Title: Florida Entomologist
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Title: Florida Entomologist
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Creator: Florida Entomological Society
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Place of Publication: Winter Haven, Fla.
Publication Date: 1980
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Insects -- Florida -- Periodicals
Insects -- Periodicals
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FLORIDA ENTOMOLOGIST

(An International Journal for the Americas)

Volume 63, No. 4 December, 1980

TABLE OF CONTENTS

1980 FALL ARMYWORM SYMPOSIUM

ALL, J. N.-Reducing the Lag Between Research Synthesis and Prac-
tical Implementation of Pest Management Strategies for the Fall
Armyworm: Introduction to the Fall Armyworm Conference
1980 .-------------- ---------.........- 357
HUNT, T. N.-Monitoring and Predicting Fall Armyworm Infestations
in North Carolina ......-.....------------- ----- ----- 361
BARFIELD, C. S., J. L. STIMAC, AND M. A. KELLER-State-of-the-Art for
Predicting Damaging Infestations of Fall Armyworm .--...-- 364

MARTIN, P. B., B. R. WISEMAN, AND R. E. LYNCH-Action Thresholds
for Fall Armyworms on Grain Sorghum and Coastal Bermuda-
grass -.... -- --- ----- .----- .- ----------------- ---.. 375

SPARKS, A. N.-Phieromones: Potential for Use in .llM-.it,.ring and
Managing Populations of the Fall Armyworm --- --. 406

LYNCH, R. E., P. B. MARTIN, AND J. W. GARNER-Cultural Manipula-
tion of Coastal Bermudagrass to Avoid Losses From the Fall
Armyworm .......-...... ....---------------- ------- 411
DAVIS, F. M.-Fall Armyworm Plant Resistance Programs 420
WISEMAN, B. R., F. M. DAVIS, AND J. E. CAMPBELL-Mechanical In-
festation Device Used in Fall Armyworm Plant Resistance Pro-
grams ---------------------- --------------- 425

LEWIS, W. J., AND D. A. NORDLUND-Employment of Parasitoids and
Predators for Fall Armyworm Control ------------------- 433

GARDNER, W. A., AND J. R. FUXA-Pathogens for the Suppression of
the Fall Armyworm .~~. ---------- 439
YOUNG, J. R.-Suppression of Fall Armyworm Populations by Incor-
poration of Insecticides Into Irrigation Water .------ 447

ALTIERI, M. A.-Diversification of Corn Agroecosystems as a Means of
Regulating Fall Armyworm Populations .-------- 450

ANDREWS, K. L.-The Whorlworm, Spodoptera frugiperda, in Central
America and Neighboring Areas 456

Continued on Back Cover

Published by The Florida Entomological Society















THE FLORIDA ENTOMOLOGICAL SOCIETY




OFFICERS FOR 1979-80


President --------
Vice-President
Secretary ........
Treasurer --------


...... E. C. Beck
-... W. L. Peters
-- F. W. Mead
.._ D. P. Wojcik


Other Members of Executive Committee


R. E. Brown
N. C. Leppla
R. H. Maltby
C. A. Musgrave Sutherland
J. L. Taylor


PUBLICATIONS COMMITTEE


E ditor ------.. --------...
Associate Editors


C. A. Musgrave Sutherland
--.........--...-- ..- A. B. Hamon
J. E. Lloyd
J. R. McLaughlin
C. W. McCoy
H. V. Weems, Jr.
.----.. ............. D. P. W ojcik


Business Manager


FLORIDA ENTOMOLOGIST is issued quarterly-March, June, September,
and December. Subscription price to non-members is $15.00 per year in
advance, $5.00 per copy. Membership in the Florida Entomological Society,
including subscription to Florida Entomologist, is $10 per year for regular
membership and $2 per year for students. Inquiries regarding membership
and subscriptions should be addressed to the Business Manager, P. O. Box
12425, University Station, Gainesville, FL 32604. Florida Entomologist is
entered as second class matter at the Post Office in DeLeon Springs and
Gainesville, FL.
Authors should consult "Instructions to Authors" on the inside cover of
all recent issues while preparing manuscripts or notes. When submitting a
paper or note to the Editor, please send the original manuscript, original
figures and tables, and 3 copies of the entire paper. Include an abstract and
title in Spanish, if possible. Upon receipt, manuscripts and notes are ac-
knowledged by the Editor and assigned to an appropriate Associate Editor
who will make every effort to recruit peer reviewers not employed by the
same agency or institution as the authors(s). Reviews from individuals
working out-of-state or in nearby countries (e.g. Canada, Mexico, and
others) will be obtained where possible.
Manuscripts and other editorial matter should be sent to the Editor,
C. A. Musgrave Sutherland, Rt. 3, Box 115H, Las Cruces, NM 88001.
Business matters for other Society officers can be sent to that individual at
the University Station address above.


This issue mailed January 23, 1981









1980 Fall Armyworm Symposium 357

REDUCING THE LAG BETWEEN RESEARCH
SYNTHESIS AND PRACTICAL IMPLEMENTATION
OF PEST MANAGEMENT STRATEGIES FOR
THE FALL ARMYWORM:
INTRODUCTION TO THE FALL ARMYWORM
CONFERENCE 1980

J. N. ALL
Department of Entomology
University of Georgia
Athens, GA 30602

ABSTRACT

In this fourth conference in a continuing series on the fall armyworm,
Spodoptera frugiperda (J. E. Smith), 20 scientists conducting specialized
research in quantitative biology, behavioral biology, agroecosystem modifica-
tion for pest suppression, host plant resistance, biological control, chemical
control, and technology of insecticide delivery will update current knowledge.
Pest management specialists will discuss current integrated programs for
fall armyworm suppression. This interaction between research personnel and
pest management specialists will provide the foundation for discussions on
research needs and incorporation of new knowledge into working pest man-
agement systems. The purpose of the conference is to decrease the lag be-
tween research discovery and practical implementation of new methodology
into an integrated pest management system for the fall armyworm.



CONCEPTUAL FRAMEWORK
This is the fourth in a continuing series on the fall armyworm, Spodoptera
frugiperda (J. E. Smith). The original presentations were made at the Fall
Armyworm Conference held in conjunction with the Southeastern Branch
meeting of the Entomological Society of America; these meetings were held
in Biloxi, MS in January 1980. Fourteen of these presentations were sub-
mitted for publication and were included in this issue of Florida Entomol-
ogist.' These meetings have been stimulated by the tremendous damage that
this pest has produced in recent years in the southern United States. The
1978 symposium on fall armyworm provided a conceptual framework of
ideas, and the published proceedings provide a foundation of knowledge on
biology and historical perspective (Sparks 1979), rearing methodology
(Perkins 1979), population characterization (Mitchell 1979, Barfield and
Jones 1979), classification of parasitic species (Ashley 1979), host plant
resistance (Wiseman and Davis 1979), and insecticidal control (Young
1979). However, new research findings in these areas have occurred and
knowledge in several additional strategy areas of fall armyworm suppression
is now available. More importantly, pest management programs for fall

'Limited numbers of separate contributions and of the entire, bound 1980 Fall Armyworm
Symposium are available as reprints from most of the senior authors.










Florida Entomologist 63 (4)


armyworm have rapidly evolved in recent years and need for representation
of these findings is generally acknowledged. Concerned scientists recognize
the need to develop a mechanism in which the rapidly expanding information
on fall armyworm biology and suppression can be continually updated and
expanded for integrated pest management. This requires close coordination
and interaction between research personnel that are concerned with develop-
ing specific suppression methodology and specialists (extension personnel and
others) concerned with developing working pest management programs for
the fall armyworm.
In this conference the current methodology for fall armyworm control
will be detailed by scientists specializing in research areas of quantitative
biology (sampling, economic threshold, population modeling), behavioral
biology, agroecosystem modification for pest suppression, host plant re-
sistance, biological control, chemical control, and technology of insecticide
delivery. Discussions by integrated pest management specialists currently
directing programs for the fall armyworm will provide the groundwork for
ensuing discussions directed at identifying research needs and synthesizing
new research knowledge into future integrated pest management programs.
Thus, this conference proposes to decrease the lag between research discovery
of methodology for detection, quantitation, and suppression of fall armyworm
infestations and the practical implementation of this methodology into an
integrated system of pest management.

CHARACTERIZING RESEARCH NEEDS
The fall armyworm is one of a few univoltive agricultural pests that
infest many agricultural areas of the United States via migration from
tropical or subtropical areas where breeding is continuous. The origin of the
sometimes massive migratory populations and the trajectories and aggrega-
tion mechanisms of the "highly mobile insects" still eludes entomologists.
Ultimately, the characterization of this migratory behavior of fall armyworm
populations will probably be the key requisite for optimum management of
this pest. Scientists are well aware of the need for this knowledge and are
cognizant of the immensity of the task. This has resulted in the recent
mobilization of entomologists in the Southeast who are currently developing
a regional effort on this problem (Movement of Fall Armyworm and Velvet-
bean Caterpillar Adults, Area of Work, Technical Committee Meeting, 15-16
January 1980, Atlanta, GA). Rapid answers from this effort can be ex-
pected, but it is generally anticipated that final resolution of the phenomenon
will require several years' research.
The pest management specialist that is administering localized programs
for the fall armyworm requires information on regional movement of fall
armyworm. When methodology is available, this type information will likely
be collected by federal and state personnel equipped to monitor population
activity over large areas. However, within localized areas fall armyworm
infestations can be sporatic and severe devastation may occur rapidly with
short duration between observable symptoms and complete crop loss. Thus,
the pest management specialist also requires methodology that he can use
directly for rapid detection of moth flights into a field or other localized
area, the ability to quickly quantify (and hopefully predict) current popula-
tion levels and developmental potential of these populations, and finally a


December, 1980


358











1980 Fall Armyworm Symposium


methodology to associate populations with crop damage potential. These are
prerequisites for determining dynamic action thresholds. Considerable effort
in these areas has been pursued and will be discussed by Drs. E. F. Suber,
T. N. Hunt, C. S. Barfield, J. L. Stimac, M. A. Keller, J. R. Young2, H. R.
Gross2, F. A. Johnson3, P. B. Martin, and A. N. Sparks.
Of key importance in characterizing fall armyworm populations and de-
veloping action thresholds is a highly sensitive and reliable sampling meth-
odology. Of particular interest is blacklight trapping, use of the sex
pheromone (Z)-9-dodecen-l-ol acetate, and absolute sampling of egg masses
on various types of trap crops. Additionally, a new technique developed by
Thomson and All (1979, 1980) that utilizes surveyors' flags shows con-
siderable promise as a sampling method. This technique has qualitative and
quantitative attributes for characterizing fall armyworm populations and the
low expense and ease of manipulation accommodate the needs of pest man-
agement specialists.
The concept of modifying cultural procedures to suppress or evade fall
armyworm infestations will be addressed by Drs. E. F. Suber4 and R. E.
Lynch. This is the essence of applied ecology and entails manipulating
agroecosystems to the disadvantage of the pest. Detrimental environmental
factors may be biotic or abiotic in character and can involve temporal and
spatial aspects that have negative influence on the biopotential of fall army-
worm populations.
Implicit in the concept of cultural control is grower acceptance of the
agronomic desirability of the proposed procedure. For example, entomol-
ogists know that planting date greatly influences damage potential of fall
armyworm. This is especially true in corn with early plantings completely
evading infestations in many areas. A current trend in southern agriculture
toward multiple cropping is of concern to many pest management specialists
because these procedures entail later than normal planting dates and higher
potential for fall armyworm damage.
The very important control method of host plant resistance will be dis-
cussed by F. M. Davis, B. R. Wiseman, and J. Campbell. In recent years
there have been encouraging findings in corn breeding programs for fall
armyworm resistance. The importance of utilizing host plant resistance in
pest management systems is obvious. Even low levels of resistance in certain
hybrids and varieties would have tremendous value when integrated with
other measures such as planting dates and insecticides.
Biological control is an important consideration for any pest manage-
ment program including the fall armyworm. W. H. Whitcomb5, W. J. Lewis,
J. R. Fuxa, and W. Gardner will address this topic which includes para-
sitoids, predators, and microbial pathogens. Certainly the potential of identi-
fying sources of entomophages and pathogens of fall armyworm in tropical
areas where populations originate has merit. Also, life tables should be

2A paper entitled "Sampling, economic injury levels, and timing of insecticide applications
in corn" by J. R. Young and H. R. Gross was not submitted for publication.
3A paper entitled "The status of thresholds and scouting techniques for fall armyworm,
Spodoptera frugiperda, on Florida crops by F. A. Johnson was not submitted in time for pub-
lication.
4Papers entitled "Spatial and Temporal Distribution of Fall Armyworm, and Economic
Importance" and "Cultural and Mechanical Suppression of Fall Armyworm Damage by
Farmers in Georgia" by E. F. Suber were not submitted for publication.
5A paper entitled "Potential of Classical Biological Control for Regulation of Fall Army-
worm Population Densities" by W. H. Whitcomb was not submitted for publication.


359










Florida Entomologist 63 (4)


determined in several areas in the United States and consideration given to
intranational as well as international movement of beneficial organisms to
needed locations for fall armyworm suppression.
Pest management specialists can effectively utilize biological control
agents by manipulating agroecosystems that enhance their biopotential.
This concept needs to be coupled with cultural control strategies directed at
the fall armyworm. It is important to recognize the dynamic interaction of
fall armyworm with biotic mortality factors and that cultural procedures
directed at one may have impact on the other as well. These types of en-
hancement strategies need to be identified by research and utilized by pest
management specialists. Additionally, the conservation concept of reducing
the impact of insecticides on beneficial insects during chemical control
operations for fall armyworm needs to be fully evaluated by research, and
spray programs need to be adjusted appropriately by pest managers.
Current pest management programs for fall armyworm emphasize the
integration of detection and economic threshold strategies with correctly
timed insecticide application. Our current knowledge of chemical control and
application technology will be updated by B. H. Wilson6, K. Wood6, L.
Stacey7, and J. R. Young. Also, the effective and efficient use of insecticides
in ongoing pest management programs will be addressed by K. Andrews and
J. French.
It is appropriate that these last topics of the conference are concerned
with current integrated pest management programs for the fall armyworm,
because it completes the development of a firm foundation for considering
the final topic of the conference which is developing a regional program for
pest management of the fall armyworm. This will be discussed by Dr. E. F.
Knipling. The advantages of a regional research approach in developing
technology for pest management is well recognized by entomologists and this
is especially relevant for the fall armyworm. However, this continuing series
of conferences demonstrates that this is not enough. Researchers must closely
interact with working pest management specialists in forums such as this
and also strive to adopt other procedures so that fall armyworm management
strategies can be constantly updated and evolved toward optimumization.

LITERATURE CITED

ASHLEY, T. R. 1979. Classification and distribution of fall armyworm para-
sites. Fla. Ent. 62: 114-23.
BARFIELD, C. S., AND J. W. JONES. 1979. Research needs for modeling pest
management systems involving defoliators in agronomic crop systems.
Fla. Ent. 62: 98-114.
MIITCHELL, E. R. 1979. Monitoring adult populations of the fall armyworm.
Fla. Ent. 62: 91-8.
PERKINS, W. D. 1979. Laboratory rearing of the fall armyworm. Fla. Ent.
62: 87-91.
SPARKS, A. N. 1979. A review of the biology of the fall armyworm. Fla. Ent.
62: 82-7.
THOMSON, M. S., AND J. N. ALL. 1979. A flag sampling method for fall army-


6A paper entitled "Conventional Chemical Toxicants Effective for Suppressing Fall Army-
worms" by B. H. Wilson and K. Wood was not presented.
'A paper entitled "Present Means of Applying Conventional Chemical Toxicants to Com-
mercial Crops Infested with Fall Armyworms" by L. Stacey was not submitted.


360


December, 1980










1980 Fall Armyworm Symposium


361


worm oviposition. Proc. S. E. Ent. Soc. Amer. 53: 10.
AND 1980. Oviposition on artificial substrates, an indicator
of fall armyworm populations in the field. Proc. S. E. Ent. Soc. Amer.
54: 10.
WISEMAN, B. R., AND F. M. DAVIS. 1979. Plant resistance to the fall army-
worm. Fla. Ent. 62: 123-30.
YOUNG, J. R. 1979. Fall armyworm: control with insecticides. Fla. Ent. 62:
130-3.





MONITORING AND PREDICTING FALL ARMYWORM
INFESTATIONS IN NORTH CAROLINA1

T. N. HUNT
Dept. of Entomology
North Carolina State University
Raleigh, NC 27607

ABSTRACT

Fall armyworm, Spodoptera frugiperda (J. E. Smith), losses are greatest
in bermudagrass and corn or sorghum planted after 1 May in North Caro-
lina. A Field Crop Fall Armyworm Alert using indicator fields of corn and
bermuda has been successful in providing an early warning of impending
fall armyworm damage.



The fall armyworm, Spodoptera frugiperda (J. E. Smith)1, migrates
into North Carolina annually in June and July. During early population de-
velopment, infestations are concentrated in succulent grass crops (corn,
bermudagrass, various weed grasses). Damage may also occur in alfalfa,
fescue, peanuts and cotton during years with greater than 15% of the late
corn acreage harboring fall armyworm larvae. Historically, first larval in-
festations have been detected in sweet corn or late-planted field corn along
the coast from Wilmington, NC, to Washington, NC, 20 June-10 July. Eco-
nomic loss is greatest in commercial coastal bermuda hay, and field corn
(grain or silage) or sorghum planted after 1 May. Surveys conducted an-
nually 1-15 August since 1977 revealed 25-50% of the late-planted corn
acreage at or above the North Carolina action threshold level.2 It is, there-
fore, understandable that corn planted during May or early June serves as
a focus for monitoring. The acreage of late-planted corn varies depending
upon the spring planting conditions; however, 35-60 thousand acres are
planted after 1 May each year.

'Lepidoptera: Noctuidae.
2Fall armyworm action threshold for pretassel corn in NC: 1) 80% or more of the plants
infested with a larva > 0.5 inch, or 2) 50% or more of the plants infested with 2 or more
larvae > 0.5 inch. In the absence of well defined economic thresholds, the above was selected
to provide growers with guidelines for proper timing of insecticide applications. The basis for
these action thresholds was derived from Henderson (1966), Pitre (1979) and Hunt (1977
unpublished work with Heliothis sea).










Florida Entomologist 63 (4)


December, 1980


FIELD CROP INSECT ALERT-DETECTION AND MONITORING
The facts cited above indicate the need for a monitoring program which
can identify areas and crops with a high probability of fall armyworm at-
tack so that growers may be alerted. Such a program (Field Crop Pest
Alert) already exists in North Carolina. The program monitors all major
field crop arthropod pests throughout the season, but concentrated attention
is given to the fall armyworm during the critical part of the growing season.
As indicated previously, fall armyworm larvae can be expected during
mid-June in the coastal area, particularly near Wilmington. High probability
fields, both sweet and field corn, are selected and scouted weekly until fall
armyworms are detected. When armyworms are detected, indicator fields are
selected in all regions known via phenological surveys to have a high per-
centage of late-planted corn or coastal bermuda fields (Fig. 1). These selected
fields are monitored weekly by Insect Alert scouts or trained program co-
operators (county agents, N.C.D.A. or U.S.D.A. personnel, etc.). Reports of
insect activity from these scouts, field monitoring stations (light trap,
pheromone trap, etc.), pest management programs and field researchers are
received weekly via an answerphone in the data reception center on the
North Carolina State University campus. As the fall armyworm population
develops and detections are recorded, a distribution pattern emerges. In-
tensive field sampling is then initiated in the areas of highest probable in-
festation. Sampling of these high probability regions (several counties) are
prioritized according to the percentage of pretassel cornfields, the concentra-
tion of bermudagrass fields and the proximity to known infestations. These
weekly surveys are designed to monitor the: (1) crop stage; (2) percent fall
armyworm larvae by stage per infested field; (3) intensity of the infestation
in terms of (a) larvae per plant, (b) percent plants infested, and (c) percent
acres infested (Table 1). Approximately 0.5-1.0 percent of the late-planted
corn acreage is sampled weekly in each designated area.













