Citation
Ecology, economics and behavior of the fall armyworm in field corn

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Title:
Ecology, economics and behavior of the fall armyworm in field corn
Creator:
Morrill, Wendell L., 1941- ( Dissertant )
Greene, Gerald L. ( Thesis advisor )
Habeck, Dale H. ( Thesis advisor )
Lloyd, James E. ( Reviewer )
Reiskind, Jonathan ( Reviewer )
Walker, Thomas J. ( Reviewer )
Browning, C. B. ( Degree grantor )
Place of Publication:
Gainesville, Fla.
Publisher:
University of Florida
Publication Date:
Copyright Date:
1971
Language:
English
Physical Description:
x, 60 leaves : ill. ; 28 cm.

Subjects

Subjects / Keywords:
Armyworms ( jstor )
Corn ( jstor )
Corn ears ( jstor )
Infestation ( jstor )
Instars ( jstor )
Larvae ( jstor )
Leaves ( jstor )
Plants ( jstor )
Tassels ( jstor )
Worms ( jstor )
Corn -- Diseases and pests ( lcsh )
Dissertations, Academic -- Entomology and Nematology -- UF
Entomology and Nematology thesis Ph. D
Fall armyworm ( lcsh )
Genre:
bibliography ( marcgt )
non-fiction ( marcgt )

Notes

Abstract:
The fall armyworm, Spodoptera frugiperda (j. E. Smith), overwinters in southern United States and migrates northward during the growing season and attacks many crops. The economic damage level in field com was determined by infesting several com growth stages with known numbers of larvae, measuring larval mortality, weighing ears to determine yields, and comparing yields of infested and uninfested plots. Infestations before tassel and ear emergence did not consistently reduce yields. Infestations, occurring as tassels and ears appeared, showed significant yield reductions in 2 out of 4 plots at a density of 0.8-1.5 worms per plant. Tassel damage was of little importance; ear feeding resulted in some damage. Larvae did not penetrate to the apical bud. In pre-tassel com, most larvae were found in the whorl and furl, while in post- tassel com, larvae were found in the ears. Preference of plant tissues did not appear to be of significant importance in larval distribution on plants, but thigmotaxis may be important. First instar larvae were positively phototactic and negatively geotactic; the responses subsided dixring the second instar. More dispersal per day was found during the first 3 days than the first 12 days of larval life. Movement was greater at higher densities. Newly emerged larvae survived 20-35 hours without feeding. Starvation at this time did not affect pupal weights or duration of the larval stage. During starvation, survival of fifth instar larvae was increased by cannibalism. Sixth instar larvae could survive through pupation without feeding. Larval dimorphism and behavioral differences were shown at high and low densities. Duration of egg development was extended at 4-15 C; mortality increased after 24 hours at 1 C and 72 hours at 4 C. Larval development was extended at 14 C; none survived to pupation at or below this temperature. Pupae survived up to 12 days at G. Pupation occurs in the ground. Development of a cold-resistant stage or selection of a cold-protected pupation site are possible methods of overwintering. Early annual appearance in the North of this pest would pose a serious threat to northern United States agriculture.
Thesis:
Thesis (Ph. D.)--University of Florida, 1971.
Bibliography:
Bibliography: leaves 56-59.
Additional Physical Form:
Also available on World Wide Web
General Note:
Typescript.
General Note:
Vita.
Statement of Responsibility:
by Wendell L. Morrill.

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University of Florida
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Copyright [name of dissertation author]. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
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Ecology, Economics, and Behavior
of the Fall Arm yworm in Field Corn













By


WENDELL L. MORRILL


A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA IN PARTIAL
FULFILLI TNT OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY


UNIVERSITY OF FLORIDA
1971














DEDICATION



This dissertation is dedicated to the people who offered assistance

and encouragement during my academic career.














ACKNOWLEDGMENTS

I thank the following people for their contribution to this work:

Dr. G. L. Greene- supervision and encouragement, Dr. James Strandberg-

photographic assistance, Dr. Dale Habeck- advice and editing, Dr. W. H.

Whitcomb- advice, Dr. T. J. Walker- editing, Dr. J. Reiskind- editing,

Dr. J. A. Cornell- statistical assistance, Mr. R. L. Burton- supplying

a sample of fall armyworms, Mr. Joel Rodriquez- translation of a paper

written in Spanish, and technicians Linda Carrol, Art Young, and Karen

Stewart for helping with rearing and handling larvae.















TABLE OF CONTENTS

PAGE

ACKNOWLEDGEi~U TS ........................................ iii

LIST OF TABLES ......................................... vi

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

ABSTRACT ............................................... ix

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

REVIEW OF LITERATURE .................................... 2

ARTIFICIAL INFESTATION .................................. 7

Materials and Methods .............................. 7

Low Level Infestation ......................... 7

Mid-level Infestation ......................... 8

High Level Infestation ........................ 9

Moisture Estimation ........................... 9

Results and Discussion ............................. 9

BEHAVIOR OF LARVAE ...................................... 23

Materials and Methods .............................. 23

Phototaxis and Geotaxis ....................... 23

Results and Discussion ............................. 27

Phototaxis and Geotaxis ....................... 27

Preference of Plant Tissues ................... 27

FIELD DISTRIBUTION OF LARVAE ............................ 32

Materials and methodss .............................. 32









Distribution on Field Corn Plants ............... 52

Distribution on Ears ............................ 53

Dispersal from Egg Masses ....................... 37

LARVAL BIOLOGY ............................................ 45

Materials an.d e..e hods ................................ 5

Starvation of Newly Emerged Larvae .............. 45

Starvation and Cannibalism of Late Instar Larvae 45

Survival and Development During Periods of
Low Temperature ................................. 45

High Density Rearing ............................ 46

Results and Discussion ............................... 46

Starvation of Newly Emerged Larvae .............. 46

Starvation and Cannibalism of Late Instar Larvae 46

High Density Rearing ............................ 50

Survival and Development During Periods of
Low Temperature ................................. 52

REFERENCES CITED .................................... ..... 56

BIOGRAPHICAL SKETCH ....................................... 60















LIST OF TABLES


PAGE

Table 1.-Per cent survival of second instar S. frugiperda
larvae placed in field corn in the early whorl growth
stage ...................................... ........ 15

Table 2.-Per cent survival of second instar S. fruginerda
larvae placed in field corn in early, mid, and late
whorl growth stages ................................ 16

Table 3.-Mean and standard deviation of numbers of S. frugiperda
larvae surviving 7-9 days after field infestation at
various corn growth stages .......................... 17

Table 4.-Estimated moisture content and yield of field corn,
1970 ..................................... ... ....... 22

Table 5.-Selection of plant tissues by S. frugiperda larvae
in a preference chamber ............................ 30

Table 6.-Distribution of S. frugiperda larvae before and
after emergence of tassels in field corn ........... 39

Table 7.-Distribution of S. frugiperda and H. zea larvae in
field corn ears ..................................... 42

Table 8.-Dispersal of S. frugiperda larvae from egg masses in
the field ........................................... 44

Table 9.-Survival of starved unfed first instar S. frugiperda
larvae ............................ .................. 47

Table 10.-Pupal weights and duration of larval stages of
S. frugiperda larvae which survived a period of
starvation after emergence from the eggs ........... 48

Table 11.-The effect of starvation and cannibalism on LDro
and per cent pupation of S. frugiperda larvae ... 49

Table 12.-Pupal weights of starved cannibalistic and
noncannibalistic sixth instar S. frugioerda larvae 51







Table 13.-Hours required for development of S. frugiperda eggs
held at low temperatures for various lengths of time
before holding at 290C. ............................. 53

Table 14.-Survival of 2 day old S, frugiperda larvae at
low temperatures ............ ........................ 54

Table 15.-Effect of periods of low temperature on survival
and time for development of S. frugiperda pupae ..... 55














LIST OF FIGURES


PAGE

Figure 1.-Growth stages of field corn .................. 10

Figure 2.-Regions of field corn ........................ 12

Figure 3.-Cross sections of a field corn plant ......... 13

Figure 4.-Yield reduction of field corn by feeding of
fall armyworm larvae ............................. 19

Figure 5.-Behavior chamber used to determine phototaxis
and geotaxis of fall armyworm larvae .............. 24

Figure 6.-Chamber used to test larval preference of various
corn tissues .................................... 26

Figure 7.-Dispersal of first instar fall armyworm larvae from
the point of introduction in the behavior chamber 28

Figure 8.-Dispersal of each fall armyworm larval instar in a
vertical behavior chamber lighted from above ...... 29

Figure 9.-Regions of field corn infested by fall armyworm
larvae ............................................ 35

Figure 10.-Size distribution of fall armyworm larvae in
several plant regions ................. .......... 36

Figure 11.-Regions of field corn plants infested by fall
armyworm larvae ..................................... 38

Figure 12.-Contrasting corn development ................ 40

Figure 13.-Fall armyworm larvae commonly enter ears by boring
into the sheath at the junction of the stalk and the ear 41


viii














Abstract of Dissertation Presented to the
Graduate Council of the University of florida in Partial ?ulfillmient
of the Requirements for the -egree of Doctor of Philosochy



ECOLOGY, ECONOMICS, AtD BEHAVIOR
OF THE FALL AIMYWORHL IN FIELD COHN



By


Wendell L. Morrill


December, 1971


Chairman: Dr. G. L. Greene
Co-chairman: Dr. D. H. Habeck
Major Department: Entomology and hematology


The fall armyworm, Spodoptera frugiperda (J. E. Smith), overwinters

in southern United States and migrates northward during the growing

season and attacks many crops. The economic damage level in field corn

was determined by infesting several corn growth stages with known

numbers of larvae, measuring larval mortality, weighing ears to determine

yields, and comparing yields of infested and uninfested plots.

Infestations before tassel and ear emergence did not consistently reduce

yields. Infestations, occurring as tassels and ears appeared, showed

significant yield reductions in 2 out of 4 plots at a density of

0.8-1.5 worms per plant.








Tassel damage was of little importance; ear feeding resulted in

some damage. Larvae did not penetrate to the apical bud. In pre-tassel

corn, most larvae were found in the whorl and furl, while in post-tassel

corn, larvae were found in the ears. Preference of plant tissues did

not appear to be of significant importance in larval distribution on

plants, but thingotaxis may be important. First instar larvae were

positively phototactic and negatively geotactic; the responses subsided

during the second instar.

More dispersal per day was found during the first 3 days than the

first 12 days of larval life. Movement was greater at higher densities.

Newly emerged larvae survived 20-35 hours without feeding. Starvation

at this time did not affect pupal weights or duration of the larval stage.

During starvation, survival of fifth instar larvae was increased by

cannibalism. Sixth instar larvae could survive through pupation without

feeding. Larval dimorphism and behavioral differences were shown at

high and low densities. Duration of egg development was extended at

4-135C; mortality increased after 24 hours at 1 C and 72 hours at 40C.

Larval development was extended at 14 C; none survived to pupation at or

below this temperature. Pupae survived up to 12 days at 0 C. Pupation

occurs in the ground. Development of a cold-resistant stage or selection

of a cold-protected pupation site are possible methods of overwintering.

Early annual appearance in the North of this pest would pose a serious

threat to northern United States agriculture.













INTRODUCTION

It is necessary to determine the economic damage level, or numbers

of insects per plant which reduce crop yield, to predict when insect

control practices will be economically feasible. Fall amyworms are

common pests in southern United States. Information on the economic

damage level of fall armyworm larvae in field corn is urgently needed

in view of the present awareness of possible environmental damage by

pesticides and the production cost squeeze. Behavioral and ecological

patterns shown by the larvae which might aid in their control are worthy

of investigation. This investigation of the behavior, biology, ecology,

and the effect of feeding on corn yield by the fall armyworm was under-

taken with these concepts in mind.












REVIEW OF LITERATURE


Early systematic history of the fall arnyworm was reviewed by

Luginbill (1928). The species was described in 1797 as Phalaena and

in 1852 Guenee placed it in the genus Lanhygna. The name accepted at

this time is Spodoptera frugiperda (J. E. Smith) according to

Blickenstaff (1965). The accepted common name is fall armyworm

(Blickenstaff 1965), although in southern United States it is unofficially

called the budworm when it inhabits corn whorls.

The fall armyworm probably originated in Central or South America

(Labrador 1967). It is an important agricultural pest of that area, for

it is reported as "first in insect species reducing agricultural

production" (Labrador 1967). It is important because of its ability to

feed on a diversity of hosts, its adaptability to areas with different

altitude and latitude, and its large fecundity (Labrador 1967). It is

called a pest of the "first order" in the United States (Luginbill 1928).

In addition to defoliating field, forage, and garden crops, it may

distribute plant pathogens such as the fungus Fusarium vasinfectun (Atk.),

causal agent of cotton wilt (Taubenhaus and Christenson 1936).

Numerous cases of damage by S. frugiperda were reported in the

Cooperative Economic Insect Report. In 1969, many instances of damage

to field corn were in late planted fields. Types of damage reported

were: defoliation, whorl damage, ear damage, and death of the plant.

Infestations accompanied by the corn earworm, Heliothis zea (Soddie),




3


and/or the European corn borer, Ostrinia nubilalis (Hubner), showed more

pronounced damage. Damage was reported in 13 and 21 states in 1969 ard

1970, respectively.

S. frugiperda overwinters in southern Florida and Texas during

severe winters and also in Louisiana and Arizona during mild winters

(Snow and Copeland 1969). Dispersion is affected by winds and te.pera:tr

and the insect is sometimes found in the northern states by late July or

August (Snow and Copeland 1969). There is no record of diapause.

Blanchard (1951) reported one generation in the northern states and

two generations in the central states per year. Vickery (1929) found

5 generations in southern Alabama and 9-11 generations in Texas per year.

Snow et al. (1968) found male moths caught on St. Croix had sharp

population peaks every 4-5 weeks, although the weather vas suitable for

year-round reproduction and overlapping generations would be expected.

Larvae feed as whorlworms, armyworms, cutworms, or perforators

(Labrador 1967). They select the whorls of corn plants, and sometimes

only one large larva is found per whorl due to cannibalism (Vickery 19215

Larvae feeding deep in the whorl are protected by their frass and are

difficult to kill (Litman 1950).

Larvae maturing in the whorl and tassel migrate to the ear when the

tassel emerges from the whorl. They cause maximum damage to developing

ears for they prevent complete fertilization and are usually not killed

by insecticide applications (Young and Hamm 1966). Larvae feed princitUlly

in the tips of young ears but bore into the side or base of ears with

kernels in the dough stage (Hinds and Dew 1915). In the South, damage

occurs at all stages of plant development, but in the North, damage is

usually confined to the ear because corn is well advanced before moths

appear (Blanchard 1951).








S. frugiperda damage is often mistaken for that of H. zea

(Luginbill 1928). S. frugiperda feeds on young plants and causes a lo?,

of vigor and stand, while feeding by H. zea at this time is of little

importance (Although they feed extensively in whorls and tassels)

(Blanchard and Douglas 1955). Although females of H. zea oviposit on

various corn parts, they select fresn silks ('uaintance and Brues 19;;,

McColloch 1920, Ditman and Cory 1931, Phillips and Barber 1933, Barber

1943). The larvae enter the ear via the silk channel, while S. frupiporc:

eggs are deposited without preference for silk and larvae enter by the

silk channel or bore through the husk (Ditman and Cory 1931, Barber 1936,

Dicke and Jenkins 1945, Blanchard et al. 1946, Kelsheimer et al. 1950,

Blanchard and Douglas 1955). Both species are aggressive, and in general,

H. zea is found in ear tips while S. frugiperda is found throughout ears,

so contact is reduced by spatial separation (Barber 1936, Dicke and

Jenkins 1945, Kelsheimer et al. 1950, Blanchard 1951, Blickenstaff 1956).

