this pest. M i c r o p 1 i t i s man i 1 ae (Ashmead) is a parasitoid of Spodoptera spp. in Thailand from where it was imported into the United States. Even though the FAW does not occur in Thailand, M^_ man i 1 ae develops successfully in larvae of the FAW under laboratory conditions (Shepard, personal comm. 1982). The biologies and distributions of 34

PAGE 46

35 some members of this genus are known (Hafez 1951, Putter and Thewke 1970). Lewis (1970) describes the life history of M_;_ crocei pes (Cresson) for H e 1 i o t h i s spp. and reports that the parasitoid prefers 1st and 2nd instars as hosts. No research dats could be found that document the life cycle and host age acceptance of man i 1 ae developing within FAW larvae, nor has this parasitoid been reported as a natural enemy of FAW anywhere within its range (Ashley 1979) The objectives of our research are to gain relevant information about the biology and host age acceptance of M. manilae when reared on FAW larvae. This information may prove useful in mass production of this parasitoid for inoculative or perhaps inundative releases should M man i 1 ae eventually demonstrate the potential of becoming a significant mortality agent of FAW populations. Materials and Methods Female parasitoids were 24 hrs old and has been exposed to males since female eclosion. Each replicate consisted of exposing FAW larvae (number varied according to experiment) to 6 female parasitoids in a plastic container (7 x 10 cm diam) with 2 screened vents (1.5 x 3.0 cm) and having honey streaked on the underside of the

PAGE 47

36 lid. During host exposure, FAW larvae fed on cubes (3 cm 3 ) of pinto bean diet (Leppa et al 1979 ) after which the larvae were transferred individually to 30-ml plastic cups that contained pinto bean diet where they remained until their fate was determined. FAW larvae were kept as 23+2C, 70_+2% RH and under a 14:10 LD photoperiod. These larvae were divided into 4 groups depending on their age: 1, 24-48 hrs; 2, 49-72 hrs, 3, 73-96 hrs; and 4, 97-130 hrs. Hosts older than 130 hrs were excluded because M man i 1 ae females would not accept them as hosts. The laboratory rearing method for man i 1 ae consisted of exposing parasitoids to approximately 50 FAW larvae which were 48-72 hrs old for 3-5 hrs. Age group acceptance — Depend i ng on host availability 4-6 replicates of 3-4 FAW larvae of the same age group were presented to two female man i 1 ae for 30 min. on the same day. Data from 4 consecutive days comprosed a single test and tests were replicated 4 different times. Developmental rates -Microp! itis mani 1 ae were exposed for 24 hrs to hosts in the four age groups. Parasitoid developmental times were determined from oviposition to pupation and from pupation to adult emergence. Progeny sex ratios were recorded for each age group.

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37 Adult 1ongevity --Freshly eclosed parasitoids were exposed to hosts under continuous light at 26+_lC and longevity was recorded for 2 groups: (1) the females (n=41) and males (n-57) were separated into different cages and (2) both sexes were kept together and allowed to mate for 2 hrs and then to oviposit for 24 hrs inside a plastic container with 20 FAW larvae. After the host exposure period, larvae were removed and adult parasitoids were retained in the plastic containers. Time of host exposure —In order to determine optimal host exposure time, 2 female man i 1 ae were exposed to 20 hosts from the 2nd age group for 15, 30, 45 and 60 min. and then removed. Four replicates were run. Results and Discussion Parasitoids displayed the highest host acceptance for 1st and 2nd age group larvae and a lesser acceptance for 3rd age group larvae (Table 1). Highest parasiti zation rates occurred most frequently in 2nd age group larvae. Significantly fewer 4th age group larvae were parasitized compared to larvae of other groups, and there were several occurrences of significant differences in host acceptance between 2nd and 3rd age group larvae. Similar results have been reported for other members of this genus (Hafez 1951, Lewis 1970). Putter and Thewke (1969) showed that

PAGE 49

38 Table 1. Percent par as i t i zat i on by M man i 1 ae of fall armyworm 1 arv ae Age group (hrs) Test numbers 3 / 1 (24-48) 24.5 a 26 7 a 26.7 a 13.2 a 2 (49-72) 28.3 a 30. 1 a 27.8 a 11.4 a 3 (73-96) 22.5 a 20. 7 b 19.5 b 12.3 a 4 (97-130) 6.9 b 5.2 c 6.8 c 3.5 b Total 369 418 521 279 a Per cent ages fol 1 owed by the same letter i n the same umn are not significantly different by Duncan's Multiple Range Test (P = 0.05)

PAGE 50

39 M. felti ae preferred 1st to 3rd instar larvae (1st to 3rd age groups) of its host Agrotis ipsilon (Hufnagel) and Harcourt (1960) demonstrated a similar instar preference for M. pi utel 1 ae Muesebeck and its host the diamond back moth Plutella maculipennis (Curtis). In contrast, Shepard et al (1983) reported that demol i tor (Wilkinson) preferred 3rd or 4th instar larvae of He! i oth i s spp. However, larvae of this size displayed a vigorous defense response and often damaged or destroyed the parasitoid. We observed also that when Mj_ man i 1 a e females attempted to oviposit in 4th age group larvae that these larvae aggressively attempted to thwart the ov i pos i t i onal attempt by swinging their heads and thoraxes from side to side in an attempt to bite the parasitoid. The larval and pupal developmental times for M man i 1 ae were similar for age groups 1-3 (Table 2). Egg to pupa and pupa to adult developmental times for M man i 1 ae parasitizing 4th age age group hosts increased by approximately 2 days. Significantly more male progeny were produced from the 1st age group in contrast to the 2nd group from which more female progeny emerged. No significant differences were present in the sex ratios of progeny from 3rd or 4th age group larvae. The highest and lowest proportions of female progeny were observed for age groups 2 and 4, respectively. Bryan et al (1969) showed that the

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40 Table 2. Developmental periods (X +_ S.E.) and progeny sex ratios for M. man i 1 ae in fall armyworm larvae Developmental period (day s) Age group Sex ratio (%) a Hosts EggPupa(hrs) exposed pupa adult Total Males Females 1 (24-48) 106 10 + 2.3 4 + 0.7 14 + 3.0 62.5 *--37.5 2 (49-72) 127 10 + 2.9 3 + 0.9 13 + 3.8 42 9 *--57 1 3 (73-96) 93 10 + 2.1 4 + 1.1 15 + 3.2 46 ,8--ns--53 2 4 (97-130) 43 12 + 1.9 6 + 1.7 18 + 3.6 46. 7--ns--55. 3 a Asterisk indicates significance at the 5% level by Student's t-test

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41 sex ratio of emerging progency of croceipes was approximately 1:1 when reared at 25C. Only a single M man i 1 ae emerged per host larvae irrespective of the age group parasitized. Bryan et al (1969) reported an occasional emergency of 2 M. croceipes adults from a single Hel i oth i s spp. larvae. Emerging man i 1 ae larvae appeared to perfer a dry surface on which to pupate and would frequently form cocoons on the underside of the lid rather than on the moist diet surface. Male and female longevity was about 6-7 days. Mating increased female longevity to approximately 10 days. An increase of approximately 10% in parasiti zation was observed when the host exposure period for M man i 1 ae females was increased from 15 to 30 min. (Table 3). Host exposure periods longer than 30 min. did not increase significantly the par as i t i zat i on rate. Biological knowledge about this paras i to id is necessary in any attempt to establish M^ man i 1 ae as an additional mortality agent in the overwintering range of FAW. Ashley et al (1982) showed that the native parasites destroyed approximately 63% of each of the 1st 4 instars and par as i t i z at i on rates followed closely the increase or decrease in FAW larval populations. Parasitization rates of 3.5-30.1% by M. mani 1 ae in FAW larvae were

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42 Table 3. Percent par as i t i zat i on of second age group fall armyworm larvae exposed to m a n i 1 a e for various amounts of time Host {% Par as i t i zat i on ) exposure (min) No. containers a (X + S.E.) 15 8 13.0 + 3.7 a 30 11 22.0 + 3.1 b 45 13 26.0 + 1.7 b 60 9 24.5 + 1.6 b a Two female parasitoids and 20 larvae/container. b Means followd by the same letter are not significant different (P<0.05) by Duncan's Multiple Range Test

PAGE 54

43 observed in the laboratory. The results of our research will be used to rear man i 1 ae and to support efforts to establish this parasitoid in the overwintering range of F AW

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INTERSPECIFIC COMPETITION BETWEEN PARASITOIDS OF THE FALL ARMYWORM Introduction The fall armyworm (FAW), Spodoptera frugiperda is a serious pest of many graminaceous crops throughout the southeastern United States. Average estimates of annual crop losses exceed $300 million (Mitchell 1979). Since overwintering occurs only in the southern portions of Florida and Texas (Lunginbill 1928), increasing FAW mortality within this range may lower the numbers of adults participating in this pest's northward migration each spring. Fifty-three species of parasitoids have been reared from field collected larvae (Ashley 1979). Knowledge of parasitoid interrelationships within FAW larval populations will increase our understanding of the factors that affects the dynamics of this pest, as well as contribute the biological control efforts. In endemic host enemy associations, interspecific competition appears to play a crucial role in structuring the parasitoid guild (Force 1974), and may influence the entire natural enemy complex as well. Parasitoids of the FAW provide a 44

PAGE 56

45 relevant model for the study of interspecific competition within the host larva because of similarities in their life cycles. Ashley et al (1982) supports the concept of interspecific competition during parasitiod development by demonstrating the presence of a dependent density pattern in percent par as i ti zat i on between Chelonus insular is Cresson and Temel ucha diff ici 1 i s Dasch. The present study assesses interspecific competition between two species of larval parasitoids, M i c r o p 1 i t i s man i 1 ae (Ashm.) and C o t e s i a ( = Apantel es ) margi ni ventr i s Cresson, and an egg-larval parasitoid C i nsul ar i s It also describes the host finding and ov i pos i t i onal sequence for marg i n i ventr i s for hosts already parasitized by C i n s u 1 ar i s In addition data are presented on host acceptance of m a n i 1 a e and mar gin i ventr i s of larvae already parasitized by i n s u 1 a r i s Materials and Methods Host eggs or larvae were obtained from a FAW colony maintained at 23-25C, 74-78% RH and under a 14:10 LD photoperiod. Moth oviposition occurred on paper towels, a portion of which were subsequently cut into sections each having 50-60 eggs. All hosts utilized in an experiment came from the same egg mass to help ensure host uniformity. In al experiments, except the fourth, these paper sections were

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46 placed in a plexiglas cage (25 cnW) and exposed to two female C i nsul ar i s (24-48 hrs old) for 24 hrs. Each mass was observed to verify that a i nsul ar i s female had parasitized the eggs. Masses attacked by two or more females and eggs close to the edge of the paper section that were not parasitized were destroyed. The larval parasitoids emerged in plexiglass cages (25 cm^) kept at 26 + 1C, 60-70% RH and under a 14:10 LD photoperiod with a fluorescent light intensity of 800 ft-c. Female parasitoids were held in these cages along with males for a minimum of 48 hrs. Unless otherwise indicated, female parasitoids were between 2 to 4 days old. Host exposure for the larval parasitoids lasted 24 hrs and was accomplished by placing parasitoids, F AW larvae, and 1.5 cm cube of FAW diet (Leppla et al 1979) into a 50-ml container (7 x 10 cm diam) with two air vents (1.5 x 3.0 cm) located near the top on opposite sides. Parasitoids were supplied with honey and water after adult eclosion and during the ov i pos i t i on al period. Following host exposure, FAW larvae were placed individually into 30-ml plastic cups that contained approximately 15 ml of diet. These cups were held in a growth chamber at 25 +_ 1C, 77-80% RH and under a 14:10 LD photoperiod. Experiment 1 Ninety FAW exposed previously to C insul ari s as eggs were divided into three equal groups.

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47 Larvae in group one, were not exposed to margi ni ventr is or M man i 1 ae and served to measure parasiti zation by C i nsul ar i s Remaining larvae were exposed as second instars (48 hrs old) to margi n i ventr i s (group two) or to Hi manilae (group three). Treatments were replicated nine times. The percent successful parasiti zation and the fate of non -par as i t i zed larvae were recorded. Experiment 2 Twenty second-i nstar larvae exposed previously to i nsul ar i s as eggs were exposed to either M man i 1 ae or marg i n i ventr i s in the plastic containers. Ten replicates were made. In the control treatment, larvae were exposed to either marginiventris or M man i 1 ae without prior par as i t i zat i on by C_^_ i nsul ar i s Experiment 3 Fall armyworm larvae exposed as eggs to C i n s u 1 a r i s and unexposed larvae were kept in separate plastic containers until the larvae were 3 days old. The ten exposed and ten unexposed larvae were transferred to new plastic containers. Two females of either margini ventris or M_^_ man i 1 ae were introduced into a container for 30 min and the number of encounters, antennal examinations, ovipositor probes with and without cuticle contact were recorded. An encounter was defined as the arresting of random locomotion that resulted from sensing the FAW larva. An examination occurred when antennal palpation of the larvae by the parasitoid was observed. A probe was

PAGE 59

48 observed. A probe was recorded when the parasitoid thrust ed its ovipositor toward the larval cuticle. Finally, an apparent oviposition took place when the parasitoid mounted the host and inserted its ovipositor. Three replicates for each parasitoid species and larval combination were examined. Further replication was not possible because of the loss of the man i 1 ae colony. Experiment 4 Eight host larvae derived from one of the following four groups were placed in a glass petri dish (15 x 100 mm diam): (1) initially parasitized by C mar g i n i ventr i s and subsequently exposed to M. manilae ; (2) initially not exposed to parasitoids and subsequently exposed to man i 1 ae ; (3) initially parasitized by M man i 1 ae and subsequently exposed to mar g i n i ventr i s ; and (4) initially not exposed to parasitoids and subsequently to L m a r g i n i v e n t r i s As hosts were attacked they were removed and replaced with fresh larva. Non-parasitized larvae served as a control. The number of host encounters, examinations and apparent ovipositions were recorded. Five replicates for each species combination were run starting on the same day hosts were parasitized and then repeated 3 and 6 days later. Experiment 5 The host finding behavior of C mar gi ni ventr i s was investigated using 4-week-old corn, sorghum, Bermudagrass (Cynondon dactylon ( L ) ) and itch

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49 grass. These plants were grown in pots (14.5 x 15 cm diam) containing a mixture of sand, perlite and peat moss (1:2:2 ratio, respectively). Supplementary nutrients were supplied with fertilizer (8-8-8 plus trace elements). FAW larvae exposed previously to C. insul ari s were allowed to become second instars. Plants were placed in wire cages (40 cm 3 ) in a greenhouse at 26-28C, 70-75% RH and 14: 10 LD photoperiod. Thirty larvae were placed randomly on the plant leaves. After 24 hrs, a female was introduced into the cage and her host finding behavior observed. Forty females were observed in sequence, their responses recorded and synthesized subsequently into common behavioral patterns. Parasiti zation by marg i n i ventr i s on FAW larvae also was measured on all four host plants. Thirty, second-instar larvae already parasitized by C i nsul ar i s were placed randomly into the plants. After 24 hrs of host larval feeding, two female margi ni ventr i s were introduced. The host larva were removed at 20-, 40-, 60-, and 80-min intervals. Three replicates for each time interval and plant species were made. Larvae were removed from the plants and placed in 30-ml cups to determine parasiti zation rates.

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50 Results and Discussion Experiment 1 Results of interspecific competition demonstrated that C i nsu 1 ar i s was significantly more competitive than man i 1 ae (Fig. 1.) However, when C marg i n i ventr i s replaced M man i 1 ae within the host larva, then marginiventris emerged more frequently than C i nsul ar i s The combined par as i t i zat i on rates for the three treatments ranged from 73-78%, which demonstrated that multiple par as i t i z at i on did not seem to affect FAW larval mortality. FAW larvae parasitized by any two of the three parasitoid species only produced a single parasitoid, which suggests the destruction of one parasitoid larva by another. Salt (1961) and Vinson and Abies (1980) reported that when multiple parasitism occurred, all but one species was usually eliminated through physical attack, physiological suppression, or both. In a few instances, especially with gregarios paras i to ids, some individualy of both species may survive (Mi 1 ler 1982 Weseloh 1983) Substantial differences were not present between the three parasitoid treatments for (1) larvae that successfully pupated and emerged as adults, (2) larvae that starved because they did not feed on the diet, (3) larvae that died from unknown causes and (4) larvae that fed on the diet but did not pupate (Table 4). Rejection of the

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FIG. 1. Mean percentage emergence of C. i nsul ar i s (C M. mani 1 ae (Mm), and C. marg i n i ventr i s~ ("Cm ) from fall armyworm larvae exposed to multiple parasiti z at ion

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Ci&Cm Ci&Mm Ci-only TREATMENT

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53 Table 4. Mean percentages for emergence of Chelonus insular is ( C i ) Microplitis mani 1 ae ( Mm ) Cotesi a marg i n i ventr is (CiJ and adu 1 1 FAW, and percentages for FAW larvae failing to mature because they refused to feed on the diet, for dying from unknown causes, and for failing to pupate 3 Parasitoid emergence Refused Unknown Did not Treatment Mm Cm Ci FAW diet causes pupate Ci x Mi 13.7a 64.3a 7.0a 3.9a 5.8a 5.4a C i x Cm 46.0b 27.4b 8.7a 4.0a 7.7a 6.5a Ci only 74.4a 7.3a 4.3a 7.7a 5.9a Treatments replicated nine times with 30 larvae/treatment. Means in the same column followed by the same letter were not significantly different by Duncan's Multiple Range Test (P = 0.05). This means for Mm (Column 2) and for Cm (Column 3) were compared using students t-test Had not pupated by the time nonpar as i t i zed larvae had emerged

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54 larval diet may be one of the sources of artificial selection encountered when an insect population is placed under laboratory colonization (Boiler and Chambers 1977). However, reasons for those larvae that fed on the diet but did not pupate or molt during the allocated period were not properly understood. Beckage ( 1982) observed Manduc a sexta (L.) larvae parasitized by Apantel es smer r i nt i e Riley often molted to larval-pupal intermediates even when parasitoids failed to emerge. Experiment 2 The proportions of margi ni ventr i s and m a n i 1 a e adults that emerged from parasitized and non-parasitized hosts were not different significantly (Table 5). C o t e s i a margi ni ventr i s parasitized significantly more hosts then mani 1 ae Larvae that were not parasitized by either parasitoid and emerged as FAW adults displayed significant differences in all four treatments. These data support the results of experiment 3, where M m a n i 1 a e females altered their ov iposi tional behavior toward hosts already parasitized by C. insularis Cotes j a margi ni ventr i s did not appear to discriminate against hosts parasitized previously by C. insularis as there were no significant differences between C_^ i nsul ar i s x C marg i n i ventr i s and C^ mar g i n i ventr i s only treatments. Vinson and Iwantsch (1980) did not discriminate against C. insul ari s parasitized tobacco budworm hosts and neither did crocei pes

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55 Table 5. Mean percentage emergence for Cotesia margi ni ventr i s (Cm) and M i c r o p 1 i t i s man i 1 ae (Mm) from FAW larvae exposed and not exposed as eggs to Che 1 onus insular is (Ci) and percents for emergence of FAW adults, larvae dying because they refused to eat the diet, and larvae not pupating. Mean emergence Refused Did not Treatment Ci Cm Mm FAW diet pupate Ci x Cm 32.5 56.5 5.0 0.0 0.0 Cm only 52.5 30.0* 4.3 6.3 Ci x Mm 48.0 37.5 13.0 0.0 0.5 Mm only 44.5* 28.5* 11.5 16.5* treatments replicated nine times with 20 larvae/treatment. Data analyzed by Student's Jttest (* = significantly different at the 5% level). Comparisons only made between treatments 1 ant 2, and 3, and 4. The means for Ci in treatments 1 and 2 were not compared statistically.

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56 Experiment 3 The behavior of man i 1 ae females were altered significantly when exposed to hosts parasitized previously by C i nsul ar i s (Table 6). This altered behavior occurred in three categories; examinations, probes, and apparent oviposition. A similar behavioral pattern was not found for marginiventris This indicated that C. marginiventris either cannot discern the presence of i nsul ar i s in the host or that the presence of i nsul ar i s does not inhibit oviposition. Vinson and Abies (1980) reported that tobacco budworm larvae parasitized previously by C i nsul ar i s also were acceptable to larval parasitoids Microplitis croceipes Cresson and Campoletis sonorensis Carlson as ovipositional sites. Experiment 4 The number of encounters, examinations, and apparent ovipositions for the two larval parasitoids were not significantly different regardless of the par as i t i zat i on sequence or the number of days between host exposure periods (Table 7). Initially, man i 1 ae made greater numbers of encounters in margi n i ventr i s parasitized larvae than in non-parasitized larvae. There was a trend for man i 1 ae to be more active with respect to encounters, examinations and ovipositions on hosts parasitized by mar g i n i ventr i s compared to nonpar as i t i zed hosts. Cotesia marginiventris was more active also on hosts parasitized previously by M. man i 1 ae than on

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57 Table 6. Mean and percents for encounters, examinations, oviposition probes and apparent ov i pos i t i on al success by C o t e s i a mar g i n i ventr i s and Microplitis manil ae in fall armyworm larvae exposed and not exposed as eggs "to" "Ch?! onus i nsul ar i s Mean a Exposure to C. insular is Encounters Examinations Probes Ovipositions Microplitis manilae Exposed 8.4 2.0 2.2 1.2 (60.8) (14.4) (15.9) (8.7) Not Exposed 8.8 3.8* 4.2* 2.6* (45.5) (19.6) (21.7) (13.4) Cotes i a marginiventris Exposed 12.8 5.8 2.6 2.8 (54.3) (22.4) (11.2) (12.1) Not exposed 14.2 5.8 2.9 2.9 (55.04) (22.5) (11.2) (11.2) Student 1 s _t-test analyzed at a = 0.05 level. Percents are in parentheses and are based upon the total number of behavioral observations (encounters + exams + probes + oviposition).

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58 Table 7. Mean for numbers of encounters, examinations and apparent ovipositions by C o t e s i a mar g^i n i ventr i s (Cm) and Mi cr o p "I i t i s m an i 1 ae (Mm) during two host exposure periods separated by different numbers of days. Second host exposure means 3 Days between Host exposure host exposure ExamTna"Apparent First Second period Encounters tions oviposition Cm Mm 0 13.2 7.8 6.8 None Mm 11.8 6.9 5.6 3 10.8 4.2 3.6 9 6 5.4 3 .0 6 10.6 8.8 4.6 9.8 8.0 4.0 Mm Cm 0 11.4 8.8 6.6 None Cm 9.6 7.8 6.0 3 15.6 9.6 5.6 14.4 8.8 5.2 6 16.8 6.9 7.8 17.4 6.8 7.0 a None of the number pairs were significantly different by Student's t-test.

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59 non-parasitized hosts. M man i 1 ae had greater ovi positional contacts with the hosts that contained C mar g i n i ventr i s larvae than C. marginiventris with host that contained man i 1 ae larvae on the first day of host exposure. This trend reversed itself on days 3 and 6. Experiment 5 The host finding and behavioral sequence for oviposition of margi ni ventr i s on FAW larvae already parasitized by C i nsul ari s on corn, sorghum, Bermudagrass and itch grass consisted on nine basic components (Fig. 2). During the sequence, preening occurred at several different steps. A typical pattern involved the following: 1. Random movement --The parasitoid female flew and walked randomly inside the cage or on the plant leaves. The upper portion of the leaf was preferred. The female held her antennae close and parallel to the substrate, or folded them back under her body. 2. Antennal pal pati on--The female started antennal palpation of the surrounding leaves and on the substrate. She held her antennae nearly parallel to the substrate and lowered her flagella slightly and raised them back to the horizontal position. This movement of the flagella frequently lasted for 5 to 25 sec. The under surface of the leaf was palpated more frequently.

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FIG. 2. Behavioral ethogram of the host finding and ovipositional sequence of m_ar g_i_n i ventr i s females on fall armyworm larvae already parasitized by the egg-larval parasitoid C i nsu 1 ar i s (Solid arrows indicate invariable pathways and dashed arrows represent alternate pathways )

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I / (3) Chemotaxis N 1 to) Antennal Palpation (4) Larval Contact ^ ^ 'A Mounting (5) r mv Random Movement s > \ \ ^ \ -> Preening 7 (9) Resting Insertion (6) / Oviposition (7) Post Antennal < ~ • Palpation 7 ~ Ovipos.tion (8)

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62 3. Chemotaxis--The parasitoid became oriented and walked rapidly toward the site where FAW larvae feeding on the leaves. She vibrated her wings frequently and moved her body in a manner that indicated excitement. 4. Larval contact--Locomoti on was arrested and antennal palpation of the host began with the apical portions of both antennae. 5. Mount i ng--The parasitoid jumped quickly onto the host, usually near the posterior portion. 6. I n ser t i on --St i ng i ng was performed immediately after the process of mounting. The wings were extended during the process. 7. Ov i pos i t i on -Th i s occurred immediately after insertion and the parasitoid moved away quickly from the host 8. Postoviposition--The parasitoid restarted antennal palpation of the substrate. The female began an integrated sequence of abdominal bending and metathoracic leg extension. Preening always occurred. 9. Resting--The parasitoid was motionless. Loke et al (1983) described the behavioral sequence of margi ni ventr i s on FAW damaged corn plants with an ethogram that consisted of 13 defined steps and divided the pattern of host finding behavior for C. marg i n i ventr i s on non-par azi ti zed FAW larvae into four phases:

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63 non-searching movement, searching, oviposition, and resting. Analysis of our ethogram and that of Loke et al (1983) showed that the elimination of certain steps in our ethogram are of particular interest because chemical cues from the earlier oviposition by i n su 1 ar i s may have altered the behavioral pattern of the female margi ni ventr i s after ovipositing in an already parasitized FAW 1 arvae. The percent parasiti zation by C. marg i n i ventr i s showed more than a two-fold increase in corn compared to sorghum and more than a four-fold increase over Bermudagrass and itch grass (Fig. 3). Sixty percent of the larvae were parasitized by mar gin i ventr i s in corn after an 80-min host exposure period. There was no increase in parasitization for Bermudagrass and itch grass after 20 min. Ashley et al (1983) found that parasitization rates for C. insular is and Temel uch a spp. were substantially higher in corn than in Bermudagrass and paragrass Brachiar i e mut i c a (L.). Cotes i a marg i n i ventr i s parasitized the highest proportion of hosts in Bermudagrass and paragrass. The differences in parasitization rates between these parasitoids may reflect a host plant preference (Ashley et al. 1983). In our study, M. manilae apparently failed to compete successfully within the host larva when this larva contain

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FIG. 3. Percentage par as it i zat i on by C. margi ni yentr i s fall armyworm larvae already exposed as eggs to U" insularis. Larvae were randomly placed on four pTant speci ed held in wire cages within a greenhouse.

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80 60 77; 40 • • Corn • •* Sorghum • • Bermudagrass • • Itch grass 20 40 TIME (m

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66 a developing C i nsul ar i s The possibility also existed that man i 1 ae recognized a previously parasitized host and failed to oviposit. Larvae parasitized as eggs by C i nsul ar i s caused a significant reduction in the number of host contacts, examinations, and apparent oviposition by M man i 1 ae Cotes i a m a r g i n i v e n t r i s oviposited in both C. i nsul ar i s parasitized and nonparasi ti zed larvae and was superior internal competitor compared to C. insularis Exposing FAW larvae that have been parasitized as eggs by C i nsul ar i s to £^ mar g i n i ven tr i s or man i 1 ae did not result in additional larval mortality. If this same situation exists under field conditions, then C. insularis may be the key regulator of FAW larval populations.

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EFFECT OF HOST AGE, PARASITOID AGE AND CHANGE OF TEMPERATURE ON INTERSPECIFIC COMPETITION BETWEEN CHELONUS INSULARIS CRESSON, COTESIA MARGINI VENTRIS HTFSW 'AND M I C R 0 P L I T I S~MA"N"I L'A'E "A'S'HffFA'P IN FALL ARMYWORM Introduction The fall armyworm (FAW), Spodoptera frugiperda occurs year-round in the tropical and subtropical areas of the western hemisphere, where it feeds on corn, sorghum, Bermudagrass and other members of the family Graminae. Damaging populations of FAW occur irregularly, and conditions conducive to outbreaks are not well understood (Barfield 1980). Estimated losses attributed to FAW reached $300 million in the southeastern United States during 1977, one of the most severe outbreak years (Sparks 1979) A very diverse complex of natural enemies, especially parasitoids, attack the larval stages of FAW (Ashley 1979). The potential for interspecific competition exists between these parasitoids because more than one species attacks the same instar. Pemberton and Willard (1918) suggested that competition between parasitoids may prevent them from regulating their hosts effectively. 67

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68 Ashley et al (1982) reported the presence of a mirror image pattern with respect to percent parasiti zation of FAW larvae by the larval parasitoids, Chel onus i nsul ar i s Cresson and Temel ucha di f f i ci 1 i s Dasch. and suggested that interspecific competition may have cuased this pattern Factors such as host age and environmental temperature affect the outcome of interspecific competition and evaluation of these factors should be of primary concern before initiating parasitoid release programs against a common host. A literature search provided no information on the effect of host age and temperature on competition among FAW parasitiods. Therefore, we selected the larval parasitoids Mi cropl i ti s m a n i 1 a e Ashmed. Cotes i a ( Apantel es ) marg i n i ventr i s Cresson and the egg-larval parasitoid fJ^ i nsul ar i s for our investigations. These two parasitoids are among the principal natural enemies regulating FAW populations in southern Florida (Ashley et al 1983). The specific objectives of our study were to determine the effects of host age, temperature and the age of C_;_ margi ni ventr i s on interspecific competition. Materials and Methods Parasitoids were kept in plexiglass cages (50 x 50 x 24 cms) at 26 C, 60-65% RH and under a 14:10 LD photoperiod

PAGE 80

69 regime with a fluorescent light intensity of 800 ft-c and were supplied with honey and water. Adults of marg i n i v e n t r i s and C i nsul ar i s came from laboratory colonies established from FAW larval collections made from corn at Hastings and Homestead, Florida, respectively (Ashley 1983). Unless otherwise noted, parasitoids were 24-48 hrs old when used. The FAW host eggs were obtained from female moths maintained in a growth chamber set at 26-27C, 70-75% RH and with a 14:10 LD photo regime. Host eggs were seperated using the technique of Gross et al (1981). All eggs utilized in the experiments came from the same egg mass to help insure host uniformity. A grid was drawn on filter paper and individual eggs were placed in the center of each square. In all experiments FAW eggs were exposed initially to two female C. insular is inside a circular plastic container (7 x 10 cm diam) with 2 screened vents (1.5 x 3.0 cm) and containing 4 cubes (1.5 cm) of FAW diet (Leppla et al 1979). Eggs attcked by two or more females and unpar as i t i zed eggs were destroyed. The grids were then cut into squares and suspended in a plastic container like those used for oviposition by C. insular is until egg hatch. These containers were kept inside an environmentally controlled cabinet set at 27C, 70% RH, with a 14:10 LD photophase. When the FAW larvae were 48 hrs old (all were second instars) they were

PAGE 81

70 exposed to two female C_j_ marginiventris for 24 hrs inside a plastic container which was similar to the one used for C i nsul ar i s The host larvae were then placed inside 30 ml plastic cups containing approximately 15 ml of diet. These cups were sealed with paper lids and placed inside the cabinet. The larvae remained in these cups and their fate recorded. The control treatment for experiments 1 and 2 consisted of larvae exposed only to margini ventris Experiment l--Host Age Forty second instar FAW larvae (head capsule width 0.4-0.5 mm) were transferred to an ovi positional unit at 12, 24, 36, 48, 60, 72, and 84 hrs of age and exposed to two female marg i n i ventr i s for 24 hrs. Each age was replicated seven times. Experiment 2--C. m a r g i n i v e n t r i s Age C o t e s i a mar g i n i ventr i s cocoons were held for adult sclosion and mating inside a plastic container similar to the one used for C. insular is oviposition. When C. marginiventris parasitoids were 24, 48, 72, 96, and 108 hrs old, two females were exposed for 24 hrs with 40 second instar FAW larvae. Treatments were replicated seven times. Experiment 3--Temper ature Effects Thirty second instar FAW larvae were exposed to two female C. marginiventris for 24 hrs. These experiments

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71 were conducted in plastic containers like those used for oviposition by C i nsul ar i s After exposure to C. marginiventris larvae were placed individually in 30 ml plastic cups and held at the following temperatures 19, 22, 25, 28 and 31C and RH 75-78% with a 14:10 LD photophase. Each treatment was replicated seven times. A control treatment was run at 26C with host larvae exposed only to insul ari s The cups were checked three times a week and larval fate recorded. In a second portion of this experiment larvae emerging from eggs parasitized by C i nsul ari s were exposed to C. marginiventris when reaching the following host ages (hrs) 6-10, 12-18, 24-30, 36-42 and 48-54. After exposure to C. marginiventris larvae were individually placed into 30 ml cups and held at the temperatures cited above. Treatments were replicated six times. The control treatment was held at 26C and the RH ranged between 70-75%. Experiment 4D i ssecti on of Mu 1 1 i par as i t i zed Hosts Host exposure to i nsul ari s followed by exposure to C marginiventris or man i 1 ae were performed as previously described. The i nsul ari s margi n i ventr i s parasitized larvae were then placed inside a plastic container for 3, 5, 7 or 9 days. The insul ari s mani 1 ae parasitized larvae were similarly held for

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72 3, 6, 8, or 10 days. Twenty to thirty host larvae were dissected at the end of each time period to determine the condition of the competing parasitoids. In the nine day treatment, C. marg i n i ventr i s larvae had emerged before dissections were done. However, since the host was still alive it was dissected to determine the fate of the immature C. insularis The descriptions of Boling and Pitre 1970) and Glogoza (1980) were used to recognize larvae of marginiventris and i nsul ar i s respectively. Results and Discussion Thirty six hr old FAW larvae produced the highest proportion of marginiventris and lowest proportion of C i nsul ar i s (Table 8). Emergence of margin i ventr i s showed significant differences between 60 and 72 hrs and 24 and 36 hrs but there were not significant differences between 12 and 24 hrs, and 72 and 84 hrs. There was not significant difference in emergence of marg i n i ventr i s from hosts 36 hrs old and the control. Loke and Ashley (1984) reported that highest rate of par as i t i zat i on by C marginiventris of FAW occurred in 48 hr old larvae (second instars). Kunnalaca and Mueller (1979) and Boling and Pitre 1970) stated that females of C. marginiventris produced the most progeny from 2 and 3 day old hosts. Larvae less than 24 hrs did not produce as many

PAGE 84

73 Table 8. Mean percentages at different host ages for emergence of Chel onus i nsuar i s ( C i ) Cotesi a marg i n i ventr i s (Cm.) and adul t f al 1 armyworm and percent mortality of FAW larvae due to (1) refused to feed on the diet, and (2) died from unknown causes. a/ Percent FAW mortality Host age b/ Parasitoid emergence Refused diet Unknown (hrs) C i Cm. FAIT and diet causes 12 25 .5a 20. 7a 45.2a 7.4a 1.1a 24 30.4a 15.7a 35.0b 12.2a 6.7ab 36 17.6a 44.2b 20.3c 13.2a 4.8ab 48 18.8a 40.1bc 16.2cd 17.4a 7.5ab 60 31.7a 32.9c 14.3cd 14.1a 6.9ab 72 52.7b 17.6a 14.8cd 11.7a 3. lab 84 45 .9b 15.2a 10. 6d 18.7a 9.6b Control 45.2b 25.6b 15.8a 8.5b a/ Treatments were replicated 7 times with 40 larvae per treatment. Means followed by same letter for a given column are not significantly different by Duncans Multiple Range Test (P = 0.05)

PAGE 85

74 C. marg i n i ventr i s as larvae between 36 and 48 hrs. Che Ion us i n s u 1 a r i s emerged more successfully than C marginiventris from larvae 12 and 24, and 72 and 84 hrs old. Emergence of C i n s u 1 a r i s in early and latter ages of the host was expected because in most cases of multiparasitism the first species that attacked the host was more successful than the second species (Doutt and De Bach 1964). The emergence pattern of C. insular is showed significant differences between larvae 60 and 72 hrs old. This difference was probably a function of the larger larvae becoming less suitable for par as i t i zat i on by C. mar g i n i ventr i s The percentage of nonpar as i t i zed larvae that became adults was greater except at 48 and 84 hrs than those that died from unknown causes or starved to death. There was a steady decrease in the percent larvae that became FAW adults as host age increased. Substantially more larvae died refusing to eat the diet and died than from unknown causes. No significant differences were found between host ages for larvae dying from refusing to feed. This rejection of larval diet may be a source of artificial selection encountered when an insect population is placed under laboratory colonization (Boiler and Chambers 1977). Ashley et al (1982) reported that a definite proportion of the FAW larval population refused to feed on the artificial diet and that diet rejection was not restricted to the early instars. Significant

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75 differences were observed for larvae dying from unknown causes between 12 and 24 hrs and 72 and 84 hrs of age. Experiment 2--C. marginiventris Age C marginiventris adults which were 48 to 96 hrs old produced more parasitoids than did those 24 or 108 hrs old (Table 9). There were no significant differences in emergence of i nsul ar i s at 24 and 108 hrs suggesting that C marginiventris was either too young or too old to start egg laying. There were no significant differences between the control and 48, 72 and 96 hrs which indicated that the presence of a C i n s u 1 a r i s larva inside the host did not reduce oviposition by marg i n i ventr i s Mean parasitization for all ages illustrated that C. insular is had a higher paras i ti zati on level (45%) than C. marginiventris (41%). Wallner (1982) reported that when two parasitoids attack the same host the parasitoid ovipositing in the host first was more successful. Significant differences were observed for emergence of C. insular is at all the ages studied. However, highest emergence for C. insular is occured at 24 and 108 hrs. Deaths due to unknown causes ranged from approximately 2.00 to 7.5 percent with the most mortality occuring in the 108 hr treatment and control. A substantially high proportion of larvae refused to eat the diet in 96, 108 hrs and control treatments.

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76 Table 9. Mean percentages for emergence of Chel onus insul ari s (C.i.), Cotesia margi ni ventr i s (Cm.) and adult FAW and percent mor t al i ty for F AU I larvae due to (1) refused to feed on the diet, (2) dietd from unknown causes, when age of C .m was changed a/ Percent FAW mortal i ty Cm. age b/ Parasitoid emregence Refused diet Unknown (hrs) C.i C .m TAW and diet causes 24 58 .5a 33.6a 2.9a 2.9a 2.0a 48 39.3b 52.5b 2.1a 3.2a 2.9ab 72 42.4bc 47 .4b 1.4a 4.9ab 3.9ab 96 30.6b 48.7b 2.1a 13.7c 5.4ab 108 54.5a 21.0c 5.9a ll.Obc 7.7b Control 55.0b 9.9a 14.8c 10.1b a/ Treatments were replicated 7 times with 40 larvae per treatment. Means followed by same letter for a given column are not significantly different by Duncans Multiple Range Test (P = 0.05)

PAGE 88

77 Male progeny were always in greater abundance in C marginiventri s regardless of parental age (Fig 4). Boling and Pitre (1970) reported that mated C. margi ni ventr i s generally produced with a sex ratio of 1:1. However, only the 72 hr age group came close to this ratio. A very high percentage of female C. insular is emerged in 96 hrs (Fig 5) and a very large percent of males emerged from the 108 hr group. Sex ratios in hymenopterous parasitoids may be affected by suitable host abundance (Rechav 1978); however, the reason for the abrupt change of sex ratio of £i i nsul ari s in the 96 and 108 hr treatments was not properly understood. Mitchell et al (1984) reported a significant shift in the sex ratio of i nsul ar i s towards males in the field between April and October. Experiment 3--Tempe r ature effects Cotes i a mar gj n i ventr i s emerged most successfully at 25C and it appeared that temperature affected the outcome of competition (Table 10). Significant differences between emergence rates were present for marg i n i ventr i s at all temperatures except 28 and 31C. There were no significant differences at 22, 25, 31 and 28C for insul ari s but significantly more emerged at 28 than at 25C. Less emergence was observed for both parasitoids at low temperatures while optimum temperatures for C. marginiventris and i nsul ari s were 25 and 31C,

PAGE 89

FIG. 4. Progeny sex ratios for C. marqi ni ventri s from different aged mar g^i n i ventr i s~ TC .m ) emerging from fall armyworm larvae par as 1 1 i zed as eggs by C i nsul ar i s

PAGE 90

100

PAGE 91

FIG. 5. Progeny sex ratios for C. i nsul ar i s (C.i.) from different aged marginiventri s~ TC .m ) emergi ng from fall armyworm larvae parasi ti zed as eggs by C. insularis

PAGE 92

100

PAGE 93

82 Cu <-+ a> II rtCu o -s 3 n> O -h 3 Cn O r+ oo cu £ fD cc ro < re 1 3 fD o o 1 O c CU — s cT fD Cl £ Cu oo 13 O — r+ fD 00 oo £ CO r+ '* 3" — h co O o 01 3 — r+ Cu 1 << < CU CL fD — i. — h r+ — h ™i fD fD -J fD r+ 3 c~f fD CT << • o £= fD n Pi ai 3 3 00 l/l -h 31 O c r+ O £ XJ fD Cl fD CT Cu 00 CC Oi fD 3 fD —1 fD 00 rT • o o 3 rt 1 o CO CO 1X5 CO INJ cn no 1X3 XI CT Co I + O 03 n CO CO CO CO cn co -P cn cn co 1+ 1+ 1+ 1+ 1+ 1 + i— • i— > ro ro iNj i— 10 CO CO CO ro cn cn co 1+ 1 + O l— cO -P* CO \+ |+ | + ro ro co o o ^1 o CU O cn -^j cn co cn ^o. Co CD o co cn 1+ 1+ 1+ 1+ 1+ | + 1— • I— • I— I— I— CO O cn -p co ro -p CT CT CT CT CT CU CO o cn I + O I + o cn o 1+ 1 + -p* o ro cn 1+ 1 + CO CO o o O o n 1X5 CT 1X3 o o 1 + CO CD 1+ 1 + CO CO 1+ 1 + *4 o O ro ro Cu 01 Ql cr CT ro cu Cu -£> cn cn cn CO cn CO ro cn i— 1 ro + 1 + 1 + 1 + 1 + 1 + > r— < CO i — 1 CO i— • >-* O o -F vO CO CO Cu CU Cu Cu Cu Cu rp 3 — -"a a fD o -s Cu r+ -J fD q 00 O cn i — cn CT CT Cu Cu CU ^0 co cn I—" CD ro i— • CO CO co co o cn cn + 1 + 1 + 1 + 1 + 3 CO co CO i— 1 ro • CO o cn vD o Q. Cl n CT Cu Cu -5 CU 00 rt"O O fD -s Q_ O fD n> 3 3 rtro -s id fD 3 o ID ro cu -t> 3 C Cl oo ro Cl Cl fD CL Cl -i. ro o cz Cu 3 C 7T l/> 3 ro o s. 3 CU CO < — CD — 1 oo o Cu X3 fD CL <• — ^"CT [ Q ro co iD v (— i ^ fD |, 23 1 fD CT r~\ 1 Cu QCu — f. CT CO ~~h fD fu ^ 00 —5 o fD 1 — \ — i O O / — — < l_ ) —3 EL 00 fD — ^ -j ^ Cu O 3EZ — 1 3 1.3 — ^ i 00 "C CI t 0 O *^ — • > Cu < Cu d Cu — ^ t u (/> CO CO 00 r" r t/> — h Cu ** Cu CO o fD T"^ oo OJ — '• — 3 — 1 + <~ r+ CO — V-J o m o — 1 Z3 r+ fD £ 1 L. 00 3" Cu CI fD — ^ Cu 3 Cu 3 -s Cu fD fD -5 Cu Cu O oa -5 c-tcu — i. fD £Z 3 Cl fD to — > ( u < Cu fD r+ r+ O 3" r+ 00 ~ h fD -1 fD — h < oo fD fD s 1 Cu r+ — O 3 n 0> fD o 3 ~ h 3 00 00 Cu r+ •* fD Cu 4— 3 S— 1Q_ 3 rr Cu fD O CL r+ £Z fD O -> 3 Cu fD r+T3 "CT fD fD fD O-h -I Cu Cu o r+ C 1 O Q_ Cu fD 3 -J 00 ro 3 O rt << -h C S. o "CT cu C 1 1 Cu Q_ 3 fD 3 a. Co fD "1 ro Cl 1

PAGE 94

83 respectively. Temperature did not affect emergence of FAW adults. A significant number of larvae were found to be alive at 19 and 22C. There was a significant difference for larvae which died for unknown reasons at 19C and the remaining temperatures. The time required for development of C^ margi ni ven tr i s from oviposition to emergence as adults ranged from 12-20 days and declined as temperature increased (Table 11). The longest emergence period for both parasitoids occured at 19C. Kunnalaca and Mueller (1979) reported the development time for margi ni ventr i s decreased between 25 and 30C. The range of time required for C i n s u 1 a r i s from oviposition to adult emergence was from 26 to 35 days. Significant differences were observed between 19 and 22C for all parameters measured. An abnormally high number of larvae was unable to pupate at 19C and development of the FAW was slower at the lower temperatures. Keller (1980) reported similar results. Cotes i a mar gj n i ventr i s emerged more successfully than C. insular is when hosts were 12-18 hrs old at 19, 22, and 25C (Fig 6). Chel onus insul ari s was more successful at host ages of 36-42 and 48-54 hrs under all temperatures indicating that marg i n i ventr i s either did not prefer older hosts or was unable to develop in them successfully. Cotes i a mar g i n i ventr is was more successful with hosts at

PAGE 95

84 Table 11. Mean (+ SE) emergence periods (days) when reared at several constant temperatures for Cotesia marginiventris (Cm.) and Chelonus insularis (C.i.) and adult f a 1 1 armyworm and percentages for FAW 1 arvae f ai 1 i ng to mature because they (1) refused to feed on the diet and died, (2) still larvae at end of test, a/ Percent Temperature b/ Parasitoid emergence Refused diet Still (C) T7T: CTm^ VM and died alive 19 35. 5+1. la 20. 1+1. 2a 40. 6+1. 3a 3.5+1.0a 60. 3+1. la 22 30. 3+1. 6b 18. 6+1. lb 34. 5+1. lb 6. 9+1. 5b 30. 3+1. 7b 25 26 3 + 1. 5b 17. 3+2. lb 28.9+2.1c 1.5 + 1. 7b 0.00c 28 27. 5+1 9b 12. 5+12. 5b 19. 5 + 1. 3d 2. 7 + 1. 7b 0.00c a/ Treatments were replicated 7 times with 30 larvae/ treatment. Means followed by same letter for a given column are not significantly different by Duncans Multiple Range Test. (P = 0.05).