Fig. 1. Numbers equal monitoring stations owned and serviced by N. C.
extension entomology programs or the U.S.D.A. tobacco biological control
program, 1979.

FIELD CROP INSECT ALERT REPORTING
Information developed by the monitoring program, coupled with weather
data, is compiled and interpreted twice each week and an alert message is
taped for use by the North Carolina Extension Service's Teletip Program.


362











1980 Fall Armyworm Symposium 363

TABLE 1. PARAMETERS MONITORED IN NORTH CAROLINA REGIONAL SURVEYS
FOR THE FALL ARMYWORM.

-% fields pretassel (estimated acreage from Crop Reporting Service)
-% pretassel fields damaged
-% pretassel fields at or above the action threshold
-Range of infestation levels (highest-lowest)
-Average # larvae/plant by size
-% plants infested
-% plants damaged
-% damaged plants infested
Possible voluntary comments: Eggs or adults observed, presence of parasites,
diseases, knowledge of chemical controls.

Extension Teletip is a toll-free telephone system for the dispersement of
concise, timely information on many subjects to the public. Insect Survey
Notes ( a weekly newsletter) serves as a detailed follow-up to the tapes and
is directed primarily to county agents. The data generated by Insect Alert
and made available through Teletip may be utilized as a base that advisors,
managers, and county agents can add specific information to about the area
with which they are most concerned. Logically, a farmer would be concerned
with the crops and farms under his management, a chemical dealer with
crops in his distribution area, and an agricultural agent with the crops for
which he is responsible countywide. Knowing the fall armyworm condition
in other areas of the state and expected trends aids each in better utilization
of scouting time. County agents combine information generated by the pro-
gram with their own scouting to develop reports on local conditions for re-
lease through mass media and grower training programs.
In addition to its direct value, the Insect Alert program reinforces annual
grower and agent training to facilitate standardized scouting procedures
and generally promotes the pest management concept. Limited understanding
of the basic biology of the fall armyworm currently precludes detailed pre-
dictions of when and where infestations will occur or their intensity. The
program can, however, provide an early warning of impending fall army-
worm damage and the geographic areas and the crops which have a 50+ %
probability of attack. During 1978 and 1979, the program provided informa-
tion which stimulated: (1) improved scouting by growers and county agents,
(2) better insecticide and rate selection, and (3) improved insecticide timing
for an estimated 10,000 A of corn each year.

LITERATURE CITED

HENDERSON, C. F., H. G. KINZER, AND E. G. THOMPSON. 1966. Growth and
yield of grain sorghum infested in the whorl with fall armyworm. J.
Econ. Ent. 59: 1001-3.
PITRE, H. N. 1979. Fall armyworm on sorghum: other hosts. Miss. Agri. and
For. Exp. Sta. Bull. 876. 12 p.










Florida Entomologist 63 (4)


December, 1980


STATE-OF-THE-ART FOR PREDICTING DAMAGING
INFESTATIONS OF FALL ARMYWORM1

C. S. BARFIELD2, J. L. STIMAC2,
AND M. A. KELLER2
Department of Entomology and Nematology
University of Florida
Gainesville, FL 32611

ABSTRACT
Information necessary for predicting infestations of the fall armyworm
(FAW), Spodoptera frugiperda (J. E. Smith), is detailed. Distinction is
made on the level of knowledge necessary for predictions of FAW infesta-
tions which are short-term, seasonal at 1 site, and seasonal over a wide area.
Polyphagy and mobility are emphasized as processes in the dynamics of
FAW which make prediction of infestation patterns difficult. Four hy-
potheses on FAW seasonal survival strategies are presented and evaluated
relative to existing information on FAW abundance and distribution.


The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), is a
member of a complex of Lepidoptera inflicting damage to annual crops in the
southeastern and central United States (Luginbill 1928). Documentation of
general aspects of FAW biology and natural history is available (e.g. Hinds
and Dew 1915, Vickery 1929, Sparks 1979). However, data sufficient for
quantitative description of some FAW ecological processes (mortality, move-
ment) are scarce. Ashley (1979) discusses parasites of FAW but does not
present or cite data useable in quantifying age-specific FAW mortality. A
conceptual model has been presented (Snow and Copeland 1969, Knipling
1978) which depicts continuous breeding FAW populations that re-populate
northward areas from southern latitudes each spring. Wood et al. (1979)
presented experimental results that appear to support this conceptual model.
However, data presented in support of this model do not distinguish between
moths emerging locally at trap sites and moths trapped after long-distance
movement. FAW adults caught in traps (Snow and Copeland 1969) may
have emerged in close proximity to traps. Similarly, FAW immature stages
(cf. Wood et al. 1979) may survive cold temperatures in non-crop habitats
as yet unsearched.
Barfield et al. (1978) presented a temperature-dependent development
model for FAW, and Barfield, Smith, Carlysle, and Mitchell (1980) investi-
gated the impact of qualitative nutritional changes on FAW development,
consumption and oviposition. Unpublished data3 are available for evaluation
of FAW development, consumption and oviposition as a function of corn,
Zea mays L., phenology. Barfield and Jones (1979) described further needs
for modeling FAW dynamics.
The FAW represents a "life style" where polyphagy and mobility seem

'Florida Agric. Exp. Sta., Journal Series No. 2258.
'Ass't. Prof., Ass't. Prof., and graduate student, respectively; Dept. Ent. and Nema., Univ.
of Florida, Gainesville 32611.
3M. A. Keller, M.S. thesis, Dept. Ent. and Nema., Univ. of Florida, Gainesville (in prepara-
tion).


364











1980 Fall Armyworm Symposium 365

extremely important to population survival (Barfield and Stimac 1980). The
erratic occurrence of FAW "outbreak years" (see Sparks 1979) and the
irregular distribution of heavy infestations lead us to believe non-crop host
plant availability, timing of crop host availability, and natural mortality
play dominant roles in the FAW's survival strategy. The polyphagous nature
of FAW would permit utilization of variable sequences of non-crop host
plants at different sites and years. Each sequence might expose FAW popula-
tions to variable amounts of natural mortality, consistent with the hetero-
genity in parasite and predator spatial and temporal distribution. A con-
ceptual model relating polyphagy, host plant availability and natural mor-
tality as effectors of movement is presented by Barfield and Stimac (1980).
Yet, virtually no data exist which could be used to test hypotheses on how
FAW populations utilize mobility and polyphagy to respond to environmental
variation. The lack of such information places severe constraints on our
ability to predict FAW infestations. To focus on where we are relative to
predicting site and time of damaging infestations of FAW, we must:

1. distinguish between the levels of knowledge needed for predicting dam-
aging infestations and for imposing post-damage suppression,
2. elucidate the roles of polyphagy and mobility in FAW dynamics, and,
3. provide a conceptual model which identifies ecosystem components re-
sponsible for FAW dynamics and which allows a test of alternative
hypotheses on how FAW infestations occur.

MONITORING AND PREDICTING FAW INFESTATIONS
Personal observations, discussions with various extension personnel and
literature sources (e.g., Luginbill 1928, Sparks 1979) lead us to make 5
qualitative observations on the FAW. First, the FAW is a "boom-or-bust"
pest. In some years, larval densities are low and not economically important;
in other years, infestations are orders-of-magnitude greater and inflict seri-
ous economic losses (see Sparks 1979). Second, "boom" years tend to follow
winters which, by standards of temperature and moisture, are qualitatively
"more severe" than winters before "bust" FAW years (Luginbill 1928).
Third, most FAW infestation patterns are unpredictable; i.e., outbreaks
move through space and time for reasons that are not understood. Fourth,
the absence of data of FAW mortality precludes evaluation of hypotheses
on reproductive strategies employed by FAW (see Barfield and Jones 1979).
The fifth observation focuses on corn, the primary host plant for FAW
(e.g. Luginbill 1928, Wiseman and Davis 1979). Biomonitoring in corn or
any other crop or non-crop host plants is necessary for quantitative evalua-
tion of "boom" or "bust" FAW population status. However, field corn is
typically not scouted for FAW infestation due to the rationale that scouting
services are not economically feasible in field corn production and to the lack
of adequate sampling methods. Sweet corn is not scouted because economic
thresholds are so low that pesticides are applied automatically regardless of
FAW presence. Close to silking, insecticide applications may be used daily
until harvest. As in field corn, however, no reliable sampling methods for
determination of FAW densities and economic thresholds have been de-
veloped. In short, monitoring of FAW densities in corn is not practiced, has
not been developed, or is ignored in lieu of calendar insecticide applications.










366 Florida Entomologist 63 (4) December, 1980

Some crops (e.g., alfalfa, pasturegrasses, sorghum) do not suffer from
the pressure of high cash value markets as do most vegetables, and progress
has been made toward developing biomonitoring schemes for FAW in these
crops. These lower value commodities provide the opportunity for initial
development of monitoring programs which may become transferable to high
cash value crops as petrochemicals become more costly, less available or less
useful. Substantial effort has been directed at the use of light and pheromone
traps as monitors of adult FAW populations in these commodities (Mitchell
1979). The utility of these trapping methods has been restricted due to the
lack of reliable methods for relating trap catches to absolute densities of
either adults or immature stages. Differential responses of FAW adults to
traps as a function of food resources, density, physical environment and trap
design have not been researched adequately (Mitchell 1979, 1979a; Roelofs
1979, Carde 1979, Croft 1979, Hartstack 1979). These responses may be very
important for a polyphagous organism which may be subjected to variable
sequences of crop and non-crop host plants, variable intraspecific densities,
and non-uniform physical environments among sites and fields. In short, few
data are available that can be used to evaluate traps as "predictors" of FAW
infestations.
We must separate needs for detection from needs for evaluation if prog-
ress is to be made toward identifying our capabilities to predict infestations.
What appears to be needed is a reliable "early warning" system which alerts
growers/pest management specialists to a potentially damaging FAW in-
festation. Trap catches of adults apparently have not been used successfully
in this manner for reasons elucidated in the previous paragraph. Efforts
focused on determination of relationships between trap catches and density
estimates of absolute populations of immature stages would be a good first-
step toward overcoming this problem. Most "early warning" systems utilize
trap crops, not light or pheromone traps (see Hunt, this symp.).
Once an infestation occurs, we must be able to evaluate the potential of
that infestation to inflict damage. Time and space dimensions of this evalua-
tion fall into 3 distinct phases, and we must focus on the relative difficulties
to be encountered in each phase. First, we need to be able to make short-term
local predictions (e.g., 1 week) of FAW's pest status. Second, we would like
to progress to making seasonal predictions at a particular site, given specific
initial conditions at that site. Third, we would like to be able to predict oc-
currences of FAW infestations over a wide area.
Achievement of phase 1 involves a re-orientation of many on-going efforts.
In this phase, emphasis must be placed on the development of reliable
sampling methods for adult and immature stages of FAW. A knowledge of
FAW development, consumption and mortality is essential even to making
1-week predictions of FAW damage relative to some density threshold.
Functionally, periodic samples would be taken weekly for determination of
FAW density and densities of relevant natural enemies. At least ambient
temperature would be required between sample dates. Knowledge of con-
sumption rates and potential mortality would be used to project the FAW
population trajectory and potential damage over the subsequent week. At the
end of that week, new samples would be taken to (1) compare FAW densities
and damage levels to those predicted and (2) determine inputs for predic-
tions the next week. These short-term predictions could serve to expose what










1980 Fall Armyworm Symposium


is not known about FAW population dynamics relevant to determination of
pest status. We see completion of phase 1 as possible in a relatively short
time. Re-orientation of on-going research efforts to provide data on adequate
FAW sampling methods, sampling methods for pertinent mortality agents,
and consumption will be necessary.
Phase 2, within-season predictions at a given site, demands more detailed
information. Here, we want to be able to sample at the onset of a FAW
infestation, and without any additional samples, predict the potential damage
to that field so that action (s) may be taken at appropriate times. A knowl-
edge of ecological/biological mechanisms dictating the population dynamics
of FAW is a prerequisite to completion of this phase. Variation in popula-
tion consumption, development, mortality, and oviposition and how those
processes fluctuate with crop phenology and physical environment would
need to be known. Specific assumptions as to net immigration rates would be
necessary. The point is that completion of phase 2 will require in-depth
knowledge of FAW dynamics and the ecological mechanisms responsible for
those dynamics at a given site.
In phase 3, we desire to predict where in space and time FAW infesta-
tions will occur. Obviously, this would be beneficial for allocation of re-
sources to combat these infestations as well as for use of preventative tactics.
The polyphagous and highly mobile nature of FAW must be understood
prior to accomplishment of this phase. Barfield and Stimac (1980) presented
a conceptual model for relating environment, host plant availability and
natural mortality to insect mobility. Rabb (1978) presented information
supporting these concepts. The FAW appears to be ideal as a model to study
how these interactions might occur. Suppose physical factors of a given
winter reduced the availability of alternate FAW host plants by a signif-
icant percentage. The unavailability of these components could result in the
production of FAW adult populations with higher proportions of more
mobile individuals which disperse to less limiting environments. Fewer host
plants might also mean fewer habitats for natural enemies which can attack
FAW. In either case, the process of mobility could be affected, and this would
re-define spatial boundaries of the FAW's life system. Availability of select
non-crop hosts in fall and spring may well determine the site-specific "over-
wintering capabilities" of FAW populations. As no published data exist on
availability of FAW life stages (especially pupae) in non-crop habitats
during colder periods, this possibility remains as a plausible explanation to
why the FAW is a "boom-or-bust" pest. As environmental factors impact
directly or indirectly (through host plants and/or natural enemies) on FAW
populations, sequences of host plants and natural mortality factors change.
Currently, we do not understand how such ecosystem dynamics impact on
FAW populations. We only know that FAW abundance may vary tre-
mendously between any 2 years or sites, and that our current monitoring
tools may vary in reliability among these sites and years. The polyphagous
nature of the FAW opens several avenues of research that bear directly on
our ability to predict infestations.
Numbers of organisms infesting individual fields from reservoirs of
mobile individuals have been conceptualized as a partitioning process (Bar-
field and Stimac 1979, Stimac and Barfield 1979). Individual fields are
coupled by both pest and beneficial flows. A good example of this can be


367










368 Florida Entomologist 63(4) December, 1980

found in the corn-peanut-soybean production system of north Florida-south
Georgia. FAW populations invade corn (from unknown sources) in early
spring. Subsequent generations move onto peanuts and, in some years (e.g.,
1977) soybean. Cues utilized to initiate movement and the direction of such
movement are not understood. Unpublished data4 indicate natural enemy
populations also move sequentially through crops coupled by pest flows. The
point is that numbers of FAW infesting a given crop field are determined
mostly by processes outside the boundary of that field. Yet, research has been
conducted almost totally within the infested field. This is analogous to treat-
ment of symptoms, not causes. What results is a haphazard success rate of
anticipation of infestations and management of FAW. Some years a given
strategy works; other years it does not. We feel these inconsistencies are
related directly to the highly mobile and polyphagous nature of FAW. We
see little hope for progressing to step 3 until these processes are understood
as related to FAW population dynamics and pest status.
Each phase has requisites for completion, and these requisites should be
met sequentially. If phase 1 cannot be completed successfully, we see little
hope for achievement of phase 3. Yet, what pest management specialists ap-
pear to desire is knowledge and prediction capabilities consistent with our
phase 3. Hopefully, we have outlined the difficulty in moving from where we
are to completion of phase 3. This should not minimize efforts to complete
phase 1, as being able to detect FAW infestations and evaluate pest status
over short time intervals would be of tremendous benefit in allocation of
management tactics.
In summary, the "life style" employed by FAW is, at best, poorly under-
stood. Does it overwinter where continuous breeding is impossible? Does it
disperse from continuously breeding populations in southern latitudes? Does
it have the capability to do either depending on select environmental signals?
How does this "life style" affect our ability to predict damaging infestations
of FAW? We propose a conceptual model of FAW dynamics as a tool for
viewing the consequences of all 3 above survival strategies. Two items will
emerge from this effort: (1) identification of needed research and (2) a
focus on survival strategies which yield results most consistent with qualita-
tive observations of FAW population changes.

A CHOICE OF HYPOTHESES
At least 4 hypotheses can be formulated on the seasonal survival strat-
egies of the FAW. As 2 of these are variations on the same hypothesis, we
shall refer to these as A1, A2, B, and C. We shall attempt to show how each
1 of these hypotheses affects our perception of FAW as a pest and how we
manage that pest. All 4 hypotheses involve variable FAW mobility, natural
mortality, host plant acceptibility, and "overwintering" periods. Existing
evidence will point to 1 of these hypotheses as "most promising," and we
will attempt to describe experiments necessary to make prediction of infesta-
tions possible.
HYPOTHESIS A : CONFINED CONTINUOUS BREEDING-PARTITIONED DISPERSAL
This is, by far, the most popular conception of FAW winter and spring
dynamics. Data in Snow and Copeland (1969) and Wood et al. (1979) have

4J. L. Stimae, Ass't. Prof., Ent. & Nema., Univ. of Florida, Gainesville.










1980 Fall Armyworm Symposium


been used as evidence for this model. Simply, this model states that FAW
populations are continuously breeding in southern latitudes (e.g., south
Florida and Texas), and that individuals from these populations disperse
northward each spring to invade crop and non-crop host plants. Two possible
sequences of host plants attacked are presented in Fig. 1. Regardless of the
host plant sequence, populations outside the continuous breeding range ulti-
mately perish because of the lack of requisites for sustained population
growth. Variation in natural mortality and host plant availability is possible
along each route.
If this occurs, we might expect to see a wave of movement northward each
spring and resultant populations breeding as far north in the winter as en-
vironmental conditions allow. This northward latitude would vary among
years.
HYPOTHESES A2: CONFINED CONTINUOUS BREEDING-LONG RANGE TRANSPORT
This hypothesis is presented as a sub-set of A, and focuses on weather
conditions at the continuous breeding sites. Here, weather fronts and pre-
vailing winds may transport FAW for deposition in areas far removed from
the source population. Figure 1 depicts this model. A2 is distinct from A, in
the emphasis placed on the incidence of physical conditions conducive to FAW
transport. As in A1, however, death results when colder periods onset.
HYPOTHESIS B: WIDE AREA SURVIVAL-DISPERSAL
This hypothesis differs from A, and A, in that it assumes FAW popula-


CONTINUOUS
BREEDING
POPULATIONS


1.





1.


-I



-I


-J


NON-CROP \ / CROP
SITE1 SITE2




POPULATION
EXTINCTION


Fig. 1. Conceptual model for partitioning of a continuously breeding fall
armyworm population by dispersal (solid lines) and by long-range transport
due to weather phenomena (dashed lines).