Ear damage and survival of various combinations of S. frugioerda, H. zea,

and the tobacco budworm, H. virescens (Fabricius), were investigated by

Wiseman and Mcllillian (1969). They concluded that of the 3 species,

H. zea caused most of the ear damage. Blanchard (1951) reported that I.

zea caused more damage than S. frugiperda. Morphological differences

which may be used in field identification of larvae commonly found in
c
corn are given by Dekle (1965).

Moths have a preoviposition period of 36 hours, with oviposition

beginning on the second night and lasting 4-17 days. Cp to 1,782 eggs

per female are laid. Oviposition occurs on cultivated and wild plants,

and is generally on the underside of leaves (Luginbill 1928), although

Vickery (1929) found more eggs on the upper surface of leaves. Viable








eggs were found on the surface of airplanes arriving in .imjni from the

Caribbean and South America (Porter and Hughes 1950).

Egg incubation is 2-5 days, and is influenced by temperature

(Luginbill 1928). Newly emerged larvae feed on empty egg shells, and

remain on the egg mass for 1-10 hours (Hinds and Dew 1915, Luginbill

1928, Vickery 1929, Blanchard 1951).

During early instars, larvae are able to disperse over relatively

long distances; silk is secreted aiding in their dispersal (Labrador

1967). During the first 2-3 instars, larvae feed on the upper epidermis

of leaves, and create a transparent "window pane" effect. There are 6

larval instars, or less commonly 7 (Olive 1955).

S. frugiperda were reared on artificial media (Randolph and Wagner

1966) and mechanized methods of mass rearing moths were developed (Burton

et al. 1966, Burton and Cox 1966, Burton and Harrell 1966, Burton 1967,

Harrell et al. 1968).

Hosts of S. frugiperda include many plants in the families Gramineae

and Leguminosae (Luginbill 1928). Larvae reared on corn foliage and grain

sorghum foliage had greater larval and pupal survival than larvae reared

on other crops (Roberts 1963). Host resistance was shown in Bermuda

grass in the form of non-preference (Leuck et al. 1968). Larvae permitted

to feed only on non-preferred hosts had reduced numbers of surviving

adults (Leuck 1970) and extended life cycles (Leuck and Skinner 1971).

Larvae offered filter paper treated with extracts of corn tissues,

ate more paper treated with leaf extract than paper treated with silk or

kernel extract (,:clMillian et al. 1967). Larvae preferred, in descending

order, extracts of sorghum, corn, tomato, cotton, tobacco, and Chinaberry

(MAIcLillian and Starks 1966). Arrestant-feeding stimulants such as tha-




6


extractable from corn may increase the effectiveness of insecticides

(Starks et al. 1967). McMillian et al. (1966) showed that larvae

assimilated 61, 52, 46, and 32% respectively of the kernels, silks,

seed, and leaves consumed.















ARTIFICIAL INFESTATION

'.Materials and Methods



Research was conducted at the Central Florida Experiment Station,

Sanford, Florida. Dixie 18 field corn was planted March 6, 25, 25, and

April 3, 1970, in plots 25 to 36 rows wide. Rows were 30 inches apart,

and plots were 300 feet long. Each plot was divided into 4 sections.

The earliest planted two plots were called "medium level", the third

plot "low level", and the fourth plot "high level" referring to the

number of applied worms, and will be called by these terms hereafter.

Plant spacing within rows averaged about 10 inches and spaces of more

than 14 inches were filled by transplanting plants; plants were removed

if intervals between plants were 8 inches or less. Plots were irrigated,

cultivated, and fertilized as needed. Plant growth stages were described

and plant regions were designated.

Low Level Infestation Fall armyworm larval infestation was simulated by

placing laboratory-reared larvae in the field. A colony of approximately

1,000 individuals was maintained in the laboratory, and field-collected

larvae were added to the colony when they were available. Two rows on

each side of the plot and alternate rows within the plot were left

untreated. Treated rows were 60 plants long. Treatments were randomly

assigned to rows at 3 levels: one worm per plant, one worm per two plants,

or one worm per four plants. Corn was treated at early whorl, mid-whorl:

or late whorl growth stage. There was one check row per replication, and




8


there were 5 replications. Second instar larvae were transferred from

5 ounce paper cups into the corn whorls by using a camel's hair brush.

Larval survival was estimated by visually inspecting plants in the

field. Evidence of feeding was recorded and maps were constructed which

showed infested and uninfested plants. Early whorl applications were

checked at 4, 7, and 14 days after treatment. Mid and late whorl

treatments were checked 8 and 9 days after treatment, respectively.

Survival was expressed as per cent of the original number of larvae placed

in the treatment.

Yield was estimated by hand picking the first (top) ear of the

first 42 plants in each treatment. Second (bottom) ears were present,

but they were very small, and it was not likely they would have been

removed by a commercial cornpicker, so they were not picked or weighed.

Ears were weighed in groups of 3. The mean ear weight minus the mean of

treated ear weights was given. Comparisons were made using analysis of

variance.

Mid-level Infestation Three rows on each side of the plots and alternate

rows were left untreated. Treated rows were 60 plants long. Treatments

were randomly assigned at 4 levels: 1, 2, 4, or 8 worms per plant.

Corn was treated at early whorl, mid-whorl, late whorl, or early tassel

growth stage. There was one check row per replication, and there were

4 replications. Larvae were transferred from 5 ounce paper cups into

corn whorls (except for the early tassel treatment when they were dropped

onto the tassel) by using a camel's hair brush.

Larval survival was estimated by removing the plants in one

replication 2-3 days after infestation, dissecting the plants, and

counting the larvae. Corn yield was estimated and compared by using the

same methods that were used in the low level plots.









High Level Infestation Treatment areas were 20 plants long and 9 rows

wide, and no within-plot rows were left untreated. Plants were removed

leaving bare ground between treatment areas. Treatment levels were

randomly assigned at 0, 1, 10, or 20 worms per plant at early, mid, or

late whorl growth stages. In preparation for the 10 and 20 worms per

plant treatment, worms were placed on small pieces of corn in 1 ounce

plastic cups and covered (10 and 20 worms per cup) and on the following

day, the cup contents were emptied into the corn whorls.

Larval survival was estimated by randomly selecting and removing

20 plants from each treated area. These plants were dissected and the

worms were counted.

Yield estimates were made by picking 42 ears from the center of

each area. The ears were weighed and the data were treated as in the

other infestations.

Moisture Estimation Five ears were randomly picked from each plot. The

ears were weighed, shelled, and the kernels were weighed and placed in

5 ounce paper cups. The cups were placed in an oven at 2250F for 5

hours. The kernels were re-weighed and the per cent of moisture was

calculated.


Results and Discussion

The plant growth stages were described on the basis of number of

visible leaf sheaths, plant height, and exposure of the tassel (Fig. 1).

These stages appeared at about one week intervals. Plant regions were

designated as furl (leaves surrounding a central roll), whorl (leaves

surrounding the furl with blades partially extended and the sheaths

concealed), upper leaves (oriented less than 450 from the stalk and

sheaths exposed), and lower leaves (oriented more than 450 from the


























-tw
." ,' i I

i I iJ ?
A B C




Figure 1.-Growth stages of field corn: A-early tassel (10 visible
leaf sheaths, tassel exposed), B-late whorl (6 visible leaf sheaths,
tassel enclosed), C-mid-whorl (5 visible leaf sheaths, tassel enclosed),
D-early whorl (3 visible leaf sheaths, tassel enclosed).







stalk) (Fig. 2). The term "furl" is used in place of "bud" which has

been commonly used for the central roll of leaves and tassel. "Bud" is

more properly used for meristematic tissue consisting of unelongated

internodes enclosed within the leaf primordia (Keeton 1967). The

meristematic tissue is located below the whorl (Fig. 3). At the present

time, the term "budworm" is used for any lepidopterous larvae which

inhabit the whorl and/or the furl of field and sweet corn.

Kiesselbach and Lyness (1945) and Camery and Weber (1953) showed

that the greatest amount of yield reduction resulting from defoliation

occurred when plants were damaged during late whorl and early tassel

growth stages, or the period of rapid ear shoot development, silking,

and fertilization. The younger the plants were prior to this stage,

the smaller the effect was. A loss of a portion of the leaves reduced

the grain yield, but the loss was not in proportion to leaf loss. At the

tassel stage (the stage most susceptible to damage), the loss of 25, 50,

and 100% of the foliage resulted in 8, 23, and 94b yield reduction,

respectively.

The amount of material consumed by larvae was shown by Luginbill

(1928), but this information does not readily convert to leaf area loss.

Worms feed in portions of the plant where leaves are not fully developed,

resulting in more defoliation than would occur if they fed on nature

leaves. In addition, the amount of defoliation increases with the depth

of larval penetration into the furl. For this reason, I approached this

problem by working with a known number of larvae per plant and

determining yield reduction.

During the summers of 1968 and 1969, work was plagued with high

natural fall armyworn infestations and low yields (due to late












C


Figure 2.-Regions of field corn: A-furl, B-whorl, C-upper leaves,
D-lower leaves.

















































Figure 3.-Cross sections of a field corn plant: A-D-furl,
D-E-bud, E-G-pithy stalk surrounded by leaf sheaths.








season planting). In 1970, corn was planted earlier, and there was

little natural larval infestation.

Survival of larvae in low level plots examined 4, 7, and 14 days

after they were placed in the field generally declined with time

(Table 1). In some cases it appeared that there were more larvae 14

days than 7 days after infestation, but the presence of worms was

estimated by evidence of feeding, and the chance of overlooking a small

larva was greater than that of overlooking a larger larva. Some of the

larvae were overlooked in earlier inspections.

A small portion of the larval mortality reported was actually the

result of larvae moving from the original plant to a neighboring plant.

The per cent of untreated plants which were infested by these moving

larvae was 1.3 for plants treated at early whorl, 1.9 for plants treated

at mid-whorl, and 7.8 for plants treated at late whorl. More movement

was evident at later corn growth stages when more leaves were touching

between plants. In 1968, early infestation of small corn by larvae

resulted in late instar larvae feeding on plants which were about 2 feet

high. These large larvae frequently moved from plant to plant. Full

grown larvae will occur in young corn when moths oviposit on corn when

it is small, when environmental factors are not conducive to corn growth,

or when larvae move from a neighboring crop into the corn.

Survival of larvae increased slightly in mid and late whorl

infestations compared with early whorl infestations (Table 2). Smaller

plants furnish less protection for the larvae than larger plants furnish.

Predators, parasites, and rain are factors which may have been influential.

Larval survival in mid-level infestations was comparatively lower

inr early tassel treatments (Table 3). At this time, tassels emerge
























I. of -l", ?I -.i
pc i'nTy l-oh L



Pl.aito per p rn

/. 1

aeplicatinn
Days after ---
irnfe&t"4ion 1 3 1 ? 3 1 s 3 S ^i

4 90 100 100 71 66 5 05 100 74 90.1
7 70 10J) 90 71 5? 26 71 71 5 75-7
14Ion o 1 0 5o 38 86 23 31 5? 74.7





















Table 2.-Per cent survival of second instar S. fruginerda larvae
placed in field corn in the early, mid, and late whorl growth stages.
Survival was estimated by field examination of the plants 7 days after
infestation.


Plants per larva


Mean


infested Replication survival

1 2 3 1 2 5 1 2 3


Early whorl
Mid-whorl
Late whorl


71 71 57
95 95 86
81 91 88


Corn
growth
stage


70 100
100 100
100 100


73.0
92.6
85.0


~~



















--il )f~ -- -r
lastoa. 7ar-v q aft~r f Inesato t, om-.i.l an~t o'
st,?,gec. sur-15v- rr 'I-, a of T)Iant,.


Corn gro-tth
stpcge


Early whorl
;,id whorl
Late w;.orl


Early whorl
Mid whorl
Late whorl
Early tassel


estimated 1 rvae per olant


Figh level inlfestation

Applied larvae per plant

1 10 20

0.9 +0.?2 1.9 -1.39 19.1 6.16
0.9 .18 8.7 1.49 11.9 3.92
1.4 -0.84 7.5 *0.22 11.4 2.98

Apid-level inarvae ~ tin

Applied larvae per plant


0.9 +0.33
0.9 ~0.36
0.9 *0.30
0.4 *0.49


1.5 -0.71
1.8 +0.52
1.6 +0.50
0.4 +1.14


3.0 +1.01
2.6 +1.23
3.5 -0.61
0.6 -0.82


8

4.7 -2.29
5.8 .73
7.2 1.20
1.1 *-.40


~I~~ __








and the leaves which comprised the furl and whorl are exposed on the

plant. The larvae remain exposed on the plant, or move to earshoots

where they tunnel between the stalk and ear or bore into the ear.

Corn yield reductions estimates (Fig. 4) showed significant (a=0.05)

loss in early whorl infestations at about 0.7, 2.5, and 3.0 worms per

plant. However, there were nonsignificant losses belov', within, and

above this range. In mid-whorl infestations, significant loss occurred

at 6.4 worms per plant. No significant reductions occurred after late

whorl infestations. After early tassel infestations, reductions were

found at 0.8 and 1.4 worms per plant.

At a yield reduction of 0.5 pound per. 5 ears, or 0.1 pound per ear,

the grower would lose $7.50 per acre (assuming 1 bushel of corn weighs

56 pounds, 14% moisture, 10 inch plant spacing in a perfect stand, 1

harvestable ear per plant, $1.00 per bushel, and 75 bushels per acre).

The relationship between the growth stage of the corn when it is

infested and the resulting yield reduction is complex. A larva feeding

on a young plant will consume as much as if it were feeding on an older

plant, but the per cent of the total plant destroyed is greater in the

younger plant. However, the younger plant will have a greater ability

to recover from the damage, as was pointed out in the artificial

defoliation studies (Kiesselbach and Lyness 1945, Camery and Weber 1953).

Infestations occurring just before tasseling will result in foliage and

ear damage (Young and Hamm 1966), and the plants are most susceptible to

defoliation damage at this time. Early instar larvae will obtain most of

their food from the small developing ears, and maximum ear damage will

result.


























EARLY WHORL INFESTATION


MID WHORL INFESTATION


2 3 I 2I 3 4 S Ao N
WORMS/PL N I


LATE WHORL INFESTATION
plotl I
.1,. p "il II +
ASPiL t IV





S2 2 S | I 1T
WORMS/PIm


.2 3 4 5 .4 A 1 3 S
WORMS/PLANT



EARLY TASSEL INFESTATION


\ 2-

2.1
s ''1-


WORMS/PLANI


Figure 4.-Yield reduction of field corn by feeding of fall armyworm
larvae. Reductions are compared with worm-free plants with a=0.05.
Estimates of numbers of larvae per plant were made 7-9 days after
second instar larvae were placed on the plants. Each of the points for
plots I-III were averaged and represent 3 replications of 42 plants for
each replication. Plot IV represents the average reduction for 1
replication, or 42 plants for each point. Significant points are below
the vertical line indicating the confidence intervals.


e J


*,


A **








Defoliation may have two effects: photosynthesis may be reduced

resulting in reduced growth and the transpiration surface may be

reduced resulting in less water loss during dry periods.