PAGE 96

OJ ^_ 4_ CD CV EZ O oj ^_ cvj 4> CM ro — 1 +-> rd 00 c he J re -a a) c =3 x: fO 1/1 +-> on 00 >>•<_>|o eu E <4— M O -rOJ -rO 00 O c 0J iOl TO 00 SQl 0) OJ cn e •> rD OJ OJ fO +-> +-> OJ > C c ai sOJ OJ rO 03 sE +-> r— O) 4o OJ-^ 4— O 3 OJ S< T) > OJ U. OJ Q_ at -a E • so io o OJ 4_ £ 00 • >> O C_5 CD E Q-o •— < S_ X co u_ to OJ CNJ

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87 24-30 hrs old at 22 and 25C than was i nsul ar i s In. general, margin i ventr i s emerged from a higher proportion of younger hosts than did C. insularis Hosts older than 36 hrs produced more i nsul ar i s regardless of temperature. Two possible explanations for this are as follows: (1) marginiventris was a better competitor in younger hosts and (2) either oviposition or successful competition was reduced in older hosts larvae containing a developing i nsul ar i s Experiment 4D i s sect i on of Multiparasiti sed Hosts Dissections of mul t i par as i t i zed larvae showed no evidence of physical attack between parasitoids during the first 5 days of host development (Table 12). However 7 days after par as i t i t i on 5 C. insularis larvae had visible melanized scars, while those of margini ventri s were unscared suggesting that margi ni ventr i s physically attacked larvae of C. insularis Vinson and Ables(1980) reported that larvae of C. insularis had visible evidence of physical attack after 3 days in hosts parasitized by the larval parasitoid Campoleis sonorensis (Carlson). Six days after par as i t i z at i on by M manilae 5 dead M mani 1 ae larvae were found in the hosts. This number of dead larvae was higher at 8 and 10 days although there was no visible evidence of physical attack. Vinson and Iwantsch (1980) reported that M. crocei pes mutilated the

PAGE 99

88 Table 12. Fate of larval parasitoid C. marginiventris (Cm.) and M. manilae (M.m.) in competition with the egg larval and parasitoid C. insularis as determined by dissection of fall armyworm (FAW). Fate of No. of FAW After exposure to C. marginiventris Competitor larvae 2nd parasitoid Fate of or species dissected when dissected C. insul ari s M. mani 1 ae cb d c.6 larvae 3 no larvae 21 eggs 5 no larvae 26 5 22 larvae 4 no larvae 19 larvae 7 no larvae 20 7 5 injured larvae 15 larvae 4 injured larvae 16 larvae 23 9 /c 3 larvae^ 3 30 3 28 larvae 2 no larvae 26 egge 3 shriveled egge 1 no egg 23 6 20 larvae 3 no larvae 5 dead larvae 12 healthy larvae 6 no larvae 20 8 20 larvae 7 dead 10 healthy larvae 3 no larvae 23 10 10 larvae 13 no larvae 10 dead larvae^ 2 no larvae /a Most of C. marginivenris have formed cocoons. /b Some larvae emerging from host to form cocoon outside. /c C. insularis larvae were not found.

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89 C. insular is larvae by physical attack and killed them in 5 days. In summary, marginiventris reproduced most successfully in 36 hr old FAW larvae. margi ni ventri s adults which were 48 to 96 hrs old produced the greatest number of parasitoids. i nsul ar i s and marginiventris developed optimally at 31 and 25C. Cotesi a margi ni ven tri s physically attacked developing C. insular is larva inside the host. Dead M m a n i 1 a e larvae were found in hosts mult i parasitized by i n s u 1 ar i s and m a n i 1 a e but the cause of the death was unknown.

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INTERSPECIFIC COMPETITION BETWEEN FALL ARMYWORM PARASITOIDS CHELONUS INSULARIS AND COTESIA MARGIN I VENTRIS INSIDE FIELD CAGE AND PLOTS I ntroduct i on The fall armyworm (FAW), Spodoptera frugiperda is one of the few argicultural pests infesting many members of the family Graminae in the United States. Each year the FAW migrate from tropical and subtropical areas to occupy a range which may extend northward to the Canadian border and westward to Montana. Major losses in late planted corn, sorghum and other susceptible crops are experienced when high populations of FAW are present. Mitchell (1979) estimated that if a severe outbreak occurred, as in 1977, losses could exceed $500 million. Ashley et al (1982) reported that up to 63% of first 4 instars are destroyes by parasitoids of FAW. Interspecific competition among parasitoids within the same host can have a significant impact on the host's population dynamics. The occurence of interspecific competition may result in the death of one or both parasitoid (Salt 1961). Therefore, this competition may be a vital component influencing the parasitoid guild 90

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91 (Zwolfer 1970). Ashley (1979) recorded 53 species in 43 genera from 10 families having been reared from FAW larvae. Two of the most frequently recovered parasitoids in the FAW overwintering region in Southern Florida were, Cotes i a (Apanteles) marg i n i ventr i s Cresson which develops in FAW larvae, and C he 1 onus insular is (Cresson) which parasitizes the egg emerges during the larval stages of FAW (Ashley et al 1982) We performed 4 experiments in the evaluation of FAW/par as i to i d interactions. The objective of the first experiment was to study the functional response of C marg i n i ventr i s when exposed to different densities of FAW previously parasitized by C i nsul ar i s In the second experiment we examined the functional response of C margi n i ventr i s to different levels of mul t i p ar as i t i zed host densities inside the laboratory. In the third experiment data were obtained on the ov i posi t i onal preferences of these two parasitoids at different FAW densities inside field cages. The fourth experiment determined the impact of C^ i nsul ar i s and C^ mar g i n i ventr i s on FAW larvae found in different regions of the plant and the surrounding environment.

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92 Materials and Methods Host and P ar as i t o i d Co 1 ony Maintenance A colony of the FAW was maintained at 23-25C, 74-78% RH and under a 14:10 LD photoperiod. Adults were fed with 10% sucrose solution. Adult FAW oviposition occurred on paper towels that were subsequently cut into sections each having a single egg mass of 50-60 eggs. These sections were placed in circular plastic cups ( 7 x 10 cm diam) having two screened vents (1.5 x 3.0 cm). These cups were used as ovipositional units and contained 4 cubes (1.5 cm) of pinto bean diet (Leppla et al 1979 ). Adult i ns u 1 ar i s and mar g i n i ventr i s were held in plexiglasss cages ( 50 x 50 x 24 cms) at 26C, 60-65% RH and 14:10 LD photo regime. Undiluted honey and water were provided to adult parasitoids. Unless otherwise noted, parasitoids were 1-4 days old when used for experimentation. Experimental Procedures for Host P ar as i t i zat i on Individual FAW eggs were isolated using the technique described by Gross et al (1981). All eggs in each replicate, came from the same egg mass. A grid was drawn on filter paper and individual eggs were placed in the center of each square, inside a plastic petri dish (100 x 15 cm). The eggs were then exposed to two female i nsul ar i s and any that were attacked more than once were discarded. After par as i ti zat i on eggs were kept in the plastic cups,

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93 with FAW diet inside an incubator at 26+lC, 75-80% RH and 24:00 LD photo regime, until the larvae emerged. When these larvae reached the second instar larvae (head capsule width 0.5-0.6 mm) they were exposed to two, C. marg i n i ventr i s females in plastic petri dishes (100 x 15 cm) for 24 hrs. The larvae were individually placed in 30 ml plastic cups containing approximately 15 ml of FAW diet. Corn variety (Pioneer x 304C) was planted at Homestead, Florida in inside field cage and in study plots. When the FAW larvae were second instars, female C. marginiventri s were released into field cages and study plots each day between 1600 and 1800 hrs until the conclusion of the release period. Corn plants adjacent to the study plots were also sampled. Plants were individually taken apart and examined for FAW larvae. Head capsule widths were measured to determine larval instars (Ashley et al 1982). Each larva was placed in a 30 ml plastic cup containing FAW diet. The cups were checked until the fate of each larva and the sex of each adult that emerged were recorded. Experiment l --Host Density. The FAW eggs were exposed to i nsul ar i s at densities of 1, 2, 4, 8, 16, 32, and 64 in a plastic container. Second instar larvae were placed in the same container with FAW diet and were exposed to two C^ marginiventri s females at the same densities for 24 hrs. Treatments containing 1 larvae/cup

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94 and 2 larvae/cup were replicated 10 times and the remaining treatments were replicated 7 times. FAW larvae were exposed to marginiventris at 24, 48, 72 and 96 hrs pf age. The larvae were transferred subsequently to 30 ml cups and their fate determined. Experiment 2--Fie1d Cages Three field cages ( 246 x 155 x 115 cm) were conducted from metal pipe frames and screened with woven cloth netting so that insect activity could be observed. Each cage contained 20 corn plants, with 91.4 cm between rows and 8 inches between plants. Methonyl was applied at the rate of 10 ml/3.79 L 7 days before the introduction of host eggs. Four randomly selected plants were pinned to one, two or three paper sections (1.54 x 5.08 CM) containing 50-6 FAW eggs. The corn plants were approximately 4 weeks old and 75-85 mm in height and the egg masses were pinned to the lower surfaces of the upper leaves within 20.3 cm of the growing terminal. Twenty female C i nsul ar i s were released into each cage just prior to sunset followed by release of 20 (\ margini ventri s females on each of the next 3 days. The experiment was repeated 3 times over a 4 month period with 3 cages per replicate. Plants with paper sections were sampled 3 days after the final introduction of C_._ marg i n i ventr i s and the remaining plants in the perimeter area were allowed to grow for 2 weeks prior to sampling.

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95 Experiment 3 — Field Plots Corn was planted in six adjacent plots, (50 x 11 m) in the center of a field previously used to produce field corn. Each plot was disked twice before planting. Seven to ten days after disking corn seeds were planted at a depth of 3.0 cm and spaced 91.4 x 243.8 cm (between rows and plants). The plots were irrigated weekly and two week after planting ammonium nitrate fertilizer (33.5% N) was broadcast over each plot at a rate of approximately 165 kg/ha. Four to five weeks after planting, plants selected at random were pinned with a paper section having approximately 50-60 F AW eggs at the following locations: (US) upper surface of leaves (within 20.3 cm from terminal) (oriented less than 45 from stalk), (LS) lower surface of leaves (oriented more than 45 from the stalks,) (ST) stalk (central stem with a pithy core), (GS) ground (within 5.08 cm from the plant), (SH) in between stalk and 1 eaf sheath (Fig 16 ) The eggs were not washed. The five treatments were replicated 6 times within the plot. A control plot was left with FAW eggs pinned into the whorl region. Starting from the first day after egg pinning, 480 C. insular is females were introduced for 3 consective days. On the 4th day 498 female marg i n i ventr i s were released. The complete experiment with 6 plots (5 with treatments + control) was replicated 3 times over a 4 month period.

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96 A sample consisted of harvesting all the plants in a 10-m area. Comparisons were made between parasitoid release plots and non release plots in terms of F AW larval damage to whorl (leaves surrounding the furl with blades partially extended and sheath concealed) and furl (leaves surrounding a central roll) and stalk. The plants with recongni zable F AW feeding in whorl, furl or stalk with FAW larvae present were defined as damaged. Results and Discussion Experiment l--Host Density The mean number of marginiventris that emerged from densities of 64 and 32 larvae produced patterns that were almost mirror images of each other (Fig 7). A density of 64 larvae/cup represented the highest mean progeny production at 48 hrs. Kunnalaca and Mueller (1979) reported that C. marginiventris parasitized between 31 and 110 hosts each day. The greatest difference in progeny densities occurred between the 64 larvae/cup density and the remaining densities. More superparasitism occured at 4 and 8 larvae than at 32 larvae suggesting that mar g i n i ventr i s exposed to lower densities attacked many hosts more than once. However at higher densities only one parasitoid emerged per host larvae which showed that C. marginiventris avoided

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FIG. 7. Mean progeny production by C. mar g i n i ventr i s at 7 host densities from eggs previously parasitized by C. i nsul ar i s

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64 larvae/cup 32 larvae/cup 16 larvae/cup 8 larvae/cup 4 larvae/cup 2 larvae/cup I larvae/cup 48 72 96 FAW AGE (hrs)

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99 super par as i t i sm at high densities (Table 13). The longevity of emerging m a r g i n i v e n t r i s was greater at lower densities than at higher densities. Substantially more larvae were found dead at higher than at lower parasitoid densities, probably due to cannibalism. (Ashley, Pers. Comm. 1985). A similar trend of progeny production was observed for C. insular is (Fig 8). The 64 larvae/cup treatment had produced the highest number of progeny. The number of progeny were related to the parasitoid density. As the number of larvae per treatment was increased a consequent increase in progeny production was observed. This is a well recognized characteristic of many parasitic hymenoptera (Legner 1969). C i nsul ar i s was more successful in progeny production than C. marg i n i ventr i s at higher densities. A number of events may have been responsible for the apparent success of C_;_ i nsul ar i s The females spent less time examining eggs before ovipositing at the higher density. Also the female C. insularis oviposited more eggs at higher host density than at lower density. C marginiventris may have detected hosts previously parasitized by C. insularis by some external stimuli and reduced oviposition. C i nsul ar i s received unpar as i t i zed eggs for oviposition. The reduction of oviposition by C marginiventris may have helped for developing insul ari s larvae to emerge without a competition.

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100 oo f— X is — | c o o CD Cu — 1 -J TO 3 X3 oo Cu cr cu < -S U3 Cu i-t3 — — O CO -5 00 fD < < lO < Cu 3 Cu Co fD -• oo oo 1 — 1 fD — 1 3 r+ ->• c 3 OO << *< c-t"O cr • o -• ft) fD -t) O N ~S ~J -h 0) 1 00 -: QfD O Cu -tl t 1 — Cu o 1 + 1 + • • CO 1 o I— 1 on m 1 • 1 + 1 + 00 oo O — '• cd i • O to < i • c 3 t 1— 3 — 1 cr -t| 1 fD — 1 i -J O n i 1 ^ I—" 00 Cu "O 1 + • — 1 1 o i— o r+ — i. • 1 1 + 1 + rv> -ll n o O o cr cu • T| *< r+ o — '• H> I/) O r+ n: C oo o O Qoo on I— 1 00 00 ro Cu • • • c+ <-+ c+ to l— CO 00 1 + 1 + 1 + -f= Q. (T> o O o fD Cu Cu • • • 3 r+ O 1— • CO IN3 00 r+ 3" 1 — <• CU 1 rtn r-r 3" fD o 00 fD 00 • • • a. r+ r+ o CO 1 + 1 + 1 + 00 Cu Cu Q_ • o o r+ 0) o 3 I— 1 o -4 -o 00 ro II Qo r-ltl • 3 o i— to en cn • t— i— I— 1 rt CO 1 + 1 + Oi —m* fD 1 + 1— > fD < o 00 ID • oo no ^1 cr • << ro i— 1 lO 1." oo o CO -^1 1 + o 1 + CTl I + o o ro on 1— CTl ro 1 + + 1 — 1 • rv> O on t— 1 3 Cu tQ

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FIG. 8. Mean progeny production by insularis at 7 host densities and parasitized by C. mar g i n i ventr i s

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50 24 48 72 96 FAW AGE (hrs)

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103 The sex ratio of marginiventris progeny favored females at densities of 2 and 4 larvae (Fig 9). The C i nsul ar i s males outnumbered females at all densities except at 4 eggs/larvae where 1:1 ratio was obtained (Fig 10). The presence of more females at low densities may be seen as a mechanism that ensures the presence of a minimum number of males to fertilize all the females. Such mechanisms have been reported in other parasitoids in which mated females are functionally virgin for a certain period of time after mating (Mackauer 1976). Experiment 2--Fie1d Cages Chel onus insul aris emerged most frequently in treatments having 1 or 2 paper sections while C. marginiventris was the major parasitoid in the 3 paper section treatment during the first and second test periods (Fig 5). In the last test period no definite emergence patterns were observed. The decrease in emergence of C. insul aris in 3 paper section treatment indicated that C. marginiventris was a better competitor in crowded host conditions. Wiseman et al (1983) reported that FAW larvae often moved from infested plants onto surrouding border plants during the 3 to 5 days after infestation. This movement may have aided marginiventris in locating hosts. i nsul ar i s emerged more successfully in 1 and 2 paper sections and appeared to search the portions of corn plants where most FAW eggs were deposited. However, Loke and Ashley (1984)

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FIG. 9. Sex ratio of m ar g i n i ventr i s from 7 host densities.

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FIG. 10. Sex ratio of C. insularis from 7 host densities.

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FIG. 11. Percent par as i t i zat i on by C i nsul ar i s and C. margi ni ventr i s from FAW larvae recovered inside from TTeld cage during 3 test perids. Vertical bars within a test period from lest to right indicate treatments 1, 2, and 3 paper sections.

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UJ o cr UJ Q_ H C. insularis C. marqiniventris < ^ 90 CO < h50 70 30 10 2 3 12 3 May 27 — ^June 29^ TEST PERIOD 2 3 July 25—

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110 reported that C. marginiventris was a day adapted species and has been observed searching for hosts in bright sunlight in corn fields. The release of two parasitoids inside the field cages resulted in an overall par as i t i zat i on rate of 60.0% for C i nsul ar i s and 37.4% for C. m arginiventris This high rate of par as i t i zat i on was similar to the field results reported by Mitchell et al ( 1984 ) where C. insular is Temel ucha difficul is Dasch. and margin i ventr i s parasitized FAW larvae at rates of 82, 10, and 2% respectively. This high rate of parasitization by C. i nsul ar i s in field cages and the field (Mitchell et al 1984) indicated that C. insular is was the principal parasitoid of FAW in southern Florida. Seventy, forty and thirty-nine percent of first instars were parasitized in treatments having 1, 2, and 3 paper sections respectively (Fig 12). Thirty percent of second instars were parasitized in 2 paper section treatment. These results were similar to those reported by Mitchell et al (1984) where 77% of the first two instars were parasitized. Ashley et al ( 1982) reported that the percent parasitization of the first 4 instars of FAW remined constant and then decreased substantially for 5th and 6th instars. Reasons for the reduction in percent parasitization in second instars was not properly understood. Mitchell et al (1984) reported the decrease of

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FIG. 12. Mean percent parasitized FAW instars in treatments 1, 2, and 3 paper sections inside field cage.

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UJ < First instar I I Second instar |il Third instar H Fourth and fifth instar S 80 N (f) 60 < rr < LU o rr LU CL 40 20 [72 3 PAPER SECTIONS

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113 the proportion of first instar larvae was probably a function of crop maturation as well as the larval population reaching a more stable age distribution. The greatest impact on FAW in all 3 treatments occured in first instars. This was similar to that reported by Vickery (1929) where first instars of FAW were preferred by C. margi ni ventr i s since they can be stung before dispersing from the egg mass. Thirty-five percent of third instars were parasitized in comparison to 15% of second instars in treatment 3. The FAW larve that did not yield parasitoids produced FAW adults, starved to death because they did not feed on the diet or died from unknown causes. The proportion of nonparasi ti zed larvae that yielded FAW adults was always greater than starved or died from unknown causes (Fig 13). Parasitoid sex ratios favored females in treatments having 3 egg masses per paper section (Table 14). Sex ratio regulation of margi n i ventr i s could be due to eigher selective fertilization of eggs or differential mortality of larvae depending on host density. Selective fertilization by C. margini ventis female in low host densities may be based on female detection of previously parasitized hosts. Many hymenopteran parasitoids can distinguish between parasitized and nonpar as i t i zed hosts (Wylie 1965) and fertilize a smaller percentage of eggs on parasitized hosts (Flanders 1939). If the female C. mar g i n i ventr i s

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FIG. 13. Mean percent of FAW larvae that became a) adults, b) starved and died c) died from unknown reasons in treatments 1, 2, and 3 paper sections.

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75 Became adults Starved and died Died from unknown reasons LU o 50 cr UJ Q_ 25 0 I 2 PAPER SECTIONS

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116 Table 14. Sex ratio + SE ( Q : C? ) for C. margi n i ven tr i s ( C .m ) and i nsul arTs ( C i ) from F AU~~ 1 arv ae par as i tized inside a field cage. Egg mass C .m C i size Sex ratio Sex ratio <50 (1 Paper section) 1.00:5.5+0.9 1.90:1.00+1.6 >50 <120 (2 ) 1.00:2.00+0.7 1.00:1.70+0.3 >120 <180 (3 ) 3.5:1.00+1.3 2.9:1.00+0.9

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117 was not capable of controlling fertilization of its eggs then high percent of males in low densities could be due to differential mortality resulting from competition among larvae for available food within the host. Local increases in the ratio of parasitoids to hosts can produce a change of sex ratio in field population of Hymenoptera ( Charnov et al 1977 ) Experiment 3 — Field Plots C. insular is emerged as the predominant parasitoid (Fig 14) on the upper (58.5%), and lower (71%) leaf surfaces, between stalks and leaf sheaths (40.5%) and the control (80.5%). A higher percentage of mar g i n i ventr i s than C. insular is emerged from the treatments placed on ground (15.5%) and stalk (35.5%). T erne 1 u c h a d iff i c u lis Dasch., Meteorus autographae Muesebeck Rogas laphygmae Viereck and several unidentified species accounted for the remaining parasitoids. Mitchell et al (1984) and Ashley et al (1982) reported that in order to abundance C i nsul ar i s T d i f f i c i 1 i s and margin i ventr i s were the principal parasitoids collected from study plots at Homestead. Therefore, releasing C. m ar g i n i yen t r i s increased its parasiti zation level above that of T. diff ici 1 i s The percent par as i t i z at i on was higher from the lower surface of leaves in comparison to the control. Morrill and Greene (1973) reported that in corn the highest number of FAW larvae were found in whorls.

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FIG. 14. Percentage par as i t i zat i on for principal parasiti soid species recovered from FAW larvae from (US) upper surface of whorl, (LS) lower surface of whorl, (GR) ground, (SH) between stalks and leaf sheath, (ST) stalk and (WH) control in corn.

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0 Chelonus insularis B Cotesia marqiniventris US LS GR SH ST WH PLOTS

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120 Our results, indicated that eggs pinned to the lower surface of leaves in whorls had highest percent parasitization. This suggested that FAW parasitoids search plant regions where the highest number of FAW larvae are found. Since the whorl is the highest part of the plant, first or second stage larvae would move up into this area (Greene and Morrill 1970). This may have accounted for the low par as i t i zat i on rates observed in hosts collected near the ground and on the stalk. Both, C. mar g i n i vent r i s and insularis were observed to be highly mobile and rapidly dispersed away from the release site. Therefore, releases could be made at several points in a field and the parasitoids would naturally disperse throughout the field. The preference of insularis for FAW eggs on the undersurface of corn leaves in early vegetative stages agreed with the findings of Waddill (1977) and Keller (1980) who reported this site as preferred location for oviposition by FAW females. The sex ratio of emerging mar g i n i ventr i s favored males in hosts collected from the upper surfaces (55%) lower surfaces (60%) of the whorl, stalks (60%), near ground level (53%), and control (70%) (Fig 15). Larvae collected between stalks and leaf sheaths yielded more female parasitoids (61%). Males predominated in emergence of C. insularis in the treatments of upper surface, lower surface, and between stalks, and leaf sheaths.

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FIG. 15. Sex ratio for mar g i n i ventr i s and i nsul ar i s recovered from FAW larvae fr~om ( US ) upper surface of whorl, (LS) lower surface of whorl, (GR) ground, (SH) between stalks and leaf sheath (ST) stalk and (WH) control in corn.

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CO q o CO < < LU o tr LU Q_ 80 70 60 50 40 30 20 10 m a m a M c. m c. insularis females LS GR SH ST LOCATION ON PLANT

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123 Significantly more medium sized larvae (head capsule width = 0.8-1. 2mm) were found between stalks and leaf sheaths and lower surfaces of the whorl (Table 15). Initially, there were more small than large larvae feeding under the lower surface and upper surface but this trend was gradually changed with more medium sized larvae found between stalks and leaf sheaths. The greatest difference between small and large larvae was found between upper leaf surface with small sized larvae. Ashley et al (1980) reported that F AW larval abundance decreased on corn plant upper surface than lower surface and this reduced abundance may be indicative of preferred feeding locations. Our experiment showed that FAW larvae prefer feeding locations such as between stalks and leaf sheaths, and lower surface. Food quality, changes with feeding location and may alter or influence larval development in FAW (Keller 1980). Feeding inside the leaf sheaths and the lower surface of whorls may be a form of protection from natural enemies. Very few large larvae were recovered in all 5 treatments. The damage to upper leaves in the whorl was significantly greater in nonpar as i to i d release plots than in parasitoid release plots (Table 16). These results suggest that differences in degree of damage between parasitoid release and non release plots were related to the impact of the parasitoids. Significant differences

PAGE 135

CD C r— CU =3 CD to 2 CL+J rO CL> O -Q TD •> cu o: • C 4_ CM S• 3 — co I 00 s• CU O 2 o E o co CU =3 •> CU • CO s4— O o sc_> i CXI CO c o ai <~ O-l— Q.00 3 ro E E ^ CO O i— Sro 44— 4-> O CO a CU CU "O cr>+-> c: n3 O ro +-> CU c CU r— IE u O CO 5(_> CU CL CU -C (O +-> c > ro rO SCU CU ro -C i — to 3 4— .— T3 ro •i+J 3 CO c ai CU CJ +-> ai ra — Q O CJ o (j (j o o o o o o • • • • • • o o o o o o JO -O _D a o CJ o O TJ o o o o CM CM CM I— ( CO • — 1 <—l o U CJ CJ TJ T3 T3 o o o O O o o o o o O o TD TJ <_> CJ CJ CJ CJ CJ o o o cn O CD — 1 CM 1 — 1 CO CJ CJ CJ CJ CJ a o o o O o o ro CM cn cn CD u CJ CJ TJ T3 TTJ '-O o o o O O o o o o O O o JTJ ro rO jO X) O o o o o o cn CM o I— I CTi < rH ro CM .— i t — ( u U CJ TJ T3 TJ o O o O o O o o ( — ) Q o ro -Q .O X3 o O O O TJ CJ o cn m CM o r— 1 — i 1— 1 ro CO -O _o O O -Q CJ CO O o o o — 1 CO cn i — ro a CJ (J CJ XJ Tj in o o o O O o o o o O O .0 _o (O rO ro rO ro cn o cn o o o o cn cn o 1 — ( cn i — i CM CM ro CM cj CJ CJ CJ T3 CD o o o o O 1 • • • • • CM o o o o o .o jQ JQ cn CO, cn o 0J cn o CM o o CV1 o CM ra ro -Q T3 CO O O CJ CJ o O cn cn O rH < — i CO i — 1 ro ro ro ro CO ro ro ro co CO oo CO OO CO CI on cn CTv cn cn <—< — i rH — t rd CVJ >^ rC a; e "-3 CO CM CU c CO CM < C rO CJ Q >l C cu TD C rO O C cn CU s E r3 ryi >1 QJ aj O > CU o cn s o s_ ->-> CO 0) CU 1— ryi a> cn d) c rO +j OS c 0J a. CO ro QJ s: s: "r0

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125 Table 16. FAW damage to different regions of corn in plots where C. insular is (C.i.) and C. marginiventris (Cm.) were released". % Damage to Corn by FAW a/ Cm. and C.i. No parasitoids Date of released released Observations Upper Surface Lower Surface Stalk Upper Surface Lower Surface Stalk May 8 19.6b 12.9c O.ld 30.5a 13.4c O.Od May 12 13.5b 9.7c O.Od 43.6a 10.1c O.Od May 16 15.5a 5.7b 0.0c 15.7a 5.2b 0.0c June 9 19.7b 30.3a 0.0c 18.9b 28.5a 0.0c June 13 14.5a 13.5a 0.0b 16.7a 13.5a 0.0b June 17 30.5b 9.5c 0.2d 53.5a 28.5b O.Od July 11 24.3a 14.7b 0.5c 22.5a 15.6b 0.3c July 15 19.7a 19.5a 0.0b 19.3a 21.5a 0.0b July 19 33.7a 19.6b 0.0c 34.5a 19.1b 0.0c a/ Treatments in the same row followed by the same letter were not significantly different by Duncans Multiple Range Test.

PAGE 137

126 were observed on May 8th, 12th, and June 17th in terms of damage to upper leaves in parasitoid release and non release plots. Damage to lower leaves also showed significant differences between these two plots on June 17th. The damage to stalks were negligible in both plots. Keller (1980) reported that mature leaves are a qualitatively better food source for FAW than developing leaves. However, FAW larvae appar to prefer developing leaves under field conditions (Morrill and Greene 1973). Since feeding on mature leaves exposes FAW larvae to natural enemies and climatic changes, concealed feeding in whorls may have survival advantage. This trend was observed on all observatio dates except June 9, July 15, in non-parasitoid release plots and June 9th, in parasitoid released plots. Cotesi a mar g i n i ventr i s and insul ari s produced the most progeny at a host density of 64 eggs/larvae per cup. Longevity of marg i n i ventr i s was greatest at a host density of 8 larvae/cup. Chelonus insul ari s had an emergence of 60% in field cages but C. marg i n i ventr i s was a better competitor at host densities above 2 egg massses per paper section. Seventy percent of all hosts in the first instars were parasitized. Chelonus insularis emerged 72% and 58.5% of the time from parasitized larvae on the lower and upper surfaced of corn leaves, respectively.

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127 Significantly more medium sized larvae were found between the stalk and the leaf sheath, on the lower surface of the whorl than in the other areas of the plant. The damage to upper leaves ws significantly greater in non-parasitized release plots than in parasitoid released plots.

PAGE 139

FIG. 16. Illustration of exhibit the placement of egg containing paper sections in different regions of corn. US Upper surface of whorl LS Lower surface of whorl GR Ground SH Between stalk and leaf sheath ST Stalk WH Whorl region

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GENERAL SUMMARY AND DISCUSSION Many factors influence the suitability of a potential insect host for parasitoid growth and development. For example, a host may be unsuited, if already parasitized or at stage of development inappropriate for parasiti zation In the case of solitary parasitoids, prior parasiti zation of the host by another parasitoid of either the same or another species can result in a host not being suitable. Thus, if two solitary parasitoids occur in the same host, one individual usually destroys the other. Whether the competition involves physical attack, secretion of toxins, physiological suppression, or selective starvation, the outcome is largely dependent upon the species involved, the parasiti zat i on sequence, and the length of the interval between attacks. A myriad of parasitoids attack FAW (Ashley 1979) and their interrelationships influence the population dynamics of the pest. At present, the basic biological strategy control for FAW is to introduce as many suitable natural enemies as possible in the hope that the "best" species or combination of species will prevail. In this regard, available theoretical and empirical evidence indicated that the level of biological control usually increases as the number of natural enemy species increases (Huffaker et al 1971). Results reported here 130

PAGE 142

131 showed that interspecific competition occurred between exotic and indigenous F AW natural enemies. My data and that of Ashley et al (1982) and Mitchell et al (1984) indicated that is is difficult to establish additional natural enemy species in the overwintering range of FAW in South Florida, because of the dominance of C. insular is Host age preference, developmental period and longevity of M^ man i 1 ae a larval parasitoid of Spodopter a spp, imported from Thailand, were studied. First (24-48) and second (49-72 hrs) age group of FAW larvae found to be most suitable for parasitoid propagation. The developmental period ranged from 13-18 days. Male and female longevity was about 6-7 days. Parasiti zation rates of 3.5-30.1% by M_^ man i 1 ae in FAW larvae were observed. This biological information will be useful in the event that M. man i 1 ae is reared for inundative or inoculative releases in overwintering range of FAW. Competition within FAW larvae by C. marg i n i ventr i s Mrcani 1 ae and i nsul ar i s revealed that margi ni ven tH_s was a superior competitor compared to insul aris but insul ari s was superior to mani 1 ae Subsequent parasitization by either C. marg i n i ventr i s or M. manilae of larvae exposed to insul ar i s as eggs did not result in additive host mortality. Description and analysis of host finding behavior by mar g i n i ventr i s in FAW larvae previously parasitized by C. insularis showed

PAGE 143

132 that this behavior consisted of 9 basic steps. These results supported the conclusion of Loke and Ashley (1984) that host finding behavior of margi ni ventr i s is influenced by chemicals from both plant and host. The percentage par as i t i zat i on by C. mar g i n i ventr i s showed more than two fold increase in corn when compared to the increase in sorghum, Bermudagrass and itch grass. M man i 1 ae females significantly altered their behavior when hosts had already been parasitized by C i n su 1 ar i s C i nsu 1 ar i s was the major parasitoid when FAW eggs were glued to upper surfaces of corn leaves (58.5%) lower surfaces (71%) and between stalks and leaf sheaths (40.5%). A higher percentage of C_;_ marg i n i ventr i s emerged from the treatments in the ground (15.5%) or the stalks (35.5%). Significant differences were observed with respect to damage to upper leaves in whorls of corn in parasitoid release plots than non parasitoid release plots and this was related to the impact of parasitoids on FAW 1 ar v ae Additional work is needed in several areas and new avenues for research opened up as a result of information gathered from studies reported here. The superiority of one parasitoid over another in multiple par as i t i z at i on results in the waste of some parasitoids. How this affects the comparative field efficiencies of all 3 parasitoids studied, as well as the population dynamics of

PAGE 144

133 the FAW, should be investigated. The predominant native parasitoid, C i nsul ari s should be investigated to determine other characteristics important in controlling its impact on FAW larval populations. These include such characteristics as spacial distribution, temporal synchronization and reproductive rates. One of the major areas requiring further research is the mechanism of dominance in competition between parasitoids. I found evidence of physical attack by margin i ventr i s on developing i n s u 1 ar i s larvae. The potential impact of interspecific competition on FAW biological control needs further research and should include studies on: (1) competition studies between C i nsul ari s and T^ d i f f i c i 1 i s since these two parasitoids are the principal species in the overwintering range of the FAW; (2) the effects of interspecific competition on parasitoid population densities; (3) more detailed studies on the developmental biologies of C. insul ari s C margini ventr i s and T difficilis in FAW larvae; and (4) more detailed life table analyses of FAW larval populations. In addition, before more exotic parasitoids are introduced, it should be determined in controlled laboratory experiments if they can successfully compete within FAW larvae, with the native species.

PAGE 145

REFERENCES Abies, J. R. and S. B. Vinson. 1981. Regulation of host larval development by the egg-larval endopar asi toi d C he 1 onus i nsul ar i s ( Hymenoptera:Braconidae) Entomophaga 26: 453-58 Agnello, A. M. 1978. Host enemy report on Sp odoptera frugiperda Unpublished term paper. Department ~of fintomol ogy and Nematology. University of Florida. Gainesville. 16 pp. Allen, W. W. and R. F. Smith. 1958. Some factors influencing the efficiency of Apantel es medicaginis Muesebeck ( HymenopterarBraconidae) as a parasite of the alfalfa caterpillar Col i as phi 1 ad i ce eurytheme Boisdural Hilgardia. 28(1): 1-42. Altahtawy, M. M. S. M. Hammad and E. M. Hegazi 1976 Studies on the dependence of Mircoplitis rufiventris kok. Hymenoptera:Braconidae) parasitizing Spodoptera littoral is Boisd. on own food as well as on food of the host. Z. Angew. Entomol 81(1): 3-13. Andrews, K L. 1980. The whorlworm, Spodoptera f r ugi perda in Central America and neighboring areas. Ma. Entomol. 63 (4): 456-7. Arther, A. P., J. E. R. Stainer and A. L. Turnbull. 1964. The interaction between 0 r g i 1 u s obscur ator Nees. (Hymenoptera:Braconidae) and Temeluc ha interruptor Grav. (Hymenoptera: Ichne urn onidaej, paras itesof the pine shoot moth Rhyac ionia buoliana (Schiff.) (Lepidoptera:01ethreutid?e) Can. Entomol 96(7) : 103-4. Ashley, T. R. 1979. Classification and distribution of fall armyworm parasites. Fla Ent. 62: 114-123. Ashley, T. R. 1983. Growth pattern alteration in fall armyworm Spodoptera frugiperda larva after parasiti zation by Apantele s mar g i n i ventr i s Campol et i s grioti Chel onus insulari s andTTpnosoma vi tticole Fla. Entomol. 66: 261-66. 134

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135 Ashley, T. R., C. S. Barfield, V. H. Waddill, and E. R. Mitchell. 1983. P ar as i t i z at i on of fall armyworm larvae on volunteer corn Bermudagr ass and paragrass. Fl a. Entomol 66: ( 2) : 267-71. Ashley, T. R., V. H. Waddill, E. R. Mitchell and J. Rye. 1982. Impact of native parasites on the fall armyworm, Spodoptera frugiperda ( Lep i dopter a : Noct u i d ae ) in South Florida and release of exotic parasites E i phosoma vitticole ( Hymenopter a : I chuemon i d ae ) Environ. Ent. 11: 833-37. Barfield, C. S., E. R. Mitchell, and S. L. Poe. 1978. A temperature dependent model for fall armyworm development. Ann. Entomol. Soc Amer. 71: 70-4. Barfield, C. S., J. L. Stimac and M. A. Keller. 1980. State of the art for predicting damaging infestations of fall armyworm. Fla. Entomol. 63: (4): 364-73. Barlett, B. R. and J. C. Ball. 1964. The development biologies of two encyrtid parasites of Coccos hesper i dum and their intrinsic competition. Ann. Ent. Soc. Amer. 57: 496-503. Beckage, N. E. 1982. Incomplete host development induced by parasitism of M an due a sexta larvae by Apantel es smer i nthi Ann. Entomol Soc. Amer. 75: 24-27 Bess, H. A. and F. H. Haramoto. 1958. Biological control of the oriental fruit fly in Hawaii. Proc. 10th Int. Congr. Entomol. 4: 835-40. Bianchi, F. A. 1944. The recent introduction of armyworm parasites from Texas. Hawaii Plant Rec. 48(3) 203-12. Boling, J.C. and H. N. Pitre. 1970. Life history of Apanteles margin iventris with descriptions of immature stages J. Kans Entomol Soc. 43: 465-70. Boiler, E. G and D. L. Chambers. 1977. Quality aspects of mass reared insects, pp. 219-236. In: R. L. Ridgeway and S. E. Vinson (eds.), Biological Control by Augmentation of Natural Enemies. Plenum Press, New York.

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136 Boyce, H. R. and G. G. Dustan. 1958. Prominent features of parasitism of twi gi ntest i ng larvae of the oriental fruit moth Gr aphol i t ha mo 1 est a (Busck) ( Lep i do pter a : Olethreutidae) i~n Ont ar to Canada. Proc. 10th Int. Congr. Entomol 4: 493-96. Broodryk, S. W. 1969. The biology of Chel onus curvimacul atus Cameron. (Hymenoptera:8raconidae) J. Entomol. Soc. South Africa. 32(1 ) : 169-89. Bryan, D. E., C. G. Jakson, and R. Patana. 1969. Laboratory studies on M i c r o p 1 i t i s croceipes a braconid parasite of Hel i othes spp. J. Econ. Ent. 62: 1141-44. Burkhart, C. C. 1953. Feeding and pupating habits of the fall armyworm in corn. J. Econ. Entomol. 45: 1035-7. Chapman, J. W. and R. W. Glaser. 1915. A preliminary list of insects which have wilt, with a comparative study of their polyhedra. J. Econ. Entomol. 8:140-9. Charles, V. K. 1941. A preliminary list of the entomogenous fungi of North America. USDA, Bur. Ent. Plant Quar. Insect Pest Bull. 21: 707-85. Charnov, E. L. and J. Bull. 1977. When is sex environmentally determined. Nature. 266: 828-30. Danks, H. W. R. L. Rabb, and D. S. Southern. 1979. Biology of insect parasites of Hel i othes larvae in North Carolina. J. Georgia. Entomol Soc 14(1): 31-7. Davis, F. M. 1980. Fall armyworm plant resistance programs. Fla. Entomol. 15: 277-82. De Bach, P. and Sundby, R. A. 1963. Competitive displacement between ecological homologues. Hilgardia 34(5): 105-66. Doutt, R. L. and P. De Bach. 1964. Some biological control concepts and questions in biological control of insect pests and weeds. P. De Bach and E. Schlinger (Eds.). Reinhold, New York, pp 124. Ehler, L. E. 1977. P ar as i t i z at i on of cabbage looper in California cotton. Environ. Entomol. 6(6): 783-4.

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137 Ehler, L. E. 1978. Competition between two natural enemies of mediterranean black scale on olive. Environ. Entomol 7: 521-3. Ehler, L. E. and R. W. Hall. 1982. Evidence for competitive exclusion of introduced natural enemies in biological control. Environ. Entomol. 11: 1-4. Fisher, R. C. 1961. A study in insect mul t i par as i t i sm II. The mechanism and control of competition for possession of the host. J. Exp. Biol. 38: 605-28. Fiske, W. F. and Thompson, W. R. 1909. Notes on the parasites of Saturnidae. J. Econ. Entomol. 2, 450-60. Flanders, S. E. 1939. Environmental control of sex in hymenopter ous insects. Ann. Entomol. Soc. America. 32: 11-26. Force, D. C. 1970. Competition among four hymenopter ous parasites of an endemic insect host. Ann. Entomol. Soc. Amer. 63: 1675-88. Force, D. C. 1974 Ecology of insect host par as i t i zed communities. Science 184: 624-632. Gardner, W. A. and J. R. Fuxa. 1980. Pathogens for the suppression of the fall armyworm. Fla. Entomol. 63(4): 439-47 Glogoza, G. 1980. Biology of Chel onus i nsul ar i s Bio. Control of insects Lab. USDA-ARS Res. Rpt. July-Dec. 75-81. Gnagliumi, D. 1982. Las plagas de la cana de azucaren Venezuela. Pages 568-9. In Minist. Agric. Crig. Centr, Invest. Agron., Maracay, Venezuela. Greene, G. L. and W. L. Morrill. 1970. Behavioral responses of newly hatched cabbage looper and fall armyworm larvae to light and gravity. J. Econ. Entomol 63: 1984-86. Gross, H. R R. Johnson, E. A. Harrell, and W D. Perkins. 1981. Method of seperating fall armyworm eggs from masses. J. Econ. Entomol. 74: 122-23.