369










Florida Entomologist 63 (4)


tions are capable of surviving winter conditions farther north than the con-
tinuous breeding zones. Subsequent spring populations then employ short
range dispersal to invade crop and non-crop host plants (Figure 2). Crops
invaded would depend upon proximity to areas (crops or non-crops) where
FAW survival occurred. Survival could occur as a "true diapause" or simply
a temperature-dependent, lengthened developmental period for a given life
stage. The main differences from the A1, As models are in the existence of
some mechanism for "overwintering" at areas farther north than zones where
continuous breeding is known to occur and in the lack of immigration as the
sole process for crop infestation outside the continuous breeding zone.
HYPOTHESIS C: COMBINATION OF A1, A2 AND B
In this model, either partitioned or long range dispersal from continuous
breeding populations or "overwintering" may be utilized by the FAW in any
given year. Which strategy is used depends upon physical environment and
how that environment impacts directly on FAW populations or indirectly
through alternate host plant availability and natural mortality. Obviously,
this is the most complex hypothesis proposed. Figure 3 depicts a possible
three-year scenario.

SUMMARY OF HYPOTHESES

We know that FAW population abundance varies widely in space and
time. We suspect that the polyphagous, highly mobile nature of FAW indi-
cates that predictions of infestations depend upon understanding various
components of the FAW's life system outside managed crops. To reiterate,
we either know or suspect the following from observational data:

1. Continuously breeding populations of FAW occur in both south Florida
and Texas,
2. FAW varies greatly in timing and abundance in crops north and west
of areas in (1),


CONTINUOUS
BREEDING
POPULATIONS


/ \ \
/ FLOW NEGLIGIBLE
I


CROP NON-CROP CROP NON-CROP
SITE1 SITE1 SITE2 SITE2




Fig. 2. Conceptual model for fall armyworm site dynamics where over-
wintering is predominant. Here, short-range dispersal from crop and/or
non-crop overwintering sites is predominately responsible for infestations.


370


December, 1980










1980 Fall Armyworm Symposium 371


- CONTINUOUS
POPULATIONS .. .---

SeYEAR d YEAR 2 YEAR 3 pu
S NON-CROP NON-CROP
S ITE1 SITE
SNON-CROP
.S ,TE S /

S CROP COP P




tions is the major source of infestation. In Year 2, a pattern similar to Year
1I E /CCROP

1 occurs; however, not all site infestations die. In Year 3, dispersal from
continuously breeding populations is minimal relative to infestations from

TPOPULE2TIO SITEPOPUL2TIO




Fig. 3. Conceptual model of a given 3-year period in fall armyworm
seasonal dynamics. In Year 1, dispersal from continuously breeding popula-
tions is the major source of infestation. In Year 2, a pattern similar to Year
1 occurs; however, not all site infestations die. In Year 3, dispersal from
continuously breeding populations is minimal relative to infestations from
sites housing surviving fall armyworm stages from Year 2.

3. FAW appear to be carried by weather fronts to places extremely far
north of continuous breeding zones.
4. FAW is highly mobile and can feed on a wide variety of host plants.

Slodel Ay appears inadequate to account for these observations. Here, in-
festation would need to come from the south annually. Pheromone trap
catches as far north as Hastings, FL in "typical" winters (Mitchell5, pers.
comm.) indicate that either moths are capable of long distance flights during
cold periods and against prevailing winds or FAW populations often survive
north of zones in extreme south Florida. FAW biological characteristics con-
ducive to upwind dispersal are not accounted for in A. Weather fronts (A)t
certainly remain plausible as a mechanism for long range transport. How-
ever, such movement of adults (see Wellington 1979, Rainey 1979) would
most likely deposit FAW in concentrations atypical of the spatial arrange-
ments qualitatively observed seasonally. A2 does not appear reasonable to
explain fluctuations in FAW abundance between years.
Hypothesis B demands the existence of an "overwintering" mechanism.
No data have been published to demonstrate diapause in FAW; however,
Barfield et al. (1979, unpub. data) demonstrated that FAW larvae and pupae
could withstand winter cold typical of north Florida. We feel B is a step
closer to reality but is not sufficient to explain FAW seasonal fluctuations.
Perhaps select combinations of nutrition influence the expression of an
"overwintering" mechanism. B does not account for this.
Hypothesis C allows the components of the FAW's life system to change
from year to year. The severity of a given winter may be reflected by the
absence of some sub-set of FAW non-crop hosts and FAW natural mortality

5E. R. Mitchell, USDA-SEA/FR, Insect Attractants Laboratory, Gainesville, FL 32602.










Florida Entomologist 63 (4)


factors sustained by those hosts. The subsequent spring would mean that
main crop infestations would result from "hop-skotching" (A1) through less
acceptable host plant communities or by long-range transport and drop-out
(A2). The next winter may be "milder" and more alternate hosts may sur-
vive. As FAW populations could withstand those winter conditions, popula-
tions would persist throughout the year. However, select natural mortality
factors survive also; and spring FAW populations may be very low, despite
winter survival much farther north than usual. Depending upon which non-
crop hosts and which natural enemies act in a given year, FAW populations
may appear earlier or later, in higher or lower densities, throughout the
southeastern USA. Long-range transport from sources outside the con-
tinental USA may add to the complications.
Hypothesis C encompasses the complexity we feel is necessary to account
for the seasonal variation in FAW abundance. C is consistent with the con-
ceptualization of Barfield and Stimac (1980) and contains the ingredients to
explain, and thus predict, the timing and magnitude of FAW infestations.
C is also consistent with complexities in movement and effects of movement
on pest management strategies as outlined by Rabb and Stinner (1978) and
Walker (1980).

CONCLUSIONS
The lack of detailed knowledge of FAW population dynamics places
severe limitations on predicting when and where damaging infestations of
FAW will occur. Prediction capabilities should be developed through phases
of detection and evaluation on short-term, within-season and between season
intervals and then over a wide area. We see completion of detection and
phase 1 evaluation as possible in a relatively short time, provided on-going
research efforts are oriented to this end. Completion of phases 2 and 3 will
demand more time and a definite change in the way we perceive FAW
dynamics relative to a given crop to be protected.
Data appear insufficient to test any of the 4 (Al, A2, B, C) hypotheses
on FAW survival strategy. Qualitatively, C appears to be most promising
because data sufficient to test C could be used to test all 4 hypotheses. C also
appears to encompass the complexity necessary to accommodate observa-
tional data on FAW abundance and distribution.
Specific experiments needed to test hypothesis C are:

1. development of markers for determining the origins of northward
and/or southward moving FAW populations,
2. derivation of meaningful statistical relationships between relative den-
sity estimators and absolute FAW densities,
3. reliable "overwintering" experiments based on response of FAW to
temperature and moisture as a function of larval food sources (s),
4. R&D of methods to detect FAW life stages at low densities,
5. systematic use of methods in 4 in non-crop host plant communities up
the Eastern Seaboard.
6. reliable experiments to determine age-specific FAW mortality in select
crop and non-crop host plant communities, and
7. determination of FAW development, consumption, oviposition, and
mobility rates as a function of larval nutrition.


372


December, 1980










1980 Fall Armyworm Symposium 373

Much discussion has been generated toward intensive management of the
FAW in south Florida as a preventative measure for infestation in crops
farther north (e.g., Knipling 1978). If hypotheses A, or A2 are realistic and
if A2 sources do not exist outside Florida, such a plan might work. However,
if B or C (or components thereof) are realistic, such a plan might not work.
Determination of the proportion of a total FAW infestation attributable to
continuous breeding reservoirs versus overwintering populations is needed
prior to evaluation of any intensive management program. Further, since
many of the FAW's natural enemies also attack other predominant pests
(e.g. Heliothis zea Boddie), the consequences of an "eradication" program
might result in a typical "secondary outbreak" phenomenon. Simply, we
know so little about FAW biology/ecology that robust management strategies
are not yet possible. We feel a precursor to management is prediction and to
prediction is understanding. The lack of sufficient understanding of FAW
dynamics is why current FAW pest management programs have not been
more reliable. To predict FAW infestations and invoke ecologically and
economically reliable management strategies, we must understand FAW
dynamics. From all indications, we are a long way from that level of under-
standing.

ACKNOWLEDGMENTS
We wish to thank Drs. E. R. Mitchell and T. R. Ashley, USDA/SEA-FR,
Insect Attractants Laboratory, Gainesville, FL, for critically reviewing this
manuscript.

LITERATURE CITED
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sites. Fla. Ent. 62: 114-23.
BARFIELD, C. S., E. R. MITCHELL, AND S. L. POE. 1978. A temperature de-
pendent model for fall armyworm development. Ann. Ent. Soc. Am.
71: 70-4.
---, AND J. W. JONES. 1979. Research needs for modeling pest manage-
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AND J. L. STIMAC. 1979. Partitioning the regional inoculum of
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Species of Lepidoptera in Southeastern U.S.A., NCSU, Raleigh, NC,
9-11 April 1979. Univ. Graphics, NCSU, Raleigh, 456 p.
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of peanut phenology on select population parameters of fall army-
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AND J. L. STIMAC. 1980. Understanding the dynamics of poly-
phagous, highly mobile insects. Proceed. Intern'l. Cong. P1. Protect.
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CARDE, R. T. 1979. Behavioral responses of moths to female-produced
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NCSU, Raleigh, NC, 9-11 April 1979. Univ. Graphics, NCSU, Raleigh.
456 p.











374 Florida Entomologist 63 (4) December, 1980

CROFT, B. A. 1979. Use of pheromone traps to monitor long-range movement
of Lepidoptera. Pages 316-25. In Movement of Highly Mobile Insects:
Research Concepts and Methodology. Proc. Res. Conf. on Movement
of Selected Species of Lepidoptera in Southeastern U.S.A., NCSU,
Raleigh, NC, 9-11 April 1979. Univ. Graphics, NCSU, Raleigh. 456 p.
HARTSTACK, A. W. 1979. Light sources, trap design and other factors affect-
ing moth catch. Pages 232-41. In Movement of Highly Mobile Insects:
Research Concepts and Methodology. Proc. Res. Conf. on Movement
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Raleigh, NC, 9-11 April 1979. Univ. Graphics. NCSU, Raleigh. 456 p.
HINDS, W. E., AND J. A. DEW. 1915. The grass worm or fall armyworm. Ala.
Agric. Exp. Sta. Bull. No. 186: 61-92.
KNIPLING, E. F. 1978. Strategic and tactical use of movement information
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Ecology and Pest Management. NASA Conf. Pub. 2070. 248 p.
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1979a. Status of pheromone identifications for selected migrant pest
species in the southeastern United States. Pages 268-71. In Movement
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Res. Conf. on Movement of Selected Species of Lepidoptera in South-
eastern U.S.A., NCSU, Raleigh, NC, 9-11 April 1979. Univ. Graphics.
NCSU, Raleigh. 456 p.
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from a wide-area view. Bull. Ent. Soc. Am. 24: 55-61.
AND R. E. STINNER. 1978. The role of insect dispersal and migra-
tion in population processes. Page 3-16. In Conf. Radar, Insect Popula-
tion Ecology and Pest Management. NASA Conf. Pub. 2070. 248 p.
RAINEY, R. C. 1979. Interactions between weather systems and populations
of locusts and noctuids in Africa. Pages 109-19. In Movement of Highly
Mobile Insects: Research Concepts and Methodology. Proc. Res. Conf.
on Movement of Selected Species of Lepidoptera in Southeastern
U.S.A., NCSU, Raleigh, NC, 9-11 April 1979. Univ. Graphics, NCSU,
Raleigh. 456 p.
ROELOFS, W. L. 1979. Pheromones and other chemical attractants:
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eastern U.S.A., NCSU, Raleigh, NC, 9-11 April 1979. Univ. Graphics,
NCSU, Raleigh. 456 p.
SNOW, J. W., AND W. W. COPELAND. 1969. Fall armyworm: use of virgin
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1980 Fall Armyworm Symposium 375

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9-11 April 1979. Univ. Graphics, NCSU, Raleigh. 456 p.
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worm. Fla. Ent. 62: 123-30.
WOOD, J. R., S. L. POE, AND N. C. LEPPLA. 1979. Winter survival of fall
armyworm pupae in Florida. Environ. Ent. 8: 249-52.



ACTION THRESHOLDS FOR FALL ARMYWORM1
ON GRAIN SORGHUM AND COASTAL BERMUDAGRASS

P. B. MARTIN, B. R. WISEMAN, AND R. E. LYNCH
Department of Entomology and Fisheries,
Coastal Plain Experiment Station,
University of Georgia,
and Southern Grain Insects Research Laboratory,
AR/SEA, U. S. Department of Agriculture,
Tifton, GA 31793

ABSTRACT
Under the present (1980) economic conditions, action thresholds for fall
armyworm Spodoptera frugiperda (J. E. Smith), on grain sorghum have
been estimated to be (1) 10% of seedling sorghum possessing egg masses,
(2) 1 larva/shoot in the whorl stage, and (3) 2 larvae/head after flowering.
In coastal bermudagrass the action threshold is between 2-10 larvae < 3/8
in. long/ft.2. It is common for economic or action thresholds to range from
guesses to thoroughly-tested management tactic initiation guidelines. Never-
theless, the action threshold concept is needed in high-energy, fossil-fuel
dependent agriculture systems to increase short-term profits and reduce con-
ventional pesticide usage. Important factors to consider in the development
of action thresholds for fall armyworm are: weather, soil types, crop cul-
ture, other herbivores, and entomophagous arthropods which affect both the
fall armyworm and the host crop, as well as the ecosystem in which they are
found. An alternative to the development of complex dynamic action thresh-
olds for use in high energy systems is the use of insect insurance; this should
be considered in conjunction with or in place of action thresholds. As we
transcend to low-energy, holistically-managed systems, there should be much
less of a need for action thresholds in our agroecosystems since these systems
must be designed to prevent, avoid, evade, circumvent, and suppress pest
problems.


Fall armyworms, Spodoptera frugiperda (J. E. Smith), are a serious pest
of several grass crops in the Western Hemisphere (Sparks 1979). Grain
sorghum (GS) planted in July or early August and coastal bermudagrass
(CBG) hay grown during these months and in September in the southern
U. S. are particularly susceptible to fall armyworm (FAW) especially if
fields are heavily fertilized and possess adequate moisture. The FAW are
capable of destroying seedling GS and reducing grain developing in the


'Lepidoptera: Noctuidae.










376 Florida Entomologist 63(4) December, 1980

heads; however, they are most commonly found in the whorl-stage of GS
where they are capable of reducing leaf surface area and can destroy the
growing point. In CBG hay pastures, FAW feed on the leaves, reducing hay
pastures to low-quality, low-yield stems. Only when FAW populations are at
very high densities do they destroy an appreciable amount of stems.
There is very limited information on the amount of damage that FAW
must do in GS or CBG before implementation of temporary-type suppression
tactics are feasible. Therefore, we have begun to develop action thresholds
(AT) for FAW (and associated arthropods) in grain sorghum and coastal
bermudagrass in south Georgia.

STATE OF THE ACTION THRESHOLD CONCEPT
The concept of an economic or action threshold for insects has certainly
been recognized as long as man has attempted to control insects that affect
his food, health, or comfort. In the distant past, energy would not have been
expended on insects at densities recognized as not being a threat to man's
well being. Recently economic-injury level and economic threshold have
emerged as popular terms for use in describing a philosophy of reducing
conventional pesticides (Stern et al. 1959) for insect control. Ordish (1952)
defined the "economic threshold" of Stern et al. (1959) and Smith and
Reynolds (1968) without using the term; later Headley (1972) more
thoroughly discussed the concept. The economic threshold is based on effective
and efficient integration of all feasible pest management tactics, and con-
serving natural enemies of pests for maximization of profits. The term eco-
nomic-injury level simply refers to the lowest number of insects that will
cause economic damage whose cost is greater than the cost of artificial con-
trol. Economic threshold, or action threshold, is the pest population density at
which control tactics should be initiated to prevent insect numbers from
reaching the economic-injury level. We prefer the term action threshold
(AT) since it better encompasses effects of control tactics and the pest
population, on beneficial biota and the environment, esthetics, and psycholog-
ical and sociological stresses to people in the agroecosystem, and not strictly
the economics of production of a particular crop.
The concept of AT appears to have been beneficial in reducing pesticide
use in at least 1 crop which FAW attacks in Georgia (Douce 1979); and it
has stimulated the development of innovative approaches to pest manage-
ment. However, the concept has also served to reinforce a reliance on con-
ventional pesticides since it has been concerned in particular with the timing
and application of insecticides (Hall and Norgaard 1973) rather than better
system design (Koenig 1980). It has given longer life to our high-energy,
fossil fuel-dependent agroecosystems, and stifled, to some extent, a transition
to holistic management of low-energy or steady state systems (Odum 1976).
Nevertheless, we support the development and use of economic thresholds in
our present high-energy systems (Koenig 1980). Thus, our research has been
committed to the development of ATs for fall armyworm (FAW) in grain
sorghum (GS) and coastal bermudagrass (CBG).
Table 1 lists all of the parameters that can affect action thresholds. In
addition, Pitre et al. (1979) have suggested the experimental approaches to
economic injury levels and AT should include: (1) laboratory studies involv-











1980 Fall Armyworm Symposium


ing (a) simulated injury and/or (b) characterization of consumption rates,
(2) artificial field studies involving (a) simulated injury, and/or (b) cages
and/or small plots with paired and/or multiple treatments, and/or (3)
natural field studies (small and/or large plots) utilizing, (a) selective
dosages of insecticides, (b) cultural or mechanical manipulations and/or (c)
pheromone and/or kairomone manipulations of biota. Hence the development
of refined dynamic ATs for pests is a task of considerable magnitude and
expense (Anon. 1979).
Although establishment of economic thresholds was 2nd on the list of
priorities developed from a poll of agricultural research entomologists3, rela-
tively little has been done towards the establishment of refined ATs for any
pest in any crop. In the case of the FAW, most ATs that have been used
have been guesses. For CBG or forage, ATs proposed have been: 1-4/ft2
(J. R. Young, Southern Grain Insects Research Labs, USDA, Tifton, GA
personal communication), 2 larvae 3/8 in. or larger/ft2 (Suber et al. 1979),
ca. 3/ft2 (D. R. Minnick, Dept. Entomology & Nematology, University of
Florida, Gainesville, personal communication), 3.5 medium-large4 larvae/ft2
5/ft2 (Hunt 1979), and "when worm populations and foliage loss indicates
control is needed" (Anon. 1973).
FAW have caused crop losses which justified the implementation of man-
agement tactics, although our timing for implementing them or other types
of management tactics may be inadequate. However, it is difficult to quickly
produce realistic cost-benefit ratios using sound scientific methodology. More-
over, there are problems in setting up simple, controlled and meaningful
experimental designs to determine ATs (Pitre et al. 1979, Morgan 1979);
and there is a high probability of reaching erroneous conclusions from ex-
periments of this type. The role of FAW in a given crop production system
is very complex and difficult to ascertain, eg. reduction of FAW populations
in pastures could hypothetically reduce parasitoids in an agroecosystem to
such an extent that the possible increase in yield in the pasturage would be
negated by the decrease in yield or increased control costs in a crop in which
Heliothis spp. becomes a secondary pest as a result of the reduced parasitism
of Heliothis spp. by the oligophagous or polyphagous parasitoids of FAW.
The ATs must fluctuate with improvement or deterioration in control tactics,
changes in the economic state of the system5, and other changes in the sys-
tem. We cannot deal with the FAW as a pest of CBG and other crops with-
out dealing with it as an animal (in a dynamic system) that has both bene-
ficial and pestiferous attributes.
The frustrations and disappointments in the crude economic or ATs de-
termined to date have been voiced by various consulting and extension
entomologists. When asked to evaluate economic or ATs in general, some of
the words or phrases used included: "Guidelines", "Ball-park 'figures' ", "Use
previous experience", "Use lower 'thresholds' than extension recommends",


2Dynamic in the sense that they change with changes in the crop and pest stage and
development and their environment (Farrington 1977).
3Maxwell, F. G. 1979. Address by the President, Southeastern Branch, ESA 53rd Meeting
of the Southeastern Branch Ent. Soc. Amer. Nashville, TN. 23-25 January 1979.
4Johnson, F. A. 1980. The status of thresholds and scouting techniques for fall armyworm
Spodoptera frugiperda on Florida crops. Fall Armyworm Conference. Biloxi, MS. January
1980.
5Lynch, R. E. 1978. Economic injury levels for the European corn borer on corn hybrids.
Meeting Ent. Soc. Amer., Houston, TX. 26-30 Nov. 1978.