Deep penetration of the larvae into the bud or parenchyma tissue

would result in the death of the growing tip, and additional plant

growth would be from the root area, and it is unlikely that ears would

be produced. Larvae were never found in the buds of corn. However,

stunted sweet corn was seen in 1969, but it was not determined if larval

feeding was the cause of the stunting. Sweet corn is comparatively

smaller than field corn, and it is more likely that larvae would reach

the bud in sweet corn.

Another type of damage that larval feeding may inflict on corn is

the prevention of fertilization of ears. Larvae are found on both

silks and tassels. One plant is able to produce enough pollen to

fertilize several plants, for in commercial seed production, 2 male

fertile rows are sufficient to pollinate 6 male sterile rows (Poehlman

1959). Plants infested with 1-9 worms per plant at the early tassel

stage showed 53% of the tassels with damage, but none of the tassels

were completely destroyed. Under these conditions, tassel feeding is of

little concern. Ample pollen was produced and no unfertilized kernels were

detected.

Larvae feeding on the silk may cause ears to be incompletely

fertilized if the feeding occurs at or immediately before the time of

pollination. When this damage occurs, complete rows of kernels are

missing from the ears. In a check of infested corn in which most of the

silks had been chewed off, 6% of the ears showed evidence of improper

pollination. Some ears showed up to 1/3 kernel loss due to improper








pollination. These ears were also infested with Heliothis zea, and the

damage is a result of feeding by the two species.

Vickery (1929) stated that one fall armyworm per plant produced as

much damage as several fall armyworms per plant, for large larvae fed

in the furl, and due to cannibalism or other interactions, only one

larva could be found there. During 1969, in an area of natural infestation,

48 out of 50 infested plants contained one fifth or sixth instar larva.

The other two plants contained 2 larvae each. Thic distribution pattern

was not found again, and it suggests that different behavior patterns

exist within the species as indicated by Labrador (1967).

An individual plant's ability to tolerate or recover from

defoliation is probably due to the availability of nutrients and moisture.

Yields of the plots in 1970 ranged from 78 to 86 bushels per acre,

and the per cent of moisture ranged from 15 to 22 (Table 4).
























Table 4.-Estimated moisture


Plot

Low level
'ld-level
reps 1-3
reps 4-6
High level


Per cent
moisture

21.19


14.74
18.94
22.34


content and yield of field corn, 170.



Kernel weight
per car, grams Bushels per are

93.20 79.44

101.12 86.24
96.20 82.06
91.58 77.90


---- --------~














BEHAVIOR OF LARVAE

Materials and Methods



Phototaxis and Geotaxis Responses of newly hatched larvae to light and

gravity were measured in a lightproof 10 X 13 X 125 cm corrugated

container. In 1969, sections from the furl region of corn plants 5 cm

long and 5 cm in diameter were strung at 10 cm intervals along a wire

which extended from end to end in the chamber. A piece of tissue paper

containing newly emerged larvae still on the egg mass was pinned on the

inside of a flap which opened midway down the side of the chamber. After

24 hours, the wire holding the furl sections was removed, and the larvae

were counted on each section. During phototaxis tests, one end of the

chamber was covered with transparent plastic and placed 20 cm from a

15 Watt incandescent bulb. Increase in temperature caused by the bulb

was less than 10C. Various combinations of chamber orientations to

gravity and light were tested. Tests were conducted at 24-28 C and about

80% RH.

The chamber was modified in 1970. The wire and furl sections were

replaced with a 2 X 2 X 125 cm wooden support on which 1 ounce plastic

cups were held with rubber bands. The cups were 1/3 full of media. An

introduction device 8.2 cm in diameter X 8 cm high was glued to the side

of the container. The bottom of the introduction chamber and the

corresponding area of the central container were cut out. A cover was

placed over the open end of the introduction container (Fig. 5). Tests

























































Figure 5.-Behavior chamber used to determine phototaxis and geotaxis
of fall armyworm larvae. Larvae were placed into the introduction
chamber and after 24 hours, the wooden support holding the media cups
was removed and the larvae in each cup were counted.


.....
~ ..
TvXr~L- ~~.......,







were conducted only with the chamber upright and with the light at the

top. All instars were tested: 279 first, 117 second, 41 third, 51

fourth, 52 fifth, and 26 sixth instar larvae. Tests were conducted at

21-270C and about 60' RH.

Preference of Plant Tissues Larval selection of various plant tissues

was tested in a preference chamber constructed of a central rectangular

cardboard container 45 cm high and 6.5 cm square onto which 24 paper

cups 4.5 cm in diameter and 7 cm high were glued by their bottom end.

The bottom of each cup and the corresponding area in the central

container was removed (Fig. 6). Covers were placed on the cups. Six

chambers were constructed.

Tissues to be tested were placed in alternate cups. For each test,

50 third or fourth instar larvae were dropped into the bottom of the

central chamber. After 24 hours, the cups were opened and the worms in

each were counted. Tests were conducted at 21-270C and about 60% RH.

Corn tissues compared were: 4 X 4 cm leaf sections vs 3 cm diameter

ears, 4 cm long X 3 cm diameter ears vs 4 X 4 cm pieces of sheath (tissue

surrounding ears), 4 X 4 cm sections of leaves held open by gluing

(Elmer's Glue ) a piece of midrib across the section vs a 4 X 4 cm section,

folded over and stapled, forming a tunnel about 1 cm in diameter (these will

be called "open" and "closed" leaves after this), and pieces of stalk,

tassel, leaf, furl, silk, and ear. Results were analyzed by using

Student's t test for the first 3 tests and analysis of variance for the

fourth test.
































6.5 X 6.5 X 45 cm
Cardboard




Soz Cup


Figure 6.-Chamber used to test larval preference of various corn
tissues. Tissues were placed in the cups, and a cover was placed on
each cup. Larvae were dropped into the central chamber, and after 24
hours, the larvae in each cup were counted.













Results and Discussion



Phototaxis and Geotaxis Most first instar larvae remained near the

point of introduction in the horizontal darkened chamber (Fig. 7 A).

When the chamber was vertical and darkened, most larvae moved upward

(Fig. 7 B). When the chamber was horizontal and lighted, most larvae

moved toward the light (Fig. 7 C). When the chamber was vertical and

the light was entering from the top, larvae moved upward (Fig. 7 D).

When the light was entering from the bottom, larvae moved downward from

the point of introduction (Fig. 7 E).

First instar larvae are positively phototactic and negatively

geotactic. The response to light is stronger than the response to

gravity. This behavior is important in the dispersal of larvae, for

they move to the upper portions of the plant where they may be blown by

the wind, or they may remain in this area and feed.

First and second instar larvae are positively phototactic and/or

negatively geotactic, but later instars do not show this response, or

the response is overshadowed by other behavior (Fig. 8). In the field,

this behavior would permit partially grown larvae to select regions of

plants other than those at the very tops of plants. For example, larvae

move downward to the ears when the tassels become exposed.

Preference of Plant Tissues Only one significant difference between

plant tissues was shown in the preference chamber tests, although the

same.nonsignificant preferences were found repeatedly (Table 5). Ear



























DARK CHAMBERS LIGHTED CHAMBERS
HORIZONTAL HORIZONTAL




VERTICAL -up VERTICAL p




YVETICAL up


i


light -





Figure 7.-Dispersal of first instar fall armyworm larvae from the
point of introduction in the behavior chamber. A and B-dark, C-light
from side, D-light from top, E-light from bottom.



















F -jp
FIRST INSTAR


FDURTH INSTAR


-- ._-1-


SECOND INSTAR



THIRD INSTAR
f -- a


FIFTH INSTAR



SIXTH INSTAR
SIXTH INSTAB


d r


Figure 8.-Dispersal of each fall armyworm larval instar in a
vertical behavior chamber lighted from above.




















Table 5.-Selection of plant tissues by S. fruginerda la-rve in a
preference chamber.


Year Materials compared

1970 ear heath vs kernels
1970 ear sheath vs kernels

1970 leaf vs ear
1970 leaf vs ear
1970 leaf vs ear
1970 leaf vs ear
1970 leaf vs ear


open vs
open vs
open vs
open vs
open vs


closed leaves
closed leaves
closed leaves
closed leaves
closed leaves


material l preferred t Significe.ce

ear sheath 0.564 as
ear sheath 1.148 ns


leaf
leaf
leaf
leaf
leaf


closed leaves
closed leaves
closed leaves
closed leaves
closed leaves


1.147
0.613
0.388
0.766
0.284

0.983
1.290
1.137
1.358
1.727


a= 0.05


1969
1969
1969
1970
1970









sheaths were consistently selected over ear kernels (nonsignificant

differences). It was observed that many nearly full grown larvae which

were attacking young ears fed on the sheaths, and formed a tunnel to tre

kernels, but the kernels were not fed upon. The larvae could have

completed their feeding period by this tine, or they could have preferred.

to continue to feed in the sheath tunnel instead of feeding on the

kernels. If the ear was not fully grown, expansion of the ear and sieant.,

caused the tunnel to close, for the overlapping layers of sheath changed

in their relative positions. This indicated that ears fed on, in this

manner, are not vulnerable to secondary attack via holes in the sheaths.

Sheath feeding by larvae is of no significance in yield reduction.

When leaves were compared with cross sections of ears, leaves were

selected in all cases (nonsignificant differences). In the field,

larvae moving out of the newly-exposed tassel usually move to the ears

to feed. These tests show larvae do not prefer ears over leaves. Other

factors must influence larval selection of feeding sites.

A comparison of open and closed leaves showed closed leaves are

preferred in all cases (1 replication out of 5 showed a significant

difference) (Table 5). This may explain why larvae seek closed areas

such as whorls, furls, and areas between stalks and leaf shoots. These

areas furnish protection from parasites, predators, and various detrimental

environmental factors.

No significant differences were found when stalks, tassels, leaves,

furls, silks, and ears were compared (a=0.05). This again indicates

plant tissues do not influence larval selection of feeding sites on corn.














FIELD DISTRIBUTION OF LARVAE

Materials and Methods



Distribution on Field Corn Plants Plots of Dixie 18 field corn were

planted June 16, 25, and July 2, 1969, and hereafter will be called

plot I, II, and III respectively. Sampling was begun in plot I when the

corn was 5 feet high, and was continued through ear development. Samples

consisted of 50 plants, and were taken twice weekly. Plants were cut at

ground level and taken into the laboratory where they were examined.

Sampling was started in plots II and III when the corn reached the height

of 35 and 11 feet, respectively. Sampling in these plots continued for

2j weeks until a period of heavy rain after which no larvae could be

found.

Corn height was measured from ground height to the highest part of

the leaves or tassels. Corn growth stages were determined and recorded,

and plant regions (furl, whorl, upper leaves, and lower leaves) were

determined and the number of worms in each region was recorded. Larvae

were grouped into 5 size categories: very small, small, medium, large,

and very large. These categories generally correspond to the first,

second, third and fourth, fifth, and sixth instars, respectively.

Determination of exact larval instars was not within the scope of this

experiment.

The mean number of larvae per 100 plants in each plant region was

estimated: (total larvae per region)/(total plants)(100). The per cent








of each size group of larvae in each plant region was estimated: (total

larvae of age group per region)/(total larvae per region)(100). Develop-

ment of plants with emphasis on growth of tassels, ears, and neristemat-c

tissue was recorded.

Distribution on Ears The distribution of fall army-vorm and corn earwor:

larvae in ears was investigated in 1970. Ear samples were taken at

random from corn which was artificially infested at the late whorl and

early tassel growth stages. Ears were examined for larvae and for feeding

damage.

Dispersal from Egg .,'asses Larval dispersal from egg masses was observed

in a 6 X 6 X 6 ft. cage covered with fiberglass Saran screen. Egg

masses from the laboratory colony were placed on plants growing in the

cage.

Egg masses from the laboratory colony were placed in the field.

Masses of 10, 100, 500, and 1,000 eggs were placed in the field.

There were two treatments; the first was examined when 90'/O of the larvae

were in the first instar. The corn was 40 inches tall at this time, and

leaves were touching between rows. Plants showing evidence of worm

presence were cut and examined in the field, and a map was made showing

the location of infested plants and numbers of worms per plant. The

second treatment was examined when most of the larvae were in the fifth

instar. At this time, the corn was 6 feet tall, but had not tasseled.

Maps were converted to tabular form, with number of larvae in 10 inch

intervals grouped and listed. There was a 9 day interval between checks.














Results and Discussion


Distribution on Corn Plants The highest number of larvae found in

corn between early and late whorl stages was in the whorls, followed by

furls, upper leaves, and lower leaves (Fig. 9). The whorl is the highest

part of the plant, and early instar larvae would move into this area.

The whorls and furls provide an enclosed area similar to that provided

in experimental closed leaves. These enclosed areas furnish some

protection from predators, parasites, and abiotic factors. Feeding in

the whorl and furl produces the most loss of leaf area because the leaves

are not fully developed in these areas. If the bud is damaged, it would

be as a result of larvae which started feeding in the whorl and tunneled

downward. During rain, small plants' whorls fill with water, but the

possibility of drowning or the increase in disease frequency was not

investigated.

The per cent of various sizes of fall armyworm larvae found in

plant regions (Fig. 10) showed large and very large larvae were not found

on lower leaves. Smaller larvae were found throughout the regions.

Larvae were never found in or on the stalk. Large larvae feeding in the

furls and whorls may have influenced smaller larvae to feed in less

preferred areas. ";hen large larvae feed in the furl, then mature, the

feeding tunnel provides access to the furl for young larvae.

Larvae which are feeding in the furl and whorl when tassels emerge

must attack the ear shoots or remain exposed while feeding on the leaves.








































0 ,



0











Furl Whorl Upper Lower
leaves leaves






Figure 9.-Regions of field corn infested by fall armyworm larvae.
Plants were examined in the early whorl through the late whorl growth
stages.




























I ery small larvae


- medium I.lvo
-large lrae







r t-] f*'i..


Furl
Furl


Whorl


Upper Lo.er
leaves leave


Figure 10.-Size distribution of fall armyworm larvae in several
plant regions. Corn was examined in the early whorl through late whorl
stages.








Distribution on plants from early whorl through mature stages, after

whorls are exposed, includes a brief period of feeding on the tassel

before moving to the ears (?ig. 11, Table 6). These larvae could

damage foliage, tassels, silks, and ears. Ear shoots were not evident

at the time of tassel emergence in some plants (?ig. 12 A). Larvae

feeding on these plants do not have a protective retreat, but must

remain exposed in they stay on the plant.

Distribution on Ears Larvae attack ears by entering through the silk

channel, or more commonly through the sheath surrounding the ear (Fig.

13). Some larvae fed on the sheath but not on the kernels. Young ears

with soft silks contained larvae in ear tips, middle of ears, and silks,

while corn earworms were found in the silk channel, ear tip, and middle

of ears (in decreasing order). Ten days later, there was a higher ratio

of corn earworms to fall armyworms. At this time, most of the corn

earworm larvae were found in the silk channel and ear tips (Table 7).

By this time, the fall armyworms had probably left the ears and pupated.

Most of the kernel loss was in the ear tip followed by the middle of

the ear. Total kernel loss was 3.9 and 2.2$ for the tip and middle of

ears, respectively. This loss was due to both species. Few young fall

armyworm larvae developed in the ears; most were partially grown, and

had moved from the whorl and furl. Corn earworm larvae usually developed

entirely in the ears, for moths prefer silks for oviposition sites.