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138 Hafez, M. 1951. Notes on the introduction and biology of Microplitis demoliter ( Hymenopter a : Br aeon i d ae ) Bull. Soc. ent. Egypte. 35: 107-21. Harcourt, D. C. 1960. Biology of the diamond-back moth PI utel 1 a macul ipenni s Curtis ( Lepi dopter a : PI utel 1 i dae ) in eastern Ontario. III. Natural enemies. Canadian Ent. 92: 420-21. Huffaker, C. B. and P. S. Messenger. 1976. Theory and practice of biological control. Academic Press, New York. 743 pp. Huffaker, C. B., P. S. Messenger and P. De Bach. 1971. The natural enemy compenent in natural control and the theory of biology control. In Biological Control. C. B. Huffaker (Ed.) Plenum, New York. 511 pp. Johnson, B. 1959 Effect of par as i t i zat i on by Aphidius pi atens i s Brethes on the developmental phys i o 1 ogy of its host, Aphis cracci vora Koch. Ent. Exp. Appl. 2: 82-99. Keller, M. 1980. Effects of temperature and corn phenology on FAW biology. M. Sc. Thesis Dept. Entomology and Nematology, Univeristy of Florida, 83 pp. Kunnalaca, S. and A. J. Mueller. 1979. A laboratory study of Apante 1 es mar g i n i yen tr i s a parasite of green cloverwornu En v i r o~. Entomol 8 : 365-368 Legner, E. F. 1969. Adult emergence interval and reproduction in parasitic hymenoptera, influenced host size and density. Ann. Entomol. Soc. America. 62: 220-26. Leppla, N.E., P. V. Vail, and J. R. Rye. 1979. Mass reading and handling techniques for the cabbage looper. Proc. Radio isotopes and radiation in Entomology Training Course. FA0/IAEA. 59-75. Lewis, W. J. 1970. Life history and anatomy of Microplitis croceipes ( Hymenopter a : Br aeon i d ae ) a parasite of Heliothes spp. ( Lepi doptera : Noctui dae) Ann. Ent. Soc. America 63: 67-71.

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139 Loke, W. H. and T. R. Ashley. 1984. Behavioral and biological responses of C o t e s i a mar q i n i ven tr i s to kairomones of the fall armyworm Spodoptera fru'giperda J. Chem. Ecol. 10 (3): 521-29. Loke, W. H., T. R. Ashley, and R. I. Sailer. 1983. Influence of fall armyworm Spodoptera frugiperda ( Lepi dopter a : Noctuidae) larvae and corn plant damage on host finding in Apan teles marg i n i ventr i s ( Hymenopter a : Br aeon i dae ) ElTv iron. Entomol 12 (3): 911-15. Luginbill, P. 1928. The fall armyworm. U. S. Dept. Agric. Tech. Bui 1 34 92 pp. Mackauer, M. 1976. Genetic problems in the production of biological contol agents. Ann. Rev. Entomol. 21: 369-85. Marsh, P. M. 1971. Keys to the nearctic genera of the families Braconidae, Aphididae, and Hybr i zont i d ae ( Hymenopter a) Ann. Entomol. Soc. Amer : 64: 841-50. Marsh, P. M. 1978. The braconid parasites ( Hymenopter a) f H e 1 i o t h e s species ( Lepi dopter a : Noctu i dae ) Proc. Entomol. Soc. Wash. 80(1): 15-36. Martin, P. B., B. R. Wiseman and R. E. Lynch. 1980. Action thresholds for fall armyworm on grain sorghum and coastal Bermudagr ass Fla. Entomol. 63(4): 375-405. Miller, J. C. 1977. Ecological relationships among parasites of Spo dop tera praef ica Environ. Entomol. 6: 581-5. Miller, J. C. 1982. Life history of insect parasitoids in successful mul t i par as i t i sm Oecologia 54: 8-9. Mitchell, E. R. 1979. Fall armyworm symposium, preface. Fl a. Entomol 62 : 81 Mitchell, E. R W. W. Copeland and A. N. Sparks. 1974. Fall armyworm: nocturnal activity of adult males as indexed by attraction to virgin females. J. Georgia. Ento. Soc. 9: 145-6.

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140 Mitchell, E. R V. H. Waddill and T. R. Ashley. 1984. Population dynamics of the fall armyworm ( Lepidoptera: Noctuidae) and its larval parasites on whorl stage corn pheremonepermeated field environments. Environ. Entomol. 13: 1618-23. Moon, R. D. 1980. Biological control through interspecific competition. Environ. Entomol. 9(6): 723-28. Morrill, W. L. 1973. Ecology, economics and behavior of the fall armyworm in field corn. M. Sc. Thesis. Department of Entomology and Nematology. University of Florida. Gainesville, 60 pp. Morrill, W. L. and G. L. Greene. 1973. Distribution of FAW larvae: 2. Influence of biology and behavior of larvae on selection of feeding sites. Environ. Entomol 2: 415-8. Mourier, H. and S. B. Hannine. 1969. Activity of pupal parasites from Muse a domestica in Denmark. Vidensk. Meddr dansk naturh Foren. 132: 211-6. Mueller, A. J. and S. Kunnalacca. 1979. Parasites of green cloverworm on soybean in Arkansas. Environ. Entomol 8: 376-79. Muesebeck, C. F. W. 1918. Two important introduced parasites of the brown tall moth, Euproctis chrysorrhea L. J. Agric. Res. 14: 191-206. Muesebeck, C. F. W. 1921. A revision of the North American species of ichneumon-flies belonging to the genus Apantel es Proc. U.S. Nat. Mus. 58: 483-76. Navas, D. 1974. Fall armyworm in rice. Proc. Tall Timbers Conf. on Ecol Anim. Control by Habitat Manage. 6: 99-106. Nickle, D. A. 1976. The peanut agro ecosystem in Central Florida: economic thresholds for defoliating noctuids ( Lepi dopter a : Noctu i d ae ) associated parasites; hyperparasitism of the Apantel es complex ( Hymenopter a: Braconidae). Ph.D. dissertation, Department of Entomology and Nematology, University of Florida. 131 pp.

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141 Olive, A. T. 1955. Life history, seasonal history and some ecological observations of the fall armyworm Laphygma frugiperda (A.S.), on sweet corn in North Carol i na. Mi Sc. Thesis. Department of Entomology. N.C. State University, Raleigh, 77 pp. Painter, R. H. 1955. Insects on Corn and teosinte in Guatemala. J. Econ. Entomol 48(1 ) : 36-42 Pair S. D., H. R. Gross and A. N. Sparks. 1985. Laboratory biology and rearing of Pi apet imorpha i ntroi ta a pupal parasite of fall armyworm. P>" oc SEW, £nto Soc. America. South Carolina, USA. Pemberton, C. E. and H. F. Willard. 1918. Interrelations of fruit fly parasites in Hawaii. J. Agri Res. 15: 419-465. Pencoe, N. L. and P. B. Martin. 1981. Development and reproduction of fall armyworms on several wild grasses. Environ. Entomol. 10: 999-1002. Pianka, E. 1970. On r and k Selection. Am. Nat. 104: 592-7 Pitre, H. N. 1979. Fall armyworm on sorghum: other hosts. Mississippi Agric. Forest Exp. Sta. Bull. 876 12^ pp. Putter, B. and S. E. Thewke. 1970. Biology of Microplitis felt i ore ( Hymenopter a: Braconidae) a parasite of bl ack cutworms Agr ot i s i ps i 1 on Ann. Ent Soc. America 63: 645-648. Rabb, R. L. and R. E. Stinner. 1978. The role of insect dispersal and migration in population processes, pp. 3-16. In Conf. radar, insect population ecology and pest management. NASA Conf. Pub. 1070. Rechav, Y. 1978. Biological and Ecological studies of the parasitoid Che Tonus inanitus ( Hymenopter a : Br aeon i d ae ) in Israel Entomophaga. 23: 95-102. Roberts, J. E. 1965. The effects of larval diet on the biology and susceptibility of the fall armyworm, Laphyama frugiperda (J. E. Smith) to insecticides. Ga. Agric. Experi Sta. Tech. Bull. N.S. 44. 22 pp.

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142 Salt, G. 1961. Competition among insect parasitoids. In: Mechanisms in biological competition. Proceedings Symposium Soc. Exp. Biol. 15: 96-119. Schroder, D. 1974. A study of interactions between the internal larval parasites of Rhyacionia buoliana Entomophaga. 19: 145-71. Shepard, M J. E. Powell, and W. A. Jones. 1983. Biology of Mi cropl i ti s demo 1 i tor ( Hymenopter a : Braconidae) an imported parasitoid of H e 1 i o t h e s spp. ( Lepi dopter a: Noctuidae) and the soybean I ooper Pseudoplusia includens ( Lep i dopter a : Noctuidae). Environ Lnt 12 : 641-45 Simmons, F. J. 1953. Interrelationships of fruit fly parasites in Eastern North America. Bull. Ent. Res. 44: 387-93. Smith, H. S. 1929. Multiple parasitism: Its relation to the biological control of insect pests. Bull. Ent. Res. 20: 141-9. Snow, J. W. and W. W. Copeland. 1969. Fall armyworm: Use of virgin female traps to detect males and to determine seasonal distribution. USDA Prod. Res. Report No. 110, 9 pp. Sparks, A. N. 1979. A review of biology of fall armyworm. Fl a. Entomol 62: 82-7 Steinhaus, E. A. 1957. New records of insect virus diseases. Hilgradia. 26: 417-30. Thompson, W. R. and H. W. Parker. 1930. Morphology and biology of Eutimner i a crassifemur an important parasite of corn borer" 7". Agr i c Res. 40: 321-45 Tietz, H. M. 1972. An index to the described life histories, early stages and hosts to the mi crol epi doptera of the contential United States and Canada. Vol I and II. Sarasota, Fla. The Allyn Museum of Entomology, 1039 pp. Tingle, F. C, T. R. Ashley, and E. R. Mitchell. 1978. Parsites of Spodoptera ex i gua Spodopter a er i dani a (Lepidoptera:Noctuidae) and Her petogr amma bipunctalis ( Lep i dopter a : Pyr al i dae) collected from Amara n thus hybr i dus in field corn. Entomophaga. 2T: 343-7

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143 Turnbull, A. L 1967. Population dynamics of exotic insects. Bull. Entomol. Soc. Amer. 13: 333-7. Turnbull, A. L. and D. A. Chant. 1961. The practice and theory of biological control of insects in Canada. Canad. J. Zool 39: 697-753. Van den Bosch, R. 1968. Comments on population dynamics of exotic insects. Bull. Entomol. Soc. Amer. 14: 112-5. Van den Bosch, R. and A. H. Haramoto. 1953. Competition among parasites of the oriental fruit fly. Proc. Hawaiian Ent. Soc. 15: 201-6. Vickery, R. A. 1929. Studies of the fall armyworm in the Gulf Coast district of Texas. USDA. Tech. Bull. 138: pp 63 Vinson, S. B. 1972. Competition and host discrimination between two species of tobacco budworm parasitoids. Ann. Entomol. Soc. Amer. 65: 229-36. Vinson, S. B and J. R. Abies. 1980. Interspecific competition among endopar asi toi ds of tobacco budworm larvae ( Lepi dopter a: Noctu i dae) Entomophaga. 25: 357-362. Vinson, S. B., Guiolott, F. S. and D. B. Hays. 1972. Rearing of Cadiochiles nigriceps in the laboratory with Heliothes virescens as hosts. Ann. Entomol. Soc. Amer .'" '6~6Y "1"1"70^7T: Vinson, S. B. and G. F. Iwantsch. 1980. Host suitability for insect parasitoids. Ann. Rev. Entomol. 25: 397-419. Waddill V. H. 1977. Shadow sampling: A fast painless mathod for collecting fall armyworm egg masses. Fla. Entomol. 60 (3): 215-216. Waddill, V. H T. R. Ashley, and E. R. Mitchell. 1985. Seasonal abundence of fall armyworm parasites in southern Florida. Proc. SEB. Ento. Soc. Amer. Greenville, South Carolina. Walker, T. J. 1980. Migrating Lepidoptera: Are butterflies better than moths? Fla. Entomol. 63: 79-98.

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144 Wa11ner, W., R. M. Weseloh, and P. S. Grinberg. 1982. Intrinsic competition between Apanteles mar g i n i ventr i s (HymenopterarBraconi dae) and Rogas lymantriae ( Hymenoptera: Braconidae) reared on Lymantria dispar (Lepidoptera:Lymantriidae) Entomophaga. 21 : 99-10 3 Watt, K. E. F. 1965. Community stability and the strategy of biological control. Can. Entomol 97: 887-95 Weiser, J. 1959. Nosema 1 aphygmae n. sp. and the internal structure of the mi cr ospor i d an spore. J. Insect Path. 1: 52-9. Weseloh, R. M. 1983. Effects of multiple parasitism on the gypsy moth parasite Apantel es mel anoscel us ( Hymenoptera:Braconidae) and Compsilura concinnata (Diptera:Tachinidae). Envi r oTT! Entomo 1 12 : 599-602 Wilson, J. W. 1933. The biology of parasites and predators of Laphyma exigua Huebner reared during the season of 1937~. M a Entomol. 17: 1-15. Wiseman, B. R. and F. M. Davis. 1979. Plant resistance to the fall armyworm. Fla. Entomol. 62 (2): 123-30. Wiseman, B. R., F. M. Davis and W. P. Williams. 1983. Fall armyworm: larval density and movement as an indication of non preference in resistant corn. Protection Ecol. 5: 135-141. Wiseman, B. R., D. B. Lueck and W. W. McMilliam. 1973. Effects of fertilizers on resistance of antigua corn to fall armyworm and corn earworm. Fla. Entomol. 56 (D:l-7. Wiseman, B. R. and W. W. McMillian. 1969. Competition and survival among the corn earworm, the tobacco budworm and the fall armyworm. J. Econ. Entomol. 62: 734.5 Wood, J. R., S. L. Poe and N. C. Leppla. 1979. Winter survival of fall armyworm pupae in Florida. Environ. Entomol 8: 249-52 Wylie, G. 1965. Discrimination between parasitized and unpar as i t i zed house fly pupae by females in N a son i a v i t r i p e n n i s (Walk) ( Hymenoptera : Pteromal i daej"! Can. Entomol 97: 279-86.

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145 Wylie, H. G 1972. Larvae competition among three hymenopterous parasite species on mu 1 t i par s i t i zed housefly pupae. Can. Entomol. 104: 1181-90. Young, J. R. 1980. Suppression of fall armyworm populations by incorporation of insecticides into irrigation water. Fla. Entomol. 63 (4): 447-50. Zwolfer, G. 1970. The structure and effect of parasite complexes attacking phytophagous host insects. P. T. den Boer and G. R. Gradwel (Eds). Proc. Adv. Study Ins. on dynamics and numbers in populations. Center for Agric. Publication and Documentation. Wageningen, Netherlands. pp. 405-18.

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BIOGRAPHICAL SKETCH Rohan Harshalal Sar athchandra Rajapakse is the only son of Mr. and Mr. Don Wilson Rajapakse of Wellawatte, Colombo, Sri Lanka. Rohan Rajapakse received his primary and secondary education at Isipathana Maha Vidyalaya, Colombo. He entered the Faculty of Agriculture of the University of Peradeniya in 1972, and graduated with second class honors in 1976. He then worked briefly as an assistant lecturer and joined the Post Graduate Institute of Agriculture (PGIA), University of Peradeniya, in 1977. Between the years 1976 and 1977, he also worked as a research assisant in entomology in Sri Lanka Cashew Corporation. He received his masters degree in entomology from PGIA, University of Peradeniya, in 1978, and joined the permanent staff of the Faculty of Agriculture, University of Ruhuna as an assistant lecturer in 1978. He taught entomology and plant pathology for undergraduate students at the University of Ruhuna until 1981. He arrived in Gainesville, Florida, in December of 1981, to pursue his studies leading to Ph.D. degree at the Department of Entomology and Nematology at the University of Florida. 146

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147 Rohan Rajapakse is a member of the Entomological Society of America, Florida Entomological Society and Sri Lanka Association of Advancement of Science. He has two sisters, Damayanthie (a high school teacher) and, Sandhya (an account ant )

PAGE 159

I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. 1 Ch ai rman Dr. Van H. Waddi Professor of Entomology Nematol ogy and I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Dr Thorn as K Ashley, Associate Professor of and Nematology ai rm an Enfomol ogy I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. John R. Strayer ssor and Entomology t o 1 o g y

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I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. This dissertation was submitted to the Graduate Faculty of the College of Agriculture and to the Graduate School and was accepted as partial fulfillment of the requirements for the degree of Doctor of Philosophy. August, 1985 Dr. Dani e1 "A." "Roberts" ~ Professor of Plant Pathology


FIG. 8. Mean progeny production by insularis at 7
host densities and parasitized by m a r g i ni v e n t r i s .


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FIG. 6. Percentage emergence of C. marginiventris and C. insularis from fall
armyworm (FAW) larvae, par as i t i zecHon egg's ~b~y ~C. insularis"! FTftJ Tarvae were
exposed at different ages to marginiventris ancl then held at 19, 22, 25, 05
28C for development.


145
Wylie, H. G. 1972. Larvae competition among three
hymenopterous parasite species on multiparsitized
housefly pupae. Can. Entomol 104: 1181-90.
Young, J. R. 1980. Suppression of fall armyworm
populations by incorporation of insecticides into
irrigation water. Fla. Entomol. 63 (4): 447-50.
Zwolfer, G. 1970. The structure and effect of parasite
complexes attacking phytophagous host insects. P. T.
den Boer and G. R. Gradwel (Eds). Proc. Adv. Study
Ins. on dynamics and numbers in populations. Center
for Agrie. Publication and Documentation. Wageningen,
Netherlands. pp. 405-18.


41
sex ratio of emerging progency of M_^ croceipes was
approximately 1:1 when reared at 25C. Only a single M.
man i 1ae emerged per host larvae irrespective of the age
group parasitized. Bryan et al. (1969) reported an
occasional emergency of 2 M. croceipes adults from a
single He!iothis spp. larvae. Emerging NL man i 1ae larvae
appeared to perfer a dry surface on which to pupate and
would frequently form cocoons on the underside of the lid
rather than on the moist diet surface.
Male and female longevity was about 6-7 days. Mating
increased female longevity to approximately 10 days. An
increase of approximately 10% in parasitization was
observed when the host exposure period for M, manilae
females was increased from 15 to 30 min. (Table 3). Host
exposure periods longer than 30 min. did not increase
significantly the parasitization rate.
Biological knowledge about this parsito id is
necessary in any attempt to establish manilae as an
additional mortality agent in the overwintering range of
FAW. Ashley et al. (1982) showed that the native para
sites destroyed approximately 63% of each of the 1st 4
instars and parasitization rates followed closely the
increase or decrease in FAW larval populations. Parasiti
zation rates of 3.5-30.1% by M. manilae in FAW larvae were


113
the proportion of first instar larvae was probably a
function of crop maturation as well as the larval popula
tion reaching a more stable age distribution. The
greatest impact on FAW in all 3 treatments occured in
first instars. This was similar to that reported by
Vickery (1929) where first instars of FAW were preferred
by marginiventris since they can be stung before
dispersing from the egg mass. Thirty-five percent of
third instars were parasitized in comparison to 15% of
second instars in treatment 3.
The FAW larve that did not yield parasitoids produced
FAW adults, starved to death because they did not feed on
the diet or died from unknown causes. The proportion of
nonparasitized larvae that yielded FAW adults was always
greater than starved or died from unknown causes (Fig 13).
Parasitoid sex ratios favored females in treatments having
3 egg masses per paper section (Table 14). Sex ratio
regulation of marginiventris could be due to eigher
selective fertilization of eggs or differential mortality
of larvae depending on host density. Selective fertili
zation by marginiventis female in low host densities
may be based on female detection of previously parasitized
hosts. Many hymenopteran parasitoids can distinguish
between parasitized and non-par as itized hosts (Wylie 1965)
and fertilize a smaller percentage of eggs on parasitized
hosts (Flanders 1939). If the female C_^ marginiventris


120
Our results, indicated that eggs pinned to the lower
surface of leaves in whorls had highest percent parasiti-
zation. This suggested that FAW parasitoids search pi ant
regions where the highest number of FAW larvae are found.
Since the whorl is the highest part of the plant, first or
second stage larvae would move up into this area (Greene
and Morrill 1970). This may have accounted for the low
par as itization rates observed in hosts collected near the
ground and on the stalk. Both, C_^ marginiventris and
insularis were observed to be highly mobile and rapidly
dispersed away from the release site. Therefore, releases
could be made at several points in a field and the parasi-
toids would naturally disperse throughout the field. The
preference of C^_ insularis for FAW eggs on the under
surface of corn leaves in early vegetative stages agreed
with the findings of Waddill (1977) and Keller (1980) who
reported this site as preferred location for oviposit ion
by FAW females.
The sex ratio of emerging C. marginiventris favored
males in hosts collected from the upper surfaces (55%)
lower surfaces (60%) of the whorl, stalks (60%), near
ground level (53%), and control (70%) (Fig 15). Larvae
collected between stalks and leaf sheaths yielded more
female parsito ids (61%). Males predominated in emergence
of C. insularis in the treatments of upper surface, lower
surface, and between stalks, and leaf sheaths.


FIG. 10. Sex ratio of C. insularis from 7 host densities.


2
imported to control introduced or native pests. General
guidelines for locating, selecting and introducing agents
for biological control have been discussed (Huffaker and
Messenger 1976). Efforts should begin with a careful
study of the life cycle of the target pest. If it appears
that exotic competitors may be beneficial then foreign
exploration should first begin in areas environmentally
similar to the intended area of releases. Species that
are candidates for introduction must be evaluated care
fully to insure that they are indeed beneficial and that
they themselves will not become pests.
Interspecific competition among natural enemies of a
given host can be of a great importance in biological
control. In classical biological control, the potential
for interspecific competition exists when more than one
species of natural enemy is released into the environment
and utilizes the same host. Regarding such multiple
species introductions, it has been suggested that such
interpecific competition could possibly lead to a decline
in the population regulation of the host (Watt 1965)
although others have refuted this idea (Huffaker et al.
1971). In endemic host enemy associations, interspecific
competition appears to play a crucial role in structuring
the parsito id guild (Force 1974) and probably influences
the entire natural enemy complex as well. Generally, the
outcome of the competition is physiologically determined


17
sculpturing on the abdomen and hind coxa, and the color
and length of the hind tibial spurs (Marsh 1978).
Life Cycle
Cotesia marginiventris is an arrhenotokus larval
endoparasitoid of several lepidopteran pests. Female
parasitoids mate and oviposit within several minutes after
emerging from the pupal case but are more aggressive when
held for 24 hrs prior to host exposure (Boling and Pitre
1970). Mating occurs with the male approaching the female
from the rear, tapping her with his antennae and then
mounting on her for approximately half a second. Both
sexes mate many times and freely with other individuals.
Fern ales often mate after having initiated egg laying
(Boling and Pitre 1970).
The egg is laid in early instar hosts. According to
Vickery (1929) first instars are parasitized before they
disperse and Kunnalaca and Mueller (1979) reported that
first instars are preferred. According to Boling and
Pitre (1970), C. marginiventris perfers to oviposit in 2
day old larva of T^_ n_i_ rather than in 1 day or 3 day old
larvae of the same species. Later host instars are less
preferred becase host larvae usually jerk violently and
this movement interfers with oviposition (Kunnalaca and
Mueller 1979 ). In general par as itization increases with


43
observed in the laboratory. The results of our research
will be used to rear man i 1ae and to support efforts to
establish this parasitoid in the overwintering range of
FAW.


76
Table 9. Mean percentages for emergence of Chelonus
in s u1 a ris (C.i.), Cotes i a marginiventr i s (C.m.) and adult FAW
and percent mortality for FAW-Tarvae due to (1) refused to feed
on the diet, (2) dietd from unknown causes, when age of C.m.
was changed a/
Percent FAW mortality
C.m. age b/
Parasitoid emregence
Refused diet
Unknown
(hr s)
C.i.
C.m.
F7\w
and diet
causes
24
58.5a
33.6a
2.9a
2.9a
2.0a
48
39.3b
52.5b
2.1a
3.2a
2.9 ab
72
42.4bc
47.4b
1.4a
4.9ab
3.9ab
96
30.6b
48.7b
2.1a
13.7c
5.4ab
108
54.5a
21.0c
5.9a
ll.Obc
7.7b
Control
_
55.0b
9.9a
14.8c
10.1b
a/ Treatments were replicated 7 times with 40 larvae per
treatment. Means followed by same letter for a given column
are not significantly different by Duncans Multiple Range
Test. (P = 0.05) .


39
M. fel tiae preferred 1st to 3rd instar larvae (1st to 3rd
age groups) of its host Agrotis psilon (Hufnagel) and
Harcourt (1960) demonstrated a similar instar preference
for M. piutel1ae Muesebeck and its host the diamond back
moth PIutel1 a maculipennis (Curtis). In contrast, Shepard
et al. (1983) reported that demo 1itor (Wilkinson)
preferred 3rd or 4th instar larvae of Heliothis spp.
However, larvae of this size displayed a vigorous defense
response and often damaged or destroyed the parasitoid.
We observed also that when mam' 1 ae females attempted to
oviposit in 4th age group larvae that these larvae
aggressively attempted to thwart the ovi pos itional attempt
by swinging their heads and thoraxes from side to side in
an attempt to bite the parasitoid.
The larval and pupal developmental times for M.
man i 1ae were similar for age groups 1-3 (Table 2). Egg to
pupa and pupa to adult developmental times for M. manilae
parasitizing 4th age age group hosts increased by approxi
mately 2 days. Significantly more male progeny were pro
duced from the 1st age group in contrast to the 2nd group
from which more female progeny emerged. No significant
differences were present in the sex ratios of progeny from
3rd or 4tn age group larvae. The highest and lowest pro
portions of female progeny were observed for age groups 2
and 4, respectively. Bryan et al. (1969) showed that the


75
50
25
0
Became adults
Starved and died
Died from unknown reasons
J L
1
2
PAPER SECTIONS
3


110
reported that _C_;_ marginiventris was a day adapted species
and has been observed searching for hosts in bright
sunlight in corn fields.
The release of two parsito ids inside the field cages
resulted in an overall par as itization rate of 60.0% for C.
i nsul ar i s and 37.4% for _C^_ marginiventris. This high rate
of parasitization was similar to the field results
reported by Mitchell et al. (1984) where insularis
Terne!ucha difficulis Dasch. and marginiventris para
sitized FAW larvae at rates of 82, 10, and 2%
respectively. This high rate of parasitization by C.
insularis in field cages and the field (Mitchell et al.
1984) indicated that C. insularis was the principal
parsito id of FAW in southern Florida.
Seventy, forty and thirty-nine percent of first
instars were parasitized in treatments having 1, 2, and 3
paper sections respectively (Fig 12). Thirty percent of
second instars were parasitized in 2 paper section treat
ment. These results were similar to those reported by
Mitchell et al. (1984) where 77% of the first two instars
were parasitized. Ashley et al ( 1982) reported that the
percent parasitization of the first 4 instars of FAW
remined constant and then decreased substantially for 5th
and 6th instars. Reasons for the reduction in percent
parasitization in second instars was not properly under
stood. Mitchell et al. (1984) reported the decrease of


58
Table 7. Mean for numbers of encounters, examinations and
apparent ovipositions by Cotesia marginiventris (Cm) and Micro-
pl i tis mani1ae (Mm) during two host exposure periods separate? by
cii ffererTT numbers of days.
Days between
Second
host exposure
means3
Host
First
exposure
Second
host exposure
period
Encounters
Examina
tions
Apparent
ovi position
Cm
Mm
0
13.2
7.8
6.8
None
Mm
11.8
6.9
5.6
3
10.8
4.2
3.6
9.6
5.4
3.0
6
10.6
8.8
4.6
9.8
8.0
4.0
Mm
Cm
0
11.4
8.8
6.6
None
Cm
9.6
00

6.0
3
15.6
9.6
5.6
14.4
8.8
5.2
6
16.8
6.9
7.8
17.4
6.8
7.0
aNone of the number pairs were significantly different by
Student's t-test.


59
non-parasitized hosts. M. man i 1ae had greater
ovi pos itional contacts with the hosts that contained C.
marginiventris larvae than C. marginiventris with host
that contained mani1ae larvae on the first day of host
exposure. This trend reversed itself on days 3 and 6.
Experiment 5. The host finding and behavioral
sequence for oviposition of marginiventris on FAW
larvae already parasitized by i n s u 1 a r i s on corn,
sorghum, Bermudagrass and itch grass consisted on nine
basic components (Fig. 2). During the sequence, preening
occurred at several different steps. A typical pattern
involved the following:
1. Random movement--The parasitoid female flew and
walked randomly inside the cage or on the plant leaves.
The upper portion of the leaf was preferred. The female
held her antennae close and parallel to the substrate, or
folded them back under her body.
2. Antennal palpation--The female started antennal
palpation of the surrounding leaves and on the substrate.
She held her antennae nearly parallel to the substrate and
lowered her flagella slightly and raised them back to the
horizontal position. This movement of the flagella
frequently lasted for 5 to 25 sec. The under surface of
the leaf was palpated more frequently.


80
70
60
50
40
30
20
10
IU C. marginiventris
| C. insularis
6-10 12-18 24-3036-42 48-54
HOST AGE (hrs)


50
Results and Discussion
Experiment 1. Results of interspecific competition
demonstrated that C. insularis was significantly more
competitive than M^ man i 1ae (Fig. 1.) However, when C.
marginiventris replaced man i 1ae within the host larva,
then marginiventris emerged more frequently than C.
insularis The combined par as itization rates for the
three treatments ranged from 73-78%, which demonstrated
that multiple par as itization did not seem to affect FAW
larval mortality. FAW larvae parasitized by any two of
the three parsito id species only produced a single
parsito id, which suggests the destruction of one
parasitoid larva by another. Salt (1961) and Vinson and
Abies (1980) reported that when multiple parasitism
occurred, all but one species was usually eliminated
through physical attack, physiological suppression, or
both. In a few instances, especially with gregarios
parasito ids, some individualy of both species may survive
(Miller 1982, Weseloh 1983).
Substantial differences were not present between the
three parasitoid treatments for (1) larvae that success
fully pupated and emerged as adults, (2) larvae that
starved because they did not feed on the diet, (3) larvae
that died from unknown causes and (4) larvae that fed on
the diet but did not pupate (Table 4). Rejection of the


24
indigenous to the United States, and was imported from
Thailand through the USDA, Stoneville Research
Quarantine Facility, Mississippi.
No taxonomic or distribution literature was located
for M^ mani 1 ae. The length of antennae in males is longer
than for the female. However, Marsh (1978) described a
closely related spp M. melianae Viereck. An unsuccessful
attempt was made to establish M^_ man i 1 ae in the FAW
overwintering range in South Florida (Ashley, Pers.
Comm 1983).
The adults are ready to oviposit soon after emer
gence. They will oviposit in FAW larvae for a period of
16-17 days. Different species of Microp1 itis attack the
early larval instars of their hosts (Altahtawy et al.
1976). The female deposits an egg through the integumant
of host larva into the hemolymph. The egg is elongated,
oval and translucent white in color. The first instar is
caudate with a relatively large head and the second instar
is vesiculate and creamy white. After the parasitoid
larva molts into the third instar, it emerges from the
host (FAW) and spins a cocoon. Although the host remains
alive after the parasitoid emerges, the host does not
develop further and stops feeding. The parasitoid larva
exits the host and pupates outside. A single parasitoid
normally develops from each host even after


INTERSPECIFIC COMPETITION OF FALL ARMYWORM
SPODOPTERA FRUGIPERDA (J.E. SMITH) PARASITOIDS,
CHELONUS INSULAR IS (CRESSON), COTESIA MARGINI VENTRIS
rCR£55$$T~m MICROPLITinWfJTTAF£5TT7\D
(HYMENOPTERA: BRACON I DAE)
By
ROHAN HARSHALAL SARATHCHANDRA RAJAPAKSE
A
IN
DISSERTATION P
THE
PARTIAL FULFI
RESENTED TO THE GRADUATE SCHOOL OF
UNIVERSITY OF FLORIDA
LLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1985

ACKNOWLEDGEMENTS
I am grateful to Dr. Van H. Waddill, chairman of my
supervisory committee, for his advice, encouragement and
guidance throughout the experimental work and preparation
of this dissertation. I am also indebted to him for
providing me financial support to pursue my studies at the
Department of Entomology and Nematology, University of
Florida.
I would like to express special thanks to Dr. Tom R.
Ashley co-chairman of supervisory committee, for inspira
tion and guidance and in preparation of this dissertation,
and for generously providing facilities and materials at
USDA Laboratory. His warm friendship and understanding is
greatly appreciated.
I am also indebted to Drs. John Strayer and Daniel
Roberts for their interest and contributions as members of
my supervisory committee, and giving invaluable encourage
ment when it was dearly needed. There are special thanks
for Dr. Stratton H. Kerr and Dr. Andrew Duncan for their
invaluable advice and suggestions.
I wish to express my gratitude to all the personnel
from both USDA Insect Attractants Laboratory at
Gainesville and TREC at Homestead who have helped me in
numerous ways in conducting my experiments. Special
thanks also go to Pamela Wilkening, Polly Hall and Delaine
Miller of USDA, Insect Attractants Lab.

My heartfelt thanks and affection go to JoAnne White
for her encouragement and assistance and to Patricia Davis
for the assistance in typing this dissertation.

TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS
LIST OF TABLES vii
LIST OF FIGURES viii
ABSTRACT x
INTRODUCTION 1
LITERATURE REVIEW 5
The Fall Armyworm, Spodoptera frugiperda
(J.E. Smith).. 5
Seasonal Distribution 5
Life History 6
Economic Status 8
Natural Mortal ity 9
Management Strategies 13
The Larval Endopar asitoid Cotesia
margi n i ventr i s Cresson 14
rTgT and Distribution 14
Description 15
Life Cycle 17
The Egg-Larval parsito id Chelonus
i nsul ar i s Cresson 19
0 r f g T n and Distribution ¡g
Description 20
Life Cycle 21
The Larval Endopar asito id Mic r 0 p1 itis
man i 1 ae Ashmead 23
Description and Distribution 23
Interspecific Competition 25
BIOLOGY AND HOST ACCEPTANCE OF MICROPLITIS
MAN I LAE (HYMENOPTERA: B R A C 0 N I D Al7~R ATDeD~DN FALL
ARMYWORM LARVAE 34
Introduction 34
Materials and Methods 35
Age group Acceptance 36
Developmental Rates 36
Adul t Longevity 37
Time of Host exposure 37
Results and Discussion 37
iv

INTERSPECIFIC COMPETITION BETWEEN PARASITOIDS OF THE FALL
ARMYWORM SPODOPTERA FRUGIPERDA
44
Introduction 44
Materials and Methods 45
Results and Discussion 50
EFFECT OF HOST AGE, PARASITOID AGE AND CHANGE OF
TEMPERATURE ON INTERSPECIFIC COMPETITION BETWEEN CHELONUS
INSULAR IS, COTES IA MARG I N I V E NTR I S AND MI CROP L I T I SHMrn[F
In TAll ArmyWWmT 67
Introduction 67
Materials and Methods 68
Experiment l--Host Age 70
Experiment 2--C. marginiventris
frge 70
Experiment 3--Temperature
Effects 70
Experiment 4 Dissection of
Multipar as itized
Hosts 71
Results and Discussion 72
INTERSPECIFIC COMPETITION BETWEEN FALL ARMYWORM
PARASITOIDS CHELONUS INSULARIS, AND COTESIA MARGINIVENTRIS
INSIDE FIELD CAGES AND PLOTS 90
Introduction 90
Materials and Methods 92
Host and Parasitoid Colony
Maintenence 92
Experimental Procedures for Host
Parasi ti zation 93
Experiment l--Host Density 96
Experiment 2 Field Cage 103
Experiment 3 Field Plot 117
Results and Discussion 120
GENERAL SUMMARY AND DISCUSSION 130
REFERENCES 134
BIOGRAPHICAL SKETCH 146
v

LIST OF TABLES
Table Page
1. Percentage par as itization by M_^ m a ni 1 a e of fall army-
worm larvae 38
2. Developmental periods (x + SE) and progeny sex ratios
for M. manilae in fall armyworm larvae 40
3. Percentage parasitization of second age group fall army-
worm larvae exposed to man i 1 ae for various amount
of time 42
4. Mean percentages for emergence of Chelonus insular is
( C. i .) Microplitis manilae (M.m.), Cotesia marg_i ni_-
ventris ( C. m .") acT_ad u Tt" T al 1 armyworm (7717)7 and
percentages of FAW larvae failing to mature because
they refused to feed on the diet, died from unknown
causes or failed to pupate 53
5. Mean percentages for emergence of Chelonus insu1 aris
(C.i.), Cotesia marginiventris (C.m.) Microplitis
manilae (M .m .J acT acTuTt~"T aTT- armyworm ( Fl*) ancT^mean
percentages of FAW larvae failing to mature because they
refused to feed on the diet or failed to pupate 55
6. Mean number and percentage of larval encounters, exami
nations, oviposit ion probes and apparent ovipositional
successes by Cotesia marginiventris and Microplitis
manilae in faTI armywcTrrn larvae exposed and not exposed
as eggs to Che! onus i nsu 1 ar i s 57
7. Mean percentages for numbers of encounters, examinations
and apparent ovipositions by C. marginiventris and
M. mam' 1 ae during 2 host exposure" "perio'ds separated by
cTTfferent numbers of days 58
8. Mean percentages at different host ages for emergence of
Chelonus insularis (C.i.) Cotesia marginiventris (C.m.),
and 3T¡Tt~rTl armyworm (FAT) ancfper cent age mortality of
FAW larvae due to (a) refusal to feed on the diet and
(2) death from unknown causes 73
9. Mean percentages for emergence of Chelonus insularis
(C.i.), Cotesia marginiventris (C.m.), ancf aduTt Yaf
armyworm (TAV) ancl percent mortality FAW larvae due
(1) refused to feed on the diet and (2) died from
unknown causes, when age of C.m. was changed
76

10. Mean percentage (+_ SE) at several constant tempera
tures for emergence of Chelonus insularis (C.i.),
Cotesia mar g i n i ventr i s (~CTm.) an3 acfu it FAW and percen
tages of FAR farva~failing to mature because they
(1) refused to feed on diet and died, (2) died from
unknown causes (3) still larvae at end of test and
(4) escaped from cup 82
11. Mean (+ SE) emergence periods (days) at several con
stant temperatures for Cotesia marginiventris (C.m.) and
Chelonus insular is (C.iTJ and" "acfuTf TAtf, ancPper cent ages
for FAW larvae failing to mature because they (1)
refused to feed on the diet and died and (2) still
larvae at end of test 84
12. Fate of the larval parasitoids C. marginiventris (C.m.)
and M. manilae (M.m.) in competition with the egg-larval
par as i toTcf ~CT insularis as determined by dissection of
fall armyworm (TAW) larvae 88
13. Mean (+ SE) for superparasitized FAW, longevity of
adult IT. marg i n i ventr i s in days and percent survival
of hosTlarvae at 7 TAW densities 100
14. Sex ratio (+ SE) ( ) for ^ mar g i n i ventr i s (C.m.)
and insularis (C.i.) from F AW larvae par as ft i zed
inside a field cage 116
15. Mean percentage of small (0.2 0.7 mm), medium
(0.8 1.2 mm), and large (1.3 2.4 mm) head capsule
widths from FAW larvae collected from undersurface,
upper sur face, ground, between stalk and leaf sheath
and stalk in corn 124
Fall armyworm feeding damage to different regions of
corn in plots where insularis (C.i.) and margini-
ventris (C.m.) were re 1 eased .. 125
16.

LIST OF FIGURES
Figure
Page
1. Mean percentage emergence of insularis (C.i.), M.
manilae (M.m.) and C. marginiventris (C.m.) from flTl
armyworm larvae exposecT to multiple par as i t i z at i on s .. . 52
2. Behavioral ethogram of the host finding and oviposi-
tional sequence of marginiventris females on fall
armyworm larvae al ready par asftTzecPby the egg-larval
parasitoid C. insularis. (Solid arrows indicate
invariable pathways and" dashed arrows represent alter
nate pathways) 61
3. Percentage parasitization by marginiventris of fall
armyworm larvae already exposed as eggs to insularis.
Larvae were randomly placed on four plant spec i es h eTcf
in wire cages within a greenhouse 65
4. Progeny sex ratios for C. marginiventris from differ
ent aged C. marginiventrTs (C .m .) emerging from fall
armyworm Trva"e" parasTfized as eggs by insularis
(C.i.) 79
5. Progeny sex ratios for C. insularis (C.i.) from differ
ent aged C. marginiventris fC.mT) emerging from fall
armyworm Tarve par asTtTz'ed as eggs by i nsul ar i s ... 81
6. Percentage emergence of C. marginiventris and C. insularis
from fall armyworm ( F AW JHarv ae, par as i tfzed as eggs By
C. insularis. FAW larvae were exposed at different ages
to C 7~margTiventris and then held at 19 22 25, or
28~for development 86
7. Mean progeny production by marginiventris at 7 host
densities from eggs previously parasitized by C.
i nsul ar i s 98
8. Mean progeny production by C. insularis at 7 host den
sities and parasitized again by ~C. ~marg~i n i ventr i s 102
9. Sex ratio of marginiventris from 7 host densities... 105
10. Sex ratio of C. insularis from 7 host densities 107
viii

11. Percentage par as itization by iins u1 a ris and C. margini-
ventr i s from FAW larvae recovere3 insTde"from TTeT3
cage during 3 test periods. Vertical bars within a
test period from left to right indicate treatments
1, 2, and 3 paper sections 109
12.Mean percentage parasitized FAW instars in treatments
1, 2, and 3 paper sections inside field cage 112
13. Mean percentage of FAW larvae that became a) adults, b)
starved and died c) died from unknown reasons in
treatments 1, 2, and 3 paper sections inside field
cage 115
14. Percentage par as itization for principle parasitoid
species recovered from FAW larvae from (US) upper
surface of whorl, (LS) lower surface of whorl,
(GR) ground, (SH) between stalks and leaf sheath,
(ST) stalk and (WH) control in corn ug
15. Sex ratios for C. marginiventris and C. insular is
recovered from "F7\W larvae from ("US) upper surface of
whorl, (LS) lower surface of whorl, (GR) ground, (SH)
between stalks and leaf sheath, (ST) stalk and (WH)
control in corn 122
16. Illustration to exhibit the placement of egg contain
ing paper sections in different regions of corn
US
Upper surface
of
upper
whor 1
LS
Lower surface
of
upper
whor 1
GR
Ground
SH
In between stalk
and sheath
ST
Stalk
WH
Whorl region.,
ix

Abstract of Dissertation Presented to the
Graduate School of the University of Florida
in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy
INTERSPECIFIC COMPETITION OF FALL ARMYWORM
SPODOPTERA FRUGIPERDA (J.E. SMITH) PARASITOIDS,
CHELONUS INSULAR IS (CRESSON), COTESIA
MfflnnrrrvrNtitit tcrtsson) and miutoputtis
mA'nTl'aT a'Shm'ad (hymenoptera: braconTd'aTT
By
Rohan Harshalal Sarathchandra Rajapakse
August, 1985
Chairman: Dr. Van H. Waddill
Co-Chairman: Dr. Thomas R. Ashley
Major Department: Entomology and Nematology
Interspecific competition within fall armyworm (FAW),
Spodoptera Frugiperda (J.E. Smith), larvae by the larval
parasitoids Cotesi a (=Apanteles) marginiventris Cresson
and Mic r o p1 itis man i 1ae Ashmead and the egg-larval
parasitoid Chelonus insular is Cresson was studied.
Experiments conducted with 4 larval age groups (1,
24-48 h; 2, 49-72 h; 3, 73-96 h; 4, 97-130 h) of the fall
armyworm revealed that the first 2 age groups were most
suitable for the development of _M. m a n i 1 a e The develop
mental period of M^ mani 1 ae ranged between 13-18 days.
Highest par as itization was observed for M. man i 1ae when 2
females were exposed to 20 hosts for 30 min at 26+lC.
x

Cotesia marginiventris was a superior competitior
relative to i n s u 1 a r i s and C^_ i nsu 1 ar i s was superior to
M. man i 1ae. Subsequent par as itization by either C.
marginiventris or M man i 1ae or larvae exposed to C.
insu1 aris as eggs did not result in additive host mortal
ity. Mic r o p1 itis man i 1ae females changed their behavior
significantly by displaying a reduction of approximately
50% in host examinations, 45% in ovipositor probes, and
55% in apparent ovipositions when C in s u1aris parasitized
larvae were presented. Cotesia marginiventris displayed a
greater number on contacts, examinations and ovi pos itional
attacks in larvae 3 and 6 days after initial
par as itization by m an i 1ae .
The maximum reproductive potential for C. margini
ventris was achieved in hosts 36 to 48 hours old and at a
temperature of 25C. The optimum parasitoid age for C.
marginiventris during the host exposure period was 48 to
96 hours. Egg to adult developmental times at 25C, were
17 and 26 days for marginiventris and C^_ i n su 1 ar i s,
respectively. In multiple parasitized larvae C, margini-
ventris appeared to physically attack and destroy the
larvae of in s u1 a ris C insularis was the predominant
species that emerged from field cage but marginiventris
was a better competitor at host densities above 120
eggs/larvae. The damage to upper leaves was significantly
greater in non-parasitoid release plots than in parasitoid
released plots.
xi

INTRODUCTION
Chemical insect pest control has become a contro
versial management strategy for several reasons. Insect
pests have frequently become resistant to pesticides, and
the costs of developing and registering a new insecticide
have risen sharply. There is also concern about the
effects of pesticides upon human health and the environ
ment. This combination of circumstances has prompted
entomologists to seek alternative control strategies lead
ing to the development of sophisticated techniques involv
ing a wide array interdisciplinary approach that have been
termed "integrated pest management". Along with the
development of strategies such as breeding resistant plant
varieties and the use of pheromones to disrupt communica
tions, there has been a resurgence of interest in the use
of entomophages.
Huffaker and Messenger (1976) defined biological con
trol as the action of predators, parasites, and pathogens
which maintains host densities at levels lower than would
occur in the absence of these natural enemies. Despite
the many successes obtained through the introduction and
release of a pest's natural enemies, this classical
biological control strategy has not always provided the
desired degree of pest control. In this strategy of
biological control, natural enemies are deliberately
1

2
imported to control introduced or native pests. General
guidelines for locating, selecting and introducing agents
for biological control have been discussed (Huffaker and
Messenger 1976). Efforts should begin with a careful
study of the life cycle of the target pest. If it appears
that exotic competitors may be beneficial then foreign
exploration should first begin in areas environmentally
similar to the intended area of releases. Species that
are candidates for introduction must be evaluated care
fully to insure that they are indeed beneficial and that
they themselves will not become pests.
Interspecific competition among natural enemies of a
given host can be of a great importance in biological
control. In classical biological control, the potential
for interspecific competition exists when more than one
species of natural enemy is released into the environment
and utilizes the same host. Regarding such multiple
species introductions, it has been suggested that such
interpecific competition could possibly lead to a decline
in the population regulation of the host (Watt 1965)
although others have refuted this idea (Huffaker et al.
1971). In endemic host enemy associations, interspecific
competition appears to play a crucial role in structuring
the parsito id guild (Force 1974) and probably influences
the entire natural enemy complex as well. Generally, the
outcome of the competition is physiologically determined

3
within the host. Thus, researchers may be unable to
predict the outcome unless they can identify and duplicate
the relevant elements of the pest's physiology under
experimental conditions.
The parsito id guild of Spodoptera frugiperda (J.E.
Smith), the fall armyworm (FAW), provides a relevant host
parasitoid association for assessing host and natural
enemy relationships. The FAW is a sporadic and
occasionally severe crop pest in the Southeastern United
States where this species is known to be able to survive
in winter (Luginbill 1928), though survival further north
is thought possible only during exceptionally mild winters
(Snow and Copeland 1969). In years of high population
density, FAW larvae may cause over $300 million in damage
(Mitchell 1979). Fifty three species of par asitoid
species have been recovered from FAW larvae (Ashley 1979)
and are responsible for significant reductions in FAW
larval populations (Ashley et al. 1982). The principal
parasitoids of the FAW either attack its eggs or the early
instars and thus provide suitable models for the study of
parasitoid interrelationships, especially with regard to
interspecific competition between the egg-larval and
larval parasitoids.
The following research was conceived to assess and
investigate the competitive abilities between the parasi
toid larvae of Chelonus insu1 aris Cresson, Cotesia

4
(Apante 1 es) marginiventris Cresson, and Microp1 itis
man i 1ae Ashmead. The objectives of the study were to (1)
study the biology of man i 1 ae an imported larval
parasitoid of Spodoptera spp in Thailand, (2) investigate
interspecific competition between larvae of the
parasitoids i nsul ar i s, C marginiventris, and M.
man i 1ae, (3) examine the effects of host and parasitoid
age, and temperature on the outcome of interspecific
competition, and (4) study the functional response of C.
marginiventris when exposed to different densities of FAW
larvae previously parasitized by C. insularis.