377











378 Florida Entomologist 63 (4) December, 1980

TABLE 1. COMPLICATING FACTORS AFFECTING THRESHOLDS FOR FALL ARMY-
WORM IN GRAIN SORGHUM OR COASTAL BERMUDAGRASS (I.E., PARAM-
ETERS THAT NEED TO BE CONSIDERED IN DEVELOPING DYNAMIC
ACTION THRESHOLDS) .

Crop value
Control costs and effectiveness
Environment
Limiting factors
Moisture
Temperature
Available nutrients
Wind
Sunlight
Photoperiod
Hail (destructive weather)
Insects and other arthropods
Diseases
Weeds
Nematodes
Factors affecting limiting factors
Host plant resistance
Hybrid vigor
Natural enemies
Agronomic practices
Chemicals
(Interactions, additive effects, multiplicative or synergistic effects)
(Managers)

*Modified from Koehler and Pimentel (1973).

"Art", "No better computer than the mind", "Have to consider pest complex",
"31 interactions in some decision-making processes", "Worry lot more with
my threshold for well-managed pastures, than one with little or no fertil-
izer", "Extension thresholds simply don't work for our area", "Have to figure
in farmer psychology", "Got to know how much the farmer is willing to
gamble", and "Dilemma".
Therefore, we would like to take issue with the term economic threshold
once again because we think it helps illustrate the problems that we as en-
tomologists and scientists create for ourselves, and which cause us to lose
credibility when we solve or approach a problem. The idea of economic, or
AT, is a misnomer. Extant crude and unrefined thresholds are really control
guidelines. Although it would be impractical to drop the term AT or economic
threshold, we do believe that in extension and popular literature, when the
terms are used, it should be made clear to the reader that they are: (1)
"guesses", (2) tentative or untested management-tactic initiation guidelines,
or (3) thoroughly-tested management-tactic initiation guidelines. We are
striving to reach as quickly as possible level 3 (thoroughly-tested manage-
ment tactic initiation guidelines) for FAW in GS and CBG, but will pres-
ently have to classify the results of our efforts in category 2.
Stern (1966) describes empirical methods for AT development as: (1)
making quantitative measurements of number of pests required to cause crop
damage in excess of costs of control; (2) observing physiological and


__










1980 Fall Armyworm Symposium


morphological abnormalities of plants recognized to be damaging and esti-
mate the AT; or (3) using marketing standards for economic thresholds.
Stone and Pedigo (1972) suggested integrating cost, marketing, and yield
data of agronomists and economists with insect feeding data obtained by
entomologists. However, development of ATs should involve much more
than this.

VARIABLES AFFECTING HOST-CROP AND FALL ARMYWORM GROWTH
AND DEVELOPMENT
It is important in the development of ATs that we be at least as con-
cerned with the production of the crop as with the target pest. Certainly
all the environmental variables that affect the coastal bermudagrass (CBG)
and grain sorghum (GS) plant must directly or indirectly affect FAW
(Table 1). Therefore, it is of necessity that we are at least as knowledgeable
of the CBG or GS as we are of the FAW. It appears that most plants in-
cluding CBG and GS have adequate reserves of roots, leaf surface, photo-
synthate, and storage capacity to withstand considerable stress without
suffering yield or quality reduction, and/or to compensate rapidly for losses.
GS is noted for its ability to withstand drought (Wall and Ross 1970, Van
Arkel 1978), hail-damage (Stickler and Pauli 1961) and insect damage. In
fact most studies (Table 2) have demonstrated from hail-damage simulations
that considerable leaf surface can be lost at certain growth stages with no
significant loss of yield.
The stage of plant development is very important (Lynch 1980) in de-
veloping ATs since certain periods are much more critical to the production
of the harvestable product than others. For instance, Makumbi and
Rubaihayo (1978) demonstrated the importance of flag leaf-size for head
filling in GS. This recognition of stage is not so critical for CBG as GS since
the time span for production of CBG hay, the most freqeunt CBG crop at-
tacked by FAW, is much shorter than that of GS, and since the FAW do
not appear to attack CBG during its entire growth period (Martin and
Goodman 1978, Martin et al. 1979b). In grain sorghum about 4 stages: the
seedling stage-1, the whorl stage-2, the pre-boot stage-4, and the soft-dough
stage-7, as described by Vanderlip (1977), may be commonly attacked by
FAW.
Another important aspect in the development of ATs for FAW in GS
and CBG concerns genetic variability. CBG is 1 hybrid that has relatively
little genetic variability. On the other hand there are numerous GS hybrids
being utilized in the southern U. S. that vary in time to boot-stage, matura-
tion, flowering-time, height, number of leaves, amount of bloom, i.e., white
waxy substance common on sorghum stems and leaves, insect resistance,
tannin content (including leaf tannin), etc. These hybrids respond differently
to stress (Martin and Wiseman 1979f).
Various authors have addressed the issue of the various variables affect-
ing crop plants, including Koehler and Pimentel (1973), Farrington (1977),
and Brown et al. (1979). Addressing the totality of stresses on the crop-host
when developing action thresholds dictates that we determine other stress
thresholds, in addition to ATs for pests. Determination of these stress
thresholds would be valuable in estimating how much additional stress or the
interaction or the multiplication of various stresses that a crop could take


379











380


Florida Entomologist 63 (4)


TABLE 2. EFFECT OF DEFOLIATION
SORGHUM YIELD.


December, 1980


AND FALL ARMYWORM DAMAGE ON GRAIN


Artificial
defoliation
or no. of %
larvae/ % yield
Reference Stage plant defoliation decrease


Henderson et al.
(1966)


Teetes and Johnson
(1973)

Stickler and Pauli
(1961)






Teetes and Johnson
(1973)

Stickler and Pauli
(1961)


Massey (personal
communication)
Teetes and Johnson
(1973)

Liu and Liu
(1935)
Harvey and
Hackerott
(1970)
Stickler and Pauli
(1961)


Whorl


Preboot


Boot







Boot


Anthesis



Anthesis

Anthesis


Milk


1/plant
"Moderate-
Heavy"
"Heavy"
2 leaves
4 leaves
6 leaves
33
50
67
Upper leaf
remaining
Lower leaf
remaining
100
2 leaves
4 leaves
6 leaves
33
50
67
100
75

2 leaves
4 leaves
6 leaves
100


Milk


Soft dough


Hard dough


- 2 leaves
4 leaves
6 leaves
- 2 leaves
4 leaves
6 leaves


*Infested with southwestern corn borer also.
*Lower leaves removed.

without suffering continued economic losses. In addition to affecting the
ability to withstand or compensate for FAW damage, the variables affecting
crop losses may operate in another related manner. Stress can cause delay
and non-uniformity in maturity, thus increasing the probability of the GS


10-27*

5
17-22
0
ca. 12
ca. 34
23
14**-54
42

59-83

32-91
93-99
0
NS
ca. 20
22
10**-57
45
91-96
56

0
ca. 20
ca. 20
25

27


0
NS
ca. 25
0
NS
NS










1980 Fall Armyworm Symposium 381

being damaged by several overlapping generations of FAW and/or other
arthropod pests, birds, and plant diseases.
The acceptibility and suitability of the GS plant or CBG itself can affect
the development of FAW considerably. We have found in our studies (Martin
unpublished data) that mg dry matter consumed by 4th-last instar FAW
may range from 134 mg for CBG grown under low fertility to 417 mg for
CBG grown under moderate fertility with pupal weights ranging from 82
mg to 310 mg, respectively. FAW have fed on a mean of 322 mg dry GS
leaf matter with mean pupal weights being 197 mg.
WEATHER-Since much of the GS grown in the world, including the south-
eastern U. S., is grown without irrigation, moisture is a major variable to
consider in development of FAW ATs in GS. For instance, if pre-boot GS
under severe moisture stress (with no rain predicted) is heavily-infested
with FAW, then it probably would be advisable not to treat the GS for
FAW6. Even GS with heads heavily infested with FAW and corn earworm,
Heliothis zea (Boddie), could be severely affected by dry hot weather and
may not produce enough grain to offset the cost of fall armyworm suppres-
sion. Under these conditions consumption of grain by FAW in the GS heads
would probably be restricted or reduced due to the rapid drying of the grain;
this would also increase the AT. Similarly if FAW were about to devastate a
field and a high probability of hail or tornado devastation of the field existed,
the AT for FAW should be raised in some proportion to the probability of
the destructive weather. Weather must be considered in the development of
AT, and a consulting entomologist advising a group of farmers must con-
sider weather above all else.
The proximity of cool weather during a growing season must receive high
consideration in most GS production in south Georgia; GS is generally
double-cropped behind an early spring-summer crop, and the danger of cool
weather or frost limiting production always exists. Because GS is very tem-
perature sensitive (Quinby et al. 1958) and the heads will not effectively fill
in cool weather, the effect FAW infestations have on delay of GS maturation
is crucial. In 1977, a planting of GS made in late July was eaten to the
ground in all plots except those protected by timely applications of dicarbo-
sulf (0.75 lb/acre)7. The maturity of all but the dicarbosulf plots was de-
layed enough that early cool fall weather resulted in no grain. Grain (712-
806 lb/acre) was harvested only in the dicarbosulf plots.
The time interval between a FAW infestation and the last weather affect-
ing the growth of CBG is generally less than that for GS (< 5 wks vs. >
10 wks, respectively). Nevertheless, weather variables affecting CBG are also
important in the development of an AT for CBG. For instance, if there is
little moisture and little predicted moisture, or if there is little time left
before the mean first-frost date, it would be best to lower the AT. Conversely,
if the probability of sufficient growing days was high, fertility was adequate
(and might possibly be lost to leaching if not utilized promptly) and mois-


"While scouting GS in south Texas, the senior author has witnessed many acres of GS
sprayed 2-3 times for sorghum midge, Contarinia sorghiella (Riley) when a rain was des-
perately needed for head-filling. Oftentimes the rains did not come and not enough grain was
produced to justify harvest. For this reason some consulting entomologists restrict their
business to irrigated acreage.
'Martin, P. B., and D. G. Cummins. 1978. Economic losses of grain sorghum to fall army-
worm: direct and indirect. 52nd Meeting of the Southeastern Branch Ent. Soc. Amer., Gaines-
ville, FL, 24-26 January 1978.










382 Florida, Entomologist 63 (4) December, 1980

ture was adequate, it might be more economical and ecologically sound to
allow the FAW present to feed and complete their development, and then
harvest subsequent bermudagrass growth. In fact, FAW do not commonly
consume the stems of CBG, and these nutrient-bearing stems are capable of
providing rapid regrowth of new leaves.
Bierne (1970) has thoroughly reviewed the direct and indirect effects of
precipitation on insect pests and Ferro et al. (1979) has reviewed the im-
portance of other weather variables. However, the only weather variable that
has received serious consideration in the development of FAW larvae is
temperature. Barfield et al. (1978) demonstrated that as the mean tempera-
ture went from 18.3 to 35.00 C, the mean development time decreased from
66.5 to 18.4 days. Thus, during warm days of July and August, when FAW
typically occur at economically-damaging densities, the action part of the AT
becomes particularly important, since foliage consumption by FAW in-
creases. In addition to this direct effect, temperature, moisture, and other
weather variables can have an indirect effect on FAW by altering the ac-
ceptibility and suitability of CBG or GS as a food source or by affecting
natural enemies. The effects of barometric pressure and solar radiation on
FAW larvae have not been studied. Nevertheless, the relationships of these
weather variables, their effect on the crop and FAW, need to be studied.
SOIL TYPES-Soil type can affect the ability of these plants to compensate
for potential yield losses because of fertility, nutrient deficiencies, pH, cation-
exchange properties, moisture and heat retention characteristics, and fertility
retention-availability characteristics. The variability of these characteristics
within a field, or over a region, affects the age distribution and composition
of both GS, in particular, or CBG and their associated insects. This greatly
affects the temporal and spatial distribution of the fauna of the field.
PESTS-The completing situation of other insects, mites, nematodes,
pathogens and weeds in the development of ATs for FAW is greater on GS
than on CBG. This is primarily because of the length of time between initial
growth and harvest, and the various stages of GS that are susceptible to
FAW and the other pests which may occur simultaneous with or subsequent
to a FAW infestation. The additional stress to which the GS might be sub-
jected because other less significant pests may cause an infestation of FAW
to be of economic importance that, had the other pest not been present, would
not have been. Other pests have interactive, additive, and multiplicative or
synergistic effects on ATs as reported for Heliothis spp. by Brown et al.
(1979) and Todd and Pitre (1979). For instance, the reduction in yield re-
sulting from simultaneous damage from Heliothis spp. and boll weevils
(Anthonomus grandis Boheman), was larger than the sum of the yield losses
when the damage was inflicted on the cotton separatelys. This type of in-
formation needs to be developed for FAW.
PARASITES, PREDATORS, AND PATHOGENS-The effect of natural enemies on
FAW is an area that has been recognized as being very important for some
time (Luginbill 1928). Ashley (1979) recently reviewed the parasitoids of
FAW and this complex currently is being studied in Texas (Ables et al. un-
published data), Florida (Barfield et al. unpublished data), Georgia (Martin


8McClendon, R. W., L. G. Brown, and J. W. Jones. 1977. Investigation of integrated pest
management strategies utilizing computer simulation of the cotton crop-insect interactions.
Annual Meet. of ASAE, Raleigh, NC. Paper No. 77-5019.










1980 Fall Armyworm Symposium


unpublished data), Alabama9 and other regions. As further data are ac-
cumulated in the characterization of the natural enemy complex, spatial and
temporal abundance, host-natural enemy density relationships, and functional
responses of the natural enemies, we will be better able to utilize this in-
formation in the development of our ATs for FAW. We believe the complex
of natural enemies is more important in generally increasing ATs in CBG
in south Georgia than in GS because at the time when FAW occur in the
perennial CBG, an excellent, diverse, and abundant complex of entomo-
phagous arthropods has begun to develop, and because of the more open
canopy of pastures. Entomophagous arthropods can reduce population den-
sities of FAW in a very short period (Martin et al. 1979b) in CBG. Reduc-
tion of these important mortality factors for FAW decreases ATs, although
if a pesticide is the culprit in this reduction, some labile or relatively selec-
tive pesticides can allow rapid resurgence of this natural enemy complex
(Martin et al. 1979d). The size of the infested area, the area treated, the
total acreage of pasturage or GS crop, and the flora and fauna surrounding
or intermingled in the pasture or GS crop are important to consider in de-
veloping and refining ATs through natural enemy sub-models.
CROP-CULTURE INCLUDING PEST MANAGEMENT-Cultural practices have an
important bearing on the development of action thresholds for FAW because
of how they affect the ability of a crop to take stress and how they affect
future management, including pest management strategies, for the cropping
system. For instance, subsoiling has rarely been shown to increase GS yields
(C. C. Dowler, USDA-Agronomy, Coastal Plain Experiment Station, Tifton,
GA, pers. comm.) under irrigation in the Coastal Plain of Georgia; however,
under stress the situation might change considerably, i.e., GS grown on sub-
soiled land might be able to withstand considerably more FAW damage than
that grown on land prepared only with a disc-harrow.
If because of weather, machine or labor availability, and market situation,
a rigorous and inflexible schedule must be set up for grain or hay harvest,
then one may not be able to tolerate a delay in grain maturation from a
certain density of FAW. Therefore, it is important to consider all the impli-
cations of crop culture. This includes ability to withstand stress and the
ability for crop production to mesh with other aspects of the cropping sys-
tem.
The effect of fertilizer on the ability of crops to avoid or withstand stress
is well documented. Lynch et al. (1980) have shown that through fertility
and hay-cutting manipulations, most CBG hay can be grown in the Coastal
Plain of Georgia before damaging populations of FAW threaten hay pro-
duction. This, then, lowers dependence on refined ATs for CBG hay.
Various methods of tillage, crop rotation, cultivation, plant spacing, plant
density, intercropping, multiple cropping, weed manipulation, and irrigation
will affect the ability of a plant to avoid, withstand, or compensate for stress.
Thus, these factors affect the AT for FAW, particularly in GS. Certainly
the indirect effect of various cultural practices and management tactics (for
pests other than FAW), might be on the growth of GS or CBG by allevia-
tion of other pest pressure or by aggravation and increasing of pest pressure

9Reed, D., and M. H. Bass. 1980. Parasites of the fall armyworm, Spodoptera frugiperda
(J. E. Smith), in Alabama. 54th Meeting of the Southeastern Branch Ent. Soc. Amer. Biloxi,
MS. 29-31, January 1980.


383










Florida Entomologist 63 (4)


(e.g., through suppression of natural enemies). But of equal importance,
chemical control stategies can have similar but often more profound detri-
mental effects such as phytotoxicity (Martin et al. 1980a), delay in maturity,
delay of senescence, or growth regulation effects, than from a desirable
alleviation of pest damage.
Crop culture also affects the environment in which the FAW occurs and
thus affects FAW development, its natural enemy complex, and the accepti-
bility and suitability of the crop host. Altieri (1980) shows how inter-
cropping and weed manipulation affect the natural enemy complex of FAW;
this is very important to consider in establishing ATs.
Cummins and Martin (1979), Martin and Cummins (unpublished data),
and Martin et al. (1979e) found some interesting relationships existing
among volunteer corn, density of FAW, and damage to GS. In 1 study, FAW
egg masses were laid at moderate densities on volunteer corn with few
masses laid on GS seedlings; when the FAW dispersed in the Ist-instar,
they infested the seedling GS and reduced the GS stand substantially.
However, where the land had been deep-turned prior to planting the
GS (Martin et al. 1979e), volunteer corn was not a problem, FAW den-
sities were lower, and the plant stand was obviously better. In the studies of
Cummins and Martin (1979) and Martin and Cummins (unpublished data),
the FAW did not heavily infest the GS plantings possessing a considerable
amount of corn until the whorl stage. In these tests, some areas untreated
with insecticides had the volunteer corn virtually eliminated by FAW; how-
ever, the GS was not badly affected by this pest. This illustrates the need to
recognize the effect of other plants within or around the crop-host on the AT;
in the 1st case of volunteer corn within a planting of seedling sorghum,
moderate densities of FAW were economically damaging; in the 2nd case,
similar densities appeared to be beneficial in eliminating competing corn
from the GS planting.
Fertilizers (R. Moss, Station Superintendant, Southwest Georgia Experi-
ment Station, Plains, GA 31780, pers. commun.) and herbicides may have an
effect on densities of both herbivorous and entomophagous arthropods and
hence affect FAW either directly or indirectly. Pest management tactics
employed against other pests whether they be cultural, chemical, or biological
affect FAW directly and indirectly. Urea solutions may have a detrimental
effect on FAW; when applied with conventional pesticides, it appears to
have an additive or synergistic effect on efficacy (Martin and McCormick
1979c). Certainly the additive, multiplicative, synergistic, and interactive
effects must be considered for all the variables previously discussed when
considering and refining ATs.