Dispersal from 2gg Masses Newly emerged larvae remained on or near the

mass for 17 hours at 260C and 5 mph wind. Other larvae left the mass

immediately after emerging at 340C. In the field cage, larvae were

observed emerging from a mass of about 100 eggs. Dispersal began after

one hour at 32 C. Twelve larvae were moving about on the highest part of






























CORN GROWTH STAGE





















SAMPLE DATE


Figure 11.-Regions of field corn plants infested by fall armyworm
larvae. The plants were examined from the early whorl through maturity.
























Table 6.-ListribuLio;i of _. friaiorda l lirve Lefcre il. Pf:r
emergence of tw=rclr in field corn. h-C.bcrC of arva. ar e;?xpr::n
as per cents.


Corn
growth
stage


I.uriner of Plant region
infested plans
examined ear
furl w7hor leaves ear sheath tnscse


Late whe"rl 47 60.0 40.0
Early tassel 29 n 0


0 0 0 n
1.0 4 0 33.0 7.0
45,,O 4_007 .. 0


Upper leaves still furnish some -r tection f- r the tassel in
cases.


















A B








-















Figure 12.-Contrasting corn development: A-tassel is completely
exposed while ear shoots are not evident; B-tassel is partially
protected by the whorl while the ear shoot has emerged. Plant A
furnishes little protection for larvae, while plant B offers protection
in the tassel-whorl region and the ear shoot provides a place for the
larvae to burrow. Larvae were never seen boring into the stalks.






















9/


Figure 13.-Fall armyworm larvae commonly enter ears by boring into
the sheath at the junction of the stalk and the ear.
























corn car. -r i ,L t:c firct -'m1! ( ,an Trer oi:'
ears sa-.plned 10 1 a t (late ae:) L'ad dry silks.



Per colit 1arvac
3Jar re6roi,
D:m'c ar
Ear age Larval species 3 a r.;a o silk tin m i dl e utt


Early s* 5.3 11.7 7.4 0.0
I. 51 23.4 18.1 2.1 0.0

Lvate 12 3.2 2.: I .1 0.0
H. 7ai 27 13.0 10.0 0.0 0.0


50








a leaf. I blew lightly on the leaf, and 7 dropped on threads which were

attached to the leaf edge. Other larvae were seen dropping on threads.

Several larvae would sometimes drop together; their threads would twist

together. Slight wind gusts stimulated dropping. No feeding was seen

at this time, except for the consumption of egg shells.. Movement over

long distances could occur when larvae are picked up and carried by the

wind.

Examination of plants surrounding egg masses placed in the field

showed there was more movement of larvae per day for the first 3 days

than per day for the first 12 days (Table 8). This suggests there is

a dispersal period before feeding begins. There was more movement

within than across rows, probably because there was more within-row

plant contact. Mean larval movement was greater at higher larval

densities. This dispersal would reduce larval contact and decrease the

amount of cannibalism. This is economically significant, for larvae

move from plants when densities are high enough to reduce yield, or

conversely, move and damage more plants.





44















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C) -,\I' N- N1 C' C







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LARVAL BIOLOGY

Materials and Methods



Starvation of Newly Emerged Larvae The length of time that newly emerged

larvae can survive without feeding was estimated by holding larvae for

various periods of time before allowing them to feed. In 1969, tests

were run at 21 *20C and about 80% RH. In 1970, tests were run at 22 +20C

and 60-70/o RH. Larvae emerged and consumed their egg shells, then they

were placed without food in covered 5 ounce paper cups. Groups of larvae

were fed at 2 hour intervals and after 2 days, surviving larvae were

counted. The LD50 was calculated after correcting for natural mortality

by using Abbot's Formula.

Starvation and Cannibalism of Late Instar Larvae Fourth, fifth, and

sixth instar larvae were held without food in 5 ounce paper cups. There

were 1, 2, or 3 larvae per cup. When there was more than one larva per

cup, cannibalism occurred. Cannibalism is expressed as a ratio of original

to final number of larvae (example: 2:1 cannibalism indicates that of

two original larvae, one survived). Pupal weights of cannibals and non-

cannibals were compared by using Student's t test.

Survival and Development During Periods of Low Temperatures The survival

of eggs, larvae, and pupae at k, 4, 13, and 290C (all temperatures were

1 C) were estimated. Eggs were held at 1, 4, and 150C for 24-168 hours,

then they were held at 290C and mortality and time for maturation were

noted. One day old larvae were held at 6, 11, and 14 C for 4, 7, and 11








days before holding them at 290C. Survival and length of time for

development were noted. Pupae were held at 0, 4, and 4-7 (fluctuating) C

for 5, 7, and 14 days before holding them at 29 C. Mortality and time

for development were noted.

High Density Hearing Egg masses of 100-500 eggs were collected from the

field and laboratory and placed in heavy 28 X 17 X 45 cm paper bags.

Various parts of corn plants were placed in the bags for larval food.

The tops of the bags were stapled shut, and they were stored at about

750F and about 655, RH.



Results and Discussion


Starvation of Newly Energed Larvae The starvation LD50 for newly emerged

larvae ranged from 20 to 55 hours (Table 9). Depending on environmental

conditions, larvae would have about a day to select or find a suitable

host. Early larval starvation did not affect the pupal weights or the

time required to complete larval development (Table 10).

Starvation and Cannibalism of Late Instar Larvae The starvation LD50

for fourth and fifth instar larvae was 26 and 75 hours, respectively

(Table 11). Sixth instar larvae were able to survive and pupate without

feeding. When more than one larva was in a cup, usually only one survived

due to cannibalism. After cannibalism occurred, there was a characteristic

dark stain on the container as a result of loss of body fluids from

wounds. Fighting resulted in scars or damaged areas on the cuticles. If

one of several larvae was damaged and body fluids were emitted, other

larvae were stimulated to attack the wounded larva.

Some fifth instar larvae were able to survive and pupate if they fed























Table 9.-Survival of starved uifcd first ir.tnr S. fr-~ ~ :
larvae.



LD5 in hours
Relative 3D
Year Temperature ho.idity rep. 1 rep. 2 rep. 3 rep, 4 rep. 5

1969 21 *0?C 80 3, 29 20 25 x :
1970 22 t2c 65 -3 35 35 32 32

Calculated by profit analysis P-nd mortality corrected by Abo L':
formula.
























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" ', o CCL'C C' C

cr X X. c' c c c C
C N N' N N N C C C C C. C









L L. L' C L L L u, L1
- r- r- I-














Table 11.-Ti. eff c of ctvti. n -nd caudib:lism on r L .,-
per cent puni ti -f -




Instar raLie L r hr rClae,

4 0 (c 26 x 0
4 :1 2 71 00 0
4 3:1 40 72 100 0
5 0 (ceck) 73 73 x 0
5 2:1 70 125 100 0
5 3:1 40 153 100 3
6 0 (check) x- x x 98
6 2:1 x x 70 100
6 3:1 x x In 56

Ratio of o'i-gi.nal nurnber of lnrvae to finl nui:er cf larvae

2Death resultirng fr'- cannibals' inc1u..ed in -.'rtality

'Death result tirn frc.; cennribalisn excluded from c-.oritanI ty

4Per cent of L.m0es one la.va :kilel all other larvae i,. the
contair-er

5Sixth ins tar l rva'e survived through "spa-tiiL








on two larvae. The LD50 increased with the rate (0, 2:1, 3:1) of

cannibalism for fourth and fifth instar larvae (Table 11). The pupal

weights of sixth instar larvae which were starved were less than those

which were cannibals, but the differences were not significant (a=0.05),

(Table 12).

High Density Rearing While rearing larvae at high densities, two

morphological and behavioral larval differences were noted during the

fourth and fifth instars. One type was dark, and more prominent spines,

held the mandibles forward, and remained on the sides of the bags where

they were separated spatially. The other type was lighter in color, had

less prominent spines, held the mouthparts downward, and remained on the

food. When the dark type was lightly touched with a camels hair brush,

they responded with a side to side sweep of their heads. The response of

the light type to this stimulation was to become motionless, drop from

their position, or retreat. Side to side head sweep motion by light

type larvae was stimulated only by a severe pinch such as a squeeze by

tweezers. The side to side head sweep was followed by a directed

mandible attack and sometimes regurgitation of gut material. Both light

and dark types were seen in the field, but late instar larvae were not

found exposed on plants, so responses to these types of stimulation were

not tested in the field.

If various conditions produce various behavioral and/or morphological

types, as is suggested by Labrador (1967), one must be careful in applying

generalizations made from one type to predictions of another type. For

example, information presented in this paper should not be used in

predicting losses which would be caused by larvae moving armyworm-style

into a field of corn.

























Tabe l c ',2:si;~it of it~-ds cL,,rmi al is ic, -,nd non-





cupmnibilici ratio

0 2:

Pupal a ~rlz 0.1102 0.1274 0. P,
Vx 0.8S0 no 1 ? 5


Ratio of original to fial nLcr of larvae

2Comparison of on- n rt~'l ith othcr cata~ories; a n.07








Survival and Development During Periods of Low Temperatures Temperature

studies show eggs hatch in 48 and 192 hours after being held at 2900C

continuously and 1 0C for 144 hours, respectively. Eggs could not survive

temperatures of 10C for 24 hours, but could survive up to 48 hours at

4 0C without increased mortality (Table 15). Larvae pupated in 7 days

when held at 290C. They survived for 48 days at 14C, but did not

pupate (Table 14). The larval stage was also extended at 6 and 110C.

Pupal mortality increased at 4 and 4-700C; pupae survived up to 11 days

at 00C (Table 15).

The fall armyworm is a more serious pest in the South than in the

North because of its late arrival in the North. Although the worms are

not tolerant of cold, millions of eggs, larvae, pupae, and adults are

exposed to varying degrees of cold. If a stage develops a method of

surviving low temperatures, the annual invasion of the North will occur

earlier in the season, and crops will be seriously threatened. If

parasites do not develop cold resistance at the same time, with

uncontrolled development in early spring, it would become a major

agricultural insect pest throughout the United States. The tremendous

adaptability of the insect has already been mentioned (Labrador 1967).

None of the stages of the insect which were tested showed signs of

developing cold hardiness, although a greatly extended larval period

was found. In addition, behavioral patterns may be slightly altered

and permit overwintering. An example of this is the construction of

pupal chambers deeper in the soil where the pupae are protected from

lethal temperatures.
























a1-:Id at low tc'noer for vaurious 10 r of ti-e u -)r2
at 290C.



F-)rs at J02' temnerature

Low temp. 0 24 48 72 96 120 144 16S

130C 48 72 96 120 144 168 1?2 x
4 0 48 72 96 120 x 7
1 48 x x x -.


60 -.ortal11t ;t no rortlity t at oth er t ce'-toera/urc/pedi 7o 7er e
cggs developed























Table 1 .-Survival of 2
temper-atures. TD.enty larvae
number urx iving is ;iven.


iay old S. fru(r eri lar;. held at .
-ere started at each temperature, and ti.,e


Day of observation


Low temn. 5

29C 16
14'C 14
11 C 15
60C 8


7 9 16 22 35 48


x x x x x
10 8 5 5 2
11 10 4 2 0
6 1 1 0 0


Larvae had pupated; pupation occurred only at this temperature


_____I___________XI_______


--



















C C C C CCC CC










CCCCCCCCC
C- 1 0 C 2 \ 1, C 'C C'
CAC I- t L -\ ..


-4
0






t4









F)
"-4


































r'
4,












'd








E-t
Cr)















;E
'cH








1j

i-4
ni
0i-
4,




C.,4


C t- C( CO C r- (C '


'I
















oj -,



C-_ C,
'C

C) '-








"C'




C,,9


O4COCCOCCC
-. e c. c C. C.
COL) [ -'-C ;-C C-*''Z
T- ,- T C CJ C,








C C Cr CC CC C
" L r. C .) C. C C) C)
Co '- C 2CC









--C CC C

C' TN LC Cc 2C G1 H o









,- L C) C) COCC C
CN (C














REFERENCES CITED


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Agr. Exp. Sta. Bul. 192. 18 p.

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Blanchard, R. A. 1951. Control of the fall armyworm. Proc. Sixth An.
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Blanchard, R. A., T. R. Chamberlin, and A. F. Satterthwalt. 1946.
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Blanchard, R. A. and W. A. Douglas. 1955. The corn earworm as an enemy
of field corn in the eastern states. USDA Farmers Bul. 1651. 18 p.

- Blickenstaff, C. C. 1956. The nature of damage to field corn by the
corn earworm, Holiothis zea (Boddie), and the fall army-orm,
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Amer. 11: 287-320.

Burton, R. L. 1967. Mass rearing the fall armyworm in the laboratory.
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v Burton, R. L. and H. C. Cox. 1966. An automated packing machine for
lepidopterous larvae. J. Econ. Entomol. 59: 907-9.

Burton, R. L. and E. A. Harrell. 1966. I.odification of a lepidopterous
larvae dispener for packaging machine. J. Econ. Entomol. 59:
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\Burton, R. L., E. A. Harrell, H. C. Cox, and W. V. Hare. 1966. Devices
to facilitate rearing of lepidopterous larvae. J. Econ. Entomol.
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Camery, I. P. and C. R. Weber. 1953. Effects of certain components of
simulated hail injury on soybeans and corn. USDA Agr. Res. Serv.
Bul. 400:- 465-504.








Cooperative Economic Insect Report. 1969. USDA Agr. Res. Serv. Vol. 19.

Cooperative Economic Insect Report. 1970. USDA Agr. Res. Serv. Vol. 20.

Dekle, G. W. 1965. Illustrated key to caterpillars on corn. Florida
Dept. Agr. Div. rlant Industry. Bul. 4. 14 p.

Dicke, F. F. and M. T. Jenkins. 1945. Susceptibility of certain strains
of field corn in hybrid combinations to damage by corn earworms.
USDA Tech. Bul. 898. 36 p.

Ditman, L. P. 1950. Fall armyworm control. J. Econ. Entomol. 43:
726-7.

Ditman, L. P. and E. N. Gory. 1931. The corn earworm, biology and
control. Marylana Agr. Exp. Sta. Bul. 328: 443-82.

Harrell, E. A., W. W. Hare, and R. L. Burton. 1968. Collecting pupae
of the fall armyworn from rearing containers. J. Econ. natomol.
61: 873-6.

Hinds, W. E. and J. A. Dew. 1915. The grass worm or fall armyworm.
Alabama Agr. Exp. Sta. Bul. 186: 61-92.

Keeton, W. T. 1967. Biological Science. W. W. Norton and Co., Inc.
New York. 455 p.

Kelsheimer, E. G., N. C. Hayslip, and J. W. Wilson. 1950. Control of
budowrms, earworms and other insects attacking sweetcorn and green
corn in Florida. Florida Agr. Exp. Sta. Bul. 466. 38 p.

Kiesselbach, T. A. and W. E. Lyness. 1945. Simulated hail injury of
corn. Agr. Exp. Sta. Univ. Nebraska. Bul. 377. 22 p.

Labrador, J. R. 1967. Estudios de biologia y combat del gusano cogollerc
del maiz. Universidad del Aulia, Maracaibo, Venezuela. 83 p.

Leuck, D. B. 1970. The role of resistance in pearl millet in control
of the fall armyworm. J. Econ. Entomol. 63: 1679-81.

Leuck, D. B. and J. L. Skinner. 1971. Resistance in peanut foliage
influencing fall armyworm control. J. Econ. Entomol. 64: 148-50.

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Luginbill, P. 1928. The fall armyTworm. USDA Tech. Bul. 54. 91 p.