LITERATURE REVIEW
The Fall Armyworm, Spodoptera frugiperda (J.E. Smith)
The fall armyworm (FAW), Spodoptera frugiperda (J. E.
Smith), (Lepidoptera:Noctuidae) inflicts damage on a large
number of agricultural crops, especially those belonging
to the family Graminae, in the Southeastern and Central
United States (Luginbill 1928) and Central America
(Andrews 1980). Corn (Zea mays L.), Sorghum (Sorghum
bicolor (L.) Moench) and Bermudagrass (Cynodon dactylon
(L) Pers.) are the favored agricultural hosts for the FAW
(Sparks 1979). Economic damage to other crops, including
alfalfa, peanuts, rice and soybean, has also been
documented (Navas 1974, Morrill 1973, Pitre 1979). Tietz
(1972) lists 68 genera of plants, many of which are weed
species, that are attacked by the FAW.
Seasonal Distribution
Unlike most other insects in the temperate region,
the FAW has no mechanism for diapause. Thus, the species
overwinters commonly in South Florida and Texas, where
temperatures do not destroy it and where hosts are
continually available (Luginbill 1928). In mild winters
it is also found in Louisiana and Arizona (Snow and
Copeland 1969). During the spring and summer the FAW
5

6
disperses again throughout the eastern and central United
States, and, in some years, into Southern Canada
(Luginbill 1928). This migration is assisted by weather
fronts (Sparks 1979). Several hypotheses have been
advanced to explain the seasonal distribution of damaging
populations of FAW (Rabb and Stinner 1978; Walker 1980;
Barfield et al. 1980). Walker (1980) presented 3 models
to account for seasonal distribution patterns. Diffusion
and freeze-back and return flight (Walker 1980), "pied
piper" effect similar to diffusion and freeze back (Rabb
and Stinner 1978) and a model on seasonal distribution
patterns as combinations of short and long range
movements, as well as periodic overwintering in as yet
undiscovered habitats (Barfield et al. 1980) explained
this aspect.
Life History
The life cycle of the FAW has been described by
Luginbill (1928), Vickery (1929), Sparks (1979) and Keller
(1980). The adults are nocturnal and at dusk initiate
flying near host plants that are suitable for feeding,
oviposition, and mating. Mitchell et al ( 1974 ) showed
that peak activity of adults occurred 6 hrs after sunset
and another small peak occurred approximately 3 hrs later.
Oviposition may occur on host plants where as many as

7
several hundred eggs may be laid in a mass and covered
with scales. Total oviposition by a female may exceed
2000 eggs over a period of up to 23 days (Luginbill 1928).
As larvae hatch from the eggs, they eat their egg shells
(Morrill and Green 1973), and as a result of negative
phototactic and geotactic behaviors, the first instars
move into the whorls of corn and sorghum (Pitre 1979).
The larvae feed preferentially on the developing leaves
and at high densities will eat the mature leaves, tassels,
ears, and the inner portions of the stalk (Luginbill 1928,
Morrill and Green 1973). Development proceeds through 6,
sometimes 7, and rarely 8 instars (Keller 1980). Tempera
ture, larval nutrition, and probably egg nutrition were
factors affecting instar number in FAW (Keller 1980).
Mature larvae drop to the ground and pupate in the soil
within a chamber located 2 to 8 cm below the surface
(Luginbill 1928). Pupation depends upon soil texture,
moisture, and temperature (Sparks 1979). Pupae have been
found on plant parts during severe outbreaks (Burkhardt
1953). After eclosin, the adults find their way to the
soil surface, locate a plant or other object on which to
cling, and inflate their wings (Sparks 1979). There is
also evidence that different host plants (Roberts 1965,
Pencoe and Martin 1981) and different temperatures affect
the biology of FAW (Barfield et al 1978).

8
Roberts (1965) reported that the larval diet can affect
the duration of larval period, pupal size, adult
longevity, fecundity, and egg viability.
Economic Status
In some years FAW larval densities are low and not
economically important while in other years high densities
inflict serious economic losses (Sparks 1979). The FAW
was recorded as an injurious pest in Georgia in 1797, and
in Florida in 1856 (Sparks 1979).
Damaging populations of FAW appear to occur
irregularly (Barfield et al 1980). FAW infestation
levels are unpredictable (Barfield et al 1980) and
conditions conductive to outbreaks are not well
understood (Keller 1980).
The FAW causes damage to corn by feeding on the
developing leaves within the whorl. In areas with severe
infestations the tassels, ears, mature leaves and stalks
are also consumed (Painter 1955). Defoliation ranges from
skeletonization of leaves by early larval instars to
complete leaf consumption by large larvae. Annual losses
due to larval feeding are estimated to be between $300 to
500 million in the United States (Mitchell 1979). Larval
food consumption has been studied by Luginbi 1 1 ( 1928) and
Barfield et al. (1980).

9
Natural Mortal ity
Various abiotic and biotic agents act as mortality
agents of FAW populations in the field. Physical environ
ment and natural mortality factors may act singly or in
combination to determine the annual distribution pattern
and densities of FAW populations (Barfield et al 1980).
Among abiotic environmental factors, temperature appears
to be an important limiting factor (Barfield et al 1980).
Low temperature may be the most important factor limiting
the winter survival of FAW (Luginbill 1928, Wood et al.
1979). Andrews (1980) reported that torrential daily
rains for several days result in drowning of small larvae
or washing them out of the whorls in corn in Central
America.
Cannibalism among larvae is an important factor
limiting population densities (Luginbill 1928). Mortality
attributable to cannibalism and intraspecific competition
is positively correlated with larval density (Wiseman and
McMillian 1969). Olive (1955) reported that first instar
larvae may destroy adjacent unhatched eggs while in the
process of devouring their own egg shells. Ashley (Pers.
Comm. 1985) studied the factors influencing cannibalism in
FAW and showed that the larval density in combination with
the amount of eatable surfae area affected cannibalism
more significantly than did the amount of non-eatable
surface area, diet volume, or photoperiod.

10
Natural mortality inflicted on FAW larvae by natural
enemies (parasitoids, predators and pathogens) in both
agricultural and wild host plant comm uni ties is believed
to play a substantial role in density regulation (Barfield
et al. 1980). Ashley (1979) presented detailed informa
tion about the classification and distribution of the FAW
parasitoids and noted that 53 species from 43 genera and
10 families have been reared from FAW larvae. Among them
18 species occur in North America; 21 species occur in
Central and South America; and 14 species are common to
all three regions (Ashley 1979). Parasitoid species
attacking FAW vary between different agroecosystems. For
example, in a study by Ashley et al. (1980) in late
planted field corn, 8 species of parasitoids, representing
the families Braconidae, Ichneumonidae, Eulophidae and
Tachinidae, were collected from FAW larvae feeding on corn
and surrounding broadleaf signal grass. Chelonus texanus
Cresson caused the highest mortality followed by Meterous
autographae Musebeck and Euplectrus piatyhypenae Howard.
Nickle (1976) reported that 7 species caused parasitiza-
tion of FAW larvae on peanuts and Apanteles marginiventris
Cresson., M. autographae and 0phion spp were responsible
for highest mortality. Ashley et al. (1983) in another
study on par as itization of FAW larvae on volunteer corn,
Bermudagrass (Cynondon dactylon (L)) and paragrass

11
(Br achiarie mutic a (L)) reported that C in s u1 a ris Cresson
was the principal parasitoid on corn and i n s u 1 ar i s and
A. marginiventris were the major parasitoids on
Bermudagrass while M. autographae parasitized the highest
proportion of hosts in paragrass, reflecting a host plant
preference. The native parasitoids C^_ i n s u 1 ar i s and A .
marginiventris were the primary species attacking FAW
larvae in South Florida and they destroyed 63% of each of
the first instars; M_^ autographae and Rogas 1 aphygmae
Viereck, as well as several tachinids and a group of
unidentified ichnuemonids, accounted for the rest of FAW
larval mortality (Ashley et al. 1982). Tingle et al.
(1978) reported that parasitoid populations attacking the
FAW on alternate host plants of, in or near crop fields
may be important sources of parasitoids that subsequently
attack FAW larvae in corn. Waddill et al ( 1985) dis
cussed the seasonal abundance of FAW parasitoids, C.
i nsul ar i s, Teme! ucha spp. 1 aphygmae, and margini
ventris in southern Florida. Mitchell et al. (1984)
reported that FAW pheremone components had no significant
effect on the level of FAW par as itization by in s u1 a ris
and Teme 1ucha difficulis Basch. The successful rearing of
a pupal parasite Diapetimorpha introita of FAW in the
laboratory has also been documented (Pair et al. 1985).
Predators and pathogens are among other natural
enemies found to play a less consistent role in regulation

12
of FAW populations. Agnello (1978) compiled a list of 10
species of Hymenoptera (8 vespids and 2 sphecids) and 6
Hemiptera (3 reduviids, 1 pentatomid, 1 nabid and 1
anthocorid), 12 Coleptera (9 carabids, 2 cicindellids and
1 coccinellid) a mammal (skunk), 3 amphibians (2 Bufo spp
and 1 Hyla spp) and a variety (13 species) of birds as
predators of FAW. An earwig, Doru spp inhabits whorls of
corn and sorghum and found to feed readily on small and
medium sized FAW larvae (Andrews 1980).
The FAW is reported to be susceptible to at least 16
species of entomogenous pathogens which includes viruses,
fungi, protozoa, nematodes and 2 strains of the bacterium
Bacillus thuringiensis Berliner (Gardner and Fuxa 1980).
Many of these occur naturally in FAW populations. A "poly
hedrosis" presumably nuclear polyhedrosis virus (NPV) was
reported as early as 1915 (Chapman and Glaser 1915) and a
granulosis virus has also been identified from FAW larvae
collected from sorghum (Steinhaus 1957). Fungi also are
natural mortality factors in FAW populations. Three
species have been reported and include Entomophthora
sphaerosperma Fresenius (Charles 1941), Nomuraea rileyi
(Farlow) Sampsom (Luginbill 1928) and Empusa spp
(Luginbill 1928). The natural occurrence of a nematode
Hexamermis spp in FAW larvae was reported from Venezuela
(Gnagliumi 1962). The only protozoan reported to occur

13
naturally in FAW is Nosema laphygmae Weiser, a microspori-
diurn from Colombia (Weiser 1959).
Management Strategies
The major management strategies reported to control
FAW are insecticides (Young 1980), cultural control
(Luginbill 1928) and host plant resistance (Wiseman et al.
1979). Young (1980) suggested the use of irrigation water
as a carrier for insecticides, thereby supplying the
volume of liquid needed to penetrate all of the plant
sites, where FAW feed. Application of granular insecti
cides directly to the whorl has been a common practice in
Central America (Andrews 1980).
The importance of mechanical and cultural control of
FAW was first reported by Luginbill (1928). Black light
traps and pheremone baited cylindrical electric grid traps
have been used to monitor seasonal populations of FAW in
Louisiana and Florida (Mitchell 1979). However, dispos
able sticky traps baited with pheromone (z)-9-dodecen-l-o 1
acetate have been used extensively in surveys in Georgia
and Florida. These traps were found to be most effective
in capturing FAW males when positioned approximately 1 m
above ground and near around preferred hosts (Mitchell
1979 ) .
Wisemann and Davis (1979) showed the importance of
resistant plant varieties in managing FAW populations.

14
The resistance of corn variety "Antigua 2 D" to FAW has
already been documented (Wiseman et al. 1973). Resistant
varieties in sorghum, peanuts, Bermudagrass, rice, and
millet have also been reported (Davis 1980).
Considering the important factors regulating FAW
populations, action thresholds (AT) for grain sorghum have
been developed (Martin et al. 1980). These action
thresholds are estimated to be 10% of seedling sorghum
possessing egg masses after flowering. However there is a
lack of information in many areas which makes it
difficult to derive dynamic AT and population models
representing the dynamics and host interactions of the
FAW.
The Larval Endoparasitoid Cotesia (=Apanteles)
marginiventris Cresson
Origin and Distribution
Cotesia (=Apanteles) marginiventris is one of the
most freqently recovered parasitoids from field collected
FAW larvae. This parasitoid was originally described from
Cuba, and is native to the West Indies (Muesebeck 1921).
It has been previously classified as Microgaster margini
ventris Cresson (1865), Apante!es grenadensis Ashmead
(1900), A. laphygmae Ashmead (1901), Apante!es (Protapan-
teles) harnedi Viereck (1912) and most recently Cotesia
marginiventris Cresson (Marsh 1978). It appears to have a
wide distribution within the United States, especially in

15
the southern states viz. Arkansas, Florida, Georgia,
Louisiana, Mississippi, Tennessee, North Carolina and
South Carolina (Wilson 1933, Mueller and Kunnalacca 1979,
Marsh 1978). Some 16 hosts of C^ margin iventris have been
reported (Miller 1977) and all are noctuids. No crop
preference is shown by this parsito id when attacking
Trichoplusia ni (Hbn.) on various food plants in
Mississippi (Boling and Pitre 1970).
Description
The egg and laral instars are described by Boling and
Pitre (1970), and the adults by Muesebeck (1921). The egg
is hymenepteriform, cylindrical with rounded ends. The
caudal end is slightly curved, and has a short peduncle.
The egg is 0.017 mm at the broad end, 0.088 mm in length
at oviposition and the peduncle is 0.0005 mm long (Boling
and Pitre 1970). The egg is found free in the hemocoel of
the host larvae. Up to 7 eggs have been found in a single
host when the host larva was exposed to several female
parsito ids. However, superparasitization does not
necessarily lead to multiple cocoon format ion. Normally
only 1 egg is found per host (Boling and Pitre 1970). The
first instar larva is white and caudate and is usually
found in the posterior part of the host's body. First
instar larvae are never found attached to the host. The

16
larva has a caudal appendage which is a modification of
the last abdominal segment into a fleshy organ and a
caudal vesicle that increases in size with longevity.
Allen and Smith (1958) reported some species of Apanteles
as being cannibalistic in the first instar; but no
cannibalism has been observed in marginiventris (Boling
and Pitre 1970). The second instar is vesiculated with a
prominent anal vesicle and the body becomes more robust.
Allen and Smith (1958) suggested that the second instar
may actually be two instars. The third instar is
hymenopteriform with no anal vesicle. This larva tapers
anteriorly and is creamy white at first, turning light
brown upon emerging from the host (Boling and Pitre 1970).
The molt to the third instar happens just prior to
parasitoid emergence, which generally occurs at approxi
mately the 4th abodminal segment in the dorsolateral area
of the host. The parasitoid initially constructs a one
sided crescent-shaped cocoon and after its body has become
seated, the larva closes the open side of the cocoon. The
cocoon is small (3mm long), ovoid, firm, smooth and com
posed of white silk surrounded by some looser threads.
The pupa is exarate and enters pupation approximately 24
hrs after form at ion of cocoon. Adults can be identified
using the keys of Marsh (1971) (to genus) and Muesebeck
(1921) (to species). The black adult is about 2-5 mm
long, has yellow legs and is recognizable by the

17
sculpturing on the abdomen and hind coxa, and the color
and length of the hind tibial spurs (Marsh 1978).
Life Cycle
Cotesia marginiventris is an arrhenotokus larval
endoparasitoid of several lepidopteran pests. Female
parasitoids mate and oviposit within several minutes after
emerging from the pupal case but are more aggressive when
held for 24 hrs prior to host exposure (Boling and Pitre
1970). Mating occurs with the male approaching the female
from the rear, tapping her with his antennae and then
mounting on her for approximately half a second. Both
sexes mate many times and freely with other individuals.
Fern ales often mate after having initiated egg laying
(Boling and Pitre 1970).
The egg is laid in early instar hosts. According to
Vickery (1929) first instars are parasitized before they
disperse and Kunnalaca and Mueller (1979) reported that
first instars are preferred. According to Boling and
Pitre (1970), C. marginiventris perfers to oviposit in 2
day old larva of T^_ n_i_ rather than in 1 day or 3 day old
larvae of the same species. Later host instars are less
preferred becase host larvae usually jerk violently and
this movement interfers with oviposition (Kunnalaca and
Mueller 1979 ). In general par as itization increases with

18
increased exposure time. Kunnalaca and Mueller (1979)
reported that oviposition was accomplished quickly with a
single ovipositor thrust and this occurred primarily
during day light hours. Multiple oviposition was common
especially when few hosts were offered to a parasite
(Boling and Pitre 1970). Total fecundity ranged from 30
to 110 eggs per female (Kunnalaca and Mueller 1979).
Time required for the development of C. marginiven-
tr i s from oviposition to cocoon formation ranged from 6 to
11 days at 30C (Boling and Pitre 1970, Kunnalaca and
Mueller 1979). Boling and Pitre (1970) reported the
optimum time for development as 7 days in T^ n_i_ and
Pseudoplasia includens (Walker) and 6 days in Heliothes
virescens (F.) within 24 hours after existing host larva.
Kunnalaca and Mueller (1979) reported an optimum develop
mental time of 8 days in Plathypena scabra (F). At 30C
and 25C, development times from cocoon to adult ranged
from 3-5 days and 4-7 days, respectively (Kunnalaca and
Mueller 1979). The sex ratio (1.5:1) favored males at
both 30C and 25C (Kunnalaca and Mueller 1979). Mean
longevity of adults at 30C and 25C was 5.6 + 2.. 5 and
9.1M.2 days, respectively and females lived longer than
males at both temperatures (Kunnalaca and Mueller 1979).
Paras itization by marginiventris resulted in
growth retardation of the host (Danks et al 1979 ).

19
Ashley (1983) reported that parasitization of FAW larvae
by marginiventris reduced maximum larval weights by
97%, compared to 6th instar non par as itized larvae. C.
marginiventris destroyed its host when the host reached
the 4th instar. Hosts parasitized by C. marginiventris
gained the least amount of weight, produced the least
amount of frass, and had shortest life expectancies and
the smallest head capsule widths compared to other
parasitoids (Ashley 1983).
Loke et al. (1983) has described the behavioral
sequence for host finding and oviposition for C.
marginiventris on corn plants artifically damaged by 2nd
instar larvae of the FAW and reported that highest
parasitization rates occurred among 2nd instar larvae
collected from leaf surfaces. Bioassay responses in C.
marginiventris females to materials derived from FAW
larvae were most intense for frass and somewhat less
intense for larval and pupal cuticle materials, scales,
exuviae and silk (Loke and Ashley 1984).
The Egg-larval Parsito id Chelonus insular is Cresson
Origin and Distribution
CFTon us insu Tar is Cresson is one of the key
parasitoids regulating FAW populations in South Florida
(Ashley et al. 1982). It has been previously classified

20
as texanus Cresson (1872), texanoides Viereck
(1905), exogyrus Viereck (1905) and bipustulatus
Viereck (1911) (Marsh 1978). C. insular is is distributed
throughout in North, Central and, South America, and the
West Indies and has been introduced into Hawaii and South
Africa (Marsh 1978).
Description
The eggs of C. insular is are white, and cylindrical,
and appear comma like in shape. They are slightly arcuate
with both ends rounded, one being larger than the other
(Glogoza 1980). The first instar larva has a prominent
square head with easily distinguishable dark, pointed,
mandibles and 7 body segments tapering from the thorax to
the abdomen (Glogoza 1980). The larva floats in the host
hemolymph. The second stage larva is cylindrical with a
tapered head. The body of the third stage is also
cylindrical and the head which is relatively narrow tapers
in the front. C. insularis causes its host to burrow in
the earth when the host reaches the 4th instar and to form
a pupation cell. After completing this cell the parasi-
toid larva consumes the entire contents of the host and
then pupates. The larva spins a cocoon by using a silky
secretion and this cocoon is cylindrical with almost flat
ends. Ashley (1983) found that of those FAW larvae

21
parasitized by C. insularis 41% died in the 4th instar
and 59% died in the 5th instar. An emerging adult tears
the silky cocoon with its mandibles and escapes through
the opening. The body length of the adult is 4.5-5.0 mm
and description of adults is found in Marsh (1978).
Life Cycle
The female parasitoids can begin to lay eggs even if
they have not mated. The antennae are used to locate the
host, the female then lands on the eggs, positions
herself, and then injects her eggs directly into the host
egg. The female may lay continously for about an hour if
left undisturbed. Superparas itism is common in the genus
Chelonus (Broodryk 1969 ) and was observed in insu1 aris
when parasitizing H_^ virescens (F.) eggs (Abies and Vinson
1981). Abies and Vinson (1981) reported that insu1 aris
appeared to examine host eggs internally as well as
externally and was able to detect previously parasitized
hosts. The average time of development from oviposition
to adult is about 26 days for males and 28 days for
females. Rechav (1978) found similar results for other
Chelonus spp. Greatest fecundity was obtained at 30C
(Glogoza 1980). Survival was highest at low temperatures
and the greatest percentage of eggs was parasitized at
35C (Glogoza 1980). Male biased sex ratios occurred at

22
20 and 40C while at 35C a 1:1 ratio was obtained
(G1ogoza 1980).
C insularis can develop in many hosts. Besides S.
frugiperda, it is also able to develop in He1 iothes
armigera ( H u b n e r) Spodoptera exigua (Hbn ) Ephestia
sericaria (Scott) (Bianchi 1944). Marsh (1978) reported
that hosts for North America include Ephestia elutella,
(Hbn), Felt i a subterrnea (F), He!iothes zea (Boddie),
Loxostege sticticalis (L.) Per idroma s aucia (Hbn),
Spodopter a e rid a nia (Ramer), Spodoptera ornithogalli
(Guenee), Spodopter a pr aef i ca Grote, and T^_ n i .
P ar as i t i z at i on of FAW by i n s u 1 a r i s reduced host
FAW larval weights by 70% and only 28% of the larvae
parsitized by in s u 1 a r i s lived past the 9th day and
these larvae displayed an unusual increase in weight prior
to destruction by the parasitoid (Ashley 1983).
Ashley et al. (1982) found that the native parasitoid
C. insularis was the primary species attacking FAW in
South Florida and it emerged from 71% of the parasitized
larvae. C. insu1aris caused the highest mortality of FAW
larvae collected from corn and broadleaf signalgrass
(Ashley et al. 1980). Ashley et al (1983) reported that
C. insularis parasitized 44% of all FAW larvae collected
from volunteer corn, Bermudagrass and paragrass and

23
regardless of the host plant, C. insularis had a parasiti-
zation rate 4 times greater than other competing parasi-
toids. Substantially higher percent par as itization was
obtained for corn than on other hosts (Ashley et al.
1983). Ashley et al. ( 1982 ) reported that C. insularis
parasitized the greatest proportion of FAW larvae having
head capsule widths of 0.3 mm. Chelonus insular is was not
recovered from larvae having head capsule widths greater
than 1.8 mm. This very clearly showed that insularis
is primarily an egg parsito id with preference to early
instars to lay eggs. Mitchell et al. (1984) reported that
two FAW pheremone components (Z9DDA and Z9TDA) had no
significant effect on the level of FAW par as itization by
its principal parasite C. insular is. The sex ratio for C.
insularis shifted from approximately 1:1 (Fernale:male)
during spring to approximately 1:4 during the summer
months but the reduced proportion of females during summer
did not lower parasi ti zation levels by i n s u 1 a r i s.
The Larval Endoparasitoid Microplitis manilae
Description and Distribution
Microplitis manilae (Ashm) is reported as an
important larval parasitoid of Spodoptera spp in Thailand
(Shepard, Pers. Comm 1982). This parasitoid is not

24
indigenous to the United States, and was imported from
Thailand through the USDA, Stoneville Research
Quarantine Facility, Mississippi.
No taxonomic or distribution literature was located
for M^ mani 1 ae. The length of antennae in males is longer
than for the female. However, Marsh (1978) described a
closely related spp M. melianae Viereck. An unsuccessful
attempt was made to establish M^_ man i 1 ae in the FAW
overwintering range in South Florida (Ashley, Pers.
Comm 1983).
The adults are ready to oviposit soon after emer
gence. They will oviposit in FAW larvae for a period of
16-17 days. Different species of Microp1 itis attack the
early larval instars of their hosts (Altahtawy et al.
1976). The female deposits an egg through the integumant
of host larva into the hemolymph. The egg is elongated,
oval and translucent white in color. The first instar is
caudate with a relatively large head and the second instar
is vesiculate and creamy white. After the parasitoid
larva molts into the third instar, it emerges from the
host (FAW) and spins a cocoon. Although the host remains
alive after the parasitoid emerges, the host does not
develop further and stops feeding. The parasitoid larva
exits the host and pupates outside. A single parasitoid
normally develops from each host even after

25
superparasitism. However, development of two parsito ids
per host occurred more frequently when larger hosts were
provided. Biology of M_;_ demo 1 i tor imported from
Queesland, Australia has been described by Shepard et al.
(1983) .
Interspecific Competition
By definition competition occurs when two or more
organisms interfere with or inhibit one another (Pianka
1970). Smith (1929) defined "multiple parasitism" to
designate the type of parasitization in which the same
individual host insect is inhabited simultaneously by the
young of two or more different species of primary parasi-
toids. Fisher (1961) reported that this type of multi
parasitism resulted in competition between the parsi
to ids. The occurrence of this type of multi parasitism
depends primarily upon the oviposit ion behavior of the two
parasitoids in response to hosts that are already parasi
tized. In general, parasitoids require a host organism
for egg deposition and the development of immature stages.
Typically, the progeny of one or neither parasitoid will
survive when individuals of different species parasitize a
single host organism (Salt 1961). Therefore interspecific
competition between parasitoids for hosts may be a vital
component influencing guild composition (Zwolfer 1970).
Interspecific competition among parasitiods may even

26
result in the competitive exclusion of certain species
(Debach and Sundby 1963).
In many cases of interspecific competition, one
species has an intrinsic superiority over its opponent and
invariably destroys it, by the use of its mandibles
(Pemberton and Willard 1918, Simmonds 1953) or by an
unspecified means of physiological suppresion (Muesebeck
1918, Fisher 1961, Salt 1961).
More commonly there is no intrinsic superiority on
the part of either parasitoid, and free competition occurs
between them, the victor completing its development and
the loser dying, either as an egg or a young larva.
Several suggestions have been made in the literature as to
the possible mechanism of competition between such soli
tary endoparas itic species. In the first place, the older
parasitoid is presumed to survive by eliminating the
younger through starvation (Fiske and Thompson 1909) thus
emphasizing the importance of time of oviposition as the
determining factor in competition. Secondly, cases of
direct physical attack by one parasitoid on another using
the mandibles for fighting has been recorded (Simmonds
1953). In these cases neither competitor has an intrinsic
advantage over the other and the result of competition is
apparently decided by the time of oviposition. The third
suggestion is that one parasitoid eliminated the other by
physiological suppression, either by conditioning the
hemolymph of the host so that it becomes unsuitable for

27
the development of any successor (Van den Bosch and
Haramoto 1953, Johnson 1959) or by the postulated
secretion of a toxic substance which kills the opponent
(Thompson and Parker 1930).
Competitive exclusion by previously introduced
parsito ids has been viewed as one of the factors that
explains the failure of introduced natural enemies in
classical biological control to become established (Ehler
and Hall 1982). The competitive exclusion hypothesis has
been subject of considerable debate in the literature.
Turnbull (1967) favored the competitive exclusion hypo
thesis while Van den Bosch (1968) rejected it. However,
Ehler and Hall (1982) presented empirical evidence in
support of competitive exclusion and stated that this
could possibly lead to the extinction of an effective
natural enemy. In fact, Force (1974) showed that a very
effective natural enemy may in fact be an inferior com-
petitior. Thus Ehler and Hall (1982) suggested that (1)
simultaneous release of several species of natural enemies
should be avoided due to interspecific competition between
them that may lead to a lower establishment rate and (2)
extra care should be taken in establishing species where
incumbent species of natural enemies exist. However Moon
(1980) reported that while the principle of competitive
exclusion may be simple and attractive, it may not
adequately apply to the heterogenous real world.

28
In classical biological control, the potential for
interspecific competition exists when more than one
species of natural enemy is released into the environment.
Regarding such multiple species introduction, it has been
suggested that such interspecific competition could
possibly lead to a decline in population regulation of the
host (Turnbull and Chant 1961, Watt 1965) although others
have refuted this as a general phenomenon (Huffaker et al.
1971). Empirical evidence generally supports multiple
species introductions (Ehler 1978). However, such
evidence comes largely from successes involving multiple
species releases without regard to instances where such
releases did not yield total success (Ehler 1977). Miller
(1977) suggested the possiblity that intrinsically
superior competitors which exhibit a relatively low repro
ductive capacity would displace or interfere with
intrinsically inferior competitors which exhibit a rela
tively high reproductive capacity. There is a concern
that such competition would result in decreased par as it i -
zation rates. A computer simulation by Watt (1965) and a
greenhouse study by Force (1970) suggested that such a
reduction in the proportion of parasitization is
possible.
Other things being equal, intrinsically superior
species imported in biological control programs probably
become established more easily than intrinsically inferior

29
ones. Examples of intrinsically superior parasitoids that
have achieved such a role are two braconids, Opiun
oophi 1 us Full. (Bess and Haramoto 1958) and Macrocentrus
ancylivorus Rohw. (Boyce and Dustan 1958). On the other
hand, an intrinsically inferior species may achieve a
higher level of parasitization in the field than its
rivals if it is extrinsical 1y superior to them. For
example, Spalangia cameroni Perk., an intrinsically
inferior species, parasitized more house fly pupae than
all other species combined because the females were able
to penetrate more deeply into areas containing hosts
(Mourier and Hannine 1969). Obviously, an intrinsic
superiority of one parasitoid over another may result in
the waste of some parasitoids, but this effect, as pointed
out by Smith (1929), is likely to be an insignificant
factor in the comparative field efficiencies of two
competing forms.
Case Studies
The superiority of Metaphycus inteolus (Timberlake)
over Microterys f1avus Howard inside the host (Coccus
hes per idiurn) in the field was contrary to the pattern of
dominance of both species when they competed within the
host (Bartlett and Ball 1964). Arther et al. (1964)
showed interactions between a braconid, Orgilus obscurator
(Nees), and an ischneumonid, Temelucha interruptor, inside

30
the pine shoot moth, Rhyaciona buoliana Schiff. They
reported that T. interruptor attacked more host larvae that
had been previously parasitized by 0^ obscurator than
unparasitized hosts. Vinson (1972) reported that in
interspecific competition between larval parsito ids
Cardiochiles nigriceps Viereck and Campo 1etis perdistinctus
(Viereck) on tobacco budworm, virescen s, that C .
perdistinctus had a slight advantage over nigriceps when
oviposition by the 2 species occurred at about the same
time. Part of the reason for the advantage by C^_ perdi s-
tinctus may be more rapid growth rate of its larvae and a
shorter egg development period. When the competitors were
of similar age, one was eliminated through physical combat.
When one competitor is 1 or 2 days older it was able to
destroy several eggs of the younger competitor. However
when older parsito id is 4 days old the younger larvae is
eliminated through physiological suppression (Vinson et al .
1972). Such suppressed larvae failed to grow and were
inactive although they may be alive. When one of the
tobacco budworm parasitoids was old or it eliminated the
younger competitor by physiological suppression (Vinson
1972). Fisher (1961) also presented evidence of physiologi
cal suppression of younger larvae by the older competitor
through the reduction of oxygen available to the younger
larva. Wylie (1972) reported that only one parasitoid

31
species survived in interspecific competition among the
pupal parasitoids N asonia vitripennis (Walk)., Muse idi-
fura zaraptor K. & L. and $p1 angi a cameroni Perk. Nasonia
vitripennis and M. zaraptor were both intrinsically
superior to cameroni if the attacks on the hosts by
their females preceded, were simultaneous with, or
followed by up to 48 hrs those by females of cameroni.
Nasonia vitripennis was intrinsically superior to M.
zaraptor if its attacked preceded that by M_^ zaraptor by
at least 24 hrs. The success of vitripennis when
competing with S. cameroni was due to differences in rates
of egg and larval development and of host utilization by
the two species. In a similar study by Wallner et al .
(1982), larval parasitoids Apanteles me!anoscelus
Ratzburg. and Rogas lymantriae (L.) inside the host
Lymantria dispar (L.) both attacked the previously
parasitized larvae but the parasitoid attacking the host
first was more successful.
The studies on mu 11ipar as itism between the internal
larval parasitoids of Rhyacionia buo 1iana Schiff. revealed
that interspecific competition took place between the
first instar larvae through direct physical attack
(Schroder 1974). However there are instances where these
internal parasitoids have coexisted within the host larva
and this provides a good example of a system of

32
"counter-balanced competition" (Zwolfer 1970). In such
systems, the competitive inferiority of a parasitoid
species in multiple parasitism is compensated for by a
superiority in other attributes such as searching
efficiency and synchronization with the host's life cycle
(Schroder 1974).
Weseloh (1983) reported that neither of the
parasitoids A^_ mel anoscel us nor Compsi 1 ura concinnata
(Meigan) destroyed each other inside the host Lymantria
dispar and both emerged from about 11% of the hosts.
These results showed that both parasitoids appeared to be
remarkably tolerant of each other in the same host and
this probably happened because they fill different niches
and so do not compete with each other within the host.
The larval parasitoids Campoletis sonorensis
(Carlson) and Microplitis croceipes Cresson are intrinsi
cally superior to C in s u1 a ris and physically attacked
the latter inside the host, virescens (Vinson and
Iwantsch 1980). In a similar study, Miller (1977)
reported that C. insularis larvae competing with A .
marginiventris inside Spodoptera praefica (Brote) were
dwarfed and nearly killed due to competition. A second
experiment involving C in s u1 a ris and Hypo soter exigue
(Vierek) yielded a similar result where ex i que was a
superior intrinsic competitor relative to C. insularis and
C. marginiventris.

33
In a study on impact of native parsito ids on FAW in
Southern Florida, Ashley et al (1982) described a mirror
image pattern of parasitization between C. insularis and
Terne!ucha spp collected from the FAW larvae. This
increase-decrease and deer ease-increase pattern between
these two parasitoids may be indicative of interspecific
competition between these parasitoids (Ashley et al .
1982). Mitchell et al ( 1984) reported the effect of two
FAW pheremone components (Z9D0A and Z9TDA) upon population
dynamics of its larval parasites and found that C.
insu1aris was the predominant species followed by T.
difficilis whose par as itization rate of FAW larvae was
initially high and then remained relatively constant for
the remainder of the experimental period. The explanation
for this type of parasitization pattern was that C.
insu1 aris was a better internal competitor than T.
difficilis (Mitchell et al. 1984).

BIOLOGY AND HOST ACCEPTANCE OF MICROPLITIS MAN I LAE
(HYMENOPTERA:BRACONIDAE ) RAISED ON FALL
ARMYWORM LARVAE
Introduction
The fall armyworm (FAW), Spodoptera frugiperda (J.E.
Smith), is a major pest of corn and Bermudagrass in the
southeastern United States (Luginbill 1928) and may extend
its range as far north as the Canadian border during the
summer and fall months (Snow and Copeland 1969). However,
since this pest has no mechanism for diapause or
overwintering its populations are restricted to portions
of south Florida and Texas during the winter months
(Luginbill 1928). Average estimates of annual crop losses
caused by the FAW exceed $300 million (Mitchell 1979).
Therefore, reducing the density of overwintering FAW
populations may result in a significant decrease in the
amount of damage done by this pest.
Mic r o p1 itis man i 1ae (Ashmead) is a parasitoid of
Spodoptera spp. in Thailand from where it was imported
into the United States. Even though the FAW does not
occur in Thailand, M. manilae develops successfully in
larvae of the FAW under laboratory conditions (Shepard,
personal comm. 1982). The biologies and distributions of
34

35
some members of this genus are known (Hafez 1951, Putter
and Thewke 1970). Lewis (1970) describes the life history
of NL. croceipes (Cresson) for Heliothis spp. and reports
that the parasitoid prefers 1st and 2nd instars as hosts.
No research dats could be found that document the life
cycle and host age acceptance of M^ man i 1 ae developing
within FAW larvae, nor has this parasitoid been reported
as a natural enemy of FAW anywhere within its range
(Ashley 1979 ) .
The objectives of our research are to gain relevant
information about the biology and host age acceptance of
M. man i 1ae when reared on FAW larvae. This information
may prove useful in mass production of this parasitoid for
inoculative or perhaps inundative releases should M.
man i 1ae eventually demonstrate the potential of becoming a
significant mortality agent of FAW populations.
Materials and Methods
Fern ale parsito ids were 24 hrs old and has been
exposed to males since female eclosin. Each replicate
consisted of exposing FAW larvae (number varied according
to experiment) to 6 female parasitoids in a plastic
container (7 x 10 cm diam) with 2 screened vents (1.5 x
3.0 cm) and having honey streaked on the underside of the

36
lid. During host exposure, FAW larvae fed on cubes (3
cm^) 0f pinto bean diet (Leppa et al 1979 ) after which
the larvae were transferred individually to 30-ml plastic
cups that contained pinto bean diet where they remained
until their fate was determined. FAW larvae were kept as
2 3+_2 C, 7 0+_2% RH and under a 14:10 LD photoperiod. These
larvae were divided into 4 groups depending on their age:
1 24-48 hr s; 2, 49-72 hrs, 3, 73-96 hrs; and 4, 97-130
hrs. Hosts older than 130 hrs were excluded because M.
man i 1ae females would not accept them as hosts. The
laboratory rearing method for mani 1 ae consisted of
exposing parasitoids to approximately 50 FAW larvae which
were 48-72 hrs old for 3-5 hrs.
Age group acceptance--Depending on host availability
4-6 replicates of 3-4 FAW larvae of the same age group
were presented to two female mani 1 ae for 30 min. on the
same day. Data from 4 consecutive days comprosed a single
test and tests were replicated 4 different times.
Developmental rates--Microplitis man i 1ae were exposed
for 24 hrs to hosts in the four age groups. Parasitoid
developmental times were determined from oviposition to
pupation and from pupation to adult emergence. Progeny
sex ratios were recorded for each age group.

37
Adult 1ongevity--Fresh1y eclosed parasitoids were
exposed to hosts under continuous light at 26+_lC and
longevity was recorded for 2 groups: (1) the females
(n=41) and males (n-57) were separated into different
cages and (2) both sexes were kept together and allowed to
mate for 2 hrs and then to oviposit for 24 hrs inside a
plastic container with 20 FAW larvae. After the host
exposure period, larvae were removed and adult parasitoids
were retained in the plastic containers.
Time of host exposure--In order to determine optimal
host exposure time, 2 female M^_ man i 1 ae were exposed to 20
hosts from the 2nd age group for 15, 30, 45 and 60 min.
and then removed. Four replicates were run.
Results and Discussion
Parasitoids displayed the highest host acceptance for
1st and 2nd age group larvae and a lesser acceptance for
3rd age group larvae (Table 1). Highest par as itization
rates occurred most frequently in 2nd age group larvae.
Significantly fewer 4th age group larvae were parasitized
compared to larvae of other groups, and there were several
occurrences of significant differences in host acceptance
between 2nd and 3rd age group larvae. Similar results
have been reported for other members of this genus (Hafez
1951, Lewis 1970). Putter and Thewke (1969) showed that

38
Table 1.
Percent
paras itization by
armyworm larvae
m a n i 1 a e
of fall
Age
Test numbers9/
group
(hr s)
1
2
3
4
1 (24-48)
24.5 a
26.7 a
26.7
a
13.2
a
2 (49-72)
28.3 a
30.1 a
27.8
a
11.4
a
3 (73-96)
22.5 a
20.7 b
19.5
b
12.3
a
4 (97-130)
6.9 b
5.2 c
6.8
c
3.5
b
Total
369
418
521
279
Percentages followed by the same letter in the same column
are not significantly different by Duncan's Multiple Range
Test (P = 0.05).