ESTABLISHMENT OF THE ECONOMIC-INJURY LEVEL

Although the action threshold changes because of many variables, the
heart of the dynamic AT, the economic-injury level, is relatively static. The
economic-injury level is truly the place to begin when developing the dynamic
ATs, as has been demonstrated by Pedigo (1972). However, as we have in-
dicated, in some situations there may be factors which could override and
make the economic-injury level unnecessary to obtain, eg. if a system man-
ager is very concerned with the esthetic value, or so concerned with con-


384


December, 1980










1980 Fall Armyworm Symposium 385

servation of the beneficial complex for other components of the agroecosys-
tem that no suppression tactics can be implemented.
INJURY-YIELD AND QUALITY RELATIONSHIPS-Grain Sorghum-Young
and Teetes (1977) in their review of grain sorghum (GS) insects stated that
armywormss often cause extensive leaf ragging in sorghum and commonly
feed within the plant whorl". However, they also state "damage rarely
justifies control of these insects except with heavy infestations on small
plants". Nevertheless, little AT work for FAW has been conducted on GS
in the past.
There is some information from hail-damage and greenbug defoliation
studies that might yield some insights into this area of research (Table 2).
Generally, 33-100% defoliation at the boot or blooming stage has resulted in
14-99% yield loss. Also, less defoliation or defoliation at a later stage has
commonly resulted in considerably less yield reduction. However, except in
years like 1977 (Sparks 1979), FAW in our area of Georgia generally attacks
seedling GS, particularly if it follows a corn crop, or whorl-stage GS.
Henderson et al. (1966) reported a 10% yield decrease in GS infested
with 1 FAW/whorl (Table 2) and Teetes and Johnson (1973) received a
12-34% decrease in yield when 4-6 leaves were removed from pre-boot stage
GS (Table 2). However, again except when FAW reaches the high densities
it did in 1977, leaf consumption by FAW is generally gradual and not rapidly
removed as in the study of Teetes and Johnson (1973).
Coastal bermudagrass-Since the FAW consumes and affects directly the
harvestable crop of coastal bermudagrass (CBG) neither we nor other re-
searchers have investigated relationships of FAW injury to CBG yields, but
rather the relationships of FAW densities to yields and quality. We do feel,
however, that an economic-damage index may be useful in the future in
determining when management tactics should be initiated.
CONSUMPTION-We have accumulated little data on consumption of GS
since we have not developed damage-yield relationship for this pest in GS
(other than an unrefined rating system) (Table 3). However, the earliest AT
conceived within our project for FAW in CBG was based on an estimate
from our own laboratory data on weight of crabgrass surface area, and
Luginbill's (1928) report of crabgrass consumption. Our estimates were
from 10 samples (551-964 mm2) of crabgrass leaves which had been grown
in the greenhouse for ca. 4 wk after clipping and fertilizing (50 Ib N, 12.5 lb
P205, and 25 lb K20). Dry weights (after 48 h at 1400F) in mg-estimated-
consumed were as follows for the various FAW larval instars; 1st-0.6,
2nd-2.4, 3rd-4.3, 4th-18.7, 5th-65.1, 6th-309.3; lst-6th-400.4; and 4th-
6th-393.1. Thus, percent of total for the various instars was 1st-0.1, 2nd-
0.6, 3rd-1.1, 4th-4.7, 5th-16.3, 6th-77.2 and 4th-6th-98.2. Note from
Fig. 1 that if we assumed a $50/ton market value for CBG and $5/acre man-
agement cost, and if we assumed similar consumption for CBG and crabgrass,
then the economic-injury level for FAW in CBG would be ca. 5 larvae/ft2
(see footnote 13 for calculation).
The amount of CBG consumed by FAW has been discussed previously.
We have found that FAW consumes from 137 to 426 mg of CBG during the
larval stage (consumption is adjusted by the 98% estimate for amount of
food consumed from the 4th-last instar). In addition Pencoe and Martin
(unpubl. data) found that the mean consumption of CBG/larva was 272 and











386

TABLE 3.


Florida Entomologist 63 (4) December, 1980

ESTIMATED NUMBERS OF 1ST-INSTAR FALL ARMYWORM LARVAE RE-
LEASED/PLANT, NUMBER RECOVERED/PLANT, DAMAGE RATING, AND
RESULTING YIELD (X FROM 3-6 CULTIVARS) OF INSECTICIDE-TREATED
(HEADS ONLY) AND UNTREATED EARLY AND LATE-PLANTED GRAIN
SORGHUM.*


Approximate no.
Ist-instar %
larvae infested/ X larvae/ Damage Yield yield
plant** plant rating+ lbs/A# decrease


Early Planting


0.6a
3.9b
4.1b
4.4b
5.2c


(V-16) -Heads Not Treated
(1978)


3.3b
5.2a
4.9a
5.0a
5.1a


1932a
1932a
1913a
1925a
1819a


Early Planting (V-16)-Heads Treated with
Insecticide (1979) ##

0 0.la 0.la 5127a
10 2.2b 5.0b 5195a
20 2.3b 6.2c 4501a


Late-Planted (VI-12)-Heads Not Treated
(1979)


0.8a
1.0a
1.0a


0.8a
4.0b
6.0a


3500a
3528a
3774a


Late Planting (VI-12)-Heads Treated with
Insecticide (1978) # #


0.2b
1.3a
1.6a
1.7a
2.2a


0.Oc
2.5b
2.6ab
2.8a
2.8a


3769a
3097b
3119b
3091b
3254b


0
20
40
+ 20
+ 40


0
1 NS*
<1 NS
6NS


0
12 NS







0
0


0
10
20
10 + 10
20 + 20











1980 Fall Armyworm Symposium


Late Planting (VI-12)-Heads Treated with
Insecticide (1979) # #

0 0.9b 1.la 4822a -
10 1.3b 4.0b 3821b 21
20 1.9a 5.8c 4172b 13

*Means followed by the same letter are not significantly different at the 5% level according
to Duncan's New Multiple Range Test. Cultural practices other than insecticide applications
are those recommended by the Georgia Cooperative Extension Service.
**Infested with a modified "bazooka" fall armyworm-applicator (Roberson et al. 1978).
tThree-5 plants dissected in the field 3-4 times after infestation.
$0 = not detectable damage, 1 some "pinhole damage", 5 = several large holes on sev-
eral leaves, and 9 = damaged to the extent that the plant was not recoverable.
#Corrected to 15% moisture.
##All plots sprayed with dimethoate, chlorpyrifos and/or methomyl every 2-4 days from
flowering to hard dough.

348 mg in 2 tests when adjusted by the 98% estimate. These consumption
estimates are invaluable in the development of economic-injury levels for
FAW in CBG. However, we need additional information on consumption at
different temperatures (including fluctuating), relative humidities, and
fertility levels.
SMALL PLOT FALL ARMYWORM DENSITY-YIELD AND QUALITY RELATION-
SHIPS-Grain sorghum-In GS our best insights into the economic-injury
level have been in small plots in the field. In an early (IV-20 and late
(VII-13) planting of GS in 1978, we infested 1 row x 20-36 ft plots with 1st-
instar FAW larvae mixed with corncob grits and dispensed with a modified
"bazooka" apparatus (Roberson et al. 1978). Rows were 3 ft wide from
middle to middle. In the last planting, rows not infested with FAW, were
treated with methomyl (0.45 lb AI/A) to prevent damage from migrating
larvae. Plots were thinned to 1.0 and 1.5 plants/row-ft for uniform densities.
Fertilizer was 85 lb N, 50 lb PO,, and 75 lb KO/A. Three-5 plants/plot
were dissected on each sampling date to estimate FAW infestations. Whole
plots were rated in stage 4 for FAW damage and 10-20 row-ft were har-
vested, dried, and threshed for yield measurements.
In an early (V-16) and late (VI-12) planting of GS in 1979, we infested
with FAW (VI-13-early, VII-10-late) 3 GS cultivars, planted as 2 row x 30-ft
plots. This yielded 6 rows that we bordered with 2-4 rows of Funk's
'G-522DR' GS treated with 0.5 lb (A.I./acre) methomyl granules 1-2 times/
week to minimize movement of FAW among plots. The design for the 1st
planting was a split-plot replicated 9 times with FAW infestation (0, 10, and
20/whorl) as the main plots, and GS cultivars (Pioneer 'B815', Northrup
'King Savanna 5', and Funk's 'G-522') as the sub-plots. The design for the
2nd-planting was similar to the 1st except that the test area was duplicated;
one area was treated with applications (every 2-4 days) of chlorpyrifos or
methomyl from flowering to hard dough for suppression of sorghum midge
and headworms, i.e., corn earworm, sorghum webworm, Celama sorghiella
(Riley), and FAW. Other cultural practices were as recommended by the
Georgia Cooperative Extension Service.
In the early planting for 1978, yields were not significantly reduced in
plots infested once with 20 or 40 larvae/whorl, or twice with these rates
(Table 3). Only in plots receiving the heaviest infestation of FAW did there
appear to be a slight reduction in yield. However, there was movement of


387










Florida Entomologist 63 (4)


December, 1980


MANAGEMENT
COST= $5/ACRE


1% L
Z A
O
150

tn-125-
%W.0 I


y 100-

Wl 75-
D
> 50-
I-
UJ 25-
d


<


. U p *


ECONOMIC INJURY LEVEL (NO./FT2)
Fig. 1. The effect of fall armyworm management-tactic costs, market
value of coastal bermudagrass hay, and consumption rates of fall armyworm
on the economic-injury level for fall armyworm in coastal bermudagrass.


388


MANAGEMENT
COST $7/ACRE


I p p u p p










1980 Fall Armyworm Symposium 389

larvae among treatments and a substantial infestation in the plots not re-
ceiving the "bazooka" treatments. In the late-planted GS (Table 3) yields
were reduced 14-18% by larval infestations that averaged 1.3-2.2/whorl.
There were slight differences in yields among hybrids in the late-planted
sorghum. However, these yield differences might be attributed to adaptability
to late-season environmental factors other than insects.
Results for 1979 were very similar to those for 1978. Despite excellent
differences in damage ratings in the early-planting (Table 3), we did not
obtain significant yield differences. Where the late-planting was treated
similarly to the late-planting in 1978 (Martin and Wiseman 1979f), i.e., all
plots were oversprayed in the bloom to hard-dough stage, treatments with
FAW had both significantly more damage to foliage and significantly less
yield (13-21% less). However, where plots were not protected from pests in
the grain development-stage, treatments that decreased photosynthate (note
significant differences in leaf damage, Table 3, untreated with insecticide)
were probably masked by relatively heavy damage from "head-pests". In
fact, heavy densities of southern green stink bugs, Nezara viridula (L.), may
account for the 16% decrease in overall mean yield of untreated late-plant-
ing (j = 3213 lb/A) from the treated late-planting (x = 3811 lb/A).
Coastal bermudagrass-In CBG we conducted similar tests in 1978 in
which we infested 6 x 12-ft plots with various densities of FAW (Table 4).
Except for test 1, all plots were enclosed with Saran@ screen cage'0. Al-
though we saw some apparent losses in yield, and there were significant
differences in larval numbers, generally yield means were not significantly
different in the plots infested with various densities of FAW larvae. It
appears from these tests that the economic-injury level is probably > 3.0
larvae/ft2-11
In similar tests in 1979 we found that normally yields were not signif-
icantly decreased by < 3.0 larvae/ft2 (Martin et al. unpubl. data). Generally
we had difficulty in getting larvae established above that density. However, in
1 test we obtained densities of FAW well above that level (Fig. 2). (These
plots were sprayed with 0.5 lb A.I./acre mevinphos before infesting, and were
infested just before a rain; they were measured for FAW and CBG yields as
in other tests in 1978 and 1979.) When plotted, we found an inverse correla-
tion of FAW and CBG yields. This test pointed out the damage that can be
done to CBG by FAW. The economic-injury level in these tests appeared to be
between 2 and 4 larvae/ft2; however, as we mentioned with the results in
1978, these larval density estimates were not from absolute samples. Note in
Fig. 2 that the higher fertility plots appeared to have a higher economic-
injury level. This would tend to indicate that increased fertility increases the
ability of the CBG to compensate for insect damage.
Although we do not have any concrete data showing a reduction in forage
quality by FAW, we do know from observations that this pest can reduce
CBG to stems and at least temporarily reduce forage quality. Thus, we are
presently evaluating forage harvested in AT tests for in vitro dry matter,
digestibility, and other quality characteristics. However, we have not been
routinely checking GS for quality characteristics.

'oWe have conducted tests which indicate that shading of the Saran screen cages (12 x
18 mesh and 20 x 20) affects yields only slightly.
"Our sampling schemes were not absolute; therefore, it is likely the economic-injury level
may have been closer to the ca. 5.0 found from consumption information.













390


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Florida Entomologist 63 (4)


December, 1980


392


















1I6


a
-I


50 LB.NITROGEN/ACRE
5 =OBSERVED YIELD VALUES
X = PREDICTED YIELD VALUES
( .""=EIL IF $50/T HAY VALUE,
$7/A MANAGEMENT TACTIC
". COST


SX







I I I I
2 4 6 8 10 12 14 16 18 20 22 24 26 28

FALL ARMYWORM/FT?


Fig. 2. Relationship of fall armyworm (mostly 3rd and 4th insfars)
densities and bermudagrass hay yields (measured 2 weeks after fall army-
worm estimates) at 2 different fertility levels.

ECONOMICS, FLUCTUATION OF PRODUCTION COSTS AND MARKET VALUE-
Although the return on the investment in GS or CBG may not be as high as
traditionally subsidized crops such as peanuts or tobacco, GS does not possess
the variation in return in Georgia (cv of 260 for 1955-76) such as that in a
traditional crop like cotton (cv of 301412 for 1955-74) (Purcell and Elrod
1978). In 1978 there appeared to be a fair potential of 17-19% return on
money invested in GS or CBG in Georgia (Givan 1978, Martin et al. 1979b).

"Strickland (1970, 1971) suggests that the net economic benefits obtainable from pest
control in this type situation are so variable that thresholds should definitely fit the individual
farmer.


17 -n --


1500-

1250-

1000-

750-

500-

250

0a










1980 Fall Armyworm Symposium 393

It appears that (1) development of dynamic ATs, (2) development of a fall
armyworm insurance plan (discussed later), and/or (3) a redesign of the
systems in such a way that FAW is no longer a pest problem would lower
the coefficient of variation reported.
Management costs, market value of CBG, and consumption rates of the
FAW affect the economic-injury level of FAW in CBG (Fig. 1)13. An in-
crease in consumption rate lowers the economic-injury level, and as the
market value of the CBG hay goes up the economic-injury level also goes
down. Finally, when the management cost goes up so does the economic-injury
level.

ESTABLISHMENT OF ACTION THRESHOLD

Determination of the AT is more complex, of course, than the economic
injury-level since the action must be taken before anticipated or predicted
economic injury occurs and since factors (Table 1) other than economics
must be considered, viz. (1) natural mortality that might occur prior to
economic injury if the suppressive action is not taken, (2) inefficiency of
suppression tactic, (3) possibility of compensation for damage by the pest,
(4) possibility of additive detrimental effects from other pests and environ-
mental stresses, (5) lag time for suppression tactic to take effect, (6) in-
direct losses to other components of the system, (7) amount of risks the
systems manager can or cannot afford to take, (8) value placed on esthetics,
(9) indirect costs to the environment from management tactics, and (10)
psychological and sociological effects of taking the action or not taking the
action.
Since conventional pesticides are commonly used in suppression tactics
for the FAW, 1 way of evaluating ATs is to test these pesticides against
population densities that appear to be near an AT, and measure yield dif-
ferences and quality. These type of tests give some measure on parameters
1-5 (mentioned in the proceeding paragraph) if they are replicated enough
over time and locations. In insecticide tests in seedling grain sorghum
(Martin and Goodman 1978), we have found in 1 test that when FAW were
reduced from densities of 1.2 larvae/row-ft to 0.2 larvae/row-ft, late-planted
GS matured early enough to produce low levels of grain (probably enough
to offset suppression tactic costs). Thus, results of this test indicate that if
worms reach densities of 1.2 small to medium-sized larvae/row-ft, it might
be advisable to treat with a pesticide of similar efficacy to dicarbosulf. Again
in tests in 1979, Marshall and Martin (1980) found that when 1.2 FAW
larvae/plant were reduced to ca. 0.2, yields were increased by as much as
39%.
In coastal bermudagrass (CBG) insecticide tests in 1978, there was an
apparent increase in yields in 2 of 5 tests where differences in mean worm
densities in the most efficacious insecticides and the untreated control were
> 3 larvae/sweep with a 15 in. (in diam.) net. However, yield "differences"
were not significant at the 0.05 level according to Duncan's New Multiple
Range Test (Martin et al. 1979b). In 1 test we did get significant differences

"The points in Fig. 1 were obtained through the following equation:
EIL = /Y (908 x 106 mg) where X cost ]A of suppression tactic in $; Y = value of
Z (43560 ft2)
hay/ton in $; Z = amount consumed in mg; 908 x 106 = mg in 1 ton; 43,560 ft2 in A.










Florida Entomologist 63 (4)


December, 1980


in yields; however, there was no clear relationship of worm control and
yields. These examples in CBG illustrate the complexity of the ATs. We
believe that generally, when FAW densities approach the AT, it is best to
refrain from initiating conventional pesticides rather than proceeding with
insurance-type applications. This is contrary to the case for explosive-pests
like sorghum midge or boll weevil.
As mentioned previously, many factors must be considered in the develop-
ment of ATs, and to a large extent common sense must be used because of
the lack of a sophisticated and effective model to include these factors in an
AT. Probably most important of these parameters is (1) natural mortality
which can occur prior to initiation of suppressive action. For example, if
the economic-injury level for FAW in CBG is 2 medium-sized larvae/ft2 and
there are 10 small larvae/ft2, it might appear that suppressive action should
be taken. This is particularly so if the suppression tactic is a conventional
pesticide, since the efficacy of these chemicals often decreases as the size of
the individual target pest increases. However, if the natural enemy complex
of FAW is high in the pasturage, it is likely that the FAW densities might
be reduced by > 80% before the caterpillars reach medium size. Therefore,
the AT in this case should be > 10 small FAW larvae/ft2.
Another area to consider is that of (2) inefficiency of suppression tactics.
If the economic-injury level for FAW in whorl-stage sorghum is 1/whorl and
a compound like carbaryl or methomyl, for which resistance has been shown
(Young and McMillan 1979, Young pers. comm.) is used as a suppression
tactic, use of these compounds may be unprofitable because of the resistance
factor and because of difficulty in achieving a high degree of control of FAW
in whorl-stage GS. Sometimes, an insecticide is not capable of providing a
high level of control or there is a high probability that the insecticide will be
improperly or untimely applied. In such cases they should not be used at all.
The (3) probability of the plant compensating for damage by the pest has
been discussed earlier, and this might increase the AT substantially. Con-
versely, there is the (4) possibility of additive detrimental effects from other
pests and environmental stresses that might be alleviated by some suppres-
sion tactics implemented against the FAW. This might decrease the AT
slightly. Table 5 presents some data on preventative treatments of carbo-
furan for greenbug, Schizaphis graminum (Rondari). In these plantings
there did not appear to be economically damaging levels of any pest other
than sorghum midge, yet there was a substantial and significant yield in-
crease in the carbofuran treatments. (Carbofuran does not give protection
against sorghum midge when applied at planting, and where the sorghum
midge damage was very high over all plots there was of course no yield re-
sponse to carbofuran.) Thus it appears that the protection of the GS from a
complex of subeconomic pests resulted in a yield increase. In tests in 1977
and 197814 preventive insecticide treatments of GS fertilized at 8 different
rates, resulted in 30% (low N) 63% (high N) yield increases even though
the insects the treatments were directed against (FAW and sorghum midge)
appeared to be at sub-economic densities. When FAW does occur on GS or
CBG, it is certainly not the only pest that occurs on these crops. There may

14Touchton, J. T., and P. B. Martin. 1980. Nitrogen and insecticide applications for ratoon-
ing grain sorghum production, (Abstract). Proc. Southern Branch Meeting Am. Soc. Agron.
Hot Springs, AR. 3-6 February 1980. 1 p.