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,ictillian, i'. W., K. J. Starks, and !. C. Bowman. 1966. Use of plant
parts for food by larvae of the corn earworm and fall armyworm.
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McMtiillian, V. W., K. J. Starks, and I. C. Bowman. 1967. Resistance in
corn to the corn earworm, Heliothis zea, and the fall army-worn,
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feeding responses to corn plant extracts. Ann. Entonol. Soc. Amer.
60: 871-3.

Olive, A. T. 1955. Life history, seasonal history, and some ecological
observations on the fall armywora, Laphyvga frugiperda (A&S), on
sweet corn in North Carolina. Thesis. North Carolina State Collese,
Raleigh. 77 p.

Phillips, V. J. and G. V. Barber. 1933. Egg laying habits and fate of
eggs of the corn earworm moth and factors affecting them. Virginia
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outer surfaces of airplanes. J. Econ. Entomol. 43: 556-7.

Quaintance, A. C. and C. T. Brues. 1905. The cotton bollworm. USDA
Entomol. Bul. 50. 15 p.

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6 p.

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insecticidal susceptibility of the fall armyworm, Lanhygma frugiperda
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1757-60.

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60: 1483-4.




59


Taubenhaus, J. J. and L. D. Christenson. 1956. Role of insects in the
distribution of cotton wilt caused by Fusarium vasinfectun. J.
Agr. Res. 55: 705-15.

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District of Texas. USDA Tech. Bul. 138. 64 p.

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among the corn earworm, tobacco budworm, and the fall army-norm.
J. Econ. Entomol. 62: 734-5.

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BIBLIOGRAPHICAL SKETCH


Wendell L. Morrill was born :,ay 22, 1941, in Ma:dison, South Dakota.

He graduated from General Beadle High School in 1959. He was employed

on a farm and worked for the Soil Conservation Service until he entered

South Dakota State University in 1963. He received his Bachelor of

Science degree in 1967 and his Master of Science Degree in 1968. Both

degrees were awarded with a major in entomology. 'While earning his

degrees, he was employed by the Entomology-Zoology Department and the

USDA Northern Grain Insects Research Laboratory.

In 1968, he accepted a research assistantship at the University

of Florida from the Department of Entomology and Nematology. He has

held that position until the present time.

Wendell Morrill is married to the former Judy Larson, and they

have one child, Jill. He is a member of Phi Sigma Biological Society

and Gamma Sigma Delta, Honor Society of Agriculture.










I certify that I have read this study and that in my opinion it

conforms to acceptable standards of scholarly presentation and is full

adequate, in scope and quality, as a dissertation for the degree of

Doctor of Philosophy.



James E. Lloyd

Associate Professor of Entomology


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.



Jonathan Reiskind

Assistant Professor of Zoology


This dissertation was submitted to the Dean of the College of

Agriculture and to the Graduate Council, and was accepted as partial

fulfillment of the requirements for the degree of Doctor of Philosophy.

December, 1971



Dean, College of Agriculture


Dean, Graduate School
















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.
'A


Gerald L. Greene, Chariman

Associate Professor of Entomology



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.



Dale H. Habeck, Co-chairman

Associate Professor of Entomology



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.



Thomas J. Walker

Professor of Entomology




Full Text

PAGE 1

Ecolo£y, Economics, and riehavior of the Fall ArmyTworra in Field Com By WENDELL L. MORRILL A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OP THE TOJIVERSITY OF FLORIDA IN PAjITIAL FULFILLI.iENT OF THE REQUIRE-'.SNTS FOR THE DEGREE OF DOCTOR OF PHILOSOPK"): UNIVERSITY OF FLORIDA 1971

PAGE 2

UNIVERSITY OF FLORIDA 3 1262 08552 4683

PAGE 3

DEDICATION This dissertation is dedicated to the people who offered assistanc and encouragement during my academic career.

PAGE 4

ACKNOWLEDGMENTS I thank the following people for their contribution to this work: Dr. G. L. Greenesupervision and encouragement, Dr. James Strandbergphotographic assistance, Dr. Dale Habeckadvice and editing. Dr. W. K. Whitcombadvice. Dr. T. J. Walkerediting. Dr. J. Reiskindediting. Dr. J. A. Cornellstatistical assistance, Mr. R. L. Burtonsupplying a sample of fall armyworms, Mr. Joel Rodriqueztranslation of a paper written in Spanish, and technicians Linda Carrol, Art Young, and Karen Stewart for helping with rearing and handling larvae.

PAGE 5

TABLE OP CONTEIiTS PAG3 ACKNOV/LEDGEivEl^TS iii LIST OP TA5LSS vi LIST OF FIGURES viii ABSTRACT ix INTRODUCTION , 1 RSVIW OF LITERATURE 2 ARTIFICIAL INFESTATION 7 Materials and I.Iethods 7 Low Level Infestation 7 Mid-level Infestation 8 High Level Infestation 9 Moistiire Estimation 9 Results and Discussion 9 BEHAVIOR OP LARVAE 25 'Materials and Methods 25 Phototaxis and Geotaxis 23 Results and Discussion 27 Phototaxis and Geotaxis 27 Preference of Plant Tissues 27 FIELD DISTRIBUTION OP LARVAE 32 Materials and .Methods 32

PAGE 6

Distribution on Field Com Plants 32 Distribution on Ears 53 Dispersal from Egg Masses 37 LARVAL BIOLOGY 45 Materials and ;.reohod3 tL5 Starvation of Newly Emerged Larvae 45 Starvation and Cannibalism of Late Instar Larvae . 45 Survival and Develop.iient During Periods of Low Temperature 45 High Density Hearing 46 Results and Discussion 46 Starvation of Newly Emerged Larvae 46 Starvation and Cannibalism of Late Instar Larvae . 46 High Density Rearing 50 Survival and Development During Periods of Low Temperature 52 REFEPlENCES CITED % BIOGRAPHICAL SKETCH 60

PAGE 7

LIST OF TABLES PAGE Table l.-Per cent survival of second ins tar S^. frugiperda larvae placed in field com in the early whorl ^ov/th stage 15 Table 2. -Per cent survival of second instar _S. frugiperda larvae placed in field com in early, raid, and late whorl growth s tages 1 6 Table 5 '-Mean and standard deviation of numbers of S^. frugiperda larvae surviving 7-9 days after field infestation at various com growth stages • 17 Table 4. -Estimated moisture content and yield of field com, 1970 22 Table 5 '-Selection of plant tissues by S. frugiperda larvae in a preference chamber 30 Table 6. -Distribution of S. frugiperda larvae before and after emergence of tassels in field com 39 Table 7. -Distribution of S_, fmagiperda and H. zea larvae in field corn ears 42 Table 8. -Dispersal of S^. frugiperda larvae from egg masses in the field 44 Table 9. -Survival of starved unfed first instar S^. frugiperda larvae 47 Table 10. -Pupal weights and duration of larval stages of S^. frugiperda larvae which survived a period of starvation after emergence from the eggs 48 Table 11. -The effect of starvation and cannibalism on LD^-^ and per cent pupation of 3_. frugiperda larvae .;.... 49 Table 12. -Pupal weights of starved cannibsLlistic and noncannibalistic sixth instar S. frugiperda larvae . 51

PAGE 8

Table 1 3. -Hours required for development of S^. frugiperda eggs held at low temperatures for various lengths of time before holding at 29°C. 55 Table 1 4. -Survival of 2 day old S. frugiperda lar-/ae at low temperatures 54 Table 1 5. -Effect of periods of low temperature on survival and time for development of S_. frugiperda pupae 55

PAGE 9

LIST OF FIGURES PAGE Figure 1 . -Growth stages of field corn 10 Figure 2. -Regions of field com 12 Figure 3. -Cross sections of a field com plant 13 Figure 4. -Yield reduction of field com by feeding of fall armyworra larvae 19 Figure 5. -Behavior chamber used to determine phototaxis and geotaxis of fall armywoTm larvae . 24 Figure 6. -Chamber used to test larval preference of various com tissues 26 Figure 7. -Dispersal of first instar fall armyworm larvae from the point of introduction in the behavior chamber . 28 Figure 8. -Dispersal of each fall armyworm larval instar in a vertical behavior chamber lighted from above 29 Figure 9. -Regions of field com infested by fall armyworm larvae 35 Figure 10. -Size distribution of fall armyworm larvae in several plant regions 3o Figure 11. -Regions of field com plants infested by fall armyworra larvae 38 Figure 12. -Contrasting com development 40 Figure 1 3. -Fall armyworm larvae commonly enter ears by boring into the sheath at the junction of the stalk and the ear 41

PAGE 10

Abstract of Dissertation Presented to the Graduate Council of the University of r'lorida in Partial r\ilfillment of the Require.T.ents for the ^^egxee of Doctor of Fnilosophy ECOLOGY, SCOi.'OMICS, AJffi BEHAVIOR OF THE PALL ARIvai/Oii'-I IN PIELD GOKN By Wendell L. Morrill December, 1971 Chairman: Dr. G. L. Greene Co-chairman: Dr. D. H. Habeck Major Department: Entomology and Hematology The fall aimyworm, Spodoptera frugiperda (j. E. Smith), overwinters in southern United States and migrates northward during the growing season and attacks many crops. The economic damage level in field com was determined by infesting several com growth stages with known numbers of larvae, measuring larval mortality, weighing ears to determine yields, and comparing yields of infested and uninfested plots. Infestations before tassel and ear emergence did not consistently reduce yields. Infestations, occurring as tassels and ears appeared, showed significant yield reductions in 2 out of 4 plots at a density of 0.8-1.5 worms per plant.

PAGE 11

TsLSsel damage was of little importance; ear feeding resulted in some damage. Larvae did not penetrate to the apical bud. In pre-tassol com, most larvae were found in the whorl and furl, while in posttassel com, larvae were found in the eajrs. Preference of plant tissues did not appear to be of significant importance in larval distribution on plants, but thigmotaxis may be important. First instar larvae were positively phototactic and negatively geotactic; the responses subsided dixring the second instar. More dispersal per day was found during the first 3 days than the first 12 days of larval life. Movement was greater at higher densities. Newly emerged larvae survived 20-35 hours without feeding. Starvation at this time did not affect pupal weights or duration of the larval stage. During staxvation, survival of fifth instar larvae was increased by cannibalism. Sixth instar larvae could survive through pupation without feeding. Larval dimorphism and behavioral differences were shown at high and low densities. Duration of egg development was extended at 4-15 C; mortality increased after 24 hours at 1 C and 72 hours at 4 C. Larval development was extended at 14 C; none survived to pupation at or below this temperature. Pupae survived up to 12 days at G. Pupation occurs in the ground. Development of a cold-resistant stage or selection of a cold-protected pupation site are possible methods of overwintering. Early annual appearance in the North of this pest would pose a serious threat to northern United States agriculture.

PAGE 12

INTRODUCTION It is necessary to determine the economic damage level, or numbers of insects per plant which reduce crop yield, to predict Trhen insect control practices will be economically feasible. Fall armyworms are common pests in southern United States. Information on the economic damage level of fall armyworm larvae in field com is urgently needed in view of the present awareness of possible environmental damage by pesticides and the production cost squeeze. Behavioral and ecological patterns shown by the larvae which might aid in their control are worthy of investigation. This investigation of the behavior, biology, ecology, and the effect of feeding on com yield by the fall armyworm was undertaken with these concepts in mind.

PAGE 13

KSVIEi-/ OP LITERATURE Early systematic history of the fall amyworra was reviewed by Luginbill (l928). The species was described in 1797 as Phalaena and in 1852 Guenee placed it in the genus Lap h ygna . The name accepted ax this time is Spodoptera frugiperda (j. E. Smith) according to Blickenstaff (1965). The accepted common name is fall arrayworm (Blickenstaff 1965), although in southern United States it is unofficially called the budworm when it inhabits com whorls. The fall armyworm probably originated in Central or South America (Labrador 1967). It is an important agricultural pest of that area, for it is reported as "first in insect species reducing agricultural •production" (Labrador 1967). It is important because of its ability to feed on a diversity of hosts, its adaptability to areas with different altitude and latitude, and its large fecundity (Labrador 1967). It is called a pest of the "first order" in the United States (Luginbill 1928). In addition to defoliating field, forage, and garden crops, it may distribute plant pathogens such as the fungus Fusarium vasinfectun (Atk.), causal agent of cotton wilt (Taubenhaus and Christenson 1936). Numerous cases of damage by S^, frugiperda were reported in the Cooperative Economic Insect Report. In 1969> many instances of damage to field com were in late planted fields. Types of damage reported were: defoliation, whorl damage, ear damage, and death of the plant. Infestations accompanied by the com earworra, Helicthis zea (Eoddie),

PAGE 14

and/or the European com borer, Ostrinia nubilali s (Hubner), shcved mora pronounced damage. Damage was reported in 1 3 and 21 states in 19^9 and 1970, respectively. _S. frugiperda overwinters in southern Florida and Texas during severe v/inters and also in Louisiana and Arizona during mild v/inters (Snow and Copelarid 19^9) • Dispersion is affected by v/inds and tenperaturi and the insect is sometimes found in the northern states by late July or August (Snow and Copeland 1969). There is no record of diapaiise. Blanchard (l95l) reported one generation in the northern states and two generations in the central states per year. Vickery (1929) found 5 generations in southern Alabama and 9-11 generations in Texas per year. Snow et al. (1968) found male moths caught on St. Croix had sharp population peaks every 4-5 weeks, although the weather ras suitable for year-round reproduction and overlapping generations wovild be expected. Larvae feed as v/horl worms, arrayworms, cutworms, or perforators .(Labrador 1967). They select the whorls of corn plants, and sometimes only one large larva is found per whorl due to cannibalism (Vickery 1925). Larvae feeding deep in the whorl are protected by their frass and are difficult to kill (Hitman 1950). Larvae maturing in the whorl and tassel migrate to the ear when the tassel emerges from the whorl. They cause maximum damage to developing ears for they prevent complete fertilization and are usually not killed by insecticide applications (Young and Hamm 1966). Larvae feed princip;illy in the tips of young ears but bore into the side or base of ears with kernels in the dough stage (Hinds and Dew 1915). In the South, damage occurs at all stages of plant development, but in the IJorth, damage is usually confined to the ear because com is well advanced before moths appear (Blanchard 1951 )«

PAGE 15

S. fru.'^iperda damage is often mistaJcen for that of K. zea (Luginbill 1928). S. frugiperda feeds on young plants and causes a loss of vigor and stand, while feeding by H, zea at this time is of little importance (Although they feed extensively in whorls and tassels) (Blanchard and Douglas 1953)« Although females of E. zea oviposit on various com parts, they select fresn silks ( -iiiaintance and rrues ^^C,^, McColloch 1920, Ditman and Cory 1931, Phillips and Barber 1933, Barber 1943)The larvae enter the ear via the silk channel, while §_. irugiperda eggs are deposited without preference for silk and larvae enter by the silk channel or bore through the husk (Ditman and Cory 1931, Barber 193^, Dicke and Jenkins 1945, Blanchard et al. 1946, Kelsheimer et al. 1950, Blanchard and Douglas 1953)« Both species are aggressive, and in general, H. zea is found in ear tips while S^. frugiperda is found throughout ea.rs, so contact is reduced by spatial separation (Barber 1936, Dicke and Jenkins 1945, Kelsheimer et al. 1950, Blanchard 1951, Blickenstaff 1956). Eax damage and survival of various combinations of S^. frugiperda , H. zea , and the tobacco budworm, H. virescens (Fabricius), were investigated by Wiseman and '.Iclillian (1969). They concluded that of the 3 species, H. zea caused most of the ear damage. Blanchard (1951) reported that ^. zea caused more damage than S_. frugiperda . rvlorphological differences which may be used in field identification of larvae commonly found in c com are given by Dekle (1965). A Moths have a preoviposition period of 36 hours, with oviposition beginning on the second night and lasting 4-17 days. Lp to 1,782 eggs per female are laid. Cviposition occurs on cultivated and wild plants, and is generally on the underside of leaves (Luginbill 1928), although Vickeiy (l929) found more eggs on the upper surface of leaves. Viable

PAGE 16

eggs were foiznd on the surface of airplanes aj:riving in i
PAGE 17

extractable from com may increase the effectiveness of insecticides (Starks et al. 1967). Mc.Millian et al. {^^G6) showed that larvae assimilated 6l , 52, 46, and ^Z/o respectively of the kernels, silks, seed, and leaves consumed.