39
M. fel tiae preferred 1st to 3rd instar larvae (1st to 3rd
age groups) of its host Agrotis psilon (Hufnagel) and
Harcourt (1960) demonstrated a similar instar preference
for M. piutel1ae Muesebeck and its host the diamond back
moth PIutel1 a maculipennis (Curtis). In contrast, Shepard
et al. (1983) reported that demo 1itor (Wilkinson)
preferred 3rd or 4th instar larvae of Heliothis spp.
However, larvae of this size displayed a vigorous defense
response and often damaged or destroyed the parasitoid.
We observed also that when mam' 1 ae females attempted to
oviposit in 4th age group larvae that these larvae
aggressively attempted to thwart the ovi pos itional attempt
by swinging their heads and thoraxes from side to side in
an attempt to bite the parasitoid.
The larval and pupal developmental times for M.
man i 1ae were similar for age groups 1-3 (Table 2). Egg to
pupa and pupa to adult developmental times for M. manilae
parasitizing 4th age age group hosts increased by approxi
mately 2 days. Significantly more male progeny were pro
duced from the 1st age group in contrast to the 2nd group
from which more female progeny emerged. No significant
differences were present in the sex ratios of progeny from
3rd or 4tn age group larvae. The highest and lowest pro
portions of female progeny were observed for age groups 2
and 4, respectively. Bryan et al. (1969) showed that the

40
Table 2. Developmental periods (X +_ S.E.) and progeny
sex ratios for M. man i 1ae in fall armyworm larvae
Developmental
period
(days)
Age
group
Sex ratio (%)a
( hr s)
Hosts
exposed
Egg-
pupa
Pupa-
ad u 11
Total
Males
Femal es
1 (24-48)
106
10 + 2.3
4 + 0.7
14 + 3.0
62.5-
--*--37.5
2 (49-72)
127
10 + 2.9
3 + 0.9
13 + 3.8
42.9-
--*--57.1
3 (73-96)
93
10 + 2.1
4 + 1.1
15 + 3.2
46.8-
-ns--53.2
4 (97-130)
43
12 + 1.9
6 + 1.7
18 + 3.6
46.7-
-ns--55.3
aAsterisk indicates significance at the 5% level by Student's
t-test.

41
sex ratio of emerging progency of M_^ croceipes was
approximately 1:1 when reared at 25C. Only a single M.
man i 1ae emerged per host larvae irrespective of the age
group parasitized. Bryan et al. (1969) reported an
occasional emergency of 2 M. croceipes adults from a
single He!iothis spp. larvae. Emerging NL man i 1ae larvae
appeared to perfer a dry surface on which to pupate and
would frequently form cocoons on the underside of the lid
rather than on the moist diet surface.
Male and female longevity was about 6-7 days. Mating
increased female longevity to approximately 10 days. An
increase of approximately 10% in parasitization was
observed when the host exposure period for M, manilae
females was increased from 15 to 30 min. (Table 3). Host
exposure periods longer than 30 min. did not increase
significantly the parasitization rate.
Biological knowledge about this parsito id is
necessary in any attempt to establish manilae as an
additional mortality agent in the overwintering range of
FAW. Ashley et al. (1982) showed that the native para
sites destroyed approximately 63% of each of the 1st 4
instars and parasitization rates followed closely the
increase or decrease in FAW larval populations. Parasiti
zation rates of 3.5-30.1% by M. manilae in FAW larvae were

42
Table 3. Percent par as i t i zation of second age group fall
armyworm larvae exposed to m a ni 1 a e for various amounts of
time
Host (% Parasitization)
exposure (min) No. containers a (X + S.E.)b
15
8
13.0
+
3.7
a
30
45
11
22.0 +
3.1
b
13
26.0 +
1.7
b
60
9
24.5 + 1.6 b
a Two female parasitoids and 20 larvae/container.
b Means followd by the same letter are not significantly
different (PC0.05) by Duncan's Multiple Range Test.

43
observed in the laboratory. The results of our research
will be used to rear man i 1ae and to support efforts to
establish this parasitoid in the overwintering range of
FAW.

INTERSPECIFIC COMPETITION BETWEEN PARASITOIDS OF
THE FALL ARMYWORM
Introduction
The fall armyworm (FAW), Spodoptera frugiperda is a
serious pest of many graminaceous crops throughout the
southeastern United States. Average estimates of annual
crop losses exceed $300 million (Mitchell 1979). Since
overwintering occurs only in the southern portions of
Florida and Texas (Lunginbil1 1928), increasing FAW mor
tality within this range may lower the numbers of adults
participating in this pest's northward migration each
spring. Fifty-three species of parsito ids have been
reared from field collected larvae (Ashley 1979).
Knowledge of parsito id interrelationships within FAW
larval populations will increase our understanding of the
factors that affects the dynamics of this pest, as well as
contribute the biological control efforts. In endemic
host enemy associations, interspecific competition appears
to play a crucial role in structuring the parasitoid guild
(Force 1974), and may influence the entire natural enemy
complex as well. Parasitoids of the FAW provide a
44

45
relevant model for the study of interspecific competition
within the host larva because of similarities in their
life cycles. Ashley et al. (1982) supports the concept of
interspecific competition during parasitiod development by
demonstrating the presence of a dependent density pattern
in percent par as itization between Chelonus insular is
Cresson and Temelucha difficilis Dasch.
The present study assesses interspecific competition
between two species of larval parasitoids, Microp1 itis
man i 1ae (Ashm.) and C o t e si a (=Apanteles) marginiventris
Cresson, and an egg-larval parasitoid C, insularis It
also describes the host finding and ovipositional sequence
for marginiventris for hosts already parasitized by C.
insu1 aris. In addition data are presented on host
acceptance of M_^ man i 1 ae and marginiventris of larvae
already parasitized by insu1 aris.
Materials and Methods
Host eggs or larvae were obtained from a FAW colony
maintained at 23-25C, 74-78% RH and under a 14:10 LD
photoperiod. Moth oviposition occurred on paper towels, a
portion of which were subsequently cut into sections each
having 50-60 eggs. All hosts utilized in an experiment came
from the same egg mass to help ensure host uniformity. In all
experiments, except the fourth, these paper sections were

46
placed in a plexigls cage (25 cm3) and exposed to two
female C. insularis (24-48 hrs old) for 24 hrs. Each mass
was observed to verify that a C^_ i nsul ar i s female had
parasitized the eggs. Masses attacked by two or more
females and eggs close to the edge of the paper section
that were not parasitized were destroyed. The larval
parasitoids emerged in plexiglass cages (25 cm3) kept at
26 +_ 1C, 60-70% RH and under a 14:10 LD photoperiod with
a fluorescent light intensity of 800 ft-c. Female
parasitoids were held in these cages along with males for
a minimum of 48 hrs. Unless otherwise indicated, female
parasitoids were between 2 to 4 days old. Host exposure
for the larval parasitoids lasted 24 hrs and was
accomplished by placing parasitoids, FAW larvae, and 1.5
cm cube of FAW diet (Leppla et al 1979 ) into a 50-ml
container (7 x 10 cm diam) with two air vents (1.5 x 3.0
cm) located near the top on opposite sides. Parasitoids
were supplied with honey and water after adult eclosin
and during the ovi pos itional period. Following host
exposure, FAW larvae were placed individually into 30-ml
plastic cups that contained approximately 15 ml of diet.
These cups were held in a growth chamber at 25 +_ 1C,
77-80% RH and under a 14:10 LD photoperiod.
Experiment 1. Ninety FAW exposed previously to C.
insu1aris as eggs were divided into three equal groups.

47
Larvae in group one, were not exposed to marginiventris
or M. man i 1ae and served to measure parasitization by C.
insularis. Remaining larvae were exposed as second
instars (48 hrs old) to C^_ margin i ventr i s (group two) or
to M. mani1ae (group three). Treatments were replicated
nine times. The percent successful parasitization and the
fate of non-par as itized larvae were recorded.
Experiment 2. Twenty second-instar larvae exposed
previously to insularis as eggs were exposed to either
M, mani 1 ae or marginiventris in the plastic containers.
Ten replicates were made. In the control treatment,
larvae were exposed to either marginiventris or M,
m a ni 1 a e without prior par as itization by insularis .
Experiment 3. Fall armyworm larvae exposed as eggs
to C in s u1 a ris and unexposed larvae were kept in separate
plastic containers until the larvae were 3 days old. The
ten exposed and ten unexposed larvae were transferred to
new plastic containers. Two females of either margini
ventris or mani 1 ae were introduced into a container for
30 min and the number of encounters, antennal examina
tions, ovipositor probes with and without cuticle contact
were recorded. An encounter was defined as the arresting
of random locomotion that resulted from sensing the FAW
larva. An examination occurred when antennal palpation of
the larvae by the parasitoid was observed. A probe was

48
observed. A probe was recorded when the parasitoid
thrusted its ovipositor toward the larval cuticle.
Finally, an apparent oviposition took place when the
parasitoid mounted the host and inserted its ovipositor.
Three replicates for each parasitoid species and larval
combination were examined. Further replication was not
possible because of the loss of the man i 1ae colony.
Experiment 4. Eight host larvae derived from one of
the following four groups were placed in a glass petri
dish (15 x 100 mm diam): (1) initially parasitized by C.
marginiventris and subsequently exposed to M. manilae; (2)
initially not exposed to parsito ids and subsequently
exposed to M_^ manilae; (3) initially parasitized by M.
manilae and subsequently exposed to C^_ margi n i ventr i s ; and
(4) initially not exposed to parasitoids and subsequently
to C. marginiventris.
As hosts were attacked they were removed and replaced
with fresh larva. Non-par as itized larvae served as a
control. The number of host encounters, examinations and
apparent ovipositions were recorded. Five replicates for
each species combination were run starting on the same day
hosts were parasitized and then repeated 3 and 6 days
later.
Experiment 5. The host finding behavior of C.
marginiventris was investigated using 4-week-old corn,
sorghum, Bermudagrass (Cynondon dactylon (L.)), and itch

49
grass. These plants were grown in pots (14.5 x 15 cm
diam) containing a mixture of sand, perlite and peat moss
(1:2:2 ratio, respectively). Supplementary nutrients were
supplied with fertilizer (8-8-8 plus trace elements). FAW
larvae exposed previously to insu1 aris were allowed to
become second instars. Plants were placed in wire cages
(40 cm3) in a greenhouse at 26-28C, 70-75% RH and 14:
10 LD photoperiod. Thirty larvae were placed randomly on
the plant leaves. After 24 hrs, a female was introduced
into the cage and her host finding behavior observed.
Forty females were observed in sequence, their responses
recorded and synthesized subsequently into common
behavioral patterns.
Parasiti zation by C_^ margi ni ventr i s on FAW larvae
also was measured on all four host plants. Thirty,
second-instar larvae already parasitized by C in su 1aris
were placed randomly into the plants. After 24 hrs of
host larval feeding, two female _C^_ margi ni ventr i s were
introduced. The host larva were removed at 20-, 40-, 60-,
and 80-min intervals. Three replicates for each time
interval and plant species were made. Larvae were removed
from the plants and placed in 30-ml cups to determine
parasitization rates.

50
Results and Discussion
Experiment 1. Results of interspecific competition
demonstrated that C. insularis was significantly more
competitive than M^ man i 1ae (Fig. 1.) However, when C.
marginiventris replaced man i 1ae within the host larva,
then marginiventris emerged more frequently than C.
insularis The combined par as itization rates for the
three treatments ranged from 73-78%, which demonstrated
that multiple par as itization did not seem to affect FAW
larval mortality. FAW larvae parasitized by any two of
the three parsito id species only produced a single
parsito id, which suggests the destruction of one
parasitoid larva by another. Salt (1961) and Vinson and
Abies (1980) reported that when multiple parasitism
occurred, all but one species was usually eliminated
through physical attack, physiological suppression, or
both. In a few instances, especially with gregarios
parasito ids, some individualy of both species may survive
(Miller 1982, Weseloh 1983).
Substantial differences were not present between the
three parasitoid treatments for (1) larvae that success
fully pupated and emerged as adults, (2) larvae that
starved because they did not feed on the diet, (3) larvae
that died from unknown causes and (4) larvae that fed on
the diet but did not pupate (Table 4). Rejection of the

FIG. 1. Mean percentage emergence of C. insularis (Ci),
M. man i 1ae (Mm), and C. marginiventris~[ Cm) fr om f a11
armyworm "1 ar v ae exposed to mu it (pe pr as i t i z at i on .

80
70
60
50
40
30
20
10
0
80
70
60
50
40
30
20
10
0
Ci&Cm Ci&Mm Ci-only
TREATMENT
Ci
Mm
B Cm

53
Table 4. Mean percentages for emergence of Chelonus insularis
(Ci), M i c r o p 1 i t i s mani 1 ae (Mm), C o t e s i a marg i n i venir i s ( CT] cl a3" u 11
FAW, and per cent ages "for FAW 1 ar v ae fafling to mature because they
refused to feed on the diet, for dying from unknown causes, and for
failing to pupate3
Parasitoid emergence
Refused
Unknown
Did no
Treatment
Mm
Cm
Ci
FAW
diet
causes
pupate
Ci
x Mi
13.7a
64.3a
7.0a
3.9a
5.8a
5.4a
Ci
x Cm
46.0b
27.4b
8.7a
4.0a
7.7a
6.5a
Ci
only
74.4a
7.3a
4.3a
7.7a
5.9a
treatments replicated nine times with 30 1 ar v ae/treatment. Means
in the same column followed by the same letter were not significantly
different by Duncan's Multiple Range Test (P = 0.05). This means for
Mm (Column 2) and for Cm (Column 3) were compared using students
_t-test.
^Had not pupated by the time nonparasitized larvae had emerged.

54
larval diet may be one of the sources of artificial
selection encountered when an insect population is placed
under laboratory colonization (Boiler and Chambers 1977).
However, reasons for those larvae that fed on the diet but
did not pupate or molt during the allocated period were
not properly understood. Beckage (1982) observed Manduca
sexta (L.) larvae parasitized by Apanteles smerrintie
Riley often molted to larval-pupal intermediates even when
parsito ids failed to emerge.
Experiment 2. The proportions of C_^ marginiventris
and M. mani 1 ae adults that emerged from parasitized and
non-parasitized hosts were not different significantly
(Table 5). Cotesia marginiventris parasitized signifi
cantly more hosts then M^ man i 1ae. Larvae that were not
parasitized by either parasitoid and emerged as FAW adults
displayed significant differences in all four treatments.
These data support the results of experiment 3, where M.
mani 1 ae females altered their ovipositional behavior
toward hosts already parasitized by insu1aris. Cotesia
marginiventris did not appear to discriminate against
hosts parasitized previously by C^_ insu1 aris as there were
no significant differences between C. insularis x C.
marginiventris and C^ marginiventris only treatments.
Vinson and Iwantsch (1980) did not discriminate against C.
insularis parasitized tobacco budworm hosts and neither
did M. croceipes .

55
Table 5. Mean percentage emergence for Cotesia marginiventris
(Cm) and Microplitis manilae (Mm) from FAW larvae exposed and not
exposed as "egg s~ ~t~o~ ~Che~l onus i nsu 1 ar i s (Ci) and percents for emergence
of FAW adults, 1 arvae "dying" because they refused to eat the diet, and
larvae not pupating.
Treatment
Mean
emergence
FAW
Refused
d i et
Did not
pupate^
Ci
Cm
Mm
C i x Cm
32.5
56.5
5.0
0.0
0.0
Cm only
52.5
30.0*
4.3
6.3
C i x Mm
48.0
37.5
13.0
0.0
0.5
Mm only
44.5*
28.5*
11.5
16.5*
treatments replicated nine times with 20 1 arv ae/treatment. Data
analyzed by Student's _t-test (* = significantly different at the 5%
level).
Comparisons only made between treatments 1 ant 2, and 3, and 4. The
means for Ci in treatments 1 and 2 were not compared statistically.

56
Experiment 3. The behavior of mani 1 ae females
were altered significantly when exposed to hosts para
sitized previously by insu1 aris (Table 6). This
altered behavior occurred in three categories; examina
tions, probes, and apparent oviposit ion. A similar
behavioral pattern was not found for marginiventris.
This indicated that marginiventris either cannot
discern the presence of insu1 aris in the host or that
the presence of insularis does not inhibit oviposition.
Vinson and Abies (1980) reported that tobacco budworm
larvae parasitized previously by insu 1aris also were
acceptable to larval parasitoids Microplitis croceipes
Cresson and Campoletis sonorensis Carlson as ovipositional
sites.
Experiment 4. The number of encounters, examina
tions, and apparent ovipositions for the two larval para
sitoids were not significantly different regardless of the
parasitization sequence or the number of days between host
exposure periods (Table 7). Initially, M_^ man i 1 ae made
greater numbers of encounters in marginiventris para
sitized larvae than in non-parasitized larvae. There was
a trend for man i 1 ae to be more active with respect to
encounters, examinations and ovipositions on hosts para
sitized by C_^ marginiventris compared to non-par as i ti zed
hosts. Cotesia marginiventris was more active also on
hosts parasitized previously by M. manilae than on

57
Table 6. Mean and percents for encounters, examinations,
oviposition probes and apparent ovipositional success by Cotesia
marginiventris and Microplitis manilae in fall armyworm larvae
exposed arT3 not exposed as eggs ~Fo"~Cfi~e 1 onus i nsu 1 ar i s.
Exposure to
C insular i s
Mean a
Encounters
Examinations
Probes
Ov i pos itions
Microplitis manilae
Exposed
8.4
2.0
2.2
1.2
(60.8)
(14.4)
(15.9)
(8.7)
Not Exposed
8.8
3.8*
4.2*
2.6*
(45.5)
(19.6)
(21.7)
(13.4)
C o t e s i a
marginiventris
Exposed
12.8
5.8
2.6
2.8
(54.3)
(22.4)
(11.2)
(12.1)
Not exposed
14.2
5.8
2.9
2.9
(55.04)
(22.5)
(11.2)
(11.2)
aStudent' s jt-test analyzed at a = 0.05 level. Percents are in
parentheses and are based upon the total number of behavioral
observations (encounters + exams + probes + oviposition).

58
Table 7. Mean for numbers of encounters, examinations and
apparent ovipositions by Cotesia marginiventris (Cm) and Micro-
pl i tis mani1ae (Mm) during two host exposure periods separate? by
cii ffererTT numbers of days.
Days between
Second
host exposure
means3
Host
First
exposure
Second
host exposure
period
Encounters
Examina
tions
Apparent
ovi position
Cm
Mm
0
13.2
7.8
6.8
None
Mm
11.8
6.9
5.6
3
10.8
4.2
3.6
9.6
5.4
3.0
6
10.6
8.8
4.6
9.8
8.0
4.0
Mm
Cm
0
11.4
8.8
6.6
None
Cm
9.6
00

6.0
3
15.6
9.6
5.6
14.4
8.8
5.2
6
16.8
6.9
7.8
17.4
6.8
7.0
aNone of the number pairs were significantly different by
Student's t-test.

59
non-parasitized hosts. M. man i 1ae had greater
ovi pos itional contacts with the hosts that contained C.
marginiventris larvae than C. marginiventris with host
that contained mani1ae larvae on the first day of host
exposure. This trend reversed itself on days 3 and 6.
Experiment 5. The host finding and behavioral
sequence for oviposition of marginiventris on FAW
larvae already parasitized by i n s u 1 a r i s on corn,
sorghum, Bermudagrass and itch grass consisted on nine
basic components (Fig. 2). During the sequence, preening
occurred at several different steps. A typical pattern
involved the following:
1. Random movement--The parasitoid female flew and
walked randomly inside the cage or on the plant leaves.
The upper portion of the leaf was preferred. The female
held her antennae close and parallel to the substrate, or
folded them back under her body.
2. Antennal palpation--The female started antennal
palpation of the surrounding leaves and on the substrate.
She held her antennae nearly parallel to the substrate and
lowered her flagella slightly and raised them back to the
horizontal position. This movement of the flagella
frequently lasted for 5 to 25 sec. The under surface of
the leaf was palpated more frequently.

FIG. 2. Behavioral ethogram of the host finding and ovi-
positional sequence of marginiventris females on fall
armyworm larvae already parasitized by the egg-larval
parasitoid C. insularis. (Solid arrows indicate invari
able pathways and dashed arrows represent alternate
pathways.)

(!)
t*
i
^ (4)
(3) Chemotaxis Larval
N 1
i/ '
& \
toy Antennal \
Palpation \
\
4'\/
r
V
Random
Movement
\
\
s
s
Contact
'A
\ /
^ 'V \U
> Preening
Mounting (5)
Insertion (6)
Antennal <
Palpation 7
*
I
i
/
/
/
/
V*
Oviposition (7)
77
Oviposition (8)

62
3. Chemotaxis--The parasitoid became oriented and
walked rapidly toward the site where FAW larvae feeding on
the leaves. She vibrated her wings frequently and moved
her body in a manner that indicated excitement.
4. Larval contact--Locomotion was arrested and
antennal palpation of the host began with the apical
portions of both antennae.
5. Mounting--The parasitoid jumped quickly onto the
host, usually near the posterior portion.
6. Insertion--Stinging was performed immediately
after the process of mounting. The wings were extended
during the process.
7. Ovi pos ition--This occurred immediately after
insertion and the parasitoid moved away quickly from the
host.
8. Postoviposition--The parasitoid restarted
antennal palpation of the substrate. The female began an
integrated sequence of abdominal bending and metathoracic
leg extension. Preening always occurred.
9. Resting--The parasitoid was motionless.
Loke et al. (1983) described the behavioral sequence
of _C^ marginiventris on FAW damaged corn plants with an
ethogram that consisted of 13 defined steps and divided
the pattern of host finding behavior for marginiventris
on non-par azi ti zed FAW larvae into four phases:

63
non-searching movement, searching, oviposition, and
resting. Analysis of our ethogram and that of Loke et al.
(1983) showed that the elimination of certain steps in our
ethogram are of particular interest because chemical cues
from the earlier oviposition by insularis may have
altered the behavioral pattern of the female margi ni -
ventris after ovipositing in an already parasitized FAW
larvae.
The percent par as itization by C marginiventris
showed more than a two-fold increase in corn compared to
sorghum and more than a four-fold increase over Bermuda-
grass and itch grass (Fig. 3). Sixty percent of the
larvae were parasitized by marginiventris in corn after
an 80-min host exposure period. There was no increase in
par as itization for Bermudagrass and itch grass after 20
min. Ashley et al. (1983) found that par as itization rates
for i nsul ar i s and T erne! ucha spp. were substantially
higher in corn than in Bermudagrass and paragrass Brachi-
arie m u tic a (L .) C o t e sia marginiventris parasitized the
highest proportion of hosts in Bermudagrass and paragrass.
The differences in par as itization rates between these
parasitoids may reflect a host plant preference (Ashley et
al. 1983).
In our study, M. man i 1ae apparently failed to compete
successfully within the host larva when this larva contain

FIG. 3. Percentage par as itization by C. marginiventris of
fall armyworm larvae already exposed as eggs to "C.
in s u1 a ris Larvae were randomly placed on four pTant
Tpecied he Id in wire cages within a greenhouse.

TIME (min)

66
a developing C in su 1aris The possibility also existed
that man i 1 ae recognized a previously parasitized host
and failed to oviposit. Larvae parasitized as eggs by C.
insu1 aris caused a significant reduction in the number of
host contacts, examinations, and apparent oviposit ion by
M. mani 1 ae. Cotesia marginiventris oviposited in both C.
insularis parasitized and nonparas itized larvae and was
superior internal competitor compared to C insularis .
Exposing FAW larvae that have been parasitized as eggs by
C i n s u 1 a r i s to marginiventris or man i 1 ae did not
result in additional larval mortality. If this same
situation exists under field conditions, then C. insular is
may be the key regulator of FAW larval populations.

EFFECT OF HOST AGE, PARASITOID AGE AND CHANGE OF
TEMPERATURE ON INTERSPECIFIC COMPETITION BETWEEN
CHELONUS INSULARIS CRESSON, COTESIA MARGINI VENTRIS
HTTRTnTE
Introduction
The fall armyworm (FAW), Spodoptera frugiperda occurs
year-round in the tropical and subtropical areas of the
western hemisphere, where it feeds on corn, sorghum,
Bermudagrass and other members of the family Graminae.
Damaging populations of FAW occur irregularly, and
conditions conducive to outbreaks are not well understood
(Barfield 1980). Estimated losses attributed to FAW
reached $300 million in the southeastern United States
during 1977, one of the most severe outbreak years (Sparks
1979).
A very diverse complex of natural enemies, especially
parasitoids, attack the larval stages of FAW (Ashley
1979). The potential for interspecific competition exists
between these parasitoids because more than one species
attacks the same instar. Pemberton and Willard (1918)
suggested that competition between parasitoids may prevent
them from regulating their hosts effectively.
67

68
Ashley et al. (1982) reported the presence of a mirror
image pattern with respect to percent par asi tization of
FAW larvae by the larval parasitoids, Che!onus insular is
Cresson and Temelucha diffici1 is Dasch. and suggested
that interspecific competition may have cuased this
pattern.
Factors such as host age and environmental tempera
ture affect the outcome of interspecific competition and
evaluation of these factors should be of primary concern
before initiating parasitoid release programs against a
common host. A literature search provided no information
on the effect of host age and temperature on competition
among FAW parasitiods. Therefore, we selected the larval
parasitoids Microplitis man i 1ae Ashmed. Cotesia
(Apanteles) marginiventris Cresson and the egg-larval
parasitoid i n s u 1 ar i s for our investigations. These two
parasitoids are among the principal natural enemies
regulating FAW populations in southern Florida (Ashley et
al. 1983). The specific objectives of our study were to
determine the effects of host age, temperature and the age
of C^ marginiventris on interspecific competition.
Materials and Methods
Parasitoids were kept in plexiglass cages (50 x 50 x
24 cms) at 26 C,60-65% RH and under a 14:10 LD photoperiod

69
regime with a fluorescent light intensity of 800 ft-c and
were supplied with honey and water. Adults of margini-
ventris and C. insularis came from laboratory colonies
established from FAW larval collections made from corn at
Hastings and Homestead, Florida, respectively (Ashley
1983). Unless otherwise noted, parasitoids were 24-48 hrs
old when used. The FAW host eggs were obtained from
female moths maintained in a growth chamber set at
26-27C, 70-75% RH and with a 14:10 LD photo regime. Host
eggs were seperated using the technique of Gross et al.
(1981). All eggs utilized in the experiments came from
the same egg mass to help insure host uniformity. A grid
was drawn on filter paper and individual eggs were placed
in the center of each square. In all experiments FAW eggs
were exposed initially to two female insularis inside a
circular plastic container (7 x 10 cm diam) with 2
screened vents (1.5 x 3.0 cm) and containing 4 cubes
(1.5 cm) of FAW diet (Leppla et al 1979). Eggs attcked
by two or more females and unparasitized eggs were de
stroyed. The grids were then cut into squares and sus
pended in a plastic container like those used for oviposi
tion by Cj_ i nsul ar i s until egg hatch. These containers
were kept inside an environmentally controlled cabinet set
at 27C, 70% RH, with a 14:10 LD photophase. When the FAW
larvae were 48 hrs old (all were second instars) they were

70
exposed to two female marginiventris for 24 hrs inside
a plastic container which was similar to the one used for
C. insularis The host larvae were then placed inside 30
ml plastic cups containing approximately 15 ml of diet.
These cups were sealed with paper lids and placed inside
the cabinet. The larvae remained in these cups and their
fate recorded. The control treatment for experiments 1
and 2 consisted of larvae exposed only to margini-
v e n t r i s .
Experiment l--Host Age
Forty second instar FAW larvae (head capsule width
0.4-0.5 mm) were transferred to an ovi pos itional unit at
12, 24, 36, 48, 60, 72, and 84 hrs of age and exposed to
two female marginiventris for 24 hrs. Each age was
replicated seven times.
Experiment 2--C. marginiventris Age
Cotesia marginiventris cocoons were held for adult
sclosion and mating inside a plastic container similar to
the one used for C. insularis oviposition. When C .
marginiventris parasitoids were 24, 48, 72, 96, and 108
hrs old, two females were exposed for 24 hrs with 40
second instar FAW larvae. Treatments were replicated
seven times.
Experiment 3--Temperature Effects
Thirty second instar FAW larvae were exposed to two
female margi ni ventr i s for 24 hrs. These experiments

71
were conducted in plastic containers like those used for
oviposition by C. insular is. After exposure to C.
marginiventris, larvae were placed individually in 30 ml
plastic cups and held at the following temperatures 19,
22, 25, 28 and 31C and RH 75-78% with a 14:10 LD photo
phase. Each treatment was replicated seven times. A
control treatment was run at 26C with host larvae exposed
only to insu1 aris. The cups were checked three times a
week and larval fate recorded.
In a second portion of this experiment larvae emerg
ing from eggs parasitized by C. insular is were exposed to
C. marginiventris when reaching the following host ages
(hrs) 6-10, 12-18, 24-30, 36-42 and 48-54. After exposure
to marginiventris larvae were individually placed into
30 ml cups and held at the temperatures cited above.
Treatments were replicated six times. The control
treatment was held at 26C and the RH ranged between
70-75%.
Experiment 4--Dissection of Mu ti parasitized Hosts
Host exposure to insu1 aris followed by exposure to
C. marginiventris or man i 1ae were performed as pre
viously described. The insu1 aris marginiventris
parasitized larvae were then placed inside a plastic
container for 3, 5, 7 or 9 days. The C. insularis M.
man i 1ae parasitized larvae were similarly held for

72
3, 6, 8, or 10 days. Twenty to thirty host larvae were
dissected at the end of each time period to determine the
condition of the competing parsito ids. In the nine day
treatment, C. marginiventris larvae had emerged before
dissections were done. However, since the host was still
alive it was dissected to determine the fate of the
immature in s u1 a ris The descriptions of Boling and
Pitre 1970) and Glogoza (1980) were used to recognize
larvae of marginiventris and i n s u 1 a r i s ,
respectively.
Results and Discussion
Thirty six hr old FAW larvae produced the highest
proportion of marginiventris and lowest proportion of
C. insularis (Table 8). Emergence of marginiventris
showed significant differences between 60 and 72 hrs and
24 and 36 hrs but there were not significant differences
between 12 and 24 hrs, and 72 and 84 hrs. There was not
significant difference in emergence of C_^ marginiventris
from hosts 36 hrs old and the control. Loke and Ashley
(1984) reported that highest rate of par as itization by C .
marginiventris of FAW occurred in 48 hr old larvae (second
instars). Kunnalaca and Mueller (1979) and Boling and
Pitre 1970) stated that females of marginiventris
produced the most progeny from 2 and 3 day old hosts.
Larvae less than 24 hrs did not produce as many

73
Table 8. Mean percentages at different host ages for
emergence of Chelonus insuaris (C.i.) Cotesia marginiventris
(C.m.) and adult fail armyworm and percent mortality of FAW
larvae due to (1) refused to feed on the diet, and (2) died
from unknown causes.a/
Host age b/
Percent
Parasitoid emergence
FAW mortality
Refused diet Unknown
(hr s)
C. i .
C.m.
FW
and diet
causes
12
25.5a
20.7a
45.2a
7.4a
1.1a
24
30.4a
15.7a
35.0b
12.2a
6.7ab
36
17.6a
44.2b
20.3c
13.2a
4.8ab
48
18.8a
40.lbc
16.2cd
17.4a
7.5 ab
60
31.7a
32.9c
14.3cd
14.1a
6.9 ab
72
52.7b
17.6a
14.8cd
11.7a
3.lab
84
45.9b
15.2a
10.6d
18.7a
9.6b
Control
_
45.2b
25.6b
15.8a
8.5b
a/ Treatments were replicated 7 times with 40 larvae per
treatment. Means followed by same letter for a given column
are not significantly different by Duncans Multiple Range
Test. (P = 0.05).

74
C. marginiventris as larvae between 36 and 48 hrs.
Chelonus insular is emerged more successfully than C.
marginiventris from larvae 12 and 24, and 72 and 84 hrs
old. Emergence of insu1 aris in early and latter ages
of the host was expected because in most cases of multi
parasitism the first species that attacked the host was
more successful than the second species (Doutt and De Bach
1964). The emergence pattern of i nsul ar i s showed
significant differences between larvae 60 and 72 hrs old.
This difference was probably a function of the larger
larvae becoming less suitable for par as itization by C.
marginiventris. The percentage of non-parasitized larvae
that became adults was greater except at 48 and 84 hrs
than those that died from unknown causes or starved to
death. There was a steady decrease in the percent larvae
that became FAW adults as host age increased. Substanti
ally more larvae died refusing to eat the diet and died
than from unknown causes. No significant differences were
found between host ages for larvae dying from refusing to
feed. This rejection of larval diet may be a source of
artificial selection encountered when an insect population
is placed under laboratory colonization (Boiler and
Chambers 1977). Ashley et al. (1982) reported that a
definite proportion of the FAW larval population refused
to feed on the artificial diet and that diet rejection was
not restricted to the early instars. Significant

75
differences were observed for larvae dying from unknown
causes between 12 and 24 hrs and 72 and 84 hrs of age.
Experiment 2--C. marginiventris Age
C. marginiventris adults which were 48 to 96 hrs old
produced more parasitoids than did those 24 or 108 hrs old
(Table 9). There were no significant differences in emer
gence of C^_ i n s u 1 a r i s at 24 and 108 hrs suggesting that C .
marginiventris was either too young or too old to start
egg laying. There were no significant differences between
the control and 48, 72 and 96 hrs which indicated that the
presence of a insu1 aris larva inside the host did not
reduce oviposition by margin iventris. Mean parasitiza-
tion for all ages illustrated that C. insularis had a
higher paras itization level (45%) than C. marginiventris
(41%). Wallner (1982) reported that when two parasitoids
attack the same host the parasitoid ovipositing in the
host first was more successful. Significant differences
were observed for emergence of i n s u 1 a r i s at all the
ages studied. However, highest emergence for C. insularis
occured at 24 and 108 hrs.
Deaths due to unknown causes ranged from approxi
mately 2.00 to 7.5 percent with the most mortality occur -
ing in the 108 hr treatment and control. A substantially
high proportion of larvae refused to eat the diet in 96,
108 hrs and control treatments.

76
Table 9. Mean percentages for emergence of Chelonus
in s u1 a ris (C.i.), Cotes i a marginiventr i s (C.m.) and adult FAW
and percent mortality for FAW-Tarvae due to (1) refused to feed
on the diet, (2) dietd from unknown causes, when age of C.m.
was changed a/
Percent FAW mortality
C.m. age b/
Parasitoid emregence
Refused diet
Unknown
(hr s)
C.i.
C.m.
F7\w
and diet
causes
24
58.5a
33.6a
2.9a
2.9a
2.0a
48
39.3b
52.5b
2.1a
3.2a
2.9 ab
72
42.4bc
47.4b
1.4a
4.9ab
3.9ab
96
30.6b
48.7b
2.1a
13.7c
5.4ab
108
54.5a
21.0c
5.9a
ll.Obc
7.7b
Control
_
55.0b
9.9a
14.8c
10.1b
a/ Treatments were replicated 7 times with 40 larvae per
treatment. Means followed by same letter for a given column
are not significantly different by Duncans Multiple Range
Test. (P = 0.05) .

77
Male progeny were always in greater abundance in C.
marginiventris regardless of parental age (Fig 4). Boling
and Pitre (1970) reported that mated C. marginiventris
generally produced with a sex ratio of 1:1. However, only
the 72 hr age group came close to this ratio. A very high
percentage of female C^_ i n s u 1 a r i s emerged in 96 hrs (Fig
5) and a very large percent of males emerged from the 108
hr group. Sex ratios in hymenopterous parasitoids may be
affected by suitable host abundance (Rechav 1978);
however, the reason for the abrupt change of sex ratio of
C. insularis in the 96 and 108 hr treatments was not
properly understood. Mitchell et al (1984) reported a
significant shift in the sex ratio of insu1 aris towards
males in the field between April and October.
Experiment 3--Temperature effects
Cotesia marginiventris emerged most successfully at
25C and it appeared that temperature affected the outcome
of competition (Table 10). Significant differences be
tween emergence rates were present for marginiventris
at all temperatures except 28 and 31C. There were no
significant differences at 22, 25, 31 and 28C for C.
insularis but significantly more emerged at 28 than at
25C. Less emergence was observed for both parasitoids at
low temperatures while optimum temperatures for C.
marginiventris and C. insularis were 25 and 31C,

FIG. 4. Progeny sex ratios for C. marqiniventris from
different aged C margi n i ventr i s~TC .m .) 'e'merg i~ng "from fall
armyworm larvae parasitized as eggs by C^_ i n su 1 ar i s .

00
90
80
70
60
50
40
30
20
10
0
24 48 72 96 108
AGE OF C. marginiventris (hrs)

FIG. 5. Progeny sex ratios for C. insularis (C.i.) from
different aged margi ni ventr i s~fC .~m erer g i ng from fall
armyworm larvae par asTtTzed as eggs by C. insularis.

100
90
80
70
60
50
40
30
20
10
0
24 48 72 96 108
AGE OF C.insularis (hrs)

C\J
CO
Table 10. Mean percentages (+ SE) when reared at several constant temperatures for emer
gence of Chelonus insularis (C.i.J* Cotes i a marginiventris (C.m.) and adult fall armyworm and
percentages for FAW~Tarvae failing to mature because they (1) refused to feed on diet and died,
(2) died from unknown causes, (3) still larvae at end of test, and (4) escaped from cup a/
Temperature
Percent
Parasitoid emergence
Refused diet
Unknown
Sti 1 1
(C)
C. i.
C.m.
FAW
and died
causes
alive
Escaped
19
10.3_+1.5 a
8.5 + 2.0 a
8.2+1.9 a
26.9 + 2.0a
15.5+ 3.4 a
30.5 + 3.0 a
3.3 + 1.4a
22
12.6+2.la
18.6+1.9b
16.1 + 1.8a
34.4 + 2.7b
3.9 + 1.2b
14.2+3.2b
2.3 + 1.2 a
25
13.6+2.6a
61.0+3.6 c
15.5 + 3.9 a
3.9+1.1d
6.0+1.8b
0.0+0.0 c
1.9+1.2ab
28
34.4+2.Ob
32.8+3.0d
15.2 +1.4a
9.3 + 1.7c
7.8+1.4b
0.5+4.9c
1.8+1.2ab
31
38.9+1.8b
29.8+3.3d
14.9 +3.0 a
9.6+0.9c
6.8+1.5b
0.0+_0.0 c
1.5+1.Oa
Control
35.5+1.4b
17.6+1.0 a
10.3 +0.8c
10.7+1.0b
1.5+l.lc
15.0+1.7c
a/ Treatments were replicated 7 times with 30 1 arvae/treatment. Means followed by same
letter for a given column was not significantly different by Duncans Multiple Range Test.
(P = 0.05).

83
respectively. Temperature did not affect emergence of FAW
adults. A significant number of larvae were found to be
alive at 19 and 22C. There was a significant difference
for larvae which died for unknown reasons at 19C and the
remaining temperatures.
The time required for development of marginiven-
tr i s from oviposition to emergence as adults ranged from
12-20 days and declined as temperature increased (Table
11). The longest emergence period for both parasitoids
occured at 19C. Kunnalaca and Mueller (1979) reported
the development time for C^_ margi ni ventr i s decreased
between 25 and 30C. The range of time required for C.
insu1aris from oviposition to adult emergence was from 26
to 35 days. Significant differences were observed between
19 and 22C for all parameters measured. An abnormally
high number of larvae was unable to pupate at 19C and
development of the FAW was slower at the lower
temperatures. Keller (1980) reported similar results.
Cotes i a marginiventris emerged more successfully than
C. insul ar i s when hosts were 12-18 hrs old at 19, 22, and
25C (Fig 6). Chelonus insularis was more successful at
host ages of 36-42 and 48-54 hrs under all temperatures
indicating that C^_ marginiventris either did not prefer
older hosts or was unable to develop in them successfully.
Cotesia marginiventris was more successful with hosts at

84
Table 11. Mean (+_ SE) emergence periods (days) when reared at
several constant temperatures for Cotes i a marginiventris (C.m.) and
Chelonus insularis (C.i.) and adult faTT'armyworm and percentages for
FW Farvae failing to mature because they (1) refused to feed on the
diet and died, (2) still larvae at end of test, a/
Percent
Temperature b/ Parasitoid emergence Refused diet Still
(C) TTT7 CTmT FAÂ¥ and died alive
19
35.5 + 1. la
20.1 + 1.2a
40.6 + 1.3a
3.5+1.0a
60.3+1.la
22
30.3+1.6b
18.6 +1.1b
34.5 +1.1b
6.9+1.5b
30.3+1.7b
25
26.3+1.5b
17.3+2. lb
28.9+2.1C
1.5+1.7b
0.00c
28
27 .5+1.9b
12.5+12.5b
19.5 +1.3d
2.7 + 1.7b
0.00c
a/ Treatments were replicated 7 times with 30 larvae/ treatment. Means
followed by same letter for a given column are not significantly
different by Duncans Multiple Range Test. (P = 0.05).

FIG. 6. Percentage emergence of C. marginiventris and C. insularis from fall
armyworm (FAW) larvae, par as i t i zecHon egg's ~b~y ~C. insularis"! FTftJ Tarvae were
exposed at different ages to marginiventris ancl then held at 19, 22, 25, 05
28C for development.

80
70
60
50
40
30
20
10
IU C. marginiventris
| C. insularis
6-10 12-18 24-3036-42 48-54
HOST AGE (hrs)

87
24-30 hrs old at 22 and 25C than was _C^_ i nsul ar i s. In.
general, marginiventris emerged from a higher propor
tion of younger hosts than did C. insu 1aris Hosts older
than 36 hrs produced more insu1 aris regardless of
temperature. Two possible explanations for this are as
follows: (1) marginiventris was a better competitor in
younger hosts and (2) either oviposit ion or successful
competition was reduced in older hosts larvae containing a
developing insularis .
Experiment 4--Dissection of Multi parasitised Hosts
Dissections of multiparasitized larvae showed no evi
dence of physical attack between parasitoids during the
first 5 days of host development (Table 12). However 7
days after par as itition 5 C insu1aris larvae had visible
melanized scars, while those of marginiventris were
unscared suggesting that marginiventris physically
attacked larvae of C. i ns u1aris. Vinson and Ables( 1980)
reported that larvae of insu1aris had visible evidence
of physical attack after 3 days in hosts parasitized by
the larval parasitoid Campole is sonorensis (Carlson). Six
days after parasitization by M. manilae, 5 dead M.
man i 1ae larvae were found in the hosts. This number of
dead larvae was higher at 8 and 10 days although there was
no visible evidence of physical attack. Vinson and
Iwantsch (1980) reported that M. croceipes mutilated the

88
Table 12. Fate of larval parasitoid C. marginiventris (C.m.) and M. manilae
(M.m.) in competition with the egg larval and parasitoid C. insularis as determined by
dissection of fall armyworm (FAW).
Competitor
species
No. of FAW
larvae
dissected
After exposure to
2nd parasitoid
when dissected
Fate of
C. insularis
Fate of
marginiventris
or
M. manilae
C.m.
26
3
23 larvae
3 no larvae
21 eggs
5 no larvae
26
5
22 larvae
4 no larvae
19 larvae
7 no larvae
20
7
5 injured larvae
15 larvae
4 injured larvae
16 larvae
23
9
/c
3 larvae^3
M.m.
30
3
28 larvae
2 no larvae
26 egge
3 shriveled egge
1 no egg
23
6
20 larvae
3 no larvae
5 dead larvae
12 healthy larvae
6 no larvae
20
8
20 larvae
7 dead
10 healthy larvae
3 no larvae
23
10
10 larvae
13 no larvae
10 dead larvae^
2 no larvae
/a Most of
C. marginivenris
have formed cocoons.
/b Some larvae emerging from host to form cocoon outside,
/c C. insularis larvae were not found.

89
C. insularis larvae by physical attack and killed them in
5 days.
In summary, C_^ marginiventris reproduced most suc
cessfully in 36 hr old FAW larvae. mar g i n i ventr i s
adults which were 48 to 96 hrs old produced the greatest
number of parasitoids. Cj_ i nsul ar i s and mar g i n i ventr i s
developed optimally at 31 and 25C. Cotesia marginiven
tr i s physically attacked developing C. i n s u 1 aris larva
inside the host. Dead man i 1ae larvae were found in
hosts mul t i par as i t i zed by C^_ i nsu 1 ar i s and man i 1 ae but
the cause of the death was unknown.