394










1980 Fall Armyworm Symposium 395

TABLE 5. EFFECT OF PLANTING DATES AND CARBOFURAN (10G) TREATMENTS
ON GRAIN SORGHUM YIELDS IN SOUTH GEORGIA.*

Lb/acre for:
Treatments
Planting date No carbofuran Carbofuran X

VI-23-77 <300 a,x <300 a,x <300 a
VI-9-77 <300 a,x <300 a,x <300 a
V-27-77 1323 b,x 1035 b,x 1179 b
VI-16-77 1237 b,x 1478 b,x 1358 b
IV-29-77 1990 c,x 3823 c,y 2907 c
IV-15-77 3672 d,x 4022 c,x 3847 d
X 2056 x 2590 y 2322

*Applied in a 5-7 in. band at ca. 1.09 lb (AI/acre) with a Noble distributor and a Gandy
5-in. Ro-Bander@ and lightly incorporated with the press wheel. Six varieties of sorghum (4
replicates) were treated or not treated with carbofuran on each planting date. Vertical means
followed by the same letter (a-e) or horizontal means followed by the same letter (x-y) are
not significantly different (P = 0.05) according to Duncan's New Multiple Range Test.

be several other pest complexes occurring at economic or sub-economic den-
sities, and there may be various interactions with these and other limiting
factors.
But despite an increase in yield from suppression of sub-economic pests
with conventional pesticides, one must also consider effects on entomophagous
arthropods and environmental contamination. And despite several examples
where insecticides directed at no detectable economic pests resulted in
profitable yields in grain, we could cite as many examples where these types
of applications did not result in yield increase. For instance in whorl-stage
GS in 1978, we reduced FAW densities from ca. 0.2 larvae/plant to signif-
icantly lower, non-detectable levels with no yield increase. In a scouting test
in 1979 (Marshall and Martin 1980) preventative insecticide treatments did
not increase yields over the untreated check.
If there is (5) a lag time for a suppression tactic to take effect, par-
ticularly when employing certain augmentative approaches to biological con-
trol (Ables et al. 1980), this must be given major consideration. Lag time
will become more important as the semiochemical technology discussed for
FAW by Lewis and Nordlund (1980) becomes feasible for use in our crop-
ping systems. In many cases the timing of these semiochemical-augmentative
approaches to biological control will be primarily concerned with density-
dependent factors and the functional-response relationships of the parasitoid-
host or predator-prey; nevertheless, lag time is an important concept to con-
sider. Although lag time for biological control tactics may be more critical to
consider than that for chemical control tactics, FAW do respond very dif-
ferently to various conventional pesticides (Young 1979). Thus lag time
should always be considered in the development of dynamic ATs.
If there is a potential for (6) indirect losses to other components of a
cropping system because FAW or other pests were not controlled by a par-
ticular suppression tactic, then the AT might be lowered. (7) Risks the sys-
tems manager desires to take are very important to consider and (8)
esthetic value of a relatively blemishless crop has to be considered. Regarding










396 Florida Entomologist 63 (4) December, 1980

esthetics, a large portion of our energies in the world are devoted to clean-
ing, painting, manicuring, and fixing to achieve beauty. Therefore, it may
not be unreasonable for a farmer to desire a relatively insect-free, un-
tattered, uniform pasture or sorghum field. It may be unrealistic, costly, and
ecologically unsound, but within the constraints of present society, it is
reality.
Certainly the (9) indirect cost of suppression tactics because of environ-
mental pollution, human and wildlife health hazards, and subtle and lasting
effects on the flora and fauna of the system must be considered. When we
develop ATs, we must be concerned about the whole system and not simply a
single pest or crop. An unwise or untimely suppression effort in a CBG
pasture might lower the beneficial complex in a CBG-cotton-soybean cropping
system to the extent that serious Heliothis spp. and Plusiinae problems might
result from this plunge in natural enemy abundance. These costs might more
than offset an increase in yield in CBG hay. On the other hand suppression
tactics for FAW in grass pasture might reduce leafhopper densities to the
extent that yields are increased in peaches due to alleviation of spread of
phony peach disease by these leafhopper vectors which may be abundant in
adjacent grass (Kalkandelen and Fox 1968). However, more cases of the
negative aspects of perturbations of systems rather than the positive aspects
have been documented (Doutt and Smith 1971); and it is much more likely
that herbivores rather than entomophages will generally "benefit" from
these perturbations.
Although difficult to weigh, the (10) psychological and sociological effects
of certain suppression tactics or overall management tactics also must be
considered. There is no need to produce an over-abundance of food and fiber
if in doing so, disharmony and unhappiness is created in individuals and in
society, i.e., if high energy systems do not fit within the social structure
(Hildebrand 1979). If we attempt to learn from natural ecosystems and live
in harmony within them, rather than attempting to create very artificial
agroecosystems, we would have fewer psychological and sociological problems
(Odum 1976).
SAMPLING SCHEMES-Various authors have pointed out the inadequacies
in our sampling schemes for various pests in assorted crops (Southwood
1966). Certainly it does not help to have refined dynamic ATs if we have
very crude sampling schemes for the pests or for the various parameters
affecting these dynamic ATs. We have pointed out the need to compare ab-
solute sampling techniques to relative sampling techniques. And of course we
must know the efficiency of estimators in relation to absolute population den-
sities.
We are presently recommending checking 3-4 locations for every 5-10
acres in a pasture for scouting CBG (Suber et al. 1979) and checking at least
10 whole plants at 3-4 locations for every 5-10 acres in a field for scouting
grain sorghum (Suber and Martin 1978). Recommendations for Florida have
been reported by Johnson4. More refined sampling schemes for FAW in
CBG are being developed (Lynch et al. unpubl. data). We hope to find
estimates on damage or relative indices of adults, eggs, and/or what will be
the best method for sampling FAW. Without these refined sampling schemes
it will be impossible to use and/or refine our dynamic ATs.
"INVESTMENT" INSURANCE AGAINST FALL ARMYWORM LOSSES-FAW dam-










1980 Fall Armyworm Symposium 397

age insurance for GS and CBG is a management tool that should be con-
sidered for eliminating conventional pesticides from the environment without
jeopardizing the income of farmers because: the occurrence of infestations is
difficult to predict; chemical and biological suppression tactics are often not
effective (either because of poor efficacy, improper application, or untimely
treatments) ; unfavorable weather may still destroy the crop despite what
one might do to suppress FAW; and there may be environmental damage
from conventional pesticides. "Investment" insurance would be particularly
valuable in the transition from high-energy systems to low-energy systems
that Koenig (1980) has pointed out we need to make. As the systems are re-
designed, i. e., habitat is effectively managed holistically, such that there are
fewer and fewer losses to FAW, insurance premiums would become lower, or
insurance companies would yield increased profits.
Certainly there are problems with insurance as is pointed out by Turpin
(1977); however, insurance does not have the lasting environmental and
health problems associated with it that insecticides do. Turpin's (1977) in-
vestigation of corn rootworm (Diabrotica undecimpunctata Barber)-corn
insurance indicated the following negative finds: (1) farmers may be re-
luctant to purchase insect insurance, (2) the infestations causing the loss
should be of a random nature, (3) there is already a U.S.D.A. Federal
All Risk Crop Insurance Program (although it does not provide an al-
ternative to soil insecticides, it will insure a crop for a maximum 75% of
the mean yields for an area, and it carries more coverage than most pro-
ducers are willing to carry), (4) farmers would have a tendency to move
away from an insurance program if they discovered a lack of insect damage
which would tend to decrease profits for the insurance company, and (5)
there is a general notion among agricultural insurance personnel (and
farmers) that crops cannot be grown without insecticides. Turpin's paper
suggests that with FAW insurance: (1) total insecticide usage would be
reduced (which could lower production costs, decrease insecticide selective
pressure on the pests, and "minimize detrimental environmental modifica-
tions associated with insecticide usage"), (2) farmers could "more accurately
assess" the level of insect problems which have been masked by insecticide
usage, and (3) system managers would have a tool that could be used "to
minimize or eliminate insecticide recommendations without jeopardizing the
income" of farmers.
Because ecosystems within which we must deal are so complex, it is dif-
ficult to predict the end result from any action within these systems. Cer-
tainly conventional chemical toxicants can cause many problems within our
systems and have numerous hidden, latent, and delayed costs. In addition,
no matter how refined, sophisticated, cautious, or technological we are, there
are risks with any action that we take: (1) that crop yields will be lost
despite these actions and (2) that the actions will be detrimental to bene-
ficial balances within our agroecosystems. We feel that it would be preferable
to have environmentally sound ATs for cultural and habitat manipulation
and biological control tactics coupled with crop insurance rather than de-
pendence on conventional pesticides. This effort would reduce short-term risks
of losing money and help increase long-term stability in our agricultural
systems.
We have 1 final point to make concerning the complexity of the pesticide










398 Florida Entomologist 63 (4) December, 1980

overuse (van den Bosch 1978) that ATs are supposed to alleviate. P. D.
Lingren (pers. commun.) once pointed out that in the Texas county where
the senior author was consulting, there was an army of crop spray planes.
Without a surplus of business (overspraying), this army of planes would
not be able to make their timely applications of pesticides on a moments
notice, i.e., put real meaning to the action part of ATs. This is a real di-
lemma, i. e., one cannot wait around too long whenever the AT is reached
to employ a suppression tactic, eg. a conventional pesticide; therefore, one
must have an army of applicators to make these timely applications. And
there must be enough business to make having these applicators profitable.
Therefore, for the AT concept to function, pesticides must be overused. We
feel this dilemma can be partially solved with insect insurance.

DYNAMIC ACTION THRESHOLDS

All the factors discussed previously in this paper must be considered in
the development of dynamic ATs. As temperature and other environmental
factors affect consumption by FAW, coastal bermudagrass (CBG) growth,
and the ability of CBG to withstand stress, economic-injury levels change.
Also, suppression tactics operate differently under various environmental
conditions of temperature, moisture, and sunlight. Another important aspect
to consider is that mortality factors such as natural enemies (particularly
predaceous arthropods), weather, unsuitable host material, and antibiosis
can rapidly move population densities above an AT to below this threshold.
Of course the attitude of each farmer-type needs to be considered (Farring-
ton 1977). As farmer attitudes change, eg. switches to more investment in-
surance, lower energy systems, different esthetic values, more religious and
moral concern for the whole of society, ATs for FAW in grain sorghum
(GS) and CBG will change.
At the present time we can probably live with relatively rigid ATs for
FAW in GS and CBG with minor adjustments by experienced consulting
entomologists (or more preferably, experienced system managers with a
strong background in ecology and entomology). We feel from our studies that
under present market values, management tactic costs, and cultural manage-
ment, the AT for FAW in CBG hay pastures should be set at somewhere
between 2 and 10 larvae < 3/8 in. long/ft2 depending on probability of
"natural" mortality shortly after the population density estimate was made.
Eg., if the pasture or surrounding crops have been recently sprayed with a
pesticide and there are few entomophages in the area, the AT should be ca.
2/ft2, particularly if the market for CBG appears to be strong and weather
conditions for growth and harvest of the hay are likely to be favorable. On
the other hand, if there are many entomophages present and/or the grass is
dry and relatively unsuitable for FAW development, the AT may be set as
high as 10 larvae/ft2. For GS we feel the AT that should be established for
whorl-stage sorghum under present (1980) market conditions should be ca. 1
larva/shoot if a suitable management tactic (which gives > 80% control
and does not disrupt favorable crop-pest relationships in the cropping sys-
tem) is available. Studies in the southwestern U. S. (Teetes and Wiseman
1979) and in Georgia (Martin and Wiseman 1980b) suggest that 2 larvae/GS
head may be a realistic action threshold for FAW in growth stages 6 and 7.
In the seedling stage, Suber and Martin (1978) set a threshold at 10% of










1980 Fall Armyworm Symposium 399

the GS possessing FAW eggs; this AT has not been tested. A change in some
of the variables will force us to abandon these relatively rigid AT concepts
employed to date. For instance, under present (1980) conditions, galloping
inflation will force us to move to more dynamic ATs.
FIELD EXPERIENCE AND MATHEMATICAL MODELING-There has recently
been some controversy about how to assimilate the impact of the various
factors covered in this paper into dynamic ATs. Newsom (1979) recently
pointed out the value of well-trained generalists and their mind-computers
for making management decisions. On the other hand, DeMichele and Bottrell
(1976) have advocated a systems approach involving a net-work of high
speed computers and minicomputers. Brown et al. (1979) point out the ad-
vantages and disadvantages of computer simulation for establishing eco-
nomic thresholds. It would appear that experienced consultants15 using in-
formation generated from "top-down" management models as well as
"bottom-up" models (Barfield and Jones 1979) and the consultant's common
sense (Dietrick 1980) would result in the dynamic guidelines for insect man-
agement, i.e., dynamic ATs, Brown et al. (1979) emphasize we need.
DYNAMIC ACTION THRESHOLDS AND THE HOLISTIC APPROACH TO SYSTEMS
MANAGEMENT-A philosophy that had developed in the crop-scouting and
consulting experiences of the senior author in the Brazos river bottom and
south Texas was, briefly, when in doubt-treat. This was carried over in his
involvement in insecticide-treatment decision guidelines for key pests on his
particular commodity responsibilities in Georgia and a decision to set ATs
for these pests at what was thought to be conservatively low.
However, the major reason for the senior author's becoming involved in
entomological research was that he thought biological control did provide a
better way to manage pestiferous arthropods than conventional pesticides.
Because of the dependent relationship of biological control and ecological
concepts (Price 1980), this interest in biological control caused him to become
cognizant of the complex intra- and inter-relationships in our agroecosystems.
Understanding these relationships is critical in developing dynamic ATs. For
instance, the pest for which some of the early work on economic thresholds
was done, had formerly been considered as the key pest of cotton in Cali-
fornia. Now after detailed studies, Gutierrez et al. (1977) have found that
Lygus bugs enhance cotton yields under most circumstances. Therefore, it is
important that we not become so mesmerized by components of world sys-
tems that we forget that we are, after all, striving for a better total-world
to live in, and not a better way to kill FAW, a more effective sampling tech-
nique for FAW, a more refined dynamic AT for FAW in CBG, or a higher
quality bale of hay.
Many factors have been considered in this paper on the development of
dynamic ATs that are very difficult to understand. For this reason they have
either simply been given a cursory look or ignored by researchers developing
ATs. Nevertheless, many of the factors that have been ignored can override
many of the decision-making processes of some consultants, farmers or
systems-managers. In addition, we generally view action or economic thresh-
olds in a simplistic fashion, including evaluations of them by extension
specialists. We do not truly know what the costs or benefits are in the

15Newsom, L. D. 1979. The next rung up the pest management ladder. Meeting Ent. Soc.
Amer., Denver, CO. 25-29 November 1979.











400 Florida Entomologist 63 (4) December, 1980

agricultural-urban systems which these ATs affect. We simply know that on
certain farm-units some ATs that have been developed appear to have had
a part in increasing profits.
We feel that it is critical for a holistic approach to systems management
to be the direction that we head and that system redesign be an option within
this approach that is seriously considered. The world is too complex to be
run without this type of approach and effective inter-disciplinary research
and planning is needed.
It is equally clear to us that we are a long way from the development of
truly dynamic ATs for most pests. We should keep farmers and the rest of
the public aware of this and inform them of the risks in their farm systems
and the surrounding environment when allowing people to make management
decisions who have limited experience with sampling, ATs, biological orga-
nisms, available management tactics, ecosystems, or decision-making proc-
esses.
We would like to list several steps that we feel will be needed for de-
velopment of dynamic ATs and a holistic approach to systems management:

(1) we must develop an attitude of energy, resource and biota conserva-
tion and become less entangled in high-energy systems and a reliance
on use of conventional pesticides within these systems. We should
study and compare intra- and inter-relationships of FAW-grain
sorghum, coastal bermudagrass, and natural enemies of FAW in
agroecosystems in the U. S. or South America which have considera-
ble diversity and little disruption with conventional pesticides, and
those with little diversity and a high rate of disruption from con-
ventional pesticides;
(2) we should attempt to critically test suppression tactics over many
areas, situations, and regions, determine ecological impact of these
suppression tactics, and study long-range cost-benefits. These tests
should involve team approaches of ecologists-entomologists and
modelers-agronomists-economists and generalists;
(3) in order to develop effective ATs we must look to the future and not
become too involved with temporary short-range problems in our
experiment station and extension service organizations; these prob-
lems will often disappear without too much harm to our systems if
we have administrators who prevent them from disrupting organized
extension and research activities;
(4) in the development of dynamic ATs and a holistic approach to sys-
tems management, we must be concerned with city-dwellers, farmers,
foreigners, and men of both considerable or little influence eco-
nomically, politically, and socially;
(5) the best way to learn to manage our artificial systems holistically
would be to study natural ecosystems and attempt to capture the
complexity, diversity, and stability of these systems.

It is often said that our systems are too complex to manage them wholly.
Certainly administrators in our bureaucracies are convinced that they have
enough problems without having to think holistically. But these are schemes
to evade true solutions to problems in our agricultural systems. We can con-
tinue to manage our systems as parts. However, our management approaches










1980 Fall Armyworm Symposium


will be more efficient and ecologically sound if we attempt to manage our
systems holistically.
Certainly the concept of dynamic ATs is very complex and there is con-
siderable additional literature that is pertinent on crops such as GS or CBG
that are so widely-grown and well-researched. But we believe we have
brought together information on the most realistic and refined ATs devel-
oped for FAW in GS and CBG to date. The type of economic threshold in-
formation that should be released by the Cooperative Extension Service is
portrayed in Fig. 1. However, it is equally important that all of the factors
listed in Table 1 be considered in decision-making processes for management
of FAW and the crop. Weather variables, crop yield projections, and para-
site and predators of FAW are 3 of the factors that should be of primary
consideration.
This paper was not meant to be all inclusive; the purpose was to stimu-
late thought in an area that needs more consideration in systems manage-
ment. Certainly many of these ideas are not new. Nevertheless, we think it
was worthwhile in our discussion of ATs for FAW in GS and CBG to dis-
cuss:
(1) the complexity of developing these ATs,
(2) the need for a transition to a holistic, interdisciplinary research and
extension effort, and
(3) the need to educate the public concerning our inadequacies in the
area of dynamic ATs.

We are aware that many will find this paper very idealistic. Nevertheless
we feel it presents relationships, concepts, and goals that should be given
serious consideration. It is important that scientists begin to have more
philosophical input into their papers, otherwise, those that need most to
interact in this manner will receive deaf ears from the administrators and
politicians that we need to keep informed (Bertrand 1979).