PAGE 18

ARTIFICIAL INFESTATION !.Iaterials ar.d I.Iethods Research was conducted at the Central Florida Experinient Station, Sanford, Florida. Dixie 18 field com was planted I-Iarch 6, 2J>, 25, and April 3, 1970, in plots 25 to 36 rows wide. Rows were 30 inches apart, and plots were JiOO feet long. Each plot was divided into 4 sections. The earliest planted two plots were called "medium level", the third plot "low level", and the fourth plot "high level" referring to the nvunber of applied worms, and will be called by these terms hereafter. Plant spacing within rows averaged about 10 inches and spaces of more than 14 inches were filled by transplanting plants; plants were removed if intervals between plants were 8 inches or less. Plots were irrigated, cultivated, and fertilized as needed. Plant growth stages were described and plant regions were designated. Low Level Infestation Fall armyworm larval infestation was simulated by placing laboratory-reared larvae in the field. A colony of approximately 1,000 individuals was maintained in the laboratory, and field-collected larvae were added to the colony when they were available. Two rows on each side of the plot and alternate rows within the plot were left untreated. Treated rows were 60 plants long. Treatments were randomly assigned to rows at 3 levels: one worm per plant, one worm per two plants, or one worm per fouj plants. Com was treated at early whorl, midwhorl; or late whorl growth stage. There was one check row per replication, and 7

PAGE 19

8 .• a there were 3 replications. Second instar larvae were transferred from 5 oimce paper cups into the com whorls by using a camel's hair brush. Larval survival was estimated by visually inspecting plants in the field. Evidence of feeding v;as recorded and maps were constructed v/hich showed infested and uninfested plants. Early whorl applications were checked at 4, 7» snd 14 days after treatment, .'.'id and late whorl treatments were checked 8 and 9 days after treatment, respectively. Survival was expressed as per cent of the original number of larvae placed in the treatment. Yield was estimated by hand picking the first (top) ear of the first 42 plants in each treatment. Second (bottom) ears were present, but they were very small, and it was not likely they would have been removed by a commercial compicker, so they were not picked or w^eighed. Ears were weighed in groups of 3« The mean ear weight minus the mean of treated ear weights was given. Comparisons were made using analysis of variance. !>lid-level Infestation Three rows on each side of the plots and alternate rows were left untreated. Treated rows were 60 plants long. Treatments were randomly assigned at 4 levels: 1, 2, 4» or 8 worms per plant. Com was treated at early whorl, mid-whorl, late whorl, or early tassel growth stage. There was one check row per replication, and there were 4 replications. Larvae were transferred from 5 ounce paper cups into com whorls (except for the early tassel treatment when they were dropped onto the tassel) by using a camel's hair brush. Larval survival was estimated by removing the plants in one replication 2-3 days after infestation, dissecting the plants, and counting the larvae. Com yield was estimated and compared by using the same methods that were used in the low level plots.

PAGE 20

High Level Infestation Treatment areas were 20 plants long and 9 rows wide, and no within-plot rows were left untreated. Plants were removed leaving bare ground between treatment areas. Treatment levels were randomly assigned at 0, 1, 10, or 20 worms per plant at early, mid, or late whorl growth stages. In preparation for the 10 and 20 v/orrns per plant treatment, worms were placed on small pieces of com in 1 ounce plastic cups and covered (10 and 20 worms per cup) and on the follo;ving day, the cup contents were emptied into the com whorls. Larval survival was estimated by randomly selecting and removing 20 plants from each treated area. These plants were dissected and the worms were counted. Yield estimates were made by picking 42 ears from the center of each area. The ears were weighed and the data were treated as in the other infestations. Moisture Estimation Five ears were randomly picked from each plot. The ears were weighed, shelled, and the kernels were weighed and placed in 5 ounce paper cups. The cups were placed in an oven at 225 F for 5 hours. The kernels were re-weighed and the per cent of moisture was calculated. Results and Discussion The plant growth stages were described on the basis of number of visible leaf sheaths, plant height, and exposure of the tassel (Fig. l). These stages appeared at about one week intervals. Plcint regions were designated as furl (leaves surrounding a central roll), whorl (leaves surrounding the furl with blades partially extended and the sheaths concealed), upper leaves (oriented less than 45 from the stalk and sheaths exposed), and lower leaves (oriented more than 45 from the

PAGE 21

10 Figure 1. -Growth stages of field corn: A-early tassel (lO visible leaf sheaths, tassel exposed), B-late whorl (6 visible leaf sheaths, tassel enclosed), C-mid-whorl (5 visible leaf sheaths, tassel enclosed), D-early whorl (3 visible leaf sheaths, tassel enclosed).

PAGE 22

11 stalk) (Pig. 2). The terra "furl" is used in place of "bud" which has been commonly used for the central roll of leaves and tassel. "Bud" is more properly used for raeristematic tissue consisting of unelongated intemodes enclosed within the leaf primordia (Keeton 1967). The meristematic tissue is located below the whorl (Fig. 5). At the present time, the terni "budworm" is used for any lepidoptercus larvae which inhabit the whorl and/or the furl of field find sweet com. Kiesselbach and Lyness (l945) and Camery and 'vVVoer (1953) showed that the greatest amount of yield reduction resulting from defoliation occurred when plants were damaged during late whorl and early tassel growth stages, or the period of rapid ear shoot development, silking, and fertilization. The younger the plants were prior to this stage, the smaller the effect was. A loss of a portion of the leaves reduced the grain yield, but the loss was not in proportion to leaf loss. At the tassel stage (the stage most susceptible to damage), the loss of 25, 50, and lOO^o of the foliage resulted in 8, 23, and 94-0 yield reduction, respectively. The amount of material consumed by larvae was shown by Luginbill (1928), but this information does not readily convert to leaf area loss. Worms feed in portions of the plant y/here leaves are not fully developed, resulting in more defoliation than would occur if they fed on nature leaves. In addition, the amoxmt of defoliation increases with the depth of larv^ penetration into the furl. For this reason, I approached this problem by working with a known number of larvae per plant and determining yield reduction. During the summers of 1963 and 1969, work was plagued with high natural fall armyworm infestations and low yields (due to late

PAGE 23

12 Figure 2. -Regions of field com: A-furl, B-whorl, C-upper leaves, D-lower leaves.

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13 Figure 3. -Cross sections of a field com plant: A-D-furl, B-E-bud, E-G-pithy stalk surro\anded by leaf sheaths.

PAGE 25

14 season planting). In 1970, com was planted earlier, and there was little natural larval infestation. Survival of larvae in low level plots examined 4, 7, and 14 days after they were placed in the field generally declined with time (Table l). In some cases it appeared that there were more larvae 14 days than 7 days after infestation, but the presence of worms was estimated by evidence of feeding, and the chance of overlooking a small larva was greater than that of overlooking a larger larva. Some of the laxvae were overlooked in earlier inspections. A small portion of the larval mortality reported was actually the result of larvae moving from the original plant to a neighboring plant. The per cent of untreated plants which were infested by these moving larvae was 1.3 for plants treated at early whorl, 1.9 for plants treated at raid-whorl, and 7.8 for plants treated at late whorl. More movement was evident at later com growth stages when more leaves were touching between plants. In 1968, early infestation of smadl com by larvae resulted in late instar larvae feeding on plants which were about 2 feet high. These large larvae frequently moved from plant to plant. Full grown larvae will occur in young com when moths oviposit on com when it is small, when environmental factors are not conducive to com growth, or when larvae move from a neighboring crop into the com. Survival of larvae increased slightly in mid and late whorl infestations compared with early whorl infestations (Table 2). Smaller plants furnish less protection for the larvae than larger plaxits furnish. Predators, parasites, and rain axe factors which may have been influential, Larval survival in mid-level infestations was comparatively lower in early tassel treatments (Table 5). At this time, tassels emerge

PAGE 26

15 Table 1.-Per cent survival of second instar S. frugiT^erda larvae placed in field corn in the _early whorl grov;th stage. Survival v;as estimated by field exaTdnation of the plants for evideiice of feeding. Plants per larva

PAGE 27

16 Table 2. -Per cent survival of second instar 3^. frugiperda larvae placed in field com in the early, mid, and late whorl growth stages. Survival was estimated by field examination of the plants 7 days after infestation.

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17 Table J.--';-— ^ ^^'^i :-viaoion of nuinoers oi larvae sur\'iving 7-9 days after Tield infestation at various com fexo?.iih stages.. Survival ?r?.s esti.T.ated ty dissecting a saT.ple of plants. Com gro"ffth stage Sstimated larvae ner nlant Eigh level in.festation Applied larvae per plant 1 10 ^0 Early whorl r.iid whorl Late 7;horl 0.9 *0.?2 0.9 *0.18 1.4 '0.S4 1.9 *1.39 8.7 *1.49 7.5 *0.22 19.1 =t6.i6 11.9 +5.92 11.4 *2.98 Mid-level infestation 1 Apolied larvae oer r>lan-! Early whorl I,!id whorl Late whorl Early tassel 0.9 *0.35 0.9 *0.36 0.9 *0.30 0.4 *0.49 1.5 *0.71 1.8 *0.52 1.6 *0.50 0.4 *1.14 3.0 +1.01 2.6 *1.23 3.5 +0.61 0.6 ^0.32 4.7 *2.29 5.S *1.78 7.2 *1.20 1.1 *1.40

PAGE 29

and the leaves v;hich comprised the furl and whorl are exposed on the plant. The larvae remain exposed on the plant, or move to earshoots where they tunnel betvreen the stalk and ear or bore into the ear. Com yield reductions estimates (Fig. 4) showed significant (a=0.05) loss in early whorl infestations at about 0.7, 2.3. snd 3.0 worms per plant, iiowever, there were nonsignificant losses belov, within, and above this range. In mid-whorl infestations, significant loss occurred at 6.4 worms per plant. No significant reductions occurred after late whorl infestations. After early tassel infestations, reductions were found at 0.8 and 1.4 worms per plant. At a yield reduction of 0.3 pound per. 3 ears, or 0.1 pound per ear, the grower would lose $7-50 per acre (assuming 1 bushel of com weighs 56 pounds, 14/j moisture, 10 inch plant spacing in a perfect stand, 1 harvestable ear per plant. Si. 00 per bushel, and 75 bushels per acre). The relationship between the growth stage of the com when it is infested and the resulting yield reduction is complex. A larva feeding on a young plant will consume as much as if it were feeding on an older plant, but the per cent of the total plant destroyed is greater in the younger plant. However, the younger plant will have a greater ability to recover from the damage, as was pointed out in the artificial defoliation studies (Kiesselbach and Lyness 1945> Camery and V/eber 1953) • Infestations occurring just before tasseling will result in foliage and ear damage (Young and Hamm 1966), and the plants are most susceptible to defoliation damage at this time. Early instar larvae will obtain most of their food from the small developing ears, and maximum ear da-:iage will result.

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19 EARLY WHORL INFESTATION >plot I plolll > plot III plot IV .4 .1 .t .1 I WORMS/PIANI ) 4 s t in LATE WHORL INFESTATION \ gl

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20 Defoliation may have two effects: photosynthesis may be reduced resulting in reduced growth and the transpiration surface may be reduced resulting in less water loss during dry periods. Deep penetration of the lar\'ae into the bud or parenchyma tissue would result in the death of the growing tip, and additional plant growth woiild be from the root area, and it is unlikely that ears would be produced. Larvae were never found in the buds of com. HoTrever, stunted sweet com was seen in 1969» but it was not determined if lar\'al feeding was the cause of the stunting. Sv/eet com is comparatively smaller than field com, and it is more likely that larvae would reach the bud in sweet com. Another type of damage that larval feeding may inflict on com is the prevention of fertilization of ears. Larvae are foiaid on both silks and tassels. One plant is able to produce enough pollen to fertilize several plants, for in commercial seed production, 2 male fertile rows are sufficient to pollinate 6 male sterile rows (Poehlraan 1959). Plants infested with 1-9 worms per plant at the early tassel stage showed 53?a of the tassels with damage, but none of the tassels were completely destroyed. Under these conditions, tassel feeding is of little concern. Ample pollen was produced and no unfertilized kernels were detected. Larvae feeding on the silk may cause ears to be incompletely fertilized if the feeding occurs at or immediately before the time of pollination. Vihen this damage occurs, complete rows of kernels aje missing from the ears. In a check of infested com in which most of the silks had been chewed off, 6>' of the eajs showed evidence of improper pollination. Some ears showed up to 1/3 kernel loss due to improper

PAGE 32

21 pollination. These ears were also infested with Heliothis zea, and the damage is a result of feeding by the two species. Vickery (l929) stated that one fall armywonn per plant produced as much damage as several fall armyvrarras per plant, for large larvae fed in the furl, and due to caiinibalism or other interactions, only one larva could be found there. During 1969» in an area of natural infestation, 48 out of 50 infested plants contained one fifth or sixth instar larva. The other two plants contained 2 larvae each. Thic distribution pattern was not found again, and it suggests that different behavior patterns exist within the species as indicated by Labrador (1967). An individual plant's ability to tolerate or recover from defoliation is probably due to the availability of nutrients and moisture. Yields of the plots in 1970 ranged from 78 to 86 bushels per acre, and the per cent of moisture ranged from 15 to 22 (Table 4)«

PAGE 33

22 Table 4«-2stiT?iated moi.sture content arid yield of field com, 19/0, Per cent Kernel weight Plot noisture per car, ^rp.sns Bushels per av: Low level 21.19 93-20 79-44 I.Iid-level reps 1-3 14-74 101.12 86.24 reps 4-6 18.94 96.20 82.06 High level 22.34 91.85 77-90

PAGE 34

BEHAVIOR OF LARVAE Materials and Llethods Photo taxis and Geo taxis Responses of newly hatched larvae to light and gravity were measured in a lightproof 10 X 13 X 125 cm corrugated container. In I969f sections from the furl region of com plants 5 cm long and 5 cm in diameter were strung at 10 cm intervals along a wire which extended from end to end in the chamber. A piece of tissue paper containing newly emerged larvae still on the egg mass was pinned on the inside of a flap which opened midway down the side of the chamber. After 24 hours, the wire holding the furl sections was removed, and the larvae were counted on each section. During phototaxis tests, one end of the chamber was covered with transparent plastic and placed 20 cm from a 15 Watt incandescent bulb. Increase in temperature caused by the bulb W£LS less than 1 C. Vario\xs combinations of chamber orientations to gravity and light were tested. Tests were conducted at 24-28 C and about 80?^ RH. The chamber was modified in 1970. The wire and furl sections were replaced with a 2 X 2 X 125 cm wooden support on which 1 ounce plastic cups were held with rubber bands. The cups were l/3 full of media. An introduction device 8.2 cm in diameter X 8 cm high was glued to the side of the container. The bottom of the introduction chamber and the corresponding area of the centraJL container were cut out. A cover was placed over the open end of the introduction container (Fig. 5)« Tests 23

PAGE 35

24 Figure 5 '-Behavior chamber used to determine phototajcis and geotaxis of fall armyworra larvae. Larvae were placed into the introduction chamber and after 24 hours, the wooden support holding the media cups was removed and the larvae in each cup were counted.