INTERSPECIFIC COMPETITION BETWEEN FALL ARMYWORM
PARASITOIDS CHELONUS IN SU LAR IS AND COTESIA
MAR6INIVENTRIS INSIDE FIELD CAGE AND PLOTS
Introduction
The fall armyworm (FAW), Spodoptera frugiperda, is
one of the few argicultural pests infesting many members
of the family Graminae in the United States. Each year
the FAW migrate from tropical and subtropical areas to
occupy a range which may extend northward to the Canadian
border and westward to Montana. Major losses in late
planted corn, sorghum and other susceptible crops are
experienced when high populations of FAW are present.
Mitchell (1979) estimated that if a severe outbreak
occurred, as in 1977, losses could exceed $500 million.
Ashley et al ( 1982 ) reported that up to 63% of first 4
instars are destroyes by parasitoids of FAW.
Interspecific competition among parasitoids within
the same host can have a significant impact on the host's
population dynamics. The occurence of interspecific
competition may result in the death of one or both
parasitoid (Salt 1961). Therefore, this competition may
be a vital component influencing the parasitoid guild
90

91
(Zwolfer 1970). Ashley (1979) recorded 53 species in 43
genera from 10 families having been reared from FAW
larvae. Two of the most frequently recovered parasitoids
in the FAW overwintering region in Southern Florida were,
Cotesia (Apanteles) marginiventris Cresson which develops
in FAW larvae, and Chelonus insularis (Cresson) which
parasitizes the egg emerges during the larval stages of
FAW (Ashley et al. 1982) .
We performed 4 experiments in the evaluation of
FAW/parasitoid interactions. The objective of the first
experiment was to study the functional response of C.
marginiventris when exposed to different densities of FAW
previously parasitized by C. insularis In the second
experiment we examined the functional response of C.
marginiventris to different levels of mu 11iparas it i zed
host densities inside the laboratory. In the third
experiment data were obtained on the ovipositional
preferences of these two parasitoids at different FAW
densities inside field cages. The fourth experiment
determined the impact of C^ insularis and C_^ margini
ventris on FAW larvae found in different regions of the
plant and the surrounding environment.

92
Materials and Methods
Host and Parasitoid Colony Maintenance
A colony of the FAW was maintained at 23-25C, 74-78%
RH and under a 14:10 LD photoperiod. Adults were fed with
10% sucrose solution. Adult FAW oviposition occurred on
paper towels that were subsequently cut into sections each
having a single egg mass of 50-60 eggs. These sections
were placed in circular plastic cups ( 7 x 10 cm diam)
having two screened vents (1.5 x 3.0 cm). These cups were
used as ovipositional units and contained 4 cubes (1.5 cm)
\
of pinto bean diet (Leppla et al 1979 ).
Adult C^_ i ns u 1 ar i s and mar g i n i ventr i s were held in
plexiglasss cages ( 50 x 50 x 24 cms) at 26C, 60-65% RH
and 14:10 LD photo regime. Undiluted honey and water were
provided to adult parsito ids. Unless otherwise noted,
parasitoids were 1-4 days old when used for
experimentation.
Experimental Procedures for Host Paras itization
Individual FAW eggs were isolated using the technique
described by Gross et al. (1981). All eggs in each repli
cate, came from the same egg mass. A grid was drawn on
filter paper and individual eggs were placed in the center
of each square, inside a plastic petri dish (100 x 15 cm).
The eggs were then exposed to two female C_^ i nsul ar i s and
any that were attacked more than once were discarded.
After parasitization, eggs were kept in the plastic cups,

93
with FAW diet inside an incubator at 26+lC, 75-80% RH and
24:00 LD photo regime, until the larvae emerged. When
these larvae reached the second instar larvae (head
capsule width 0.5-0.6 mm) they were exposed to two, C.
marginiventris females in plastic petri dishes (100 x 15
cm) for 24 hrs. The larvae were individually placed in 30
ml plastic cups containing approximately 15 ml of FAW diet.
Corn variety (Pioneer x 304C) was planted at
Homestead, Florida in inside field cage and in study
plots. When the FAW larvae were second instars, female C.
marginiventris were released into field cages and study
plots each day between 1600 and 1800 hrs until the con
clusion of the release period. Corn plants adjacent to
the study plots were also sampled. Plants were individ
ually taken apart and examined for FAW larvae. Head
capsule widths were measured to determine larval instars
(Ashley et al 1982). Each larva was placed in a 30 ml
plastic cup containing FAW diet. The cups were checked
until the fate of each larva and the sex of each adult
that emerged were recorded.
Experiment l--Host Density. The FAW eggs were
exposed to i nsul ar i s at densities of 1, 2, 4, 8, 16,
32, and 64 in a plastic container. Second instar larvae
were placed in the same container with FAW diet and were
exposed to two C_^ marginiventris females at the same
densities for 24 hrs. Treatments containing 1 larvae/cup

94
and 2 larvae/cup were replicated 10 times and the
remaining treatments were replicated 7 times. FAW larvae
were exposed to Cj_ marg i n i ventr i s at 24, 48 72 and 96 hrs
pf age. The larvae were transferred subsequently to 30 ml
cups and their fate determined.
Experiment 2--Field Cages
Three field cages ( 246 x 155 x 115 cm) were conduct
ed from metal pipe frames and screened with woven cloth
netting so that insect activity could be observed. Each
cage contained 20 corn plants, with 91.4 cm between rows
and 8 inches between plants. Methonyl was applied at the
rate of 10 ml/3.79 L 7 days before the introduction of
host eggs. Four randomly selected plants were pinned to
one, two or three paper sections (1.54 x 5.08 CM) contain
ing 50-6 FAW eggs. The corn plants were approximately 4
weeks old and 75-85 mm in height and the egg masses were
pinned to the lower surfaces of the upper leaves within
20.3 cm of the growing terminal. Twenty female C.
insu1aris were released into each cage just prior to
sunset followed by release of 20 marginiventris females
on each of the next 3 days. The experiment was repeated
3 times over a 4 month period with 3 cages per replicate.
Plants with paper sections were sampled 3 days after the
final introduction of C. marginiventris and the remaining
plants in the perimeter area were allowed to grow for 2
weeks prior to sampling.

95
Experiment 3--Fie1d Plots
Corn was planted in six adjacent plots, (50 x 11 m)
in the center of a field previously used to produce field
corn. Each plot was disked twice before planting. Seven
to ten days after disking corn seeds were planted at a
depth of 3.0 cm and spaced 91.4 x 243.8 cm (between rows
and plants). The plots were irrigated weekly and two week
after planting ammonium nitrate fertilizer (33.5% N) was
broadcast over each plot at a rate of approximately 165
kg/ha. Four to five weeks after planting, plants selected
at random were pinned with a paper section having approxi
mately 50-60 FAW eggs at the following locations: (US)
upper surface of leaves (within 20.3 cm from terminal)
(oriented less than 45 from stalk), (LS) lower surface of
leaves (oriented more than 45 from the stalks,) (ST)
stalk (central stem with a pithy core), (GS) ground
(within 5.08 cm from the plant), (SH) in between stalk and
1 eaf sheath (Fig 16).
The eggs were not washed. The five treatments were
replicated 6 times within the plot. A control plot was
left with FAW eggs pinned into the whorl region. Starting
from the first day after egg pinning, 480 insularis
females were introduced for 3 consective days. On the 4th
day 498 female marginiventris were released. The
complete experiment with 6 plots (5 with treatments +
control) was replicated 3 times over a 4 month period.

96
A sample consisted of harvesting all the plants in a 10-m
area.
Comparisons were made between parasitoid release
plots and non release plots in terms of FAW larval damage
to whorl (leaves surrounding the furl with blades
partially extended and sheath concealed) and furl (leaves
surrounding a central roll) and stalk. The plants with
recongnizab1e FAW feeding in whorl, furl or stalk with FAW
larvae present were defined as damaged.
Results and Discussion
Experiment l--Host Density
The mean number of marginiventris that emerged
from densities of 64 and 32 larvae produced patterns that
were almost mirror images of each other (Fig 7). A den
sity of 64 larvae/cup represented the highest mean progeny
production at 48 hrs. Kunnalaca and Mueller (1979)
reported that marginiventris parasitized between 31 and
110 hosts each day. The greatest difference in progeny
densities occurred between the 64 larvae/cup density and
the remaining densities.
More super par as itism occured at 4 and 8 larvae than
at 32 larvae suggesting that marginiventris exposed to
lower densities attacked many hosts more than once. How
ever at higher densities only one parasitoid emerged per
host larvae which showed that C. marginiventris avoided

FIG. 7. Mean
host densities
insularis.
progeny production by C. marginiventris at 7
from eggs previously par as itized by C.

20
15
10
5
0
FAW AGE (hrs)
24

99
superparasitism at high densities (Table 13). The longev
ity of emerging m a r gi niv e n t ris was greater at lower
densities than at higher densities. Substantially more
larvae were found dead at higher than at lower parasitoid
densities, probably due to cannibalism. (Ashley, Pers.
Comm. 1985).
A similar trend of progeny production was observed
for C. insularis (Fig 8). The 64 larvae/cup treatment had
produced the highest number of progeny. The number of
progeny were related to the parasitoid density. As the
number of larvae per treatment was increased a consequent
increase in progeny production was observed. This is a
well recognized characteristic of many parasitic
hymenoptera (Legner 1969). C. insularis was more success
ful in progeny production than margin i ventris at higher
densities. A number of events may have been responsible
for the apparent success of C. insularis. The females
spent less time examining eggs before ovipositing at the
higher density. Also the female insularis oviposited
more eggs at higher host density than at lower density.
C. marginiventris may have detected hosts previously
parasitized by C. insularis by some external stimuli and
reduced oviposition. C. insularis received unparasitized
eggs for oviposition. The reduction of oviposition by C.
marginiventris may have helped for developing C. insularis
larvae to emerge without a competition.

Table 13. Means (j^SE) numbers of FAW hosts attacked at 7 densities by marginiventris.
Host density3
Mean numbers of
1
2
4
8
16
32
64
Hosts super-
parasitized
0.5+ 0.1
1.1+0.01
1.3+0.2
1.3+0.02
1.1 + 1 .2
1.0+0.02
1.2+0.05
Longevity of
progeny
6.1+0.7
5.6 + 0.7
5.1+ 0.8
7.4 + 0.1
4.1 +1 3
4.3+1.6
4.6 +1 7
Survival of
1 arv ae
1 + 0.0
2 + 0.0
3.9 + 0.1
8.0+.07
15.3+0.7
29.7+07
54.2+_2 .1
a/ Seven replications at each host density,
b/ Significant by student "t" test at P=0.05 level.

FIG. 8. Mean progeny production by insularis at 7
host densities and parasitized by m a r g i ni v e n t r i s .

50
40
30
20
10
0
FAW AGE (hrs)
24
48

103
The sex ratio of marginiventris progeny favored
females at densities of 2 and 4 larvae (Fig 9). The C.
insu1aris males outnumbered females at all densities
except at 4 eggs/larvae where 1:1 ratio was obtained (Fig
10). The presence of more females at low densities may be
seen as a mechanism that ensures the presence of a minimum
number of males to fertilize all the females. Such
mechanisms have been reported in other parsito ids in
which mated females are functionally virgin for a certain
period of time after mating (Mackauer 1976).
Experiment 2--Fie1d Cages
Che!onus insu 1aris emerged most frequently in treat
ments having 1 or 2 paper sections while marginiventris
was the major parasitoid in the 3 paper section treatment
during the first and second test periods (Fig 5). In the
last test period no definite emergence patterns were
observed. The decrease in emergence of C. insu1 aris in 3
paper section treatment indicated that C. marginiventris
was a better competitor in crowded host conditions.
Wiseman et al. (1983) reported that FAW larvae often moved
from infested plants onto surrouding border plants during
the 3 to 5 days after infestation. This movement may have
aided marginiventris in locating hosts. insularis
emerged more successfully in 1 and 2 paper sections and
appeared to search the portions of corn plants where most
FAW eggs were deposited. However, Loke and Ashley (1984)

FIG. 9. Sex ratio of _C^_ marginiventris from 7 host
densities.

MEAN NUMBER OF ADULTS
FAW LARVAL DENSITY

FIG. 10. Sex ratio of C. insularis from 7 host densities.

MEAN NUMBER OF ADULTS
FAW LARVAL DENSITY

FIG. 11. Percent par as itization by C. insular is and C.
margi ni ventr i s from FAW larvae recovered TrfsT3efrom TTeld
cage during 3 test perids. Vertical bars within a test
period from lest to right indicate treatments 1, 2, and 3
paper sections.

90
70
50
30
10
Ip IP
insularis
marginiventris
2
2 3
- May 27
June 29-
TEST PERIOD
3

110
reported that _C_;_ marginiventris was a day adapted species
and has been observed searching for hosts in bright
sunlight in corn fields.
The release of two parsito ids inside the field cages
resulted in an overall par as itization rate of 60.0% for C.
i nsul ar i s and 37.4% for _C^_ marginiventris. This high rate
of parasitization was similar to the field results
reported by Mitchell et al. (1984) where insularis
Terne!ucha difficulis Dasch. and marginiventris para
sitized FAW larvae at rates of 82, 10, and 2%
respectively. This high rate of parasitization by C.
insularis in field cages and the field (Mitchell et al.
1984) indicated that C. insularis was the principal
parsito id of FAW in southern Florida.
Seventy, forty and thirty-nine percent of first
instars were parasitized in treatments having 1, 2, and 3
paper sections respectively (Fig 12). Thirty percent of
second instars were parasitized in 2 paper section treat
ment. These results were similar to those reported by
Mitchell et al. (1984) where 77% of the first two instars
were parasitized. Ashley et al ( 1982) reported that the
percent parasitization of the first 4 instars of FAW
remined constant and then decreased substantially for 5th
and 6th instars. Reasons for the reduction in percent
parasitization in second instars was not properly under
stood. Mitchell et al. (1984) reported the decrease of

FIG. 12. Mean percent parasitized FAW instars in
treatments 1, 2, and 3 paper sections inside field cage.

80
60
40
20
First instar
I I Second instar
Third instar
E3 Fourth and fifth instar
v.
2
i
I 2 3
PAPER SECTIONS

113
the proportion of first instar larvae was probably a
function of crop maturation as well as the larval popula
tion reaching a more stable age distribution. The
greatest impact on FAW in all 3 treatments occured in
first instars. This was similar to that reported by
Vickery (1929) where first instars of FAW were preferred
by marginiventris since they can be stung before
dispersing from the egg mass. Thirty-five percent of
third instars were parasitized in comparison to 15% of
second instars in treatment 3.
The FAW larve that did not yield parasitoids produced
FAW adults, starved to death because they did not feed on
the diet or died from unknown causes. The proportion of
nonparasitized larvae that yielded FAW adults was always
greater than starved or died from unknown causes (Fig 13).
Parasitoid sex ratios favored females in treatments having
3 egg masses per paper section (Table 14). Sex ratio
regulation of marginiventris could be due to eigher
selective fertilization of eggs or differential mortality
of larvae depending on host density. Selective fertili
zation by marginiventis female in low host densities
may be based on female detection of previously parasitized
hosts. Many hymenopteran parasitoids can distinguish
between parasitized and non-par as itized hosts (Wylie 1965)
and fertilize a smaller percentage of eggs on parasitized
hosts (Flanders 1939). If the female C_^ marginiventris

FIG. 13. Mean percent of FAW larvae that became a)
adults, b) starved and died c) died from unknown reasons
in treatments 1, 2, and 3 paper sections.

75
50
25
0
Became adults
Starved and died
Died from unknown reasons
J L
1
2
PAPER SECTIONS
3

116
Table 14. Sex ratio + SE ( q : <5* ) for C. marginiven-
tris (C.m.) and C. insularTs (C.i.) from FAWlarvae parasi
tized inside a field cage.
Egg mass
size
C.m. C.i.
Sex ratio (9:6) Sex ratio ($:?)
1.00:5.5+0.9 1.90:1.00+1.6
1.00:2.00+0.7 1.00:1.70+0.3
<50 (1 Paper section)
>50 <120 (2 . )
>120 <180 (3 . )
3.5:1.00+1.3
2.9:1.00+0.9

117
was not capable of controlling fertilization of its eggs
then high percent of males in low densities could be due
to differential mortality resulting from competition among
larvae for available food within the host. Local
increases in the ratio of parasitoids to hosts can produce
a change of sex ratio in field population of Hymenoptera
(Charnov et al. 1977 ) .
Experiment 3--Field Plots
C. insularis emerged as the predominant parasitoid
(Fig 14) on the upper (58.5%), and lower (71%) leaf sur
faces, between stalks and leaf sheaths (40.5%) and the
control (80.5%). A higher percentage of marginiventris
than C. insu1 aris emerged from the treatments placed on
ground (15.5%) and stalk (35.5%). Teme!ucha difficulis
Dasch., Meteor us autographae Muesebeck Rogas 1aphygmae
Viereck and several unidentified species accounted for the
remaining parasitoids. Mitchell et al ( 1984 ) and Ashley
et al. (1982) reported that in order to abundance C.
insu1 aris. T. difficilis and marginiventris were the
principal parasitoids collected from study plots at
Homestead. Therefore, releasing C. marginiventris
increased its par as itization level above that of T.
difficilis. The percent par as itization was higher from
the lower surface of leaves in comparison to the control.
Morrill and Greene (1973) reported that in corn the
highest number of FAW larvae were found in whorls.

FIG. 14. Percentage par as itization for principal
parasitisoid species recovered from FAW larvae from (US)
upper surface of whorl, (LS) lower surface of whorl, (GR)
ground, (SH) between stalks and leaf sheath, (ST) stalk
and (WH) control in corn.

80
70
60
50
40
30
20
10
Chelonus insularis
R Cotesia marqiniventris
H Other parasitoids
US LS GR SH ST
PLOTS

120
Our results, indicated that eggs pinned to the lower
surface of leaves in whorls had highest percent parasiti-
zation. This suggested that FAW parasitoids search pi ant
regions where the highest number of FAW larvae are found.
Since the whorl is the highest part of the plant, first or
second stage larvae would move up into this area (Greene
and Morrill 1970). This may have accounted for the low
par as itization rates observed in hosts collected near the
ground and on the stalk. Both, C_^ marginiventris and
insularis were observed to be highly mobile and rapidly
dispersed away from the release site. Therefore, releases
could be made at several points in a field and the parasi-
toids would naturally disperse throughout the field. The
preference of C^_ insularis for FAW eggs on the under
surface of corn leaves in early vegetative stages agreed
with the findings of Waddill (1977) and Keller (1980) who
reported this site as preferred location for oviposit ion
by FAW females.
The sex ratio of emerging C. marginiventris favored
males in hosts collected from the upper surfaces (55%)
lower surfaces (60%) of the whorl, stalks (60%), near
ground level (53%), and control (70%) (Fig 15). Larvae
collected between stalks and leaf sheaths yielded more
female parsito ids (61%). Males predominated in emergence
of C. insularis in the treatments of upper surface, lower
surface, and between stalks, and leaf sheaths.

FIG. 15. Sex ratio for C_^ marg i n i ventr i s
recovered from FAW larvae from (US) upper
whorl, (LS) lower surface of whorl, (GR)
between stalks and leaf sheath (ST) stalk
in corn.
and insularis
surface of
ground, (SH)
and (WH) control

80
§ C, marqiniventris males
I C, marqiniventris females
ED C. insularis males
M C. insularis females
cn
Q
70
O
\
CO
60
<
cr
<
50
Q_
1
40
LJ
O
30
cr
LU
CL
20
10
US LS GR SH
WH
LOCATION ON PLANT

123
Significantly more medium sized larvae (head capsule
width = 0.8-1.2mm) were found between stalks and leaf
sheaths and lower surfaces of the whorl (Table 15).
Initially, there were more small than large larvae feeding
under the lower surface and upper surface but this trend
was gradually changed with more medium sized larvae found
between stalks and leaf sheaths. The greatest difference
between small and large larvae was found between upper
leaf surface with small sized larvae. Ashley et al.
(1980) reported that FAW larval abundance decreased on
corn plant upper surface than lower surface and this
reduced abundance may be indicative of preferred feeding
locations. Our experiment showed that FAW larvae prefer
feeding locations such as between stalks and leaf sheaths,
and lower surface. Food quality, changes with feeding
location and may alter or influence larval development in
FAW (Keller 1980). Feeding inside the leaf sheaths and
the lower surface of whorls may be a form of protection
from natural enemies. Very few large larvae were
recovered in all 5 treatments.
The damage to upper leaves in the whorl was signifi
cantly greater in nonparasitoid release plots than in
parasitoid release plots (Table 16). These results
suggest that differences in degree of damage between
parasitoid release and non release plots were related to
the impact of the parasitoids. Significant differences

Table 15. Mean percentage of small (0.2-0.7), medium (0.8-1.2), large (1.3-2.4) head capsule
widthsfrom FAW larvae collected from upper surface (US), lower surface (LS), ground (GR), between
stalk and leaf sheath (SH) and stalk (ST) in corn, a/
Percent
Col lection
Date Small Medium Large
US
LS
GR
SH
ST
US
LS
GR
SH
ST
US
LS
GR
SH
ST
May 14, 1983
15.6a
20.5a
2.0c
10.5b
0.5c
11.0b
15.0b
0.0c
15.0b
0.5c
0.0c
1.0c
0.0c
2.0c
0.0c
May 27, 1983
17.0a
10.5b
0.0c
15.0ab
0.0c
10.0b
17.0a
0.0c
12.0b
0.0c
3.0c
2.0c
0.0c
10.0b
0.0c
June 14, 1983
8.0b
10.5b
0.0c
25.5a
0.0c
8.0b
12.0b
0.0c
30.0a
0.0c
2.0c
1.0c
0.0c
3.0c
0.0c
June 28, 1983
10.0b
12.0b
0.0c
20.0a
0.0c
5.0c
10.0b
O.Od
21.0a
O.Od
5.0c
4.5cd
O.Od
12.0b
O.Od
Aug. 14, 1983
3.0cd
10.8b
O.Od
31.0a
O.Od
14.5b
3.0d
O.Od
14.0b
O.Od
5.0c
4.0cd
O.Od
12.0b
O.Od
Aug. 28, 1983
3.5c
12.5b
O.Od
29.0a
O.Od
3.0d
8.5cd
O.Od
19.0b
O.Od
6.0d
8.6cd
O.Od
O.Od
O.Od
a/ Means in the same row followed by same letter were not significantly different by Duncans
Multiple Range Test (5% level).

125
Table 16. FAW damaqe to different regions of corn in plots
where C. insularis (C.i.) and C. marginiventris (C.m.) were
released.
% Damage to Corn by FAW a/
Date of
Observations
C.m. and C.
released
i.
No
parasi toids
released
Upper
Surface
Lower
Surface
Stalk
Upper
Surface
Lower
Surface
Stalk
May 8
19.6b
12.9c
O.ld
30.5a
13.4c
O.Od
May 12
13.5b
9.7c
O.Od
43.6a
10.1c
O.Od
May 16
15.5a
5.7b
0.0c
15.7a
5.2b
0.0c
June 9
19.7b
30.3a
0.0c
18.9b
28.5a
0.0c
June 13
14.5a
13.5a
0.0b
16.7a
13.5a
0.0b
June 17
30.5b
9.5c
0.2d
53.5a
28.5b
O.Od
July 11
24.3a
14.7b
0.5c
22.5a
15.6b
0.3c
July 15
19.7a
19.5a
0.0b
19.3a
21.5a
0.0b
July 19
33.7a
19.6b
0.0c
34.5a
19.1b
0.0c
a/ Treatments in the same row followed by the same letter were
not significantly different by Duncans Multiple Range Test.

126
were observed on May 8th, 12th, and June 17th in terms of
damage to upper leaves in parasitoid release and non
release plots. Damage to lower leaves also showed
significant differences between these two plots on June
17th. The damage to stalks were negligible in both plots.
Keller (1980) reported that mature leaves are a qualita
tively better food source for FAW than developing leaves.
However, FAW larvae appar to prefer developing leaves
under field conditions (Morrill and Greene 1973). Since
feeding on mature leaves exposes FAW larvae to natural
enemies and climatic changes, concealed feeding in whorls
may have survival advantage. This trend was observed on
all observatio dates except June 9, July 15, in
non-parasitoid release plots and June 9th, in parasitoid
released plots.
Cotesia marginiventris and insularis produced the
most progeny at a host density of 64 eggs/larvae per cup.
Longevity of marginiventris was greatest at a host
density of 8 larvae/cup. Chelonus insularis had an
emergence of 60% in field cages but C_^ marg i n i ventr i s was
a better competitor at host densities above 2 egg massses
per paper section. Seventy percent of all hosts in the
first instars were parasitized. Chelonus insular is
emerged 72% and 58.5% of the time from parasitized larvae
on the lower and upper surfaced of corn leaves,
respectively.

127
Significantly more medium sized larvae were found between
the stalk and the leaf sheath, on the lower surface of the
whorl than in the other areas of the plant. The damage to
upper leaves ws significantly greater in non-parasitized
release plots than in parasitoid released plots.

FIG. 16. Illustration of exhibit the placement of egg
containing paper sections in different regions of corn.
US Upper surface of whorl
LS Lower surface of whorl
GR Ground
SH Between stalk and leaf sheath
ST Stalk
WH Whorl region


GENERAL SUMMARY AND DISCUSSION
Many factors influence the suitability of a potential
insect host for parasitoid growth and development. For
example, a host may be unsuited, if already parasitized or
at stage of development inappropriate for parasitization.
In the case of solitary parasitoids, prior parasitization
of the host by another parasitoid of either the same or
another species can result in a host not being suitable.
Thus, if two solitary parasitoids occur in the same host,
one individual usually destroys the other. Whether the
competition involves physical attack, secretion of toxins,
physiological suppression, or selective starvation, the
outcome is largely dependent upon the species involved,
the parasitization sequence, and the length of the inter
val between attacks. A myriad of parasitoids attack FAW
(Ashley 1979) and their interrelationships influence the
population dynamics of the pest. At present, the basic
biological strategy control for FAW is to introduce as
many suitable natural enemies as possible in the hope that
the "best" species or combination of species will prevail.
In this regard, available theoretical and empirical
evidence indicated that the level of biological control
usually increases as the number of natural enemy species
increases (Huffaker et al 1971). Results reported here
130

131
showed that interspecific competition occurred between
exotic and indigenous FAW natural enemies. My data and
that of Ashley et al. (1982) and Mitchell et al. (1984)
indicated that is is difficult to establish additional
natural enemy species in the overwintering range of FAW in
South Florida, because of the dominance of C. insu 1aris.
Host age preference, developmental period and longe
vity of NL man i 1 ae, a larval parasitoid of Spodopter a spp,
imported from Thailand, were studied. First (24-48) and
second (49-72 hrs) age group of FAW larvae found to be
most suitable for parasitoid propagation. The develop
mental period ranged from 13-18 days. Male and female
longevity was about 6-7 days. Paras itization rates of
3.5-30.1% by M^ mani1ae in FAW larvae were observed. This
biological information will be useful in the event that M.
man i 1ae is reared for inundative or inoculative releases
in overwintering range of FAW.
Competition within FAW larvae by C. marginiventris,
M. man i 1 ae and i nsul ar i s revealed that C_^ marg i n i ven -
tris was a superior competitor compared to C. insularis
but i n s u 1 a r i s was superior to ^ man i 1 ae. Subsequent
par as i t i zat i on by either marginiventris or man i 1 ae
of larvae exposed to insu1 aris as eggs did not
result in additive host mortality. Description and
analysis of host finding behavior by C. marginiventris in
FAW larvae previously parasitized by C. insularis showed

132
that this behavior consisted of 9 basic steps. These
results supported the conclusion of Loke and Ashley (1984)
that host finding behavior of marginiventris is
influenced by chemicals from both plant and host. The
percentage par as itization by marginiventris showed more
than two fold increase in corn when compared to the
increase in sorghum, Bermudagrass, and itch grass. M.
man i 1ae females significantly altered their behavior when
hosts had already been parasitized by C in s u1aris .
C. insu1aris was the major parasitoid when FAW eggs
were glued to upper surfaces of corn leaves (58.5%) lower
surfaces (71%) and between stalks and leaf sheaths
(40.5%). A higher percentage of marginiventris emerged
from the treatments in the ground (15.5%) or the stalks
(35.5%). Significant differences were observed with
respect to damage to upper leaves in whorls of corn in
parasitoid release plots than non parasitoid release plots
and this was related to the impact of parasitoids on FAW
larvae.
Additional work is needed in several areas and new
avenues for research opened up as a result of information
gathered from studies reported here. The superiority of
one parasitoid over another in multiple parasitization
results in the waste of some parasitoids. How this
affects the comparative field efficiencies of all 3
parasitoids studied, as well as the population dynamics of

133
the FAW, should be investigated. The predominant native
parasito id, C. in s u1aris, should be investigated to
determine other characteristics important in controlling
its impact on FAW larval populations. These include such
characteristics as spacial distribution, temporal
synchronization and reproductive rates. One of the major
areas requiring further research is the mechanism of
dominance in competition between parasitoids. I found
evidence of physical attack by marginiventris on
developing insularis larvae.
The potential impact of interspecific competition on
FAW biological control needs further research and should
include studies on: (1) competition studies between C.
insu1aris and T^ difficilis, since these two parasitoids
are the principal species in the overwintering range of
the FAW; (2) the effects of interspecific competition on
parasitoid population densities; (3) more detailed studies
on the developmental biologies of C. insularis, C.
marginiventris and T_. difficilis in FAW larvae; and (4)
more detailed life table analyses of FAW larval popula
tions. In addition, before more exotic parasitoids are
introduced, it should be determined in controlled
laboratory experiments if they can successfully compete
within FAW larvae, with the native species.

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Netherlands. pp. 405-18.

BIOGRAPHICAL SKETCH
Rohan Harshalal Sarathchandra Rajapakse is the only
son of Mr. and Mr. Don Wilson Rajapakse of Wellawatte,
Colombo, Sri Lanka. Rohan Rajapakse received his primary
and secondary education at Isipathana Maha Vidyalaya,
Colombo. He entered the Faculty of Agriculture of the
University of Peradeniya in 1972, and graduated with
second class honors in 1976. He then worked briefly as an
assistant lecturer and joined the Post Graduate Institute
of Agriculture (PGIA), University of Peradeniya, in 1977.
Between the years 1976 and 1977, he also worked as a
research assisant in entomology in Sri Lanka Cashew
Corporation. He received his masters degree in entomology
from PGIA, University of Peradeniya, in 1978, and joined
the permanent staff of the Faculty of Agriculture,
University of Ruhuna as an assistant lecturer in 1978. He
taught entomology and plant pathology for undergraduate
students at the University of Ruhuna until 1981. He
arrived in Gainesville, Florida, in December of 1981, to
pursue his studies leading to Ph.D. degree at the
Department of Entomology and Nematology at the University
of Florida.
146

147
Rohan Rajapakse is a member of the Entomological
Society of America, Florida Entomological Society and Sri
Lanka Association of Advancement of Science. He has two
sisters, Damayanthie (a high school teacher) and, Sandhya
(an account ant).

I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.
Dr. Van H. Wadd fTT, Chairman
Professor of Entomology and
Nemato1ogy
I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.
lomas K. Ashley, Lo-Ufairman
Associate Professor of Enromology
and Nematology
I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.
Dr. \john R. Strayer
Prcof^ssor and Entomology wid
N eVat o 1 o g y

I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.
Professor of Plant Pathology
This dissertation was submitted to the Graduate Faculty
of the College of Agriculture and to the Graduate School
and was accepted as partial fulfillment of the
requirements for the degree of Doctor of Philosophy.
August, 1985
Dean



MEAN NUMBER OF ADULTS
FAW LARVAL DENSITY


27
the development of any successor (Van den Bosch and
Haramoto 1953, Johnson 1959) or by the postulated
secretion of a toxic substance which kills the opponent
(Thompson and Parker 1930).
Competitive exclusion by previously introduced
parsito ids has been viewed as one of the factors that
explains the failure of introduced natural enemies in
classical biological control to become established (Ehler
and Hall 1982). The competitive exclusion hypothesis has
been subject of considerable debate in the literature.
Turnbull (1967) favored the competitive exclusion hypo
thesis while Van den Bosch (1968) rejected it. However,
Ehler and Hall (1982) presented empirical evidence in
support of competitive exclusion and stated that this
could possibly lead to the extinction of an effective
natural enemy. In fact, Force (1974) showed that a very
effective natural enemy may in fact be an inferior com-
petitior. Thus Ehler and Hall (1982) suggested that (1)
simultaneous release of several species of natural enemies
should be avoided due to interspecific competition between
them that may lead to a lower establishment rate and (2)
extra care should be taken in establishing species where
incumbent species of natural enemies exist. However Moon
(1980) reported that while the principle of competitive
exclusion may be simple and attractive, it may not
adequately apply to the heterogenous real world.


Abstract of Dissertation Presented to the
Graduate School of the University of Florida
in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosophy
INTERSPECIFIC COMPETITION OF FALL ARMYWORM
SPODOPTERA FRUGIPERDA (J.E. SMITH) PARASITOIDS,
CHELONUS INSULAR IS (CRESSON), COTESIA
MfflnnrrrvrNtitit tcrtsson) and miutoputtis
mA'nTl'aT a'Shm'ad (hymenoptera: braconTd'aTT
By
Rohan Harshalal Sarathchandra Rajapakse
August, 1985
Chairman: Dr. Van H. Waddill
Co-Chairman: Dr. Thomas R. Ashley
Major Department: Entomology and Nematology
Interspecific competition within fall armyworm (FAW),
Spodoptera Frugiperda (J.E. Smith), larvae by the larval
parasitoids Cotesi a (=Apanteles) marginiventris Cresson
and Mic r o p1 itis man i 1ae Ashmead and the egg-larval
parasitoid Chelonus insular is Cresson was studied.
Experiments conducted with 4 larval age groups (1,
24-48 h; 2, 49-72 h; 3, 73-96 h; 4, 97-130 h) of the fall
armyworm revealed that the first 2 age groups were most
suitable for the development of _M. m a n i 1 a e The develop
mental period of M^ mani 1 ae ranged between 13-18 days.
Highest par as itization was observed for M. man i 1ae when 2
females were exposed to 20 hosts for 30 min at 26+lC.
x


93
with FAW diet inside an incubator at 26+lC, 75-80% RH and
24:00 LD photo regime, until the larvae emerged. When
these larvae reached the second instar larvae (head
capsule width 0.5-0.6 mm) they were exposed to two, C.
marginiventris females in plastic petri dishes (100 x 15
cm) for 24 hrs. The larvae were individually placed in 30
ml plastic cups containing approximately 15 ml of FAW diet.
Corn variety (Pioneer x 304C) was planted at
Homestead, Florida in inside field cage and in study
plots. When the FAW larvae were second instars, female C.
marginiventris were released into field cages and study
plots each day between 1600 and 1800 hrs until the con
clusion of the release period. Corn plants adjacent to
the study plots were also sampled. Plants were individ
ually taken apart and examined for FAW larvae. Head
capsule widths were measured to determine larval instars
(Ashley et al 1982). Each larva was placed in a 30 ml
plastic cup containing FAW diet. The cups were checked
until the fate of each larva and the sex of each adult
that emerged were recorded.
Experiment l--Host Density. The FAW eggs were
exposed to i nsul ar i s at densities of 1, 2, 4, 8, 16,
32, and 64 in a plastic container. Second instar larvae
were placed in the same container with FAW diet and were
exposed to two C_^ marginiventris females at the same
densities for 24 hrs. Treatments containing 1 larvae/cup


FIG. 3. Percentage par as itization by C. marginiventris of
fall armyworm larvae already exposed as eggs to "C.
in s u1 a ris Larvae were randomly placed on four pTant
Tpecied he Id in wire cages within a greenhouse.


53
Table 4. Mean percentages for emergence of Chelonus insularis
(Ci), M i c r o p 1 i t i s mani 1 ae (Mm), C o t e s i a marg i n i venir i s ( CT] cl a3" u 11
FAW, and per cent ages "for FAW 1 ar v ae fafling to mature because they
refused to feed on the diet, for dying from unknown causes, and for
failing to pupate3
Parasitoid emergence
Refused
Unknown
Did no
Treatment
Mm
Cm
Ci
FAW
diet
causes
pupate
Ci
x Mi
13.7a
64.3a
7.0a
3.9a
5.8a
5.4a
Ci
x Cm
46.0b
27.4b
8.7a
4.0a
7.7a
6.5a
Ci
only
74.4a
7.3a
4.3a
7.7a
5.9a
treatments replicated nine times with 30 1 ar v ae/treatment. Means
in the same column followed by the same letter were not significantly
different by Duncan's Multiple Range Test (P = 0.05). This means for
Mm (Column 2) and for Cm (Column 3) were compared using students
_t-test.
^Had not pupated by the time nonparasitized larvae had emerged.


Table 13. Means (j^SE) numbers of FAW hosts attacked at 7 densities by marginiventris.
Host density3
Mean numbers of
1
2
4
8
16
32
64
Hosts super-
parasitized
0.5+ 0.1
1.1+0.01
1.3+0.2
1.3+0.02
1.1 + 1 .2
1.0+0.02
1.2+0.05
Longevity of
progeny
6.1+0.7
5.6 + 0.7
5.1+ 0.8
7.4 + 0.1
4.1 +1 3
4.3+1.6
4.6 +1 7
Survival of
1 arv ae
1 + 0.0
2 + 0.0
3.9 + 0.1
8.0+.07
15.3+0.7
29.7+07
54.2+_2 .1
a/ Seven replications at each host density,
b/ Significant by student "t" test at P=0.05 level.


FIG. 9. Sex ratio of _C^_ marginiventris from 7 host
densities.


(!)
t*
i
^ (4)
(3) Chemotaxis Larval
N 1
i/ '
& \
toy Antennal \
Palpation \
\
4'\/
r
V
Random
Movement
\
\
s
s
Contact
'A
\ /
^ 'V \U
> Preening
Mounting (5)
Insertion (6)
Antennal <
Palpation 7
*
I
i
/
/
/
/
V*
Oviposition (7)
77
Oviposition (8)


INTRODUCTION
Chemical insect pest control has become a contro
versial management strategy for several reasons. Insect
pests have frequently become resistant to pesticides, and
the costs of developing and registering a new insecticide
have risen sharply. There is also concern about the
effects of pesticides upon human health and the environ
ment. This combination of circumstances has prompted
entomologists to seek alternative control strategies lead
ing to the development of sophisticated techniques involv
ing a wide array interdisciplinary approach that have been
termed "integrated pest management". Along with the
development of strategies such as breeding resistant plant
varieties and the use of pheromones to disrupt communica
tions, there has been a resurgence of interest in the use
of entomophages.
Huffaker and Messenger (1976) defined biological con
trol as the action of predators, parasites, and pathogens
which maintains host densities at levels lower than would
occur in the absence of these natural enemies. Despite
the many successes obtained through the introduction and
release of a pest's natural enemies, this classical
biological control strategy has not always provided the
desired degree of pest control. In this strategy of
biological control, natural enemies are deliberately
1


INTERSPECIFIC COMPETITION BETWEEN FALL ARMYWORM
PARASITOIDS CHELONUS IN SU LAR IS AND COTESIA
MAR6INIVENTRIS INSIDE FIELD CAGE AND PLOTS
Introduction
The fall armyworm (FAW), Spodoptera frugiperda, is
one of the few argicultural pests infesting many members
of the family Graminae in the United States. Each year
the FAW migrate from tropical and subtropical areas to
occupy a range which may extend northward to the Canadian
border and westward to Montana. Major losses in late
planted corn, sorghum and other susceptible crops are
experienced when high populations of FAW are present.
Mitchell (1979) estimated that if a severe outbreak
occurred, as in 1977, losses could exceed $500 million.
Ashley et al ( 1982 ) reported that up to 63% of first 4
instars are destroyes by parasitoids of FAW.
Interspecific competition among parasitoids within
the same host can have a significant impact on the host's
population dynamics. The occurence of interspecific
competition may result in the death of one or both
parasitoid (Salt 1961). Therefore, this competition may
be a vital component influencing the parasitoid guild
90


EFFECT OF HOST AGE, PARASITOID AGE AND CHANGE OF
TEMPERATURE ON INTERSPECIFIC COMPETITION BETWEEN
CHELONUS INSULARIS CRESSON, COTESIA MARGINI VENTRIS
HTTRTnTE
Introduction
The fall armyworm (FAW), Spodoptera frugiperda occurs
year-round in the tropical and subtropical areas of the
western hemisphere, where it feeds on corn, sorghum,
Bermudagrass and other members of the family Graminae.
Damaging populations of FAW occur irregularly, and
conditions conducive to outbreaks are not well understood
(Barfield 1980). Estimated losses attributed to FAW
reached $300 million in the southeastern United States
during 1977, one of the most severe outbreak years (Sparks
1979).
A very diverse complex of natural enemies, especially
parasitoids, attack the larval stages of FAW (Ashley
1979). The potential for interspecific competition exists
between these parasitoids because more than one species
attacks the same instar. Pemberton and Willard (1918)
suggested that competition between parasitoids may prevent
them from regulating their hosts effectively.
67


144
Wallner, W., R. M. Weseloh, and P. S. Grinberg. 1982.
Intrinsic competition between Apanteles marginiventris
(Hymenoptera:Braeonidae) and Rogas lymantriae
(Hymenoptera:Braeonidae) reared on Lymant~r fa ~d i spar
(Lepidoptera:Lymantriidae) Entomoph ag a. TT: 99-1(93 .
Watt, K. E. F. 1965. Community stability and the strategy
of biological control. Can. Entorno!. 97: 887-95.
Weiser, J. 1959. Nosema 1aphygmae n. sp. and the internal
structure of the microsporidan spore. J. Insect Path.
1: 52-9.
Weseloh, R. M. 1983. Effects of multiple parasitism on
the gypsy moth parasite Apanteles me!anoscelus
(HymenopterarBraconidae) and CompsiTura concTnata
(Diptera:Tachinidae). Envi r oTk EntornoT. T?: ??£-602 .
Wilson, J. W. 1933. The biology of parasites and
predators of Laphyma exigua Huebner reared during the
season of 1932T TTa. Entorno!. 17: 1-15.
Wiseman, B. R. and F. M. Davis. 1979. Plant resistance
to the fall armyworm. Fla. Entomol 62 (2 ): 123-30 .
Wiseman, B. R., F. M. Davis and W. P. Williams. 1983.
Fall armyworm: larval density and movement as an
indication of non preference in resistant corn.
Protection Ecol 5: 135-141.
Wiseman, B. R., D. B. Lueck and W. W. McMilliam. 1973.
Effects of fertilizers on resistance of antigua corn to
fall armyworm and corn earworm. Fla. Entomol. 56
(1):1-7 .
Wiseman, B. R. and W. W. McMillian. 1969. Competition
and survival among the corn earworm, the tobacco
budworm and the fall armyworm. J. Econ. Entomol. 62:
734.5
Wood, J. R., S. L. Poe and N. C. Leppla. 1979. Winter
survival of fall armyworm pupae in Florida. Environ.
Entomol 8: 249-52 .
Wylie, G. 1965. Discrimination between parasitized and
unparasitized house fly pupae by females in Nasonia
vitripennis (Walk) (Hymenoptera:Pteromalidaej^ Can.
Entomol 97: 279-86.


95
Experiment 3--Fie1d Plots
Corn was planted in six adjacent plots, (50 x 11 m)
in the center of a field previously used to produce field
corn. Each plot was disked twice before planting. Seven
to ten days after disking corn seeds were planted at a
depth of 3.0 cm and spaced 91.4 x 243.8 cm (between rows
and plants). The plots were irrigated weekly and two week
after planting ammonium nitrate fertilizer (33.5% N) was
broadcast over each plot at a rate of approximately 165
kg/ha. Four to five weeks after planting, plants selected
at random were pinned with a paper section having approxi
mately 50-60 FAW eggs at the following locations: (US)
upper surface of leaves (within 20.3 cm from terminal)
(oriented less than 45 from stalk), (LS) lower surface of
leaves (oriented more than 45 from the stalks,) (ST)
stalk (central stem with a pithy core), (GS) ground
(within 5.08 cm from the plant), (SH) in between stalk and
1 eaf sheath (Fig 16).
The eggs were not washed. The five treatments were
replicated 6 times within the plot. A control plot was
left with FAW eggs pinned into the whorl region. Starting
from the first day after egg pinning, 480 insularis
females were introduced for 3 consective days. On the 4th
day 498 female marginiventris were released. The
complete experiment with 6 plots (5 with treatments +
control) was replicated 3 times over a 4 month period.