ACKNOWLEDGEMENTS

We would like to acknowledge P. A. Goodman, F. A. Marshall, N. Pencoe,
J. Garner, J. R. Young, W. D. Perkins, M. Kegle, E. Belk, B. G. Lastinger,
and L. A. Atkins for their advice and assistance in many ways. We would
like to thank, especially, Dr. A. N. Sparks for facilitating the excellent co-
operation between scientists at the Southern Grain Insects Research Labora-
tory, AR/SEA, USDA and the Department of Entomology-Fisheries, Coastal
Plain Experiment Station, Tifton, GA. Also, several consulting entomologists
provided invaluable insights in the development of this paper. And we ap-
preciate the constructive criticism and review of this paper by J. D. Dutcher,
S. Nilakhe, D. A. Nordlund, B. H. Wilson, D. C. Sheppard, and J. R. Young.
Finally, the senior author is grateful to M. Altieri for his contagious drive
and sense of priority, and for encouraging him not to be so weak, indolent,
or procrastinating so as not to develop and follow the philosophy in which he
believes.
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Heliothis Species on Cotton, Soybeans, and Other Host Plants. South-
ern Coop. Ser. Bull. 231.
TURPIN, F. T. 1977. Insect insurance: potential management tool for corn
insects. Bull. Ent. Soc. Am. 23: 181-4.
VAN ARKEL, H. 1978. The forage and grain yield of sorghum and maize as
affected by soil moisture conservation, lodging and harvesting losses.
Neth. J. Agr. Sci. 26: 181-90.
VAN DEN BOSCH, R. 1978. The Pesticide Conspiracy. Doubleday and Co.,
Inc. Garden City, NY. 208 p.
VANDERLIP, R. 1977. Stages of plant growth in sorghum. Sorghum News-
letter 19: 123.
WALL, J. S., AND W. M. Ross. 1970. Sorghum production and utilization.
The Avi Publishing Co., Inc. Wesport, CT. 702 p.
YOUNG, J. R. 1979. Assessing the movement of the fall armyworm
(Spodoptera frugiperda) using insecticide resistance and wind pat-
tern. Pages 344-53. In R. L. Rabb and G. G. Kennedy (eds.) Movement
of Highly Mobile Insects: Concepts and Methodology in Research.
Proceedings of a Conference, "Movement of Selected Species of
Lepidoptera in the Southeastern U. S.". Raleigh, NC. 9-11 April 1979.
YOUNG, W. R., AND G. L. TEETES. 1977. Sorghum entomology. Ann. Rev. Ent.
22: 193-218.
AND W. W. MCMILLIAN. 1979. Differential feeding by two strains of
fall armyworm larvae on carbaryl treated surfaces. J. Econ. Ent. 72:
202-3.










Florida Entomologist 63(4)


December, 1980


PHEROMONES: POTENTIAL FOR USE IN MONITORING
AND MANAGING POPULATIONS OF THE
FALL ARMYWORM1'2'3

ALTON N. SPARKS
Southern Grain Insects Research Laboratory
SEA, AR, USDA
Tifton, GA 31793

ABSTRACT

Four closely related pheromone compounds have been identified from
virgin female fall armyworms, Spodoptera frugiperda (J. E. Smith). Of
these, (Z)-9-dodecen-l-ol acetate [(Z)-9-DDA], when used in conjunction
with electric grid traps, has proved the most effective and economical for
monitoring male populations. Attempts to disrupt mating via air permea-
tion of pheromones or phermone mimics have been encouraging or not, de-
pending on the evaluation method used. (Z) -9, (E) -12-tetradecadien-1-ol
acetate caused significant reductions in the catch of males responding to
traps containing (Z)-9-DDA or virgin females in the treated areas. (Z)-9-
tetradecen-1-ol acetate and (Z)-9-DDA have not significantly decreased
mating of fall armyworms in 30 ft x 100 ft screened cages. The potential
use of pheromones for population management of fall armyworms will be
decided only when their effect on in-field mating is determined over large
acreages where low pest populations are relatively isolated from migrating
masses of insects.


Luginbill's (1928) classical work on the fall armyworm, Spodoptera
frugiperda (J. E. Smith), has been the most authoritative and complete
source of information concerning this species. The published papers pre-
sented at a Fall Armyworm Symposium at the 1978 Southeastern Branch of
the Entomological Society of America, convened in Gainesville, FL, con-
stitute a review and significant updating of the biology, ecology, and control
of the fall armyworm (Mitchell 1979a).
Beroza (1960) was the first to suggest permeating the atmosphere of crop
environments with sex pheromones to disrupt mating, prevent reproduction,
and reduce infestations of economically damaging insect pests. Twenty years
later, Rothschild (in press) summarized the progress, current status, and
prospects for using this method to effect mating disruption of Lepidoptera. In
his review, he noted 170 mating disruption trials. Of these, 25% were suc-
cessful in decreasing crop infestation; 75% were considered as exploratory.
In over 40% of the trials, reduction in males trapped at pheromone or virgin
female sites was the sole criterion for disruption. In ca. 50% of the trials,
success was measured by response of males to tethered, clipped-wing, or
otherwise decoyed females in forest insect trials and ca. 25% in field and
orchard insect trials. Thus, the mating status and behavior of native females

'Lepidoptera: Noctuidae.
2In cooperation with the University of Georgia College of Agriculture Experiment Stations,
Coastal Plain Station, Tifton, GA 31793. Accepted for publication 20 August 1980.
'Mention of a proprietary product in this paper does not constitute an endorsement of this
product by the USDA.


406










1980 Fall Armyworm Symposium


were completely neglected in the majority of cases, though these criteria are
the most important for evaluating the success of mating disruption with
highly mobile Lepidoptera, especially in field crops. This paper does not
present a comprehensive review of literature, but will explore the behavior
of the fall armyworm adult as related to its sex pheromone and the potential
of this relationship for assessing and/or managing populations of fall army-
worms.

ISOLATION, IDENTIFICATION, AND TESTING OF PHEROMONES
Sekul and Cox (1965) reported that the female fall armyworm moth
elaborates a substance that evokes a mating response in the male. Sekul and
Sparks (1967) then isolated, identified, synthesized, and laboratory tested
the substance they believed to be the fall armyworm pheromone, (Z)-9-
tetradecen-1-ol acetate [(Z)-9-TDA]. During the following 4 years, a series of
tests was conducted by entomologists at the Southern Grain Insects Research
Laboratory to determine the potential of (Z)-9-TDA for managing the fall
armyworm. The results (Sparks unpublished data) proved the compound in-
effective as a lure for trapping males in pheromone sticky traps. However,
in 1968, when Sparks, Wiseman, and McMillian (unpublished data) evapo-
rated (Z) -9-TDA into a greenhouse atmosphere where fall armyworm pupae
had been placed for emergence, they found that the progeny of mating fe-
males caused significantly different damage to corn in treated and check
plots located in adjacent glass-partitioned 20 ft x 20 ft sections of a green-
house. Also, when Snow and Copeland (unpublished data) sprayed (Z) -9-
TDA on corn plants immediately surrounding sticky traps containing virgin
female fall armyworms, male capture was significantly reduced.
Mitchell and Doolittle (1976) documented that (Z) -9-TDA was not an
effective lure for male fall armyworms. Meanwhile, Sekul and Sparks (1976),
having realized that (Z)-9-TDA was not the complete pheromone of the fall
armyworm, continued their search until they isolated, identified, synthesized,
and field tested a 2nd component, (Z)-9-dodecen-l-ol acetate [(Z)-9-DDA],
from virgin females. This compound is currently used as the most practical
bait in pheromone traps, although Jones and Sparks (1979) reported that
the addition of small quantities of (Z) -9-TDA to (Z)-9-DDA used as a bait
in sticky traps would increase catches. In subsequent studies, Klun and
Sparks (unpublished data) identified 2 additional compounds from ovipositor
washes of fall armyworm virgin females; however, field tests of combinations
of all 4 compounds in various ratios failed to reveal a combination that was
more effective than or as economical as (Z) -9-DDA alone, for catching males.

PHEROMONE MONITORING OF FALL ARMYWORM POPULATIONS
Snow and Copeland (1969) were first to use virgin female fall armyworms
to capture males in traps. The technique was used to determine the presence
and distribution of the insect on the Island of St. Croix (Snow et al., 1968).
Mitchell et al. (1974a) indexed nocturnal activity of fall armyworm males
responding to virgin females in traps. Subsequently, Tingle and Mitchell
(1975) used pheromone bait as lure in 7 trap designs and compared the
effectiveness of traps in capturing fall armyworm males. They reported the
electrocutor grid trap 10-12 times more effective than all other traps. Further


407










408 Florida Entomologist 63 (4) December, 1980

discussion of trap monitoring of adult fall armyworms is presented by
Mitchell (1979b). Also, Tingle and Mitchell (1979) conducted pheromone
trap-placement studies around corn, peanuts, and grasses in north Florida.
Since catches ranged from 0 to 7.4 males/trap per night, they concluded that
1 trap/4 ha could be used to survey for low density populations of fall army-
worms.
The fact that virgin females or fall armyworm pheromone will catch fall
armyworm males in traps is, therefore, well documented. It has also been
proven that 1 trap is more efficient than another in capturing males and that
trap efficiency varies with trap design (Sparks et al. 1979 a,b). The disturb-
ing fact is that there is no known way of relating pheromone trap catches
with population density. To index populations of the fall armyworm with
pheromone traps, one must be capable of deciphering the meaning of a catch
of 5 males/trap per night or 25 males/trap per night. At present, with no
additional information, the only conclusion regarding either of those trap
catches would be that fall armyworm males are in the area. Experience has
taught that the catch of 5 males/trap could reflect the catch of males from a
light density population wherein most of the females are mated, or the catch
from a dense population wherein most of the females are virgin. The same
would be true for the catch of 25 males/trap per night. Or, the differences in
these 2 catches could reflect only differences in the efficiency of 2 types of
traps evaluated.
In the winter-spring of 1978 and throughout the fall-winter-spring of
1979, trap lines baited with (Z) -9-DDA were used in efforts to index the
early-season or first generation of fall armyworms in north Florida and
south Georgia. In both years, late instar larvae were found in whorl-stage
corn prior to the time adult males were captured in pheromone traps (un-
published data-Gross, Martin, Mitchell, Sparks). These data may indicate:
(1) that mated females migrate into and infest a host crop prior to male
migration, (2) that the pheromone is not complete, (3) that when the male
population is extremely low, a trap with only ca. 3% efficiency in capturing
males lured to within 1 m is simply too inefficient to detect a low population
or (4) the effect of a combination of these alternatives.

PHEROMONES FOR MANAGING FALL ARMYWORM POPULATIONS
The response of fall armyworm males to pheromones dispensed in traps
of different design is not totally dissimilar (Sparks et al. 1979 a,b) even
though the efficiency of traps of different design in actually capturing at-
tracted males does vary considerably. For example, Lingren et al. (1978)
tested the effectiveness of 4 types of traps-electric grid, directional live, pie
plate, and cone-against fall armyworm males and found that they captured
34, 14, 3, and 4%, respectively, of the males that were lured to within 1 m of
the trap. Sparks et al. (1979 a,b) reported very similar relative efficiencies of
the same trap types in capturing males of the corn earworm, Heliothis zea
(Boddie), and the tobacco budworm, Heliothis virescens (F.), when the traps
were baited with the respective pheromones of those species.
It has been calculated that traps would have to remove a high percentage
of the fall armyworm males to be effective as control agents. Then, if the
most effective trap collects only 34% of the attracted males, it appears un-
likely that 95% of the male population of a polyphagous lepidopteran species










1980 Fall Armyworm Symposium 409

could ever be trapped in sufficient time to prevent mating, oviposition, and
subsequent larval populations.
Published results of attempts to suppress or manage fall armyworms by
use of the pheromone or pheromone mimics are scarce. When Mitchell et al.
(1974b) evaporated selected chemicals into the atmosphere of an 81 m2 plot,
as little as 10% (Z) -7-dodecen-l-ol acetate or (Z)-9,(E)-12-tetradecadien-
1-ol acetate, evaporated from wicks attached to the traps, reduced catches of
male fall armyworm moths attracted to traps baited with (Z) -9-DDA, the
most effective fall armyworm lure. Also, when these compounds were evapo-
rated in plots surrounding a grid trap in which virgin females were used as
bait, the catch of males was reduced. They concluded that these synthetic
pheromones might be considered for suppressing fall armyworm populations
on a regional basis.
In a follow-up to that research, Mitchell et al. (1976) evaporated ca.
90 mg (Z)-9-, (E)-12-tetradecadien-1-ol acetate/acre per night in plots of ca.
0.2 ha. The center of each plot contained virgin females (with clipped
wings) in screened cages (ca. 1 m diam x 1.2 m high) designed so that males
could enter. When percentage mated females in control and treated plots was
compared, fall armyworm mating was reduced by an estimated 88.3% in the
treated plots.
In a short series of unreplicated experiments, Sparks (unpublished data)
evaporated the equivalent of 75 mg and 7.5 g of (Z) -9-TDA and (Z) -9-DDA
from 50 cigarette filters attached to 0.027 ha of plants covered by a 30 ft x
100 ft screened cage. Laboratory-reared fall armyworm females and males
were introduced and observed. No significant decrease in mating was ob-
served.
The available data pertaining to the use of pheromone or pheromone
mimics as a viable method of managing fall armyworm populations therefore
do not present a convincing argument. The true potential, however, should
not be decided until such time as the technique is evaluated on large plots
(perhaps 100+ ha) of suitable host plants where low pest populations are
relatively isolated from migrating masses of insects. Further, I conclude that
researchers conducting these studies will have to spend night after night
making field observations of the mating behavior of the fall armyworm. This
type of evaluation is essential to determine the absolute effect of the
pheromone on the communication between wild males and females in their
ecological habitat. It cannot be too strongly emphasized that the critical ele-
ment in evaluating the efficiency of a pheromone management program is the
effect of treatments on the wild male-female interactions, and the only known
way to gain that information is through actual field observation.

LITERATURE CITED
BEROZA, M. 1960. Insect attractants are taking hold. Agric. Chem. 15: 37-40.
JONES, R. L., AND A. N. SPARKS. 1979. (Z) -9-tetradecen-l-ol acetate: A
secondary sex pheromone of the fall armyworm, Spodoptera frugiperda
(J. E. Smith). J. Chem. Ecol. 5: 721-5.
LINGREN, P. D., A. N. SPARKS, J. R. RAULSTON, AND W. W. WOLF. 1978. Ap-
plications for nocturnal studies of insects. In Proceedings ESA Sym-
posium: Night Vision Equipment for Studying Nocturnal Behavior of
Insects. Bull. Ent. Soc. Am. 24: 206-12.
LUGINBILL, P. 1928. The fall armyworm. USDA Tech. Bull. No. 34. 92 p.










410 Florida Entomologist 63 (4) December, 1980

MITCHELL, E. R. 1979a. Fall Armyworm Symposium. Fla. Ent. 62: 81.
1979b. Monitoring adult populations of the fall armyworm. Ibid. 62:
91-8.
A. H. BAUMHOVER, AND M. JACOBSON. 1976. Reduction of mating
potential of male Heliothis spp. and Spodoptera frugiperda in field
plots treated with disruptants. Environ. Ent. 5: 484-6.
AND R. E. DOOLITTLE. 1976. Sex pheromones of Spodoptera exigua,
S. eridania, and S. frugiperda: Bioassay for field activity. J. Econ.
Ent. 69: 324-6.
W. W. COPELAND, AND A. N. SPARKS. 1974a. Fall armyworm:
Nocturnal activity of adult males as indexed by attraction to virgin
females. J. Ga. Ent. Soc. 9: 145-6.
W. W. COPELAND, A. N. SPARKS, AND A. A. SEKUL. 1974b. Fall army-
worm: Disruption of pheromone communication with synthetic ace-
tates. Environ. Ent. 3: 778-80.
ROTHSCHILD, G. H. L. Current status and prospects for mating disruption
of lepidopterous pests. E. R. Mitchell, Ed. In Management of Insect
Pests with Semiochemicals: Concept and Practice. Plenum Press, New
York, NY. (In press).
SEKUL, A. A., AND H. C. Cox. 1965. Sex pheromone in the fall armyworm,
Spodoptera frugiperda (J. E. Smith). BioScience 15: 670-1.
AND A. N. SPARKS. 1967. Sex pheromone of the fall armyworm
moth: Isolation, identification, and synthesis. J. Econ. Ent. 60: 1270-2.
AND 1976. Sex attractant of the fall armyworm moth. USDA
Tech. Bull. 1542. 6 p.
SNOW, J. W., AND W. W. COPELAND. 1969. Fall armyworm: Use of virgin
female traps to detect males and determine seasonal distribution.
USDA Prod. Res. Rep. No. 110. 9 p.
-- W. C. CANTELO, R. L. BURTON, AND S. D. HENSLEY. 1968. Popula-
tions of fall armyworm, corn earworm, and sugarcane borer on St.
Croix, U. S. Virgin Islands. J. Econ. Ent. 61: 1757-60.
SPARKS, A. N., J. E. CARPENTER, J. A. KLUN, AND B. G. MULLINIX. 1979a.
Field responses of male Heliothis zea (Boddie) to pheromonal stimuli
and trap design. J. Ga. Ent. Soc. 14: 318-25.
-- J. R. RAULSTON, P. D. LINGREN, J. E. CARPENTER, J. A. KLUN, AND
B. G. MULLINIX. 1979b. Field responses of Heliothis virescens (F.)
males to pheromonal stimuli and traps. Bull. Ent. Soc. Am. 25: 268-74.
TINGLE, F. C., AND E. R. MITCHELL. 1975. Capture of Spodoptera frugiperda
and S. exigua in pheromone traps. J. Econ. Ent. 68: 613-5.
AND 1979. Factors affecting pheromone trap catches in corn
and peanuts. Environ. Ent. 8: 989-92.










1980 Fall Armyworm Symposium


411


CULTURAL MANIPULATION OF
COASTAL BURMUDAGRASS TO AVOID
LOSSES FROM THE FALL ARMYWORM1'2

R. E. LYNCH3, P. B. MARTIN4, AND J. W. GARNER4

ABSTRACT
The effects of fertilization, harvest frequency, and insect control on yield
of coastal bermudagrass, Cynodon dactylon (L.) Pers., were evaluated to
develop means for the cultural manipulation of the fall armyworm,
Spodoptera frugiperda (J. E. Smith). A split application of nitrogen, applied
by 1 June, allowed production of > 80% of the annual yield by 1 August. In
most years, fall armyworm larval populations peaked after 1 August. There-
fore, most of the bermudagrass yield can be produced prior to the occurrence
of critical fall armyworm densities.


Coastal bermudagrass, Cynodon dactylon (L.) Pers., is the most widely
grown forage grass in the southern United States, occupying over 6 million
acres (Burton 1964). In Georgia alone, ca. 1.6 million acres of bermuda-
grasses, primarily coastal, are grown as perennial pastures. These bermuda-
grass pastures serve as hosts to a wide variety of insects, many of which can
drastically reduce the yield of these pastures (Byers 1967, Hawkins et al.
1979, Osborn 1912). Cultural methods, such as spring burning for the two-
lined spittlebug, Prosapia bicincta (Say) (Beck 1963), and frequent mowing
for leafhoppers and planthoppers (Hawkins et al. 1979), have been developed
to aid in the control of some of these insects. However, cultural methods have
not been developed to reduce yield losses from 1 of the major pests of ber-
mudagrass, the fall armyworm, Spodoptera frugiperda (J. E. Smith). Ber-
mudagrasses are some of the preferred hosts of this insect (Luginbill 1928),
and populations often exceed 10 larvae/sq ft (Lynch et al. 1980) or 20
larvae/sweep (Martin and McCormick 1979).
Several possible alternatives are available for cultural manipulation of
the fall armyworm. These include: (1) the use of fertilization and/or harvest
frequency to stimulate bermudagrass growth before damaging populations
of the fall armyworm occur; (2) harvest of bermudagrass when fall army-
worm larval populations exceed the economic injury level rather than control
the insects with an insecticide; (3) delay harvest before peak fall armyworm
moth flight so that the bermudagrass is not attractive for oviposition (1st-
instar larvae are most prevalent in new growth of bermudagrass (Byers
1967), an indication that the new growth is probably most attractive for
oviposition); and (4) harvest bermudagrass following the peak moth flight
to destroy heavy infestations of 1st- or 2nd-instar larvae, if the grass is in
an attractive stage of regrowth during the moth flight.