PAGE 36

25 were conducted only with the chamber upright and with the light at the top. All instars were tested: 279 first, 11? second, 41 third, 51 fourth, 52 fifth, and 26 sixth instar larvae. Tests were conducted, at 21-27°C and about 60';b RH. Preference of Plant Tissues Larval selection of various plant tissues was tested in a preference chajnber constructed of a central rectangular cardboard container 45 cm high and 6.5 cm square onto which 24 paper cups 4.5 cm in diameter and 7 cm high were glued by their bottom end. The bottom of each cup and the corresponding area in the central container was removed (Fig. 6). Covers were placed on the cups. Six chambers were constructed. Tissues to be tested were placed in alternate cups. For each test, 50 third or fourth instar larvae were dropped into the bottom of the central chamber. After 24 hours, the cups were opened and the worms in each were counted. Tests were conducted at 21-27 G and about 60;^^ RH. Com tissues compared were: 4 X 4 cm leaf sections vs 3 cm diameter ears, 4 cm long X 5 cm diameter ears vs 4 X 4 cm pieces of sheath (tissue surrounding ears), 4 X 4 cm sections of leaves held open by gluing (Elmer's Glue ) a piece of midrib across the section vs a 4 X 4 cm section, folded over and stapled, forming a tunnel about 1 cm in diameter (these will be called "open" and "closed" leaves after this), and pieces of stalk, tassel, leaf, furl, silk, and ear. Results were analyzed by using Student's t test for the first 3 tests and analysis of variance for the fourth test.

PAGE 37

26 6.5 X 6.5 X 45 cr Cardboard 5oi Cup Figure 6. -Chamber used to test larval preference of various com tissues. Tissues were placed in the cups, and a cover was placed on each cup. Larvae were dropped into the central chamter, and after 24 hours, the lairvae in each cup were counted.

PAGE 38

Results and Discussion Phototaxis and Geo taois Most first instar lair/ae regained near the point of introduction in the horizontal darkened chaTiber {Fig. 7 A). V/hen the chamber was vertical and darkened, most lar/ae noved upward (Fig. 7 B). V/hen the chamber was horizontal and lighted, most larvae moved toward the light (Fig. 7 C). V^hien the chamber was vertical and the light was entering from the top, larvae moved upward (Fig. 7 !*)• When the light was entering from the bottom, larvae moved dov^Tiward from the point of introduction (Fig. 7 E). First instar larvae are positively phototactic and negatively geotactic. The response to li^t is stronger than the response to gravity. This behavior is important in the dispersal of lar\^ae, for they move to the upper portions of the plant where they may be blown by the wind, or they may remsdn in this area and feed. First and second instar larvae are positively phototactic and/or negatively geotactic, but later instars do not show this response, or the response is overshadowed by other behavior (Fig. 8). In the field, this behavior would permit partially grown larvae to select regions of plants other than those at the very tops of plants. For example, larvae move downward to the ears when the tassels become exposed. Preference of Plant Tissues Only one significant difference between plant tissues was shown in the preference chamber tests, although the same, nonsignificant preferences were found repeatedly (Table 5)« ^sJ^ 27

PAGE 39

28 DARK CHAMBERS HORIZONTAl LIGHTED CHAMBER^ HORIZONTAL VERTICAI IVERTICAL -»-up 4— ^__ VERTICAL up^ light ^ Figure 7. -Dispersal of first instar fall armyworm larvae from the point of introduction in the behavior charnber. A and B-dark, C-light from side, D-light from top, E-light from bottom.

PAGE 40

29

PAGE 41

30 Table 5« -Selection of plant tissues by S. preference chEurber. 'rugiperd?larvae in Year T.'aterials compared '.laterial preferred Signixicance 1970 ear rheath vs kernels 1970 ear :^heath vs kernels 1970 leaf vs ear 1970 leaf vs ear 1970 leaf vs ear 1970 leaf vs ear 1970 leaf vs ear 1969 open vs closed leaves 1969 open vs closed leaves 19o9 open vs closed leaves 1970 open vs closed leaves 1970 open vs closed leaves ear sheath

PAGE 42

31 sheaths were consistently selected over ear kernels (nonsignificant differences). It was observed that many nearly full grown larvae which were attacking yoiing ears fed on the sheaths, and formed a tminel to tne kernels, but the kernels v/ere not fed upon. The larvae could have completed their feeding period by this time, or they could have preferred to continue to feed in the sheath tunnel instead of feeding on the kernels. If the ear was not fully grc-fm, expansion of the ear and sheath caused the tunnel to close, for the overlapping layers of sheath changed in their relative positions. This indicated that ears fed on, in this manner, are not vulnerable to secondary attack via holes in the sheatlis. Sheath feeding by larvae is of no significance in yield reduction. When leaves were compared with cross sections of ears, leaves v/ere selected in all cases (nonsignificant differences). In the field, larvae moving out of the newly-exposed tassel usually move to the ears to feed. These tests show larvae do not prefer ears over leaves. Other factors must influence larval selection of feeding sites. A comparison of open and closed leaves showed closed leaves are preferred in all cases (l replication out of 5 shov/ed a significant difference) (Table 5)» This may explain v/hy larvae seek closed areas such as whorls, furls, and areas between stalks and leaf shoots. These areas furnish protection from parasites, predators, and various detrimental environmental factors. No significant differences were found when stalks, tassels, leaves, furls, silks, and ears were compared (a=0.05). This again indicates plant tissues do not influence larval selection of feeding sites on corn.

PAGE 43

FIELD DISTRIBUTION OP LARVAE L laterials and Methods Distribution on Field Com Plants Plots of Dixie 18 field com were planted June 16, 25> and July 2, 1969» and hereafter will be called plot I, II, and III respectively. Sampling was begun in plot I when the com was 5 feet high, and v/as continued through ear development. Samples consisted of 50 plants, and were taken twice weekly. Plants v/ere cut at ground level and taken into the laboratory where they were examined. Sampling was started in plots II and III when the com reached the height of 3-and 1^ feet, respectively. Sampling in these plots continued for 2g weeks until a period of heavy rain after which no larvae could be found. Com height was measured from ground height to the highest part of the leaves or tassels. Com growth stages were determined and recorded, and plant regions (furl, whorl, upper leaves, and lower leaves) were determined and the number of worms in each region was recorded. Larvae were grouped into 5 size catagories: very small, small, medium, large, and very large. These categories generally correspond to the first, second, third and fourth, fifth, and sixth instars, respectively. Determination of exact larval instars was not within the scope of this experiment. The mean number of laxvae per 100 plants in each plant region was estimated: (total larvae per region)/ (total plants)(lOO). The per cent 32

PAGE 44

33 of each size group of larvae in each plant region was estimated: (total larvae of age group per region)/(total larvae per region)(lOO) . Development of plants v/ith emphasis on growth of tassels, ears, and neristenatic tissue was recorded. Distribution on Zars The distribution of fall arniyA-orra and corn ear'.vorni larvae in ears was investigated in 1970. Ear samples were taken at random from com which was artificially infested at the late whorl and early tassel growth stages. Ears viexe exainined for larvae and for feeding damage. Dispersal from Egg Masses Larval dispersal from egg masses was observea in a 6 X 6 X 6 ft. cage covered with fiberglass Saran® screen. Egg masses from the laboratory colony were placed on plants growing in the cage. Egg masses from the laboratory colony were placed in the field. Masses of 10, 100, 500, and 1,000 eggs were placed in the field. There were two treatments; the first was examined when S&yo of the larvae were in the first ins tar. The com was 40 inches tall at this time, and leaves were touching between rows. Plants showing evidence of worm presence were cut and examined in the field, and a map vias made showing the location of infested plants and numbers of worms per plant. The second treatment was examined when most of the larvae were in the fifth instar. At this time, the com was 6 feet tall, but had not tassel ed. Maps were converted to tabular form, with nmnber of larvae in 10 inch intervals grouped and listed. There was a 9 day interval between checks.

PAGE 45

Results and Discussion Distribution on Corn Plants The highest nunber of larvae found in com between early and late whorl stages was in the whorls, followed by furls, upper leaves, and lower leaves (i'ig. 3). The whorl is the highest part of the plant, and early ins tar larvae would move into this area. The whorls and furls provide an enclosed area similar to that provided in experimental closed leaves. These enclosed areas furnish some protection from predators, parasites, and abiotic factors. Feeding in the whorl and furl produces the most loss of leaf area because the leaves are not fully developed in these areas. If the bud is damaged, it would be as a result of larvae v/hich started feeding in the whorl and tunneled downward. During rain, small plants' whorls fill with water, but the possibility of drowning or the increase in disease frequency was not investigated. The per cent of various sizes of fall armyworra larvae found in plant regions (Fig. 10 j showed large and very large larvae were not found on lower leaves. Smaller larvae were found throughout the regions. Larvae were never found in or on the stalk. Large larvae feeding in the furls and whorls may have influenced smaller larvae to feed in less preferred areas. V.hen large larvae feed in the furl, then mature, the feeding tunnel provides access to the furl for young larvae. Larvae which are feeding in the furl and whorl when tassels emerge must attack the ear shoots or remain exposed v/hile feeding on the leaves. 34

PAGE 46

35 20i UC 161 140 120 100 80' 60' 40' 20'

PAGE 47

36 Figure 10. -Size distribution of fall armyworra larvae in several plant regions. Com was examined in the early whorl through late whorl stages.

PAGE 48

57 Distritution on plants from early v.'horl through mature stages, after whorls are exposed, includes a brief period of feeding on the tassel before moving to the ears (?ig. 11, Table 6). These larvae could damage foliage, tassels, silks, and ears. Ear shoots were not evident at the time of tassel emergence in some plants (r'ig. 12 a). Larvae feeding on these plants do not have a protective retreat, but must remain exposed in they stay on the plant. Distribution on Bars Larvae attack ears by entering through the si]k channel, or more commonly through the sheath surrounding the ear (Fig. 15). Some larvae fed on the sheath but not on the kernels. Young ea.rs with soft silks contained larvae in ear tips, middle of ears, and silks, while com earv.orms were found in the silk channel, ear tip, and mid.dle of ears (in decreasing order). Ten days later, there was a higher ratio of com earv/orms to fall a:L-:.iyworms . At this time, most of the com earworm larvae were found in the silk channel and ear tips (Table 1 ) . By this time, the fall armyworms had probably left the ears and pupated. Most of the kernel loss was in the ear tip followed by the middle of the ear. Total kernel loss was 3.9 and 2.2/j for the tip and middle of ears, respectively. This loss was due to both species. Few young fall arrayworm larvae developed in the ears; most were partially grown, and had moved from the whorl and furl. Com earv-orm larvae usually developed entirely in the ears, for moths prefer silks for oviposition sites. Dispersal from Egg Masses Kewly emerged larvae remained on or near the mass for 1? hours at 26°C and 5 mph wind. Other larvae left the mass immediately after emerging at 34 C. In the field cage, larvae were observed emerging from a mass of about 100 eggs. Dispersal began after one hour at 32°C. Twelve larvae were moving about on the highest part of

PAGE 49

58 CORN GROWTH STAGE 1 1

PAGE 50

39 Table 6.-I'istribubion of 3. frufti?crda larvae before aiid after e.-nergence of tasoeln in field corn. i?j~.'osx3 of larvae are expressed as rser cents. Com I-JLunber of Plant r.-j^-ion grov^th infested plants ' stage examined ear furl wiiorl l6aves ear sheath tassel Late ;

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40 Figure 12. -Contrasting com development: A-tassel is completely exposed, while ear shoots are not evident; Btassel is partially protected by the whorl while the ear shoot has emerged. Plant A furnishes little protection for larvae, while plant B offers protection in the tassel-whorl region and the ear shoot provides a place for the larvae to burrow. Larvae were never seen boring into the stalks.

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41 Figure 1 J. -Pall armyworm larvae commonly enter ears by boring into the sheath at the junction of the stalk and the ear.

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42 Table Y^-^^istribution of S. fru gj-nercn ^.d d. ?ea lar/ae in fie].: corn earr; . Z^rc in the first sample (early age^ arid fresh silk v/Iiile ears sa-npled 10 da^r;. later (late age) had dry silks. Per cent larvae Sar region Kunber Jar pge Lar"/al srtecies Isr/ae silk tin ni^ddle butt Zarly |; Late ^' fa-

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43 a leaf. I blew lightly on the leaf, and 7 dropped on threads which were attached to the leaf edge. Other larvae v/ere seen dropping on threads. Several larvae would sometimes drop together; their threads vrould tv/ist together. Slight v.'ind gusts stimulated dropping. No feeding was seen at this time, except for the consuumption of egg shells.. I.Iovement over long distances could occur when larvae are picked up and carried by the wind. Examination of plants surrounding egg masses placed in the field showed there was more movement of larvae per day for the first 3 days than per day for the first 12 days (Table 8). This suggests there is a dispersal period before feeding begins. There was more movement within than across rows, probably because there was more withinrow plant contact. Mean larval movement was greater at higher larval densities. This dispersal v/ould reduce larval contact and decrease the amount of cannibalism. This is economically significant, for larvae move from plants when densities are high enough to reduce yield, or conversely, move and damage more plants.

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44 >> 'J t— > •w c CM CO CM K^ r— cr. Tc CO "^rvo 1^ N \ c. cj c c

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LARVAL BIOLOGY Materials and ?.!ethods Starvation of Newly Emerged Larvae The length of time that newly emerged larvae can survive without feeding was estimated by holding larvae for various periods of time before allowing them to feed. In 1969, tests were run at 21 +2°C and about SCyi RH. In 1970, tests were run at 22 *2°C and 60-705^ RH. Larvae emerged and consumed their egg shells, then they were placed without food in covered 5 ounce paper cups. Groups of larvae were fed at 2 hour intervals and after 2 days, surviving larvae were counted. The LD was calculated after correcting for natural mortality by using Abbot's Formizla. Starvation and Cannibalism of Late Instar Larvae Fourth, fifth, and sixth instar larvae were held without food in 5 ounce paper cups. There were 1, 2, or 3 larvae per cup. V/hen there was more than one larva per cup, cannibalism occurred. Cannibalism is expressed as a ratio of original to final number of larvae (example: 2:1 cannibalism indicates that of two original larvae, one survived). Pupal weights of cannibals and noncannibals were compared by using Student's t test. Survival and Development iHiring Periods of Low Temperatures The survival of eggs, larvae, and pupae at k, 4, 13, and 29 C (all temperatures were +1 C) were estimated. Eggs were held at 1 , 4, and 13 C for 24-168 hours, then they were held at 29°C and mortality and time for maturation were noted. One day old larvae were held at 6, 11, and 14 C for 4, 7, and 11 45

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46 days before holding them at 29 C. Survival and length of time for development were noted. Pupae were held at 0, /\> and 4-7 (fluctuating) C for 5, 7, and 14 days before holding them at 29 C Mortality and time for development were noted. High Density Rearing Egg masses of 100-500 eggs were collected frorr. the field and laboratory and placed in heavy 28 X 17 X 45 cm paper bags. Various parts of corn plants were placed in the bags for larval food. The tops of the bags were stapled shut, and they were stored at about 75°F and about 63<-^o BE. Results and Discussion Starvation of Newly Emerged Larvae The star\''ation LDc,-) ^or nev/ly emerged larvae ranged from 20 to 35 hours (Table 9). Depending on environmental conditions, larvae would have about a day to select or find a suitable host. Early larval starvation did not affect the pupal weights or the time required to complete laxval development (Table 10). Starvation and Cannibalism of Late Instsir Larvae The starvation LDj.^ for fourth and fifth instar larvae was 26 and 73 hours, respectively (Table 11}. Sixth instar larvae were able to survive and pupate Y/ithcut feeding. V^lien more than one larva was in a cup, usually only one sur/ived due to cannibalism. After cannibalism occurred, there was a characteristic dark stain on the container as a result of loss of body fluids from wounds. Fighting resulted in scars or damaged areas on the cuticles. If one of several Isirvae was damaged and body fluids were emitted, other larvae were stimulated to attack the wounded larva. Some fifth instar larvae were able to survive and pupate if they fed

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47 Table 9. -Survival of starved unfed first ins tar S. frugi perda 1 arv ae . LD^„ in hours 50 Relative Year Terrpsrature huT.idity rep. 1 rep. 2 re-p. ; rep. 4 rep. 5 I96Q 21 *2'^C 80 *3^^ 29 20 25 X X 1970 22 ^2"c 65 ^5/^ 35 35 35 3:^ 32 Calculated by probit analysis and niortality corrected oy Abbot's formula.