100
90
80
70
60
50
40
30
20
10
0
24 48 72 96 108
AGE OF C.insularis (hrs)


ACKNOWLEDGEMENTS
I am grateful to Dr. Van H. Waddill, chairman of my
supervisory committee, for his advice, encouragement and
guidance throughout the experimental work and preparation
of this dissertation. I am also indebted to him for
providing me financial support to pursue my studies at the
Department of Entomology and Nematology, University of
Florida.
I would like to express special thanks to Dr. Tom R.
Ashley co-chairman of supervisory committee, for inspira
tion and guidance and in preparation of this dissertation,
and for generously providing facilities and materials at
USDA Laboratory. His warm friendship and understanding is
greatly appreciated.
I am also indebted to Drs. John Strayer and Daniel
Roberts for their interest and contributions as members of
my supervisory committee, and giving invaluable encourage
ment when it was dearly needed. There are special thanks
for Dr. Stratton H. Kerr and Dr. Andrew Duncan for their
invaluable advice and suggestions.
I wish to express my gratitude to all the personnel
from both USDA Insect Attractants Laboratory at
Gainesville and TREC at Homestead who have helped me in
numerous ways in conducting my experiments. Special
thanks also go to Pamela Wilkening, Polly Hall and Delaine
Miller of USDA, Insect Attractants Lab.


42
Table 3. Percent par as i t i zation of second age group fall
armyworm larvae exposed to m a ni 1 a e for various amounts of
time
Host (% Parasitization)
exposure (min) No. containers a (X + S.E.)b
15
8
13.0
+
3.7
a
30
45
11
22.0 +
3.1
b
13
26.0 +
1.7
b
60
9
24.5 + 1.6 b
a Two female parasitoids and 20 larvae/container.
b Means followd by the same letter are not significantly
different (PC0.05) by Duncan's Multiple Range Test.


47
Larvae in group one, were not exposed to marginiventris
or M. man i 1ae and served to measure parasitization by C.
insularis. Remaining larvae were exposed as second
instars (48 hrs old) to C^_ margin i ventr i s (group two) or
to M. mani1ae (group three). Treatments were replicated
nine times. The percent successful parasitization and the
fate of non-par as itized larvae were recorded.
Experiment 2. Twenty second-instar larvae exposed
previously to insularis as eggs were exposed to either
M, mani 1 ae or marginiventris in the plastic containers.
Ten replicates were made. In the control treatment,
larvae were exposed to either marginiventris or M,
m a ni 1 a e without prior par as itization by insularis .
Experiment 3. Fall armyworm larvae exposed as eggs
to C in s u1 a ris and unexposed larvae were kept in separate
plastic containers until the larvae were 3 days old. The
ten exposed and ten unexposed larvae were transferred to
new plastic containers. Two females of either margini
ventris or mani 1 ae were introduced into a container for
30 min and the number of encounters, antennal examina
tions, ovipositor probes with and without cuticle contact
were recorded. An encounter was defined as the arresting
of random locomotion that resulted from sensing the FAW
larva. An examination occurred when antennal palpation of
the larvae by the parasitoid was observed. A probe was


45
relevant model for the study of interspecific competition
within the host larva because of similarities in their
life cycles. Ashley et al. (1982) supports the concept of
interspecific competition during parasitiod development by
demonstrating the presence of a dependent density pattern
in percent par as itization between Chelonus insular is
Cresson and Temelucha difficilis Dasch.
The present study assesses interspecific competition
between two species of larval parasitoids, Microp1 itis
man i 1ae (Ashm.) and C o t e si a (=Apanteles) marginiventris
Cresson, and an egg-larval parasitoid C, insularis It
also describes the host finding and ovipositional sequence
for marginiventris for hosts already parasitized by C.
insu1 aris. In addition data are presented on host
acceptance of M_^ man i 1 ae and marginiventris of larvae
already parasitized by insu1 aris.
Materials and Methods
Host eggs or larvae were obtained from a FAW colony
maintained at 23-25C, 74-78% RH and under a 14:10 LD
photoperiod. Moth oviposition occurred on paper towels, a
portion of which were subsequently cut into sections each
having 50-60 eggs. All hosts utilized in an experiment came
from the same egg mass to help ensure host uniformity. In all
experiments, except the fourth, these paper sections were


23
regardless of the host plant, C. insularis had a parasiti-
zation rate 4 times greater than other competing parasi-
toids. Substantially higher percent par as itization was
obtained for corn than on other hosts (Ashley et al.
1983). Ashley et al. ( 1982 ) reported that C. insularis
parasitized the greatest proportion of FAW larvae having
head capsule widths of 0.3 mm. Chelonus insular is was not
recovered from larvae having head capsule widths greater
than 1.8 mm. This very clearly showed that insularis
is primarily an egg parsito id with preference to early
instars to lay eggs. Mitchell et al. (1984) reported that
two FAW pheremone components (Z9DDA and Z9TDA) had no
significant effect on the level of FAW par as itization by
its principal parasite C. insular is. The sex ratio for C.
insularis shifted from approximately 1:1 (Fernale:male)
during spring to approximately 1:4 during the summer
months but the reduced proportion of females during summer
did not lower parasi ti zation levels by i n s u 1 a r i s.
The Larval Endoparasitoid Microplitis manilae
Description and Distribution
Microplitis manilae (Ashm) is reported as an
important larval parasitoid of Spodoptera spp in Thailand
(Shepard, Pers. Comm 1982). This parasitoid is not


83
respectively. Temperature did not affect emergence of FAW
adults. A significant number of larvae were found to be
alive at 19 and 22C. There was a significant difference
for larvae which died for unknown reasons at 19C and the
remaining temperatures.
The time required for development of marginiven-
tr i s from oviposition to emergence as adults ranged from
12-20 days and declined as temperature increased (Table
11). The longest emergence period for both parasitoids
occured at 19C. Kunnalaca and Mueller (1979) reported
the development time for C^_ margi ni ventr i s decreased
between 25 and 30C. The range of time required for C.
insu1aris from oviposition to adult emergence was from 26
to 35 days. Significant differences were observed between
19 and 22C for all parameters measured. An abnormally
high number of larvae was unable to pupate at 19C and
development of the FAW was slower at the lower
temperatures. Keller (1980) reported similar results.
Cotes i a marginiventris emerged more successfully than
C. insul ar i s when hosts were 12-18 hrs old at 19, 22, and
25C (Fig 6). Chelonus insularis was more successful at
host ages of 36-42 and 48-54 hrs under all temperatures
indicating that C^_ marginiventris either did not prefer
older hosts or was unable to develop in them successfully.
Cotesia marginiventris was more successful with hosts at


92
Materials and Methods
Host and Parasitoid Colony Maintenance
A colony of the FAW was maintained at 23-25C, 74-78%
RH and under a 14:10 LD photoperiod. Adults were fed with
10% sucrose solution. Adult FAW oviposition occurred on
paper towels that were subsequently cut into sections each
having a single egg mass of 50-60 eggs. These sections
were placed in circular plastic cups ( 7 x 10 cm diam)
having two screened vents (1.5 x 3.0 cm). These cups were
used as ovipositional units and contained 4 cubes (1.5 cm)
\
of pinto bean diet (Leppla et al 1979 ).
Adult C^_ i ns u 1 ar i s and mar g i n i ventr i s were held in
plexiglasss cages ( 50 x 50 x 24 cms) at 26C, 60-65% RH
and 14:10 LD photo regime. Undiluted honey and water were
provided to adult parsito ids. Unless otherwise noted,
parasitoids were 1-4 days old when used for
experimentation.
Experimental Procedures for Host Paras itization
Individual FAW eggs were isolated using the technique
described by Gross et al. (1981). All eggs in each repli
cate, came from the same egg mass. A grid was drawn on
filter paper and individual eggs were placed in the center
of each square, inside a plastic petri dish (100 x 15 cm).
The eggs were then exposed to two female C_^ i nsul ar i s and
any that were attacked more than once were discarded.
After parasitization, eggs were kept in the plastic cups,


80
60
40
20
First instar
I I Second instar
Third instar
E3 Fourth and fifth instar
v.
2
i
I 2 3
PAPER SECTIONS


11. Percentage par as itization by iins u1 a ris and C. margini-
ventr i s from FAW larvae recovere3 insTde"from TTeT3
cage during 3 test periods. Vertical bars within a
test period from left to right indicate treatments
1, 2, and 3 paper sections 109
12.Mean percentage parasitized FAW instars in treatments
1, 2, and 3 paper sections inside field cage 112
13. Mean percentage of FAW larvae that became a) adults, b)
starved and died c) died from unknown reasons in
treatments 1, 2, and 3 paper sections inside field
cage 115
14. Percentage par as itization for principle parasitoid
species recovered from FAW larvae from (US) upper
surface of whorl, (LS) lower surface of whorl,
(GR) ground, (SH) between stalks and leaf sheath,
(ST) stalk and (WH) control in corn ug
15. Sex ratios for C. marginiventris and C. insular is
recovered from "F7\W larvae from ("US) upper surface of
whorl, (LS) lower surface of whorl, (GR) ground, (SH)
between stalks and leaf sheath, (ST) stalk and (WH)
control in corn 122
16. Illustration to exhibit the placement of egg contain
ing paper sections in different regions of corn
US
Upper surface
of
upper
whor 1
LS
Lower surface
of
upper
whor 1
GR
Ground
SH
In between stalk
and sheath
ST
Stalk
WH
Whorl region.,
ix


LIST OF FIGURES
Figure
Page
1. Mean percentage emergence of insularis (C.i.), M.
manilae (M.m.) and C. marginiventris (C.m.) from flTl
armyworm larvae exposecT to multiple par as i t i z at i on s .. . 52
2. Behavioral ethogram of the host finding and oviposi-
tional sequence of marginiventris females on fall
armyworm larvae al ready par asftTzecPby the egg-larval
parasitoid C. insularis. (Solid arrows indicate
invariable pathways and" dashed arrows represent alter
nate pathways) 61
3. Percentage parasitization by marginiventris of fall
armyworm larvae already exposed as eggs to insularis.
Larvae were randomly placed on four plant spec i es h eTcf
in wire cages within a greenhouse 65
4. Progeny sex ratios for C. marginiventris from differ
ent aged C. marginiventrTs (C .m .) emerging from fall
armyworm Trva"e" parasTfized as eggs by insularis
(C.i.) 79
5. Progeny sex ratios for C. insularis (C.i.) from differ
ent aged C. marginiventris fC.mT) emerging from fall
armyworm Tarve par asTtTz'ed as eggs by i nsul ar i s ... 81
6. Percentage emergence of C. marginiventris and C. insularis
from fall armyworm ( F AW JHarv ae, par as i tfzed as eggs By
C. insularis. FAW larvae were exposed at different ages
to C 7~margTiventris and then held at 19 22 25, or
28~for development 86
7. Mean progeny production by marginiventris at 7 host
densities from eggs previously parasitized by C.
i nsul ar i s 98
8. Mean progeny production by C. insularis at 7 host den
sities and parasitized again by ~C. ~marg~i n i ventr i s 102
9. Sex ratio of marginiventris from 7 host densities... 105
10. Sex ratio of C. insularis from 7 host densities 107
viii


FIG. 15. Sex ratio for C_^ marg i n i ventr i s
recovered from FAW larvae from (US) upper
whorl, (LS) lower surface of whorl, (GR)
between stalks and leaf sheath (ST) stalk
in corn.
and insularis
surface of
ground, (SH)
and (WH) control


7
several hundred eggs may be laid in a mass and covered
with scales. Total oviposition by a female may exceed
2000 eggs over a period of up to 23 days (Luginbill 1928).
As larvae hatch from the eggs, they eat their egg shells
(Morrill and Green 1973), and as a result of negative
phototactic and geotactic behaviors, the first instars
move into the whorls of corn and sorghum (Pitre 1979).
The larvae feed preferentially on the developing leaves
and at high densities will eat the mature leaves, tassels,
ears, and the inner portions of the stalk (Luginbill 1928,
Morrill and Green 1973). Development proceeds through 6,
sometimes 7, and rarely 8 instars (Keller 1980). Tempera
ture, larval nutrition, and probably egg nutrition were
factors affecting instar number in FAW (Keller 1980).
Mature larvae drop to the ground and pupate in the soil
within a chamber located 2 to 8 cm below the surface
(Luginbill 1928). Pupation depends upon soil texture,
moisture, and temperature (Sparks 1979). Pupae have been
found on plant parts during severe outbreaks (Burkhardt
1953). After eclosin, the adults find their way to the
soil surface, locate a plant or other object on which to
cling, and inflate their wings (Sparks 1979). There is
also evidence that different host plants (Roberts 1965,
Pencoe and Martin 1981) and different temperatures affect
the biology of FAW (Barfield et al 1978).


FIG. 16. Illustration of exhibit the placement of egg
containing paper sections in different regions of corn.
US Upper surface of whorl
LS Lower surface of whorl
GR Ground
SH Between stalk and leaf sheath
ST Stalk
WH Whorl region


INTERSPECIFIC COMPETITION BETWEEN PARASITOIDS OF THE FALL
ARMYWORM SPODOPTERA FRUGIPERDA
44
Introduction 44
Materials and Methods 45
Results and Discussion 50
EFFECT OF HOST AGE, PARASITOID AGE AND CHANGE OF
TEMPERATURE ON INTERSPECIFIC COMPETITION BETWEEN CHELONUS
INSULAR IS, COTES IA MARG I N I V E NTR I S AND MI CROP L I T I SHMrn[F
In TAll ArmyWWmT 67
Introduction 67
Materials and Methods 68
Experiment l--Host Age 70
Experiment 2--C. marginiventris
frge 70
Experiment 3--Temperature
Effects 70
Experiment 4 Dissection of
Multipar as itized
Hosts 71
Results and Discussion 72
INTERSPECIFIC COMPETITION BETWEEN FALL ARMYWORM
PARASITOIDS CHELONUS INSULARIS, AND COTESIA MARGINIVENTRIS
INSIDE FIELD CAGES AND PLOTS 90
Introduction 90
Materials and Methods 92
Host and Parasitoid Colony
Maintenence 92
Experimental Procedures for Host
Parasi ti zation 93
Experiment l--Host Density 96
Experiment 2 Field Cage 103
Experiment 3 Field Plot 117
Results and Discussion 120
GENERAL SUMMARY AND DISCUSSION 130
REFERENCES 134
BIOGRAPHICAL SKETCH 146
v


FIG. 14. Percentage par as itization for principal
parasitisoid species recovered from FAW larvae from (US)
upper surface of whorl, (LS) lower surface of whorl, (GR)
ground, (SH) between stalks and leaf sheath, (ST) stalk
and (WH) control in corn.


96
A sample consisted of harvesting all the plants in a 10-m
area.
Comparisons were made between parasitoid release
plots and non release plots in terms of FAW larval damage
to whorl (leaves surrounding the furl with blades
partially extended and sheath concealed) and furl (leaves
surrounding a central roll) and stalk. The plants with
recongnizab1e FAW feeding in whorl, furl or stalk with FAW
larvae present were defined as damaged.
Results and Discussion
Experiment l--Host Density
The mean number of marginiventris that emerged
from densities of 64 and 32 larvae produced patterns that
were almost mirror images of each other (Fig 7). A den
sity of 64 larvae/cup represented the highest mean progeny
production at 48 hrs. Kunnalaca and Mueller (1979)
reported that marginiventris parasitized between 31 and
110 hosts each day. The greatest difference in progeny
densities occurred between the 64 larvae/cup density and
the remaining densities.
More super par as itism occured at 4 and 8 larvae than
at 32 larvae suggesting that marginiventris exposed to
lower densities attacked many hosts more than once. How
ever at higher densities only one parasitoid emerged per
host larvae which showed that C. marginiventris avoided


36
lid. During host exposure, FAW larvae fed on cubes (3
cm^) 0f pinto bean diet (Leppa et al 1979 ) after which
the larvae were transferred individually to 30-ml plastic
cups that contained pinto bean diet where they remained
until their fate was determined. FAW larvae were kept as
2 3+_2 C, 7 0+_2% RH and under a 14:10 LD photoperiod. These
larvae were divided into 4 groups depending on their age:
1 24-48 hr s; 2, 49-72 hrs, 3, 73-96 hrs; and 4, 97-130
hrs. Hosts older than 130 hrs were excluded because M.
man i 1ae females would not accept them as hosts. The
laboratory rearing method for mani 1 ae consisted of
exposing parasitoids to approximately 50 FAW larvae which
were 48-72 hrs old for 3-5 hrs.
Age group acceptance--Depending on host availability
4-6 replicates of 3-4 FAW larvae of the same age group
were presented to two female mani 1 ae for 30 min. on the
same day. Data from 4 consecutive days comprosed a single
test and tests were replicated 4 different times.
Developmental rates--Microplitis man i 1ae were exposed
for 24 hrs to hosts in the four age groups. Parasitoid
developmental times were determined from oviposition to
pupation and from pupation to adult emergence. Progeny
sex ratios were recorded for each age group.


LITERATURE REVIEW
The Fall Armyworm, Spodoptera frugiperda (J.E. Smith)
The fall armyworm (FAW), Spodoptera frugiperda (J. E.
Smith), (Lepidoptera:Noctuidae) inflicts damage on a large
number of agricultural crops, especially those belonging
to the family Graminae, in the Southeastern and Central
United States (Luginbill 1928) and Central America
(Andrews 1980). Corn (Zea mays L.), Sorghum (Sorghum
bicolor (L.) Moench) and Bermudagrass (Cynodon dactylon
(L) Pers.) are the favored agricultural hosts for the FAW
(Sparks 1979). Economic damage to other crops, including
alfalfa, peanuts, rice and soybean, has also been
documented (Navas 1974, Morrill 1973, Pitre 1979). Tietz
(1972) lists 68 genera of plants, many of which are weed
species, that are attacked by the FAW.
Seasonal Distribution
Unlike most other insects in the temperate region,
the FAW has no mechanism for diapause. Thus, the species
overwinters commonly in South Florida and Texas, where
temperatures do not destroy it and where hosts are
continually available (Luginbill 1928). In mild winters
it is also found in Louisiana and Arizona (Snow and
Copeland 1969). During the spring and summer the FAW
5


139
Loke, W. H. and T. R. Ashley. 1984. Behavioral and
biological responses of Cotesia marginiventris to
kairomones of the fall armyworm Spodoptera frugiperda.
J. Chem. Ecol. 10 (3): 521-29.
Loke, W. H., T. R. Ashley, and R. I. Sailer. 1983.
Influence of fall armyworm Spodoptera frugiperda
(Lepidoptera: Noctuidae) larvae and corn plant damage
on host finding in Apante!es margini ventris
(Hymenoptera: Br aconTcTae)'. v iron! n tomo IT 12 (3):
911-15.
Luginbi11, P. 1928. The fall armyworm. U. S. Dept.
Agrie. Tech. Bull. 34, 92 pp.
Mackauer, M. 1976. Genetic problems in the production of
biological contol agents. Ann. Rev. Entomol. 21:
369-85.
Marsh, P. M. 1971. Keys to the nearctic genera of the
families Braconidae, Aphididae, and Hybrizontidae
(Hymenoptera). Ann. Entomol. Soc. Amer: 64: 841-50.
Marsh, P. M. 1978. The braconid parasites (Hymenoptera)
of He1 iothes species (Lepidoptera:Noctuidae). Proc.
EntomoTT Soc. Wash. 80(1): 15-36.
Martin, P. B., B. R. Wiseman and R. E. Lynch. 1980.
Action thresholds for fall armyworm on grain sorghum
and coastal Bermudagrass. Fla. Entomol. 63(4):
375-405.
Miller, J. C. 1977. Ecological relationships among
parasites of Spodoptera praefica. Environ. Entomol.
6: 581-5.
Miller, J. C. 1982. Life history of insect parsito ids in
successful mu 11ipar as itism. Oecologia 54: 8-9.
Mitchell, E. R. 1979. Fall armyworm symposium, preface.
Fla. Entomol 62 : 81.
Mitchell, E. R., W. W. Copeland and A. N. Sparks. 1974.
Fall armyworm: nocturnal activity of adult males as
indexed by attraction to virgin females. J. Georgia.
Ento. Soc. 9: 145-6.


16
larva has a caudal appendage which is a modification of
the last abdominal segment into a fleshy organ and a
caudal vesicle that increases in size with longevity.
Allen and Smith (1958) reported some species of Apanteles
as being cannibalistic in the first instar; but no
cannibalism has been observed in marginiventris (Boling
and Pitre 1970). The second instar is vesiculated with a
prominent anal vesicle and the body becomes more robust.
Allen and Smith (1958) suggested that the second instar
may actually be two instars. The third instar is
hymenopteriform with no anal vesicle. This larva tapers
anteriorly and is creamy white at first, turning light
brown upon emerging from the host (Boling and Pitre 1970).
The molt to the third instar happens just prior to
parasitoid emergence, which generally occurs at approxi
mately the 4th abodminal segment in the dorsolateral area
of the host. The parasitoid initially constructs a one
sided crescent-shaped cocoon and after its body has become
seated, the larva closes the open side of the cocoon. The
cocoon is small (3mm long), ovoid, firm, smooth and com
posed of white silk surrounded by some looser threads.
The pupa is exarate and enters pupation approximately 24
hrs after form at ion of cocoon. Adults can be identified
using the keys of Marsh (1971) (to genus) and Muesebeck
(1921) (to species). The black adult is about 2-5 mm
long, has yellow legs and is recognizable by the


FIG. 13. Mean percent of FAW larvae that became a)
adults, b) starved and died c) died from unknown reasons
in treatments 1, 2, and 3 paper sections.


147
Rohan Rajapakse is a member of the Entomological
Society of America, Florida Entomological Society and Sri
Lanka Association of Advancement of Science. He has two
sisters, Damayanthie (a high school teacher) and, Sandhya
(an account ant).


00
90
80
70
60
50
40
30
20
10
0
24 48 72 96 108
AGE OF C. marginiventris (hrs)


37
Adult 1ongevity--Fresh1y eclosed parasitoids were
exposed to hosts under continuous light at 26+_lC and
longevity was recorded for 2 groups: (1) the females
(n=41) and males (n-57) were separated into different
cages and (2) both sexes were kept together and allowed to
mate for 2 hrs and then to oviposit for 24 hrs inside a
plastic container with 20 FAW larvae. After the host
exposure period, larvae were removed and adult parasitoids
were retained in the plastic containers.
Time of host exposure--In order to determine optimal
host exposure time, 2 female M^_ man i 1 ae were exposed to 20
hosts from the 2nd age group for 15, 30, 45 and 60 min.
and then removed. Four replicates were run.
Results and Discussion
Parasitoids displayed the highest host acceptance for
1st and 2nd age group larvae and a lesser acceptance for
3rd age group larvae (Table 1). Highest par as itization
rates occurred most frequently in 2nd age group larvae.
Significantly fewer 4th age group larvae were parasitized
compared to larvae of other groups, and there were several
occurrences of significant differences in host acceptance
between 2nd and 3rd age group larvae. Similar results
have been reported for other members of this genus (Hafez
1951, Lewis 1970). Putter and Thewke (1969) showed that


125
Table 16. FAW damaqe to different regions of corn in plots
where C. insularis (C.i.) and C. marginiventris (C.m.) were
released.
% Damage to Corn by FAW a/
Date of
Observations
C.m. and C.
released
i.
No
parasi toids
released
Upper
Surface
Lower
Surface
Stalk
Upper
Surface
Lower
Surface
Stalk
May 8
19.6b
12.9c
O.ld
30.5a
13.4c
O.Od
May 12
13.5b
9.7c
O.Od
43.6a
10.1c
O.Od
May 16
15.5a
5.7b
0.0c
15.7a
5.2b
0.0c
June 9
19.7b
30.3a
0.0c
18.9b
28.5a
0.0c
June 13
14.5a
13.5a
0.0b
16.7a
13.5a
0.0b
June 17
30.5b
9.5c
0.2d
53.5a
28.5b
O.Od
July 11
24.3a
14.7b
0.5c
22.5a
15.6b
0.3c
July 15
19.7a
19.5a
0.0b
19.3a
21.5a
0.0b
July 19
33.7a
19.6b
0.0c
34.5a
19.1b
0.0c
a/ Treatments in the same row followed by the same letter were
not significantly different by Duncans Multiple Range Test.


72
3, 6, 8, or 10 days. Twenty to thirty host larvae were
dissected at the end of each time period to determine the
condition of the competing parsito ids. In the nine day
treatment, C. marginiventris larvae had emerged before
dissections were done. However, since the host was still
alive it was dissected to determine the fate of the
immature in s u1 a ris The descriptions of Boling and
Pitre 1970) and Glogoza (1980) were used to recognize
larvae of marginiventris and i n s u 1 a r i s ,
respectively.
Results and Discussion
Thirty six hr old FAW larvae produced the highest
proportion of marginiventris and lowest proportion of
C. insularis (Table 8). Emergence of marginiventris
showed significant differences between 60 and 72 hrs and
24 and 36 hrs but there were not significant differences
between 12 and 24 hrs, and 72 and 84 hrs. There was not
significant difference in emergence of C_^ marginiventris
from hosts 36 hrs old and the control. Loke and Ashley
(1984) reported that highest rate of par as itization by C .
marginiventris of FAW occurred in 48 hr old larvae (second
instars). Kunnalaca and Mueller (1979) and Boling and
Pitre 1970) stated that females of marginiventris
produced the most progeny from 2 and 3 day old hosts.
Larvae less than 24 hrs did not produce as many


29
ones. Examples of intrinsically superior parasitoids that
have achieved such a role are two braconids, Opiun
oophi 1 us Full. (Bess and Haramoto 1958) and Macrocentrus
ancylivorus Rohw. (Boyce and Dustan 1958). On the other
hand, an intrinsically inferior species may achieve a
higher level of parasitization in the field than its
rivals if it is extrinsical 1y superior to them. For
example, Spalangia cameroni Perk., an intrinsically
inferior species, parasitized more house fly pupae than
all other species combined because the females were able
to penetrate more deeply into areas containing hosts
(Mourier and Hannine 1969). Obviously, an intrinsic
superiority of one parasitoid over another may result in
the waste of some parasitoids, but this effect, as pointed
out by Smith (1929), is likely to be an insignificant
factor in the comparative field efficiencies of two
competing forms.
Case Studies
The superiority of Metaphycus inteolus (Timberlake)
over Microterys f1avus Howard inside the host (Coccus
hes per idiurn) in the field was contrary to the pattern of
dominance of both species when they competed within the
host (Bartlett and Ball 1964). Arther et al. (1964)
showed interactions between a braconid, Orgilus obscurator
(Nees), and an ischneumonid, Temelucha interruptor, inside


117
was not capable of controlling fertilization of its eggs
then high percent of males in low densities could be due
to differential mortality resulting from competition among
larvae for available food within the host. Local
increases in the ratio of parasitoids to hosts can produce
a change of sex ratio in field population of Hymenoptera
(Charnov et al. 1977 ) .
Experiment 3--Field Plots
C. insularis emerged as the predominant parasitoid
(Fig 14) on the upper (58.5%), and lower (71%) leaf sur
faces, between stalks and leaf sheaths (40.5%) and the
control (80.5%). A higher percentage of marginiventris
than C. insu1 aris emerged from the treatments placed on
ground (15.5%) and stalk (35.5%). Teme!ucha difficulis
Dasch., Meteor us autographae Muesebeck Rogas 1aphygmae
Viereck and several unidentified species accounted for the
remaining parasitoids. Mitchell et al ( 1984 ) and Ashley
et al. (1982) reported that in order to abundance C.
insu1 aris. T. difficilis and marginiventris were the
principal parasitoids collected from study plots at
Homestead. Therefore, releasing C. marginiventris
increased its par as itization level above that of T.
difficilis. The percent par as itization was higher from
the lower surface of leaves in comparison to the control.
Morrill and Greene (1973) reported that in corn the
highest number of FAW larvae were found in whorls.


FIG. 4. Progeny sex ratios for C. marqiniventris from
different aged C margi n i ventr i s~TC .m .) 'e'merg i~ng "from fall
armyworm larvae parasitized as eggs by C^_ i n su 1 ar i s .


57
Table 6. Mean and percents for encounters, examinations,
oviposition probes and apparent ovipositional success by Cotesia
marginiventris and Microplitis manilae in fall armyworm larvae
exposed arT3 not exposed as eggs ~Fo"~Cfi~e 1 onus i nsu 1 ar i s.
Exposure to
C insular i s
Mean a
Encounters
Examinations
Probes
Ov i pos itions
Microplitis manilae
Exposed
8.4
2.0
2.2
1.2
(60.8)
(14.4)
(15.9)
(8.7)
Not Exposed
8.8
3.8*
4.2*
2.6*
(45.5)
(19.6)
(21.7)
(13.4)
C o t e s i a
marginiventris
Exposed
12.8
5.8
2.6
2.8
(54.3)
(22.4)
(11.2)
(12.1)
Not exposed
14.2
5.8
2.9
2.9
(55.04)
(22.5)
(11.2)
(11.2)
aStudent' s jt-test analyzed at a = 0.05 level. Percents are in
parentheses and are based upon the total number of behavioral
observations (encounters + exams + probes + oviposition).


143
Turnbul1, A.
insects.
L. 1967. Population dynamics of exotic
Bull. Entomol. Soc. Amer. 13: 333-7.
Turnbull, A. L. and D. A. Chant. 1961. The practice and
theory of biological control of insects in Canada.
Caad. J. Zool 39: 697-753 .
Van den Bosch, R. 1968. Comments on population dynamics
of exotic insects. Bull. Entomol. Soc. Amer. 14:
112-5.
Van den Bosch, R. and A. H. Haramoto. 1953. Competition
among parasites of the oriental fruit fly. Proc.
Hawaiian Ent. Soc. 15: 201-6.
Vickery, R. A. 1929. Studies of the fall armyworm in the
Gulf Coast district of Texas. USDA. Tech. Bull. 138:
pp 63.
Vinson, S. B. 1972. Competition and host discrimination
between two species of tobacco budworm parasitoids.
Ann. Entomol. Soc. Amer. 65: 229-36.
Vinson, S. B. and J. R. Abies. 1980. Interspecific
competition among endopar as itoids of tobacco budworm
larvae (Lepidoptera:Noctuidae). Entomophaga. 25:
357-362.
Vinson, S. B., Guiolott, F. S. and D. B. Hays. 1972.
Rearing of Cadiochiles nigriceps in the laboratory
with He1 iothes virescens as hosts. Ann. Entomol. Soc.
Amer. 6Ti TT70-
Vinson, S. B. and G. F. Iwantsch. 1980. Host suitability
for insect parasitoids. Ann. Rev. Entomol. 25:
397-419.
Waddill V. H. 1977. Shadow sampling: A fast painless
mathod for collecting fall armyworm egg masses. Fla.
Entomol. 60 (3): 215-216.
Waddill, V. H., T. R. Ashley, and E. R. Mitchell. 1985.
Seasonal abundence of fall armyworm parasites in
southern Florida. Proc. SEB. Ento. Soc. Amer.
Greenville, South Carolina.
Walker, T. J. 1980. Migrating Lepidoptera: Are
butterflies better than moths? Fla. Entomol. 63:
79-98.


15
the southern states viz. Arkansas, Florida, Georgia,
Louisiana, Mississippi, Tennessee, North Carolina and
South Carolina (Wilson 1933, Mueller and Kunnalacca 1979,
Marsh 1978). Some 16 hosts of C^ margin iventris have been
reported (Miller 1977) and all are noctuids. No crop
preference is shown by this parsito id when attacking
Trichoplusia ni (Hbn.) on various food plants in
Mississippi (Boling and Pitre 1970).
Description
The egg and laral instars are described by Boling and
Pitre (1970), and the adults by Muesebeck (1921). The egg
is hymenepteriform, cylindrical with rounded ends. The
caudal end is slightly curved, and has a short peduncle.
The egg is 0.017 mm at the broad end, 0.088 mm in length
at oviposition and the peduncle is 0.0005 mm long (Boling
and Pitre 1970). The egg is found free in the hemocoel of
the host larvae. Up to 7 eggs have been found in a single
host when the host larva was exposed to several female
parsito ids. However, superparasitization does not
necessarily lead to multiple cocoon format ion. Normally
only 1 egg is found per host (Boling and Pitre 1970). The
first instar larva is white and caudate and is usually
found in the posterior part of the host's body. First
instar larvae are never found attached to the host. The


66
a developing C in su 1aris The possibility also existed
that man i 1 ae recognized a previously parasitized host
and failed to oviposit. Larvae parasitized as eggs by C.
insu1 aris caused a significant reduction in the number of
host contacts, examinations, and apparent oviposit ion by
M. mani 1 ae. Cotesia marginiventris oviposited in both C.
insularis parasitized and nonparas itized larvae and was
superior internal competitor compared to C insularis .
Exposing FAW larvae that have been parasitized as eggs by
C i n s u 1 a r i s to marginiventris or man i 1 ae did not
result in additional larval mortality. If this same
situation exists under field conditions, then C. insular is
may be the key regulator of FAW larval populations.


73
Table 8. Mean percentages at different host ages for
emergence of Chelonus insuaris (C.i.) Cotesia marginiventris
(C.m.) and adult fail armyworm and percent mortality of FAW
larvae due to (1) refused to feed on the diet, and (2) died
from unknown causes.a/
Host age b/
Percent
Parasitoid emergence
FAW mortality
Refused diet Unknown
(hr s)
C. i .
C.m.
FW
and diet
causes
12
25.5a
20.7a
45.2a
7.4a
1.1a
24
30.4a
15.7a
35.0b
12.2a
6.7ab
36
17.6a
44.2b
20.3c
13.2a
4.8ab
48
18.8a
40.lbc
16.2cd
17.4a
7.5 ab
60
31.7a
32.9c
14.3cd
14.1a
6.9 ab
72
52.7b
17.6a
14.8cd
11.7a
3.lab
84
45.9b
15.2a
10.6d
18.7a
9.6b
Control
_
45.2b
25.6b
15.8a
8.5b
a/ Treatments were replicated 7 times with 40 larvae per
treatment. Means followed by same letter for a given column
are not significantly different by Duncans Multiple Range
Test. (P = 0.05).


35
some members of this genus are known (Hafez 1951, Putter
and Thewke 1970). Lewis (1970) describes the life history
of NL. croceipes (Cresson) for Heliothis spp. and reports
that the parasitoid prefers 1st and 2nd instars as hosts.
No research dats could be found that document the life
cycle and host age acceptance of M^ man i 1 ae developing
within FAW larvae, nor has this parasitoid been reported
as a natural enemy of FAW anywhere within its range
(Ashley 1979 ) .
The objectives of our research are to gain relevant
information about the biology and host age acceptance of
M. man i 1ae when reared on FAW larvae. This information
may prove useful in mass production of this parasitoid for
inoculative or perhaps inundative releases should M.
man i 1ae eventually demonstrate the potential of becoming a
significant mortality agent of FAW populations.
Materials and Methods
Fern ale parsito ids were 24 hrs old and has been
exposed to males since female eclosin. Each replicate
consisted of exposing FAW larvae (number varied according
to experiment) to 6 female parasitoids in a plastic
container (7 x 10 cm diam) with 2 screened vents (1.5 x
3.0 cm) and having honey streaked on the underside of the


20
15
10
5
0
FAW AGE (hrs)
24


My heartfelt thanks and affection go to JoAnne White
for her encouragement and assistance and to Patricia Davis
for the assistance in typing this dissertation.


21
parasitized by C. insularis 41% died in the 4th instar
and 59% died in the 5th instar. An emerging adult tears
the silky cocoon with its mandibles and escapes through
the opening. The body length of the adult is 4.5-5.0 mm
and description of adults is found in Marsh (1978).
Life Cycle
The female parasitoids can begin to lay eggs even if
they have not mated. The antennae are used to locate the
host, the female then lands on the eggs, positions
herself, and then injects her eggs directly into the host
egg. The female may lay continously for about an hour if
left undisturbed. Superparas itism is common in the genus
Chelonus (Broodryk 1969 ) and was observed in insu1 aris
when parasitizing H_^ virescens (F.) eggs (Abies and Vinson
1981). Abies and Vinson (1981) reported that insu1 aris
appeared to examine host eggs internally as well as
externally and was able to detect previously parasitized
hosts. The average time of development from oviposition
to adult is about 26 days for males and 28 days for
females. Rechav (1978) found similar results for other
Chelonus spp. Greatest fecundity was obtained at 30C
(Glogoza 1980). Survival was highest at low temperatures
and the greatest percentage of eggs was parasitized at
35C (Glogoza 1980). Male biased sex ratios occurred at


TIME (min)


137
Ehler, L. E. 1978. Competition between two natural
enemies of mediterranean black scale on olive.
Environ. Entomol 7: 521-3.
Ehler, L. E. and R. W. Hall. 1982. Evidence for
competitive exclusion of introduced natural enemies in
biological control. Environ. Entomol. 11: 1-4.
Fisher, R. C. 1961. A study in insect mu 11iparas itism II.
The mechanism and control of competition for possession
of the host. J. Exp. Biol. 38: 605-28.
Fiske, W. F. and Thompson, W. R. 1909. Notes on the
parasites of Saturnidae. J. Econ. Entomol. 2, 450-60.
Flanders, S. E. 1939. Environmental control of sex in
hymenopterous insects. Ann. Entomol. Soc. America. 32:
11-26.
Force, D. C. 1970. Competition among four hymenopterous
parasites of an endemic insect host. Ann. Entomol.
Soc. Amer. 63: 1675-88.
Force, D. C. 1974 Ecology of insect host-par as itized
communities. Science 184: 624-632.
Gardner, W. A. and J. R. Fuxa. 1980. Pathogens for the
suppression of the fall armyworm. Fla. Entomol. 63(4):
439-47.
Glogoza, G. 1980. Biology of Chelonus insularis. Bio.
Control of insects Lab. USD71-ART Tes~ frpT. July-Dee.
75-81.
Gnagliumi, D. 1982. Las plagas de la cana de azucaren
Venezuela. Pages 568-9. In Minist. Agrie. Crig.
Centr, Invest. Agron., Maracay, Venezuela.
Greene, G. L. and W. L. Morrill. 1970. Behavioral
responses of newly hatched cabbage looper and fall
armyworm larvae to light and gravity. J. Econ.
Entomol. 63: 1984-86.
Gross, H. R., R. Johnson, E. A. Harrell, and W D. Perkins.
1981. Method of seperating fall armyworm eggs from
masses. J. Econ. Entomol. 74: 122-23.


84
Table 11. Mean (+_ SE) emergence periods (days) when reared at
several constant temperatures for Cotes i a marginiventris (C.m.) and
Chelonus insularis (C.i.) and adult faTT'armyworm and percentages for
FW Farvae failing to mature because they (1) refused to feed on the
diet and died, (2) still larvae at end of test, a/
Percent
Temperature b/ Parasitoid emergence Refused diet Still
(C) TTT7 CTmT FAÂ¥ and died alive
19
35.5 + 1. la
20.1 + 1.2a
40.6 + 1.3a
3.5+1.0a
60.3+1.la
22
30.3+1.6b
18.6 +1.1b
34.5 +1.1b
6.9+1.5b
30.3+1.7b
25
26.3+1.5b
17.3+2. lb
28.9+2.1C
1.5+1.7b
0.00c
28
27 .5+1.9b
12.5+12.5b
19.5 +1.3d
2.7 + 1.7b
0.00c
a/ Treatments were replicated 7 times with 30 larvae/ treatment. Means
followed by same letter for a given column are not significantly
different by Duncans Multiple Range Test. (P = 0.05).


50
40
30
20
10
0
FAW AGE (hrs)
24
48


77
Male progeny were always in greater abundance in C.
marginiventris regardless of parental age (Fig 4). Boling
and Pitre (1970) reported that mated C. marginiventris
generally produced with a sex ratio of 1:1. However, only
the 72 hr age group came close to this ratio. A very high
percentage of female C^_ i n s u 1 a r i s emerged in 96 hrs (Fig
5) and a very large percent of males emerged from the 108
hr group. Sex ratios in hymenopterous parasitoids may be
affected by suitable host abundance (Rechav 1978);
however, the reason for the abrupt change of sex ratio of
C. insularis in the 96 and 108 hr treatments was not
properly understood. Mitchell et al (1984) reported a
significant shift in the sex ratio of insu1 aris towards
males in the field between April and October.
Experiment 3--Temperature effects
Cotesia marginiventris emerged most successfully at
25C and it appeared that temperature affected the outcome
of competition (Table 10). Significant differences be
tween emergence rates were present for marginiventris
at all temperatures except 28 and 31C. There were no
significant differences at 22, 25, 31 and 28C for C.
insularis but significantly more emerged at 28 than at
25C. Less emergence was observed for both parasitoids at
low temperatures while optimum temperatures for C.
marginiventris and C. insularis were 25 and 31C,


6
disperses again throughout the eastern and central United
States, and, in some years, into Southern Canada
(Luginbill 1928). This migration is assisted by weather
fronts (Sparks 1979). Several hypotheses have been
advanced to explain the seasonal distribution of damaging
populations of FAW (Rabb and Stinner 1978; Walker 1980;
Barfield et al. 1980). Walker (1980) presented 3 models
to account for seasonal distribution patterns. Diffusion
and freeze-back and return flight (Walker 1980), "pied
piper" effect similar to diffusion and freeze back (Rabb
and Stinner 1978) and a model on seasonal distribution
patterns as combinations of short and long range
movements, as well as periodic overwintering in as yet
undiscovered habitats (Barfield et al. 1980) explained
this aspect.
Life History
The life cycle of the FAW has been described by
Luginbill (1928), Vickery (1929), Sparks (1979) and Keller
(1980). The adults are nocturnal and at dusk initiate
flying near host plants that are suitable for feeding,
oviposition, and mating. Mitchell et al ( 1974 ) showed
that peak activity of adults occurred 6 hrs after sunset
and another small peak occurred approximately 3 hrs later.
Oviposition may occur on host plants where as many as


141
Olive, A. T. 1955. Life history, seasonal history and
some ecological observations of the fall armyworm
Laphygma frugiperda (A.S.), on sweet corn in North
Carolina". M. Sc. Thesis. Department of Entomology.
N.C. State University, Raleigh, 77 pp.
Painter, R. H. 1955. Insects on Corn and teosinte in
Guatemala. J. Econ. Entomol 48(1) :36-42.
Pair S. D., H. R. Gross and A. N. Sparks. 1985. Labora
tory biology and rearing of Diapetimorpha introita a
pupal parasite of fall armywoTmt Pr oc. SeTTI into'. Soc.
America. South Carolina, USA.
Pemberton, C. E. and H. F. Willard. 1918. Interrelations
of fruit fly parasites in Hawaii. J. Agri. Res. 15:
419-465.
Pencoe, N. L. and P. B. Martin. 1981. Development and
reproduction of fall armyworms on several wild grasses.
Environ. Entomol. 10: 999-1002.
Pianka, E. 1970. On r and k Selection. Am. Nat. 104:
592-7 .
Pitre, H. N. 1979. Fall armyworm on sorghum: other hosts.
Mississippi Agrie. Forest Exp. Sta. Bull. 876 12^ pp.
Putter, B. and S. E. Thewke. 1970. Biology of
Micropl itis fe11iore (Hymenoptera: Braconidae) a
parasite of black cutworms Agrotis psilon. Ann. Ent.
Soc. America 63: 645-648.
Rabb, R. L. and R. E. Stinner. 1978. The role of insect
dispersal and migration in population processes, pp.
3-16. In Conf. radar, insect population ecology and
pest management. NASA Conf. Pub. 1070.
Rechav, Y. 1978. Biological and Ecological studies of
the parasitoid Chelonus in an i tus
( Hymenopter a : Br aeon i cfae) ~Tri Israel Entomophaga. 23:
95-102.
Roberts, J. E. 1965. The effects of larval diet on the
biology and susceptibility of the fall armyworm,
Laphyama frugiperda (J. E. Smith) to insecticides. Ga.
Agrie. Experi Sta. Tech. Bull. N.S. 44. 22 pp.


94
and 2 larvae/cup were replicated 10 times and the
remaining treatments were replicated 7 times. FAW larvae
were exposed to Cj_ marg i n i ventr i s at 24, 48 72 and 96 hrs
pf age. The larvae were transferred subsequently to 30 ml
cups and their fate determined.
Experiment 2--Field Cages
Three field cages ( 246 x 155 x 115 cm) were conduct
ed from metal pipe frames and screened with woven cloth
netting so that insect activity could be observed. Each
cage contained 20 corn plants, with 91.4 cm between rows
and 8 inches between plants. Methonyl was applied at the
rate of 10 ml/3.79 L 7 days before the introduction of
host eggs. Four randomly selected plants were pinned to
one, two or three paper sections (1.54 x 5.08 CM) contain
ing 50-6 FAW eggs. The corn plants were approximately 4
weeks old and 75-85 mm in height and the egg masses were
pinned to the lower surfaces of the upper leaves within
20.3 cm of the growing terminal. Twenty female C.
insu1aris were released into each cage just prior to
sunset followed by release of 20 marginiventris females
on each of the next 3 days. The experiment was repeated
3 times over a 4 month period with 3 cages per replicate.
Plants with paper sections were sampled 3 days after the
final introduction of C. marginiventris and the remaining
plants in the perimeter area were allowed to grow for 2
weeks prior to sampling.


FIG. 1. Mean percentage emergence of C. insularis (Ci),
M. man i 1ae (Mm), and C. marginiventris~[ Cm) fr om f a11
armyworm "1 ar v ae exposed to mu it (pe pr as i t i z at i on .


28
In classical biological control, the potential for
interspecific competition exists when more than one
species of natural enemy is released into the environment.
Regarding such multiple species introduction, it has been
suggested that such interspecific competition could
possibly lead to a decline in population regulation of the
host (Turnbull and Chant 1961, Watt 1965) although others
have refuted this as a general phenomenon (Huffaker et al.
1971). Empirical evidence generally supports multiple
species introductions (Ehler 1978). However, such
evidence comes largely from successes involving multiple
species releases without regard to instances where such
releases did not yield total success (Ehler 1977). Miller
(1977) suggested the possiblity that intrinsically
superior competitors which exhibit a relatively low repro
ductive capacity would displace or interfere with
intrinsically inferior competitors which exhibit a rela
tively high reproductive capacity. There is a concern
that such competition would result in decreased par as it i -
zation rates. A computer simulation by Watt (1965) and a
greenhouse study by Force (1970) suggested that such a
reduction in the proportion of parasitization is
possible.
Other things being equal, intrinsically superior
species imported in biological control programs probably
become established more easily than intrinsically inferior


30
the pine shoot moth, Rhyaciona buoliana Schiff. They
reported that T. interruptor attacked more host larvae that
had been previously parasitized by 0^ obscurator than
unparasitized hosts. Vinson (1972) reported that in
interspecific competition between larval parsito ids
Cardiochiles nigriceps Viereck and Campo 1etis perdistinctus
(Viereck) on tobacco budworm, virescen s, that C .
perdistinctus had a slight advantage over nigriceps when
oviposition by the 2 species occurred at about the same
time. Part of the reason for the advantage by C^_ perdi s-
tinctus may be more rapid growth rate of its larvae and a
shorter egg development period. When the competitors were
of similar age, one was eliminated through physical combat.
When one competitor is 1 or 2 days older it was able to
destroy several eggs of the younger competitor. However
when older parsito id is 4 days old the younger larvae is
eliminated through physiological suppression (Vinson et al .
1972). Such suppressed larvae failed to grow and were
inactive although they may be alive. When one of the
tobacco budworm parasitoids was old or it eliminated the
younger competitor by physiological suppression (Vinson
1972). Fisher (1961) also presented evidence of physiologi
cal suppression of younger larvae by the older competitor
through the reduction of oxygen available to the younger
larva. Wylie (1972) reported that only one parasitoid


46
placed in a plexigls cage (25 cm3) and exposed to two
female C. insularis (24-48 hrs old) for 24 hrs. Each mass
was observed to verify that a C^_ i nsul ar i s female had
parasitized the eggs. Masses attacked by two or more
females and eggs close to the edge of the paper section
that were not parasitized were destroyed. The larval
parasitoids emerged in plexiglass cages (25 cm3) kept at
26 +_ 1C, 60-70% RH and under a 14:10 LD photoperiod with
a fluorescent light intensity of 800 ft-c. Female
parasitoids were held in these cages along with males for
a minimum of 48 hrs. Unless otherwise indicated, female
parasitoids were between 2 to 4 days old. Host exposure
for the larval parasitoids lasted 24 hrs and was
accomplished by placing parasitoids, FAW larvae, and 1.5
cm cube of FAW diet (Leppla et al 1979 ) into a 50-ml
container (7 x 10 cm diam) with two air vents (1.5 x 3.0
cm) located near the top on opposite sides. Parasitoids
were supplied with honey and water after adult eclosin
and during the ovi pos itional period. Following host
exposure, FAW larvae were placed individually into 30-ml
plastic cups that contained approximately 15 ml of diet.
These cups were held in a growth chamber at 25 +_ 1C,
77-80% RH and under a 14:10 LD photoperiod.
Experiment 1. Ninety FAW exposed previously to C.
insu1aris as eggs were divided into three equal groups.


FIG. 5. Progeny sex ratios for C. insularis (C.i.) from
different aged margi ni ventr i s~fC .~m erer g i ng from fall
armyworm larvae par asTtTzed as eggs by C. insularis.


31
species survived in interspecific competition among the
pupal parasitoids N asonia vitripennis (Walk)., Muse idi-
fura zaraptor K. & L. and $p1 angi a cameroni Perk. Nasonia
vitripennis and M. zaraptor were both intrinsically
superior to cameroni if the attacks on the hosts by
their females preceded, were simultaneous with, or
followed by up to 48 hrs those by females of cameroni.
Nasonia vitripennis was intrinsically superior to M.
zaraptor if its attacked preceded that by M_^ zaraptor by
at least 24 hrs. The success of vitripennis when
competing with S. cameroni was due to differences in rates
of egg and larval development and of host utilization by
the two species. In a similar study by Wallner et al .
(1982), larval parasitoids Apanteles me!anoscelus
Ratzburg. and Rogas lymantriae (L.) inside the host
Lymantria dispar (L.) both attacked the previously
parasitized larvae but the parasitoid attacking the host
first was more successful.
The studies on mu 11ipar as itism between the internal
larval parasitoids of Rhyacionia buo 1iana Schiff. revealed
that interspecific competition took place between the
first instar larvae through direct physical attack
(Schroder 1974). However there are instances where these
internal parasitoids have coexisted within the host larva
and this provides a good example of a system of


FIG. 7. Mean
host densities
insularis.
progeny production by C. marginiventris at 7
from eggs previously par as itized by C.


138
Hafez, M. 1951. Notes on the introduction and biology of
Microplitis demoliter (Hymenoptera:Braeonidae). Bull.
Soc. ent. Egypte. 35: 107-21.
Harcourt, D. C. 1960. Biology of the diamond-back moth
PIutel1 a maculipennis Curtis (Lepidoptera:PIutel1idae)
in eastern Ontario. III. Natural enemies. Canadian
Ent. 92: 420-21.
Huffaker, C. B. and P. S. Messenger. 1976. Theory and
practice of biological control. Academic Press, New
York. 743 pp.
Huffaker, C. B., P. S. Messenger and P. De Bach. 1971.
The natural enemy compenent in natural control and the
theory of biology control. In Biological Control. C.
B. Huffaker (Ed.) Plenum, New York. 511 pp.
Johnson, B. 1959 Effect of par as itization by Aphidius
platensis Brethes on the developmental physiology of
its host, Aphis craccivora Koch. Ent. Exp. Appl. 2:
82-99.
Keller, M. 1980. Effects of temperature and corn
phenology on FAW biology. M. Sc. Thesis Dept.
Entomology and Nematology, Univeristy of Florida,
83 pp.
Kunnalaca, S. and A. J. Mueller. 1979. A laboratory
study of Apante 1 es marginiventris, a parasite of green
cloverwornT nV fro~ Entomol 8 : 365-368 .
Legner, E. F. 1969. Adult emergence interval and
reproduction in parasitic hymenoptera, influenced host
size and density.
220-26.
Ann. Entorno 1.
Soc.
America.
62:
Leppla, N.E., P. V.
Vail, and J. R.
Rye.
1979 .
Mass
reading and handling techniques for the cabbage looper.
Proc. Radio isotopes and radiation in Entomology
Training Course. FAO/IAEA. 59-75.
Lewis, W. J. 1970. Life history and anatomy of
Microplitis croceipes (Hymenoptera:Braeonidae), a
parasite of Heliothes spp. (Lepi doptera : Noctuidae).
Ann. Ent. So~c~. Airier fc a 63: 67-71 .


70
exposed to two female marginiventris for 24 hrs inside
a plastic container which was similar to the one used for
C. insularis The host larvae were then placed inside 30
ml plastic cups containing approximately 15 ml of diet.
These cups were sealed with paper lids and placed inside
the cabinet. The larvae remained in these cups and their
fate recorded. The control treatment for experiments 1
and 2 consisted of larvae exposed only to margini-
v e n t r i s .
Experiment l--Host Age
Forty second instar FAW larvae (head capsule width
0.4-0.5 mm) were transferred to an ovi pos itional unit at
12, 24, 36, 48, 60, 72, and 84 hrs of age and exposed to
two female marginiventris for 24 hrs. Each age was
replicated seven times.
Experiment 2--C. marginiventris Age
Cotesia marginiventris cocoons were held for adult
sclosion and mating inside a plastic container similar to
the one used for C. insularis oviposition. When C .
marginiventris parasitoids were 24, 48, 72, 96, and 108
hrs old, two females were exposed for 24 hrs with 40
second instar FAW larvae. Treatments were replicated
seven times.
Experiment 3--Temperature Effects
Thirty second instar FAW larvae were exposed to two
female margi ni ventr i s for 24 hrs. These experiments


54
larval diet may be one of the sources of artificial
selection encountered when an insect population is placed
under laboratory colonization (Boiler and Chambers 1977).
However, reasons for those larvae that fed on the diet but
did not pupate or molt during the allocated period were
not properly understood. Beckage (1982) observed Manduca
sexta (L.) larvae parasitized by Apanteles smerrintie
Riley often molted to larval-pupal intermediates even when
parsito ids failed to emerge.
Experiment 2. The proportions of C_^ marginiventris
and M. mani 1 ae adults that emerged from parasitized and
non-parasitized hosts were not different significantly
(Table 5). Cotesia marginiventris parasitized signifi
cantly more hosts then M^ man i 1ae. Larvae that were not
parasitized by either parasitoid and emerged as FAW adults
displayed significant differences in all four treatments.
These data support the results of experiment 3, where M.
mani 1 ae females altered their ovipositional behavior
toward hosts already parasitized by insu1aris. Cotesia
marginiventris did not appear to discriminate against
hosts parasitized previously by C^_ insu1 aris as there were
no significant differences between C. insularis x C.
marginiventris and C^ marginiventris only treatments.
Vinson and Iwantsch (1980) did not discriminate against C.
insularis parasitized tobacco budworm hosts and neither
did M. croceipes .


TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS
LIST OF TABLES vii
LIST OF FIGURES viii
ABSTRACT x
INTRODUCTION 1
LITERATURE REVIEW 5
The Fall Armyworm, Spodoptera frugiperda
(J.E. Smith).. 5
Seasonal Distribution 5
Life History 6
Economic Status 8
Natural Mortal ity 9
Management Strategies 13
The Larval Endopar asitoid Cotesia
margi n i ventr i s Cresson 14
rTgT and Distribution 14
Description 15
Life Cycle 17
The Egg-Larval parsito id Chelonus
i nsul ar i s Cresson 19
0 r f g T n and Distribution ¡g
Description 20
Life Cycle 21
The Larval Endopar asito id Mic r 0 p1 itis
man i 1 ae Ashmead 23
Description and Distribution 23
Interspecific Competition 25
BIOLOGY AND HOST ACCEPTANCE OF MICROPLITIS
MAN I LAE (HYMENOPTERA: B R A C 0 N I D Al7~R ATDeD~DN FALL
ARMYWORM LARVAE 34
Introduction 34
Materials and Methods 35
Age group Acceptance 36
Developmental Rates 36
Adul t Longevity 37
Time of Host exposure 37
Results and Discussion 37
iv


80
70
60
50
40
30
20
10
Chelonus insularis
R Cotesia marqiniventris
H Other parasitoids
US LS GR SH ST
PLOTS


C\J
CO
Table 10. Mean percentages (+ SE) when reared at several constant temperatures for emer
gence of Chelonus insularis (C.i.J* Cotes i a marginiventris (C.m.) and adult fall armyworm and
percentages for FAW~Tarvae failing to mature because they (1) refused to feed on diet and died,
(2) died from unknown causes, (3) still larvae at end of test, and (4) escaped from cup a/
Temperature
Percent
Parasitoid emergence
Refused diet
Unknown
Sti 1 1
(C)
C. i.
C.m.
FAW
and died
causes
alive
Escaped
19
10.3_+1.5 a
8.5 + 2.0 a
8.2+1.9 a
26.9 + 2.0a
15.5+ 3.4 a
30.5 + 3.0 a
3.3 + 1.4a
22
12.6+2.la
18.6+1.9b
16.1 + 1.8a
34.4 + 2.7b
3.9 + 1.2b
14.2+3.2b
2.3 + 1.2 a
25
13.6+2.6a
61.0+3.6 c
15.5 + 3.9 a
3.9+1.1d
6.0+1.8b
0.0+0.0 c
1.9+1.2ab
28
34.4+2.Ob
32.8+3.0d
15.2 +1.4a
9.3 + 1.7c
7.8+1.4b
0.5+4.9c
1.8+1.2ab
31
38.9+1.8b
29.8+3.3d
14.9 +3.0 a
9.6+0.9c
6.8+1.5b
0.0+_0.0 c
1.5+1.Oa
Control
35.5+1.4b
17.6+1.0 a
10.3 +0.8c
10.7+1.0b
1.5+l.lc
15.0+1.7c
a/ Treatments were replicated 7 times with 30 1 arvae/treatment. Means followed by same
letter for a given column was not significantly different by Duncans Multiple Range Test.
(P = 0.05).


55
Table 5. Mean percentage emergence for Cotesia marginiventris
(Cm) and Microplitis manilae (Mm) from FAW larvae exposed and not
exposed as "egg s~ ~t~o~ ~Che~l onus i nsu 1 ar i s (Ci) and percents for emergence
of FAW adults, 1 arvae "dying" because they refused to eat the diet, and
larvae not pupating.
Treatment
Mean
emergence
FAW
Refused
d i et
Did not
pupate^
Ci
Cm
Mm
C i x Cm
32.5
56.5
5.0
0.0
0.0
Cm only
52.5
30.0*
4.3
6.3
C i x Mm
48.0
37.5
13.0
0.0
0.5
Mm only
44.5*
28.5*
11.5
16.5*
treatments replicated nine times with 20 1 arv ae/treatment. Data
analyzed by Student's _t-test (* = significantly different at the 5%
level).
Comparisons only made between treatments 1 ant 2, and 3, and 4. The
means for Ci in treatments 1 and 2 were not compared statistically.


91
(Zwolfer 1970). Ashley (1979) recorded 53 species in 43
genera from 10 families having been reared from FAW
larvae. Two of the most frequently recovered parasitoids
in the FAW overwintering region in Southern Florida were,
Cotesia (Apanteles) marginiventris Cresson which develops
in FAW larvae, and Chelonus insularis (Cresson) which
parasitizes the egg emerges during the larval stages of
FAW (Ashley et al. 1982) .
We performed 4 experiments in the evaluation of
FAW/parasitoid interactions. The objective of the first
experiment was to study the functional response of C.
marginiventris when exposed to different densities of FAW
previously parasitized by C. insularis In the second
experiment we examined the functional response of C.
marginiventris to different levels of mu 11iparas it i zed
host densities inside the laboratory. In the third
experiment data were obtained on the ovipositional
preferences of these two parasitoids at different FAW
densities inside field cages. The fourth experiment
determined the impact of C^ insularis and C_^ margini
ventris on FAW larvae found in different regions of the
plant and the surrounding environment.


116
Table 14. Sex ratio + SE ( q : <5* ) for C. marginiven-
tris (C.m.) and C. insularTs (C.i.) from FAWlarvae parasi
tized inside a field cage.
Egg mass
size
C.m. C.i.
Sex ratio (9:6) Sex ratio ($:?)
1.00:5.5+0.9 1.90:1.00+1.6
1.00:2.00+0.7 1.00:1.70+0.3
<50 (1 Paper section)
>50 <120 (2 . )
>120 <180 (3 . )
3.5:1.00+1.3
2.9:1.00+0.9


90
70
50
30
10
Ip IP
insularis
marginiventris
2
2 3
- May 27
June 29-
TEST PERIOD
3


GENERAL SUMMARY AND DISCUSSION
Many factors influence the suitability of a potential
insect host for parasitoid growth and development. For
example, a host may be unsuited, if already parasitized or
at stage of development inappropriate for parasitization.
In the case of solitary parasitoids, prior parasitization
of the host by another parasitoid of either the same or
another species can result in a host not being suitable.
Thus, if two solitary parasitoids occur in the same host,
one individual usually destroys the other. Whether the
competition involves physical attack, secretion of toxins,
physiological suppression, or selective starvation, the
outcome is largely dependent upon the species involved,
the parasitization sequence, and the length of the inter
val between attacks. A myriad of parasitoids attack FAW
(Ashley 1979) and their interrelationships influence the
population dynamics of the pest. At present, the basic
biological strategy control for FAW is to introduce as
many suitable natural enemies as possible in the hope that
the "best" species or combination of species will prevail.
In this regard, available theoretical and empirical
evidence indicated that the level of biological control
usually increases as the number of natural enemy species
increases (Huffaker et al 1971). Results reported here
130


I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.
Professor of Plant Pathology
This dissertation was submitted to the Graduate Faculty
of the College of Agriculture and to the Graduate School
and was accepted as partial fulfillment of the
requirements for the degree of Doctor of Philosophy.
August, 1985
Dean


38
Table 1.
Percent
paras itization by
armyworm larvae
m a n i 1 a e
of fall
Age
Test numbers9/
group
(hr s)
1
2
3
4
1 (24-48)
24.5 a
26.7 a
26.7
a
13.2
a
2 (49-72)
28.3 a
30.1 a
27.8
a
11.4
a
3 (73-96)
22.5 a
20.7 b
19.5
b
12.3
a
4 (97-130)
6.9 b
5.2 c
6.8
c
3.5
b
Total
369
418
521
279
Percentages followed by the same letter in the same column
are not significantly different by Duncan's Multiple Range
Test (P = 0.05).


140
Mitchell, E. R., V. H. Waddill and T. R. Ashley. 1984.
Population dynamics of the fall armyworm (Lepidoptera:-
Noctuidae) and its larval parasites on whorl stage corn
pheremone-permeated field environments. Environ.
Entomol. 13: 1618-23.
Moon, R. D. 1980. Biological control through
interspecific competition. Environ. Entomol. 9(6):
723-28.
Morrill, W. L. 1973. Ecology, economics and behavior of
the fall armyworm in field corn. M. Sc. Thesis.
Department of Entomology and Nematology. University of
Florida. Gainesville, 60 pp.
Morrill, W. L. and G. L. Greene. 1973. Distribution of
FAW larvae: 2. Influence of biology and behavior of
larvae on selection of feeding sites. Environ.
Entorno 1 2: 415-8.
Mourier, H. and S. B. Hannine. 1969. Activity of pupal
parasites from Musca domestica in Denmark. Vidensk.
Meddr dansk naturh Toren. 132: 211-6.
Mueller, A. J. and S. Kunnalacca. 1979. Parasites of
green cloverworm on soybean in Arkansas. Environ.
Entomol 8: 376-79.
Muesebeck, C. F. W. 1918. Two important introduced
parasites of the brown tall moth, Euproctis chrysorrhea
L. J. Agrie. Res. 14: 191-206.
Muesebeck, C. F. W. 1921. A revision of the North
American species of ichneumon-flies belonging to the
genus Apante!es. Proc. U.S. Nat. Mus. 58: 483-76.
Navas, D. 1974. Fall armyworm in rice. Proc. Tall
Timbers Conf. on Ecol. Anim. Control by Habitat
Manage. 6: 99-106.
Nickle, D. A. 1976. The peanut agro ecosystem in Central
Florida: economic thresholds for defoliating noctuids
(Lepidoptera:Noctuidae) associated parasites; hyper
parasitism of the Apanteles complex (Hymenoptera:
Braconidae). Ph.D~ dissertation, Department of
Entomology and Nematology, University of Florida. 131
PP


REFERENCES
Abies, J. R. and S. B. Vinson. 1981. Regulation of host
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Altahtawy, M. M., S. M. Hammad and E. M. Hegazi 1976.
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134


89
C. insularis larvae by physical attack and killed them in
5 days.
In summary, C_^ marginiventris reproduced most suc
cessfully in 36 hr old FAW larvae. mar g i n i ventr i s
adults which were 48 to 96 hrs old produced the greatest
number of parasitoids. Cj_ i nsul ar i s and mar g i n i ventr i s
developed optimally at 31 and 25C. Cotesia marginiven
tr i s physically attacked developing C. i n s u 1 aris larva
inside the host. Dead man i 1ae larvae were found in
hosts mul t i par as i t i zed by C^_ i nsu 1 ar i s and man i 1 ae but
the cause of the death was unknown.


LIST OF TABLES
Table Page
1. Percentage par as itization by M_^ m a ni 1 a e of fall army-
worm larvae 38
2. Developmental periods (x + SE) and progeny sex ratios
for M. manilae in fall armyworm larvae 40
3. Percentage parasitization of second age group fall army-
worm larvae exposed to man i 1 ae for various amount
of time 42
4. Mean percentages for emergence of Chelonus insular is
( C. i .) Microplitis manilae (M.m.), Cotesia marg_i ni_-
ventris ( C. m .") acT_ad u Tt" T al 1 armyworm (7717)7 and
percentages of FAW larvae failing to mature because
they refused to feed on the diet, died from unknown
causes or failed to pupate 53
5. Mean percentages for emergence of Chelonus insu1 aris
(C.i.), Cotesia marginiventris (C.m.) Microplitis
manilae (M .m .J acT acTuTt~"T aTT- armyworm ( Fl*) ancT^mean
percentages of FAW larvae failing to mature because they
refused to feed on the diet or failed to pupate 55
6. Mean number and percentage of larval encounters, exami
nations, oviposit ion probes and apparent ovipositional
successes by Cotesia marginiventris and Microplitis
manilae in faTI armywcTrrn larvae exposed and not exposed
as eggs to Che! onus i nsu 1 ar i s 57
7. Mean percentages for numbers of encounters, examinations
and apparent ovipositions by C. marginiventris and
M. mam' 1 ae during 2 host exposure" "perio'ds separated by
cTTfferent numbers of days 58
8. Mean percentages at different host ages for emergence of
Chelonus insularis (C.i.) Cotesia marginiventris (C.m.),
and 3T¡Tt~rTl armyworm (FAT) ancfper cent age mortality of
FAW larvae due to (a) refusal to feed on the diet and
(2) death from unknown causes 73
9. Mean percentages for emergence of Chelonus insularis
(C.i.), Cotesia marginiventris (C.m.), ancf aduTt Yaf
armyworm (TAV) ancl percent mortality FAW larvae due
(1) refused to feed on the diet and (2) died from
unknown causes, when age of C.m. was changed
76


9
Natural Mortal ity
Various abiotic and biotic agents act as mortality
agents of FAW populations in the field. Physical environ
ment and natural mortality factors may act singly or in
combination to determine the annual distribution pattern
and densities of FAW populations (Barfield et al 1980).
Among abiotic environmental factors, temperature appears
to be an important limiting factor (Barfield et al 1980).
Low temperature may be the most important factor limiting
the winter survival of FAW (Luginbill 1928, Wood et al.
1979). Andrews (1980) reported that torrential daily
rains for several days result in drowning of small larvae
or washing them out of the whorls in corn in Central
America.
Cannibalism among larvae is an important factor
limiting population densities (Luginbill 1928). Mortality
attributable to cannibalism and intraspecific competition
is positively correlated with larval density (Wiseman and
McMillian 1969). Olive (1955) reported that first instar
larvae may destroy adjacent unhatched eggs while in the
process of devouring their own egg shells. Ashley (Pers.
Comm. 1985) studied the factors influencing cannibalism in
FAW and showed that the larval density in combination with
the amount of eatable surfae area affected cannibalism
more significantly than did the amount of non-eatable
surface area, diet volume, or photoperiod.


69
regime with a fluorescent light intensity of 800 ft-c and
were supplied with honey and water. Adults of margini-
ventris and C. insularis came from laboratory colonies
established from FAW larval collections made from corn at
Hastings and Homestead, Florida, respectively (Ashley
1983). Unless otherwise noted, parasitoids were 24-48 hrs
old when used. The FAW host eggs were obtained from
female moths maintained in a growth chamber set at
26-27C, 70-75% RH and with a 14:10 LD photo regime. Host
eggs were seperated using the technique of Gross et al.
(1981). All eggs utilized in the experiments came from
the same egg mass to help insure host uniformity. A grid
was drawn on filter paper and individual eggs were placed
in the center of each square. In all experiments FAW eggs
were exposed initially to two female insularis inside a
circular plastic container (7 x 10 cm diam) with 2
screened vents (1.5 x 3.0 cm) and containing 4 cubes
(1.5 cm) of FAW diet (Leppla et al 1979). Eggs attcked
by two or more females and unparasitized eggs were de
stroyed. The grids were then cut into squares and sus
pended in a plastic container like those used for oviposi
tion by Cj_ i nsul ar i s until egg hatch. These containers
were kept inside an environmentally controlled cabinet set
at 27C, 70% RH, with a 14:10 LD photophase. When the FAW
larvae were 48 hrs old (all were second instars) they were


142
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Biology of Microp1 itis demolitor (Hymenoptera:
Braconi dae)~ imported parasitoid of He!iothes spp.
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hybridus in field corn. Entomophaga. IT: 5-7._


63
non-searching movement, searching, oviposition, and
resting. Analysis of our ethogram and that of Loke et al.
(1983) showed that the elimination of certain steps in our
ethogram are of particular interest because chemical cues
from the earlier oviposition by insularis may have
altered the behavioral pattern of the female margi ni -
ventris after ovipositing in an already parasitized FAW
larvae.
The percent par as itization by C marginiventris
showed more than a two-fold increase in corn compared to
sorghum and more than a four-fold increase over Bermuda-
grass and itch grass (Fig. 3). Sixty percent of the
larvae were parasitized by marginiventris in corn after
an 80-min host exposure period. There was no increase in
par as itization for Bermudagrass and itch grass after 20
min. Ashley et al. (1983) found that par as itization rates
for i nsul ar i s and T erne! ucha spp. were substantially
higher in corn than in Bermudagrass and paragrass Brachi-
arie m u tic a (L .) C o t e sia marginiventris parasitized the
highest proportion of hosts in Bermudagrass and paragrass.
The differences in par as itization rates between these
parasitoids may reflect a host plant preference (Ashley et
al. 1983).
In our study, M. man i 1ae apparently failed to compete
successfully within the host larva when this larva contain


11
(Br achiarie mutic a (L)) reported that C in s u1 a ris Cresson
was the principal parasitoid on corn and i n s u 1 ar i s and
A. marginiventris were the major parasitoids on
Bermudagrass while M. autographae parasitized the highest
proportion of hosts in paragrass, reflecting a host plant
preference. The native parasitoids C^_ i n s u 1 ar i s and A .
marginiventris were the primary species attacking FAW
larvae in South Florida and they destroyed 63% of each of
the first instars; M_^ autographae and Rogas 1 aphygmae
Viereck, as well as several tachinids and a group of
unidentified ichnuemonids, accounted for the rest of FAW
larval mortality (Ashley et al. 1982). Tingle et al.
(1978) reported that parasitoid populations attacking the
FAW on alternate host plants of, in or near crop fields
may be important sources of parasitoids that subsequently
attack FAW larvae in corn. Waddill et al ( 1985) dis
cussed the seasonal abundance of FAW parasitoids, C.
i nsul ar i s, Teme! ucha spp. 1 aphygmae, and margini
ventris in southern Florida. Mitchell et al. (1984)
reported that FAW pheremone components had no significant
effect on the level of FAW par as itization by in s u1 a ris
and Teme 1ucha difficulis Basch. The successful rearing of
a pupal parasite Diapetimorpha introita of FAW in the
laboratory has also been documented (Pair et al. 1985).
Predators and pathogens are among other natural
enemies found to play a less consistent role in regulation


8
Roberts (1965) reported that the larval diet can affect
the duration of larval period, pupal size, adult
longevity, fecundity, and egg viability.
Economic Status
In some years FAW larval densities are low and not
economically important while in other years high densities
inflict serious economic losses (Sparks 1979). The FAW
was recorded as an injurious pest in Georgia in 1797, and
in Florida in 1856 (Sparks 1979).
Damaging populations of FAW appear to occur
irregularly (Barfield et al 1980). FAW infestation
levels are unpredictable (Barfield et al 1980) and
conditions conductive to outbreaks are not well
understood (Keller 1980).
The FAW causes damage to corn by feeding on the
developing leaves within the whorl. In areas with severe
infestations the tassels, ears, mature leaves and stalks
are also consumed (Painter 1955). Defoliation ranges from
skeletonization of leaves by early larval instars to
complete leaf consumption by large larvae. Annual losses
due to larval feeding are estimated to be between $300 to
500 million in the United States (Mitchell 1979). Larval
food consumption has been studied by Luginbi 1 1 ( 1928) and
Barfield et al. (1980).


103
The sex ratio of marginiventris progeny favored
females at densities of 2 and 4 larvae (Fig 9). The C.
insu1aris males outnumbered females at all densities
except at 4 eggs/larvae where 1:1 ratio was obtained (Fig
10). The presence of more females at low densities may be
seen as a mechanism that ensures the presence of a minimum
number of males to fertilize all the females. Such
mechanisms have been reported in other parsito ids in
which mated females are functionally virgin for a certain
period of time after mating (Mackauer 1976).
Experiment 2--Fie1d Cages
Che!onus insu 1aris emerged most frequently in treat
ments having 1 or 2 paper sections while marginiventris
was the major parasitoid in the 3 paper section treatment
during the first and second test periods (Fig 5). In the
last test period no definite emergence patterns were
observed. The decrease in emergence of C. insu1 aris in 3
paper section treatment indicated that C. marginiventris
was a better competitor in crowded host conditions.
Wiseman et al. (1983) reported that FAW larvae often moved
from infested plants onto surrouding border plants during
the 3 to 5 days after infestation. This movement may have
aided marginiventris in locating hosts. insularis
emerged more successfully in 1 and 2 paper sections and
appeared to search the portions of corn plants where most
FAW eggs were deposited. However, Loke and Ashley (1984)


Table 15. Mean percentage of small (0.2-0.7), medium (0.8-1.2), large (1.3-2.4) head capsule
widthsfrom FAW larvae collected from upper surface (US), lower surface (LS), ground (GR), between
stalk and leaf sheath (SH) and stalk (ST) in corn, a/
Percent
Col lection
Date Small Medium Large
US
LS
GR
SH
ST
US
LS
GR
SH
ST
US
LS
GR
SH
ST
May 14, 1983
15.6a
20.5a
2.0c
10.5b
0.5c
11.0b
15.0b
0.0c
15.0b
0.5c
0.0c
1.0c
0.0c
2.0c
0.0c
May 27, 1983
17.0a
10.5b
0.0c
15.0ab
0.0c
10.0b
17.0a
0.0c
12.0b
0.0c
3.0c
2.0c
0.0c
10.0b
0.0c
June 14, 1983
8.0b
10.5b
0.0c
25.5a
0.0c
8.0b
12.0b
0.0c
30.0a
0.0c
2.0c
1.0c
0.0c
3.0c
0.0c
June 28, 1983
10.0b
12.0b
0.0c
20.0a
0.0c
5.0c
10.0b
O.Od
21.0a
O.Od
5.0c
4.5cd
O.Od
12.0b
O.Od
Aug. 14, 1983
3.0cd
10.8b
O.Od
31.0a
O.Od
14.5b
3.0d
O.Od
14.0b
O.Od
5.0c
4.0cd
O.Od
12.0b
O.Od
Aug. 28, 1983
3.5c
12.5b
O.Od
29.0a
O.Od
3.0d
8.5cd
O.Od
19.0b
O.Od
6.0d
8.6cd
O.Od
O.Od
O.Od
a/ Means in the same row followed by same letter were not significantly different by Duncans
Multiple Range Test (5% level).


48
observed. A probe was recorded when the parasitoid
thrusted its ovipositor toward the larval cuticle.
Finally, an apparent oviposition took place when the
parasitoid mounted the host and inserted its ovipositor.
Three replicates for each parasitoid species and larval
combination were examined. Further replication was not
possible because of the loss of the man i 1ae colony.
Experiment 4. Eight host larvae derived from one of
the following four groups were placed in a glass petri
dish (15 x 100 mm diam): (1) initially parasitized by C.
marginiventris and subsequently exposed to M. manilae; (2)
initially not exposed to parsito ids and subsequently
exposed to M_^ manilae; (3) initially parasitized by M.
manilae and subsequently exposed to C^_ margi n i ventr i s ; and
(4) initially not exposed to parasitoids and subsequently
to C. marginiventris.
As hosts were attacked they were removed and replaced
with fresh larva. Non-par as itized larvae served as a
control. The number of host encounters, examinations and
apparent ovipositions were recorded. Five replicates for
each species combination were run starting on the same day
hosts were parasitized and then repeated 3 and 6 days
later.
Experiment 5. The host finding behavior of C.
marginiventris was investigated using 4-week-old corn,
sorghum, Bermudagrass (Cynondon dactylon (L.)), and itch


26
result in the competitive exclusion of certain species
(Debach and Sundby 1963).
In many cases of interspecific competition, one
species has an intrinsic superiority over its opponent and
invariably destroys it, by the use of its mandibles
(Pemberton and Willard 1918, Simmonds 1953) or by an
unspecified means of physiological suppresion (Muesebeck
1918, Fisher 1961, Salt 1961).
More commonly there is no intrinsic superiority on
the part of either parasitoid, and free competition occurs
between them, the victor completing its development and
the loser dying, either as an egg or a young larva.
Several suggestions have been made in the literature as to
the possible mechanism of competition between such soli
tary endoparas itic species. In the first place, the older
parasitoid is presumed to survive by eliminating the
younger through starvation (Fiske and Thompson 1909) thus
emphasizing the importance of time of oviposition as the
determining factor in competition. Secondly, cases of
direct physical attack by one parasitoid on another using
the mandibles for fighting has been recorded (Simmonds
1953). In these cases neither competitor has an intrinsic
advantage over the other and the result of competition is
apparently decided by the time of oviposition. The third
suggestion is that one parasitoid eliminated the other by
physiological suppression, either by conditioning the
hemolymph of the host so that it becomes unsuitable for


INTERSPECIFIC COMPETITION OF FALL ARMYWORM
SPODOPTERA FRUGIPERDA (J.E. SMITH) PARASITOIDS,
CHELONUS INSULAR IS (CRESSON), COTESIA MARGINI VENTRIS
rCR£55$$T~m MICROPLITinWfJTTAF£5TT7\D
(HYMENOPTERA: BRACON I DAE)
By
ROHAN HARSHALAL SARATHCHANDRA RAJAPAKSE
A
IN
DISSERTATION P
THE
PARTIAL FULFI
RESENTED TO THE GRADUATE SCHOOL OF
UNIVERSITY OF FLORIDA
LLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
1985




FIG. 12. Mean percent parasitized FAW instars in
treatments 1, 2, and 3 paper sections inside field cage.


127
Significantly more medium sized larvae were found between
the stalk and the leaf sheath, on the lower surface of the
whorl than in the other areas of the plant. The damage to
upper leaves ws significantly greater in non-parasitized
release plots than in parasitoid released plots.


80
70
60
50
40
30
20
10
0
80
70
60
50
40
30
20
10
0
Ci&Cm Ci&Mm Ci-only
TREATMENT
Ci
Mm
B Cm


87
24-30 hrs old at 22 and 25C than was _C^_ i nsul ar i s. In.
general, marginiventris emerged from a higher propor
tion of younger hosts than did C. insu 1aris Hosts older
than 36 hrs produced more insu1 aris regardless of
temperature. Two possible explanations for this are as
follows: (1) marginiventris was a better competitor in
younger hosts and (2) either oviposit ion or successful
competition was reduced in older hosts larvae containing a
developing insularis .
Experiment 4--Dissection of Multi parasitised Hosts
Dissections of multiparasitized larvae showed no evi
dence of physical attack between parasitoids during the
first 5 days of host development (Table 12). However 7
days after par as itition 5 C insu1aris larvae had visible
melanized scars, while those of marginiventris were
unscared suggesting that marginiventris physically
attacked larvae of C. i ns u1aris. Vinson and Ables( 1980)
reported that larvae of insu1aris had visible evidence
of physical attack after 3 days in hosts parasitized by
the larval parasitoid Campole is sonorensis (Carlson). Six
days after parasitization by M. manilae, 5 dead M.
man i 1ae larvae were found in the hosts. This number of
dead larvae was higher at 8 and 10 days although there was
no visible evidence of physical attack. Vinson and
Iwantsch (1980) reported that M. croceipes mutilated the


68
Ashley et al. (1982) reported the presence of a mirror
image pattern with respect to percent par asi tization of
FAW larvae by the larval parasitoids, Che!onus insular is
Cresson and Temelucha diffici1 is Dasch. and suggested
that interspecific competition may have cuased this
pattern.
Factors such as host age and environmental tempera
ture affect the outcome of interspecific competition and
evaluation of these factors should be of primary concern
before initiating parasitoid release programs against a
common host. A literature search provided no information
on the effect of host age and temperature on competition
among FAW parasitiods. Therefore, we selected the larval
parasitoids Microplitis man i 1ae Ashmed. Cotesia
(Apanteles) marginiventris Cresson and the egg-larval
parasitoid i n s u 1 ar i s for our investigations. These two
parasitoids are among the principal natural enemies
regulating FAW populations in southern Florida (Ashley et
al. 1983). The specific objectives of our study were to
determine the effects of host age, temperature and the age
of C^ marginiventris on interspecific competition.
Materials and Methods
Parasitoids were kept in plexiglass cages (50 x 50 x
24 cms) at 26 C,60-65% RH and under a 14:10 LD photoperiod


I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.
Dr. Van H. Wadd fTT, Chairman
Professor of Entomology and
Nemato1ogy
I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.
lomas K. Ashley, Lo-Ufairman
Associate Professor of Enromology
and Nematology
I certify that I have read this study and that in my
opinion it conforms to acceptable standards of scholarly
presentation and is fully adequate, in scope and quality,
as a dissertation for the degree of Doctor of Philosophy.
Dr. \john R. Strayer
Prcof^ssor and Entomology wid
N eVat o 1 o g y


133
the FAW, should be investigated. The predominant native
parasito id, C. in s u1aris, should be investigated to
determine other characteristics important in controlling
its impact on FAW larval populations. These include such
characteristics as spacial distribution, temporal
synchronization and reproductive rates. One of the major
areas requiring further research is the mechanism of
dominance in competition between parasitoids. I found
evidence of physical attack by marginiventris on
developing insularis larvae.
The potential impact of interspecific competition on
FAW biological control needs further research and should
include studies on: (1) competition studies between C.
insu1aris and T^ difficilis, since these two parasitoids
are the principal species in the overwintering range of
the FAW; (2) the effects of interspecific competition on
parasitoid population densities; (3) more detailed studies
on the developmental biologies of C. insularis, C.
marginiventris and T_. difficilis in FAW larvae; and (4)
more detailed life table analyses of FAW larval popula
tions. In addition, before more exotic parasitoids are
introduced, it should be determined in controlled
laboratory experiments if they can successfully compete
within FAW larvae, with the native species.


19
Ashley (1983) reported that parasitization of FAW larvae
by marginiventris reduced maximum larval weights by
97%, compared to 6th instar non par as itized larvae. C.
marginiventris destroyed its host when the host reached
the 4th instar. Hosts parasitized by C. marginiventris
gained the least amount of weight, produced the least
amount of frass, and had shortest life expectancies and
the smallest head capsule widths compared to other
parasitoids (Ashley 1983).
Loke et al. (1983) has described the behavioral
sequence for host finding and oviposition for C.
marginiventris on corn plants artifically damaged by 2nd
instar larvae of the FAW and reported that highest
parasitization rates occurred among 2nd instar larvae
collected from leaf surfaces. Bioassay responses in C.
marginiventris females to materials derived from FAW
larvae were most intense for frass and somewhat less
intense for larval and pupal cuticle materials, scales,
exuviae and silk (Loke and Ashley 1984).
The Egg-larval Parsito id Chelonus insular is Cresson
Origin and Distribution
CFTon us insu Tar is Cresson is one of the key
parasitoids regulating FAW populations in South Florida
(Ashley et al. 1982). It has been previously classified


10. Mean percentage (+_ SE) at several constant tempera
tures for emergence of Chelonus insularis (C.i.),
Cotesia mar g i n i ventr i s (~CTm.) an3 acfu it FAW and percen
tages of FAR farva~failing to mature because they
(1) refused to feed on diet and died, (2) died from
unknown causes (3) still larvae at end of test and
(4) escaped from cup 82
11. Mean (+ SE) emergence periods (days) at several con
stant temperatures for Cotesia marginiventris (C.m.) and
Chelonus insular is (C.iTJ and" "acfuTf TAtf, ancPper cent ages
for FAW larvae failing to mature because they (1)
refused to feed on the diet and died and (2) still
larvae at end of test 84
12. Fate of the larval parasitoids C. marginiventris (C.m.)
and M. manilae (M.m.) in competition with the egg-larval
par as i toTcf ~CT insularis as determined by dissection of
fall armyworm (TAW) larvae 88
13. Mean (+ SE) for superparasitized FAW, longevity of
adult IT. marg i n i ventr i s in days and percent survival
of hosTlarvae at 7 TAW densities 100
14. Sex ratio (+ SE) ( ) for ^ mar g i n i ventr i s (C.m.)
and insularis (C.i.) from F AW larvae par as ft i zed
inside a field cage 116
15. Mean percentage of small (0.2 0.7 mm), medium
(0.8 1.2 mm), and large (1.3 2.4 mm) head capsule
widths from FAW larvae collected from undersurface,
upper sur face, ground, between stalk and leaf sheath
and stalk in corn 124
Fall armyworm feeding damage to different regions of
corn in plots where insularis (C.i.) and margini-
ventris (C.m.) were re 1 eased .. 125
16.


71
were conducted in plastic containers like those used for
oviposition by C. insular is. After exposure to C.
marginiventris, larvae were placed individually in 30 ml
plastic cups and held at the following temperatures 19,
22, 25, 28 and 31C and RH 75-78% with a 14:10 LD photo
phase. Each treatment was replicated seven times. A
control treatment was run at 26C with host larvae exposed
only to insu1 aris. The cups were checked three times a
week and larval fate recorded.
In a second portion of this experiment larvae emerg
ing from eggs parasitized by C. insular is were exposed to
C. marginiventris when reaching the following host ages
(hrs) 6-10, 12-18, 24-30, 36-42 and 48-54. After exposure
to marginiventris larvae were individually placed into
30 ml cups and held at the temperatures cited above.
Treatments were replicated six times. The control
treatment was held at 26C and the RH ranged between
70-75%.
Experiment 4--Dissection of Mu ti parasitized Hosts
Host exposure to insu1 aris followed by exposure to
C. marginiventris or man i 1ae were performed as pre
viously described. The insu1 aris marginiventris
parasitized larvae were then placed inside a plastic
container for 3, 5, 7 or 9 days. The C. insularis M.
man i 1ae parasitized larvae were similarly held for


FIG. 11. Percent par as itization by C. insular is and C.
margi ni ventr i s from FAW larvae recovered TrfsT3efrom TTeld
cage during 3 test perids. Vertical bars within a test
period from lest to right indicate treatments 1, 2, and 3
paper sections.


123
Significantly more medium sized larvae (head capsule
width = 0.8-1.2mm) were found between stalks and leaf
sheaths and lower surfaces of the whorl (Table 15).
Initially, there were more small than large larvae feeding
under the lower surface and upper surface but this trend
was gradually changed with more medium sized larvae found
between stalks and leaf sheaths. The greatest difference
between small and large larvae was found between upper
leaf surface with small sized larvae. Ashley et al.
(1980) reported that FAW larval abundance decreased on
corn plant upper surface than lower surface and this
reduced abundance may be indicative of preferred feeding
locations. Our experiment showed that FAW larvae prefer
feeding locations such as between stalks and leaf sheaths,
and lower surface. Food quality, changes with feeding
location and may alter or influence larval development in
FAW (Keller 1980). Feeding inside the leaf sheaths and
the lower surface of whorls may be a form of protection
from natural enemies. Very few large larvae were
recovered in all 5 treatments.
The damage to upper leaves in the whorl was signifi
cantly greater in nonparasitoid release plots than in
parasitoid release plots (Table 16). These results
suggest that differences in degree of damage between
parasitoid release and non release plots were related to
the impact of the parasitoids. Significant differences