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48 c n >> ;» rt -I Q

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49 Table I1.-Tii& effect of Etarvation and carinibalis.-p. en LD^^ aixd per cent pupation of Z. f ruigi^erda larvae. -^ "

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50 on two larvae. The LD_^ increased with the rate (O, 2:1, Jjl) of cannibalism for fourth and fifth instar larvae (Table 11 ). The pupal weights of sixth instar larvae which were starved were less than those which were cannibals, but the differences were not significant (a=0.05), (Table 12). High Density Hearing Vrnile rearing larvae at high densities, two morphological and behavioral larval differences were noted during the fourth and fifth instars. One type was dark, and more prominent spines, held the mandibles forward, and remained on the sides of the bags where they were separated spatially. The other type was lighter in color, had less prominent spines, held the mouthparts downi^ard, and remained on the food. 'Alien the dark type was lightly touched with a camels hair brush, they responded with a side to side sweep of their heads. The response of the light type to this stimulation was to become motionless, drop from their position, or retreat. Side to side head sweep motion by light type larvae was stimulated only by a severe pinch such as a squeeze by tweezers. The side to side head sweep was followed by a directed mandible attack and sometimes regurgitation of gut material. Both light and dark types were seen in the field, but late instar larvae were not found exposed on plants, so responses to these types of stimulation were not tested in the field. If various conditions produce various behavioral and/or morphological types, as is suggested by Labrador {^^6^), one must be careful in applying generalizations made from one type to predictions of another type. ?or example, information presented in this paper should not be used in predicting losses which would be caused by larvae moving amyworra-style into a field of com.

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51 Table 12.-Pu^al '.veielits of starved cannilialistic and noncannibalistic si:cth instar S. frugi';?erda larvae. Cannibalism ratio 2:1 ^:1 Pupal weight, grajns 0.1102 0.1274 0.1 590 t" X 0.882 ns I.256 ns Ratio of original to final number of larvae 2 Conparison of non-cannioal with other catagories; a=0.05

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52 Survival and Development During Periods of Low Temperatures Temperature studies show eggs hatch in 48 and 192 hours after being held at 29 C continuously and 15 C for 144 hours, respectively. Eggs could not sur-/ive temperatures of 1 C for 24 hours, but could survive up to 48 hours at 4 C without increased mortality (Table Ij). Larvae pupated in 7 days when held at 29 C. They survived for 48 days at 14 C, but did not pupate (Table 14). The larval stage was also extended at 6 and 11 C. Pupal mortality increased at 4 and 4-7 C; pupae survived up to 11 days at 0°C (Table 15). The fall armjTvorm is a more serious pest in the South than in the North because of its late arrival in the North. Although the worms are not tolerant of cold, millions of eggs, larvae, pupae, and adiilts are exposed to varying degrees of cold. If a stage develops a method of surviving low temperatures, the annual invasion of the North will occur earlier in the season, and crops will be seriously threatened. If parasites do not develop cold resistance at the same time, with uncontrolled development in early spring, it would become a major agricultural insect pest throughout the United States. The tremendous adaptability of the insect has already been mentioned (Labrador 1967). None of the stages of the insect which were tested showed signs of developing cold hardiness, although a greatly extended larval period was found. In addition, behavioral patterns may be slightly altered and permit overwintering. An example of this is the construction of pupal chcirabers deeper in the soil where the pupae are protected from lethal temperatures.

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55 Table l^.-IIours required for develo-nirient of S. rrugj-nerda eggs at : at 29^C. held at low ter.peratures for various lengths of time before lioldirig Hours at low tenDer.-^.ture Low temp. 24 48 72 96 120 144 16' 13!?C 43 72 96 120 144 168 192 4 C 48 72 96 120 X X X V 1°C 48 X X X X X X : 605^ mortality; no mortality at other ter?.perature/periodG where eggs developed

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54 Tabic 14.-Sur\'-ival of 2 iay old S^. fru&lperda lar.'ae held, at lev.' temperatures. Tv.'enty larvae were started at each temperature, and the number surv'iving is i^iveii.

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55 o -P CO S a c 0) -J •^ o o o o c c o o CD ^--^ L(^ \0 CN ON TCO tv-\ TTTTTCvJ CM Cvl f4

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REFERENCES CITED Barber, G. W. 1936. The com earivorm in southeastern Georgia. Georgia Agr, Exp. Sta. Bui. 192. 18 p. Barber, G. V/. 1945« Oviposition habits of the earworm moth in relation to infestation in the ears and to control. J. Econ. Entoniol. 56: 611-8. Blanchard, R. A. 1951. Control of the fall arrayworm. Proc. Sixth An. Meeting North Central States Branch Amer. Assoc. Econ. Entomol. 69-71 . Blanchard, R. A., T. R. Chamberlin, and A. F. Satterthwalt. 19^6. Controlling the fall anriyAvorra in sweet com and popcorn with DIiT. J. Econ. Entomol. 39: 81?. Blanchard, R. A. and V/. A. Douglas. 1955« -he com eanvorm as an enemy of field com in the eastern states. USBA Fanners Eul. 165I. 18 p. ' Blickenstaff , C. C. 1956. The nature of damage to field com by the com earworm, Heliothis zea (Boddie), and the fall armynorm, Laphygma f rugi pe rd a ( A&S ) . Dissertation, Iowa State College, Ames. 121 p. Blickenstaff, C. C. 1965. Common names of insects. Bui. Entomol. £oc. Amer. 11: 287-320. Burton, R. L. 1967. I.Iass rearing the fall arrayn'orm in the laboratory. USDA Agr. Res. Serv. 33-117. V Burton, R. L. and H. C. Cox. 1966. An automated packing machine for lepidopterous larvae. J. Econ. Entomol. 59: 907-9. Burton, R. L. and E. A. Karrell. 1966. I.todification of a lepidopterous larvae dispener for packaging machine. J. Econ. Entomol. 59: 1544-5. \ Burton, R. L., E. A. Harrell, H. C. Cox, and W. W. Hare. 1966. Devices to facilitate rearing of lepidopterous larvae. J. Econ. Entomol. 59: 594-6. Camery, M. P. and C. R. 'vVeber. 1953. Effects of certain components of simulated hail injury on soybeans and com. USDA Agr. Res. 3er".". Bui. 400:465-504. 56

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57 Cooperative l!]conomio Insect Report. 1969. USDA Agr. Res. Serv. "Vol. 19. Cooperative Economic Insect Report. 1970. USDA Agr. Res. Ser'/. Vol. 20. Dekle, G. V/. 1965Illustrated key to caterpillars on com. Florida Dept. AgT, Div. Plant Industry. 5ul. 414 p. Dicke, P. F. and M. T. Jenkins. 1945Susceptibility of certain strains of field corn in hybrid combinations to daiiage by com earworras. USDA Tech. Bui. 893. 36 p. Ditman, L. P. 1950. Fall arrayworm control. J. Econ. Entomol. 45: 726-7. Ditman, L. P. and E. N. Cory. 1951 • The com earworm, biology and control, .'.laryland Agr. Exp. Sta. iiul. 528: 445-82. Harrell, E. A., V/. 7/. Hare, and R. L. Burton. 1968. Collecting pupae of the fall armyv/onn from rearing containers. J. Econ. Entoniol. 61 : 873-6. Hinds, W. E. and J. A. Dew. 1915. The grass worm or fall armyworm. Alabama Agr. Exp. Sta. Bui. 186: 6l-92. Keeton, Vf. T. 1967. Biological Science. W. \L Norton and Co., Inc. Neyr York. 455 p. Kelsheimer, E. G. , N. C. Kayslip, and J. W. Wilson. 1950. Control of . budowrms, earv/orms and other insects attacking sweetcom and green com in Florida. Florida Agr. Exp. Sta. Bui. 466. 38 P. Kiesselbach, T. A. and W. E. Lyness. 1945. Simulated hail injury of com. Agr. Exp. Sta. Univ. Nebraska. Bui. 377. 22 p. Labrador, J. R. 1967. Estudios de biologia y combate del gusano cogollero del niaiz. Universidad del Aulia, i'.iaracaibo , Venezuela. 83 p. Leuck, D. B. 1970. The role of resistance in pearl millet in control of the fall armyworm. J. Econ. Entomol. 63: 1679-81. Leuck, D. B. and J. L. Skinner. 1971. Resistance in peanut foliage influencing fall armyworm control. J. Econ. Entomol. 64: 148-50. Leuck, D. B. , C. M. Taliaferro, G. Yi. Burton, and M. C. Bowman. 1968. Resistance in bermuda grass to the fall armyivorm. J. Econ. Entomol. 61 : 1521-2. Luginbill, P. 1928. The fall array7/orra. USDA Tech. Bui. 34. 91 P. McColloch, J. W. 1920. A study of the oviposition of the com earworm with relation to certain phases of the life economy and measures of control. J. Econ. Entomol. 15: 242-55.

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58 McMillian, V/. W. and K. J. Starks. 1966. Feeding responses of some noctuid larvae (lepiriopterous) to plant extracts, iiim, Entomol. Soc. Mer. 59: 51d-9. Mclviillian, A'. V/. , K. J. Starks, and 1,1. C. Bovmian. 1966. Use of plant parts for food by larvae of the com earworm and fall armyworm. Ann. Entomol. Soc. Amer. 59: 865-4* Mciilillian, W. W. , K. J. Starks, and M. C. Bowman. 196?. Resistance in com to the com ear'.vorm, Heliothis zea, and the fall armT-^-rom, Spodoptera frugiperda (Lepidoptera: I^octuidae). Part I. Larval feeding: responses to com plant extracts. Ann. Entomol. Soc. Ainer. 60: 871-3. Olive, A. T. 1955. Life history, seasonal history, and some ecolo^iical observations on the fall annywonn, Laphygma fntginerda (a&S), on sweet com in North Carolina. Thesis. Korth Carolina State Collefje, Raleigh. 77 p. Phillips, V.'. J. and G. V/. Barber. 1933. Egg laying habits and fate of eggs of the corn earworm moth and factors affecting them. Virginia (Blacksburg) Agr. Exp. Sta. Tech. Bui. 47. 9 p. Poehlman, J. M. 1959. Breeding field crops. Henry Holt and Co., Inc., New York. 427 p. Porter, J. E. and J. H. Hughes. 1950. Insect eggs transported on trie outer surfaces of airplanes. J. Econ. Entomol. 43: 556-7. Quaintance, A. C. and C. T. Brij.es. 1905. The cotton bollv/orrn. USDA Entomol. Bui. 50. 13 p. Randolph, N. M. and P. M. V/agner. 1966. Biology and control of the fall armyworm. Texas A&M University Agr. Exp. Sta. Rept. PR-2431. 6 p. Roberts, J. E. 1963. The effect of larval diet on the biology and insecticidal susceptibility of the fall armyworm, Laphy gma frugiperd.a (Smith). Dissertation. Kansas State University^ I.Ianhattan. 99 p. Snow, J. W. , V/. Y/. Cantelo, R. L. Burton, and S. D. Hensley. 1968. Populations of the fall armyv/orms, corn earworms, and sugarcane borer on St. Croix, U.S. Virgin Islands. J. Econ. Entomol. 61 : 1757-60. Snow, J. V*. and W. Vi. Copeland. 1969. Fall armyworm: use of virgin female traps to detect males and to determine seasonal distribution. USDA Agr. Res. Serv. Production Research Report. 110. 9 p. Starks, K. J., J. R. Young, and '.V. W. Llci'Iillian. 1967. Arrestantfeeding stimulants from com used in conjunction with an insecticide against lajrvae of the corn earworm and fall armywomi. J. Econ. Enton?Gl, 60: 1483-4.

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59 Taubenhaus, J. J. and L, D. Christenson. 1936. Role of insects in the distribution of cotton wilt caused by Risarium vasinfectum . J. Agr. Res. 53: 705-15. Vickery, K. A. 1929. Studies on the fall armyworm in the Gulf Coast District of Texas. USDA Tech. Bui. 138. 64 p. Wiseman, B. R. and Y/. W. iMcLIillian. 1969. Competition and survival among the com earvrorm, tobacco budworm, and the fall arriyworm. J. Econ. Sntomol. 62: 734-5. Yo\ing, J. R. and J. J. Hamm. ^^66, Huclear-polyhedrosis viruses in control of com ear^vorm and fall armyivorm in sweet com. J. Scon. Entomol. 59: 382-4.

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BIBLIOGRAPHICAL SKETCH Wendell L. Ttorrill was bom ".lay 22, 1941 » in Madison, South Dakota. He graduated from General Beadle High School in 1959. He was employed on a farm and worked for the Soil Conservation Service until he entei'ed South Dakota State University in 19^3. He received his Bachelor of Science degree in 196? and. his I.Iaster of Science Degree in 1968. Both degrees were awarded with a major in entomology. ViTiile earning his degrees, he was employed by the Entomology-Zoology Department and the USDA Northern Grain Insects Research Laboratory. In 1968, he accepted a research assistantship at the University of Florida from the Department of Entomology and Kematology. He has held that position until the present time. Wendell Morrill is married to the former Judy Larson, and they have one child, Jill. He is a member of Phi Sigma Biological Society and Gamma Signa Delta, Honor Society of Agriculture. 60

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I certify that I have read this study arid that in my opinion it conforms to acceptable standards of scholarly presentation and is full;, adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. James E. Lloyd Associate Professor of Entomology I certify that I have read this study and that in my opinion it conforms to acceptable staLndards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. 2: Jonathan Reiskind Assistant Professor of Zoology This dissertation was submitted to the Dean of the College of Agriculture and to the Graduate Council, and was accepted as partial fulfillment of the requirements for the degree of Doctor of Philosophy. December, 1971 Dean, College of Agricjiltilre Dean, Graduate School

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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. <^ /^ y / -/ Gerald L. Greene, Chariman Associate Professor of Entomology 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. Dale H. Habeck, Co-chairman Associate Professor of Entomology 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. Cjl^. (] u.; '' r Thomas J. Walker Professor of Entomology

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