'Lepidoptera: Noctuidae.
2This research was supported in part by the University of Georgia Project CSRS 6E 00295,
Integrated Management of Insects of Pastures and Forages on the Georgia Coastal Plain, and
by AR, SEA, USDA Project 20240. Accepted for publication 20 August 1980.
'Southern Grain Insects Research Laboratory, AR, SEA, USDA, Tifton, GA 31793.
4Department of Entomology and Fisheries, Coastal Plain Experiment Station, Univ. of
Georgia, Tifton, GA 31793.










Florida Entomologist 63 (4)


December, 1980


Although present in other crops at a much earlier date, damaging popu-
lations of the fall armyworm in coastal bermudagrass generally do not
occur in south Georgia before late July to early August (Martin unpub-
lished data). Furthermore, evaluation of previous research on the influence
of nitrogen rate and harvest frequency (Burton et al. 1963, Prine and
Burton 1956) indicated that these factors may be utilized to stimulate ber-
mudagrass growth and subsequent yield prior to 1 August, thus avoiding
major damage by the fall armyworm. We report here results of research
conducted to test his hypothesis.

METHODS AND MATERIALS
An established coastal bermudagrass hay pasture that contained small
amounts of bahiagrass (Paspalum notatum Fliigge), goosegrass (Eleusine
indica (L.) Gaertn.), and common bermudagrass was utilized for the re-
search. Since the pasture had not been managed for several years, the entire
area was fertilized with 39:31:62 lbs/A (N:P:K) prior to initiation of the
experiment. A split-split plot arrangement of treatments with 4 replications
was employed with fertilization as the whole plot, cutting frequency as the
subplot, and insect control as the sub-subplot. Whole plots were: 1) initial
fertilization with no subsequent fertilization; 2) 200 lbs N/A applied in a
split application, i.e., an initial fertilization in the spring before cutting and
the remainder applied in 2 applications before 1 June; 3) 200 lbs N/A in a
continuous application, i.e., an initial fertilization in the spring before cutting
followed by an application after each 5-week cutting for 5 applications; 4)
400 lbs N/A applied in a split application as in 2; and 5) 400 lbs N/A ap-
plied continuously as in 3. All fertilizer regimes were maintained in a 4:1:2
ratio of N, P205, and K20. Two cutting frequencies, 2-1/2- and 5-week in-
tervals, were used as the subplots. The sub-subplots were 9 ft x 9 ft, sep-
arated from other sub-subplots by a 3-ft border, and consisted of fall army-
worm control with methomyl, S-methyl N-[(methylcarbamoyl)oxy]thioaceti-
midate5, versus no insect control. Methomyl (0.45 lb AI/A) was applied with
a C02-powered backpack sprayer at 7 gal/A, 30 psi, and with 8001E even
flat-spray tips. Plots for insect control were treated on 18 August and 8
and 26 September in 1978 and at weekly intervals from 10 July through 16
October in 1979.
Plots for grass yields were cut and harvested during 1978 and 1979 with
a Sensation@ plot harvester with a rear grass catcher. The bermudagrass
was cut to 2-3 in. and weighed for wet yields. A subsample was taken from
each plot, immediately sealed in a plastic bag, stored in an ice chest, and
later weighed, dried in an oven at ca. 220C, and reweighed for dry-matter
determinations.
At weekly intervals, 10 samples of all sub-subplots were obtained with a
15-in. diam sweep net. Data were recorded on the abundance of S. frugiperda
(J. E. Smith), Mocis latipes (Gu6nee), Anticla infecta (Ochsenheimer),
leafhoppers, grasshoppers, and entomophages. In addition, 3 coastal bermuda-
grass hay pastures in 1977 and 1978 and 4 in 1979 were sampled at ca.
weekly intervals during the fall armyworm moth flight to follow larval pop-

5Mention of a proprietary product does not constitute an endorsement of this product by
the USDA or the University of Georgia.


412










1980 Fall Armyworm Symposium


ulations in these fields. These pastures were sampled in 1977 and 1978 with
a 15-in. diam sweep net (4-6 series of 25 sweeps) in a diagonal path across
the field and alternating the diagonal on each sampling date. In 1979, each
field was divided into 4 quadrants, and 10 series of 25 sweeps with a 15-in.
diam sweep net were taken in each quadrant.

RESULTS AND DISCUSSION

Annual dry-matter yields were highly significant between years. In 1978,
the average yield for all treatments was 6.94 tons per acre as compared with
only 4.79 tons per acre in 1979. These differences corresponded primarily to
higher rainfall in 1978 during May and June (4.69 and 4.65 in., respectively)
than in 1979 (2.89 and 2.93 in., respectively). Similar differences between
years, as influenced by moisture, were reported by Prine and Burton (1956).
As might be expected, fertilization rates had the greatest effect on annual
dry-matter yields (Table 1). An initial fertilization with ca. 40 lbs N/A
produced an average yield of only 2.97 tons per acre as compared with 5.58
and 7.60 tons/acre with the addition of 200 and 400 lbs of N/acre, respec-
tively. Furthermore, a split application of 400 lbs of N/A significantly in-
creased the annual yield as compared with a continuous application of the
same rate. However, this difference due to application regimes was not
present at the lower fertilization rate. These response differences led to a
significant year X fertilizer interaction, since in 1978, a split application of
either 200 or 400 lbs/acre produced a higher annual yield (significantly so
at 400 lbs/acre) than the continuous application of equal rates. The reverse
was observed in 1979 in that the annual yield for the continuous fertilization
regime was slightly greater, though not significantly, than the yield for the
split regime.
Dry-matter annual yields were significantly greater when bermudagrass
was harvested every 5 weeks than when it was harvested every 2-1/2 weeks.
These results were similar to those reported by Burton et al. (1963) with a
fertilization rate of 600 lbs N/acre. A significant year X harvest frequency
interaction was also noted as a result of the magnitude of the yields between
the 2 harvest frequencies. In 1978, annual yields of 6.49 and 7.38 tons/acre
were produced by the 2-1/2- and 5-week cutting frequencies, respectively;
while only 4.74 and 4.84 tons/acre, respectively, were produced in 1979.
Insect control also significantly increased the annual yield of coastal ber-
mudagrass. Plots treated with methomyl averaged 5.96 tons/acre while un-
treated plots averaged only 5.77. However, sweep-net samples of the plots,
taken at weekly intervals, showed that fall armyworms failed to reach
economic levels and that leafhoppers were the most abundant phytophagous
insects present, especially during the latter part of the growing season.
Hawkins et al. (1979) and Byers (1967) previously reported increased yields
after control of leafhoppers.
The result of the analyses for bermudagrass yield by 1 August was sim-
ilar to that for the annual yield: yields were significantly different between
years, fertilization had the greatest effect on yield, the 5-week harvest fre-
quency outyielded the 2-1/2-week harvest frequency, and the interactions
were similar. However, there were 2 important differences between the an-
nual yield and the yields by 1 August. First, the yield by 1 August was sig-
nificantly greater for both the 200 and 400 lbs N/acre fertilization rates when


413













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Florida Entomologist 63 (4)


applied in a split application by June than were the same rates applied con-
tinuously, i.e., every 5 weeks. Secondly, differences in yield by 1 August due
to insect control were not significant: the untreated and methomyl-treated
plots yielded 4.66 and 4.73 tons/acre, respectively. These data suggest that
the primary insect pressure to bermudagrass occurs after 1 August. Indeed,
Genung and Mead (1969), Wilson et al. (1973), and Byers and Jung (1979)
showed that leafhopper populations reached their peak in late summer, i.e.,
after 1 August.
Table 2 presents data on the percentage of coastal bermudagrass dry-
matter yield produced by 1 August. Previous data (Hart et al. 1965, Burton
et al. 1969) have indicated that ca. 65-75% of the total yield of coastal ber-
mudagrass could be produced by 1 August. Furthermore, evaluation of tem-
perature accumulations above 550 F, i.e., temperatures favorable for ber-
mudagrass growth (Monson personal communication) from 1922-1967 in-
dicated that 63% of the growing degree days from April to September are


-. Field 1
1977


June


July August Sept. Oct.


Fig. 1. Seasonal abundance of fall armyworm larvae in coastal bermuda-
grass hay pastures. Berrien County, GA, 1977.


December, 1980


416










1980 Fall Armyworm Symposium


accumulated by the end of July. Indeed, yields in excess of 75-85% of the
annual yield can be produced by 1 August. Considerable differences were also
noted between the 2 procedures for fertilization: 86.3 and 82.8% of the total
annual yield were produced by 1 August with a split application of 200 and
400 lbs N/acre, respectively; whereas only 76.1% of the annual yield was
produced by 1 August with 200 or 400 lbs N/A applied in a continuous
regime. Mowing schedules or insect control had little influence on the per-
centage of dry-matter yield produced by 1 August.
Figures 1, 2, and 3 present the seasonal abundance of fall armyworm
larvae in coastal bermudagrass pastures in 1977, 1978, and 1979, respectively.
1977 was a year of epidemic fall armyworm population densities; in 1979,
fall armyworm larval densities were only moderate until after 1 August.
Only in 1978 did fall armyworm larval densities reach severe levels prior to
1 August. In this year, populations peaked ca. 15 July in 2 of the 3 fields
sampled.


June


* -9 Field 1

-- Field 2
- -* Field 3
1978


July


I'
I.'


I'



A
II
.1


I


August Sept.


Oct.


Fig. 2. Seasonal abundance of fall armyworm larvae in coastal bermuda-
grass hay pastures. Tift County, GA, 1978.


417









Florida Entomologist 63 (4)


*--.-e Field 1
** .* Field 2


S*---* Field 3
8 --- Field 4
1979


June


S


July August


'I
II
I'
it
I'
I'

I ~


I t


A'11


Sept.


Oct.


Fig. 3. Seasonal abundance of fall armyworm larvae in coastal bermuda-
grass hay pastures. Tift County, GA, 1979.
In conclusion, fertilization to stimulate coastal bermudagrass yields ap-
pears to be a viable method to evade fall armyworm damage. A split applica-
tion of N, applied by 1 June, will produce > 80% of the annual yield by 1
August. In most years, fall armyworm larval populations reach a peak after
this time. Thus, the major portion of the bermudagrass yield can be produced
prior to critical fall armyworm densities.

ACKNOWLEDGMENT
We are grateful to C. Cutler and F. A. Marshall of the Department of
Entomology and Fisheries, Georgia Coastal Plain Experiment Station for
their technical assistance.

LITERATURE CITED
BECK, E. W. 1963. Observations on the biology and cultural-insecticidal con-
trol of Prosapia bicincta, a spittlebug, on Coastal bermudagrass. J.


418


December, 1980










1980 Fall Armyworm Symposium


Econ. Ent. 56: 747-52.
BURTON, G. W. 1973. Breeding better forages to help feed man and preserve
and enhance the environment. BioScience 23: 705-10.
-- J. E. JACKSON, AND R. H. HART. 1963. Effects of cutting frequency
and nitrogen on yield, in vitro digestibility, and protein, fibers, and
carotene content of coastal bermudagrass. Agron. J. 55: 500-2.
-- W. S. WILKINSON, AND R. L. CARTER. 1969. Effect of nitrogen,
phosphorus, and potassium levels and clipping frequency on the forage
yield and protein, carotene, and xanthophyll content of Coastal ber-
mudagrass. Agron. J. 61: 60-3.
BYERS, R. A. 1967. Increased yields of Coastal bermudagrass after applica-
tion of insecticides to control insect complex. J. Econ. Ent. 60: 315-8.
- AND J. A. JUNG. 1979. Insect populations of forage grasses: effect of
nitrogen fertilization and insecticides. Environ. Ent. 8: 11-8.
GENUNG, W. G., AND F. W. MEAD. 1969. Leafhopper populations
(Homoptera: Cicadellidae) on five pasture grasses in the Florida
everglades. Fla. Ent. 52: 165-70.
HART, R. H., G. W. BURTON, AND J. E. JACKSON. 1965. Seasonal variation in
chemical composition and yield of coastal bermudagrass as affected by
nitrogen fertilization schedule. Agron. J. 57: 381-2.
HAWKINS, J. A., B. H. WILSON, C. L. MONDART, B. D. NELSON, R. A. FARLOW,
AND P. E. SCHILLING. 1979. Leafhoppers and planthoppers in coastal
bermudagrass: effect on yield and quality and control by harvest fre-
quency. J. Econ. Ent. 72: 101-4.
LUGINBILL, P. 1928. The fall armyworm. USDA Tech. Bull. No. 34. 89 p.
LYNCH, R. E., P. B. MARTIN, AND J. W. GARNER. 1980. Fall armyworm in-
festations in Coastal bermudagrass: Comparison of sampling methods
and distribution. J. Econ. Ent. (In press).
MARTIN, P. B., AND W. C. MCCORMICK. 1979. Coastal bermudagrass: fall
armyworm suppression, Tifton, 1977. Insecticide and Acaricide Tests
4: 204b.
OSBORN, H. 1912. Leafhoppers affecting cereals, grasses, and forage crops.
USDA, Dept. Ent. Bull. 108. 123 p.
PRINE, G. M., AND G. W. BURTON. 1956. The effect of nitrogen rate and
clipping frequency upon the yield, protein content and certain morpho-
logical characteristics of Coastal bermudagrass (Cynodon dactylon
(L.)) Pers. Agron. J. 48: 296-301.
WILSON, B. H., S. PHILLIPS, AND H. M. HARRIS. 1973. Species and seasonal
occurrence of leafhoppers and planthoppers in a coastal bermudagrass
pasture in the Macon Ridge area of Louisiana. J. Econ. Ent. 66:
1346-7.


419










420 Florida Entomologist 63 (4) December, 1980

FALL ARMYWORM PLANT RESISTANCE PROGRAMS1

FRANK M. DAVIS
Crop Science and Agricultural Engineering Research Laboratory
Agricultural Research, SEA, USDA
Mississippi State, MS 39762

ABSTRACT
Plant resistance research programs in corn, sorghum, peanuts, bermuda-
grass, and rice are involved with screening, developing, and releasing germ-
plasm resistant to the fall armyworm, Spodoptera frugiperda (J. E. Smith).
Effort and progress in identifying, developing, and releasing germplasm re-
sistant to the fall armyworm and program needs and benefits are discussed.


Wiseman and Davis (1979) reviewed the state of the art of plant re-
sistance to the fall armyworm, Spodoptera frugiperda (J. E. Smith), at the
1978 Fall Armyworm Conference. I report here on the present commitment
in the United States to the breeding of crop cultivars resistant to the fall
armyworm, including progress in identifying and releasing germplasm
sources to the public. I also discuss the needs and benefits of these programs.
The information presented is based on Current Research Information System
Project Reports and from personal communications with scientists conducting
research within these programs.
Plant breeders and entomologists work as teams in identifying, develop-
ing, and releasing plant germplasm resistant to fall armyworm for corn, Zea
mays L., sorghum, Sorghum bicolor (L.) Moench, peanuts, Arachis hypogaea
L., bermudagrass, Cynodon dactylon (L.) Pers., and rice, Oryza sativa L. The
total scientific effort (state and federal plant breeders and entomologists)
working in this area is estimated as 0.50 and 1.40 scientific years, respec-
tively. Table 1 shows these estimates broken down by crop.

CORN
The fall armyworm and other corn insect pests are a major concern of
plant resistance teams of Agricultural Research (SEA, USDA) at Tifton,
GA, and Mississippi State, MS. In addition, the International Maize and
Wheat Improvement Center (CIMMYT) in Mexico has a team that is con-
tributing to the US effort. Researchers in both countries are cooperating by
sharing germplasm, infestation and evaluation techniques, and rearing tech-
niques for the fall armyworm. Recently, the CIMMYT team developed a
simple, efficient, and inexpensive method of plant infestation wherein first-
instar lepidopteran larvae can be used (Mihm et al. 1978).
Also some commercial corn seed companies have demonstrated considera-
ble interest in developing hybrids resistant to the fall armyworm. In fact, 3
companies have entomologists who are rearing this insect and are using it in
their screening and hybrid development programs.
At Tifton, Wiseman et al. 1973 have conducted basic studies on the effect


1Lepidoptera: Noctuidae.










1980 Fall Armyworm Symposium 421

TABLE 1. ESTIMATED SCIENTIFIC EFFORT IN FEDERAL AND STATE AGENCIES IN
THE UNITED STATES CONCERNED WITH IDENTIFYING, DEVELOPING,
AND RELEASING CULTIVARS RESISTANT TO THE FALL ARMYWORM.* **

Estimated SY's
Plant En-
Crop Organization Location Breeder tomologist

Corn AR Tifton, GA 0.10 0.35
Mississippi
State, MS 0.25 0.25
Total 0.35 0.60
Sorghum AR Tifton, GA 0.05 0.10
Peanuts AR Tifton, GA 0.05 0.30
Bermudagrass AR Tifton, GA 0.05 0.30
Rice SAES Beaumont, TX 0.10
Grand
Total 0.50 1.40

*These estimates include only those programs that have CRIS projects which include plant
resistance to the fall armyworm.
**Fall armyworm is one of several insects in which plant resistance research is being con-
lucted within these programs.

of crop fertilizers on the resistance of 'Antigua 2D' to the fall armyworm.
Wiseman et al. (1974, 1980) have developed techniques for artificially infest-
ing corn plants with fall armyworm eggs and larvae that should enhance
identification and development of fall armyworm resistant genotypes. At
Mississippi State, 2 inbreds (Mp496 and Mp703) and 3 populations
(MpSWCB-1, MpSWCB-2, and MpSWCB-4) that have leaf-feeding re-
sistance to the fall armyworm and the southwestern corn borer, Diatraea
grandiosella (Dyar), have been released (Williams, personal communica-
tion). The primary source of this resistance is 'Antigua Groups 1 and 2'.
Also, Williams et al. (1978) have obtained genetic information on the re-
sistant fall armyworm plant genotypes developed in Mississippi. Scott et al.
(1977) reported that resistant hybrids yielded at least twice as much as
susceptible commercial hybrids when the 2 types were planted late in the
summer under large fall armyworm populations.

SORGHUM

Resistance to the fall armyworm in sorghum is being investigated by the
same Tifton team that works on corn. Even though statistical differences
between sorghum lines for leaf-feeding by the fall armyworm have been re-
ported (McMillian and Starks, 1967), the level of resistance is not very high.
Therefore, the Tifton team is in the process of screening seedlings of some
4,000 entries of the world sorghum collection (obtained from CIMMYT and
U.S. Plant Introduction Stations) for a higher source of resistance. A new
infestation procedure developed by Roberson et al. (1978) for this work
should enhance the chances of identifying resistant sources. Agricultural
Research entomologists at Stillwater, OK have also recently begun a limited
screening of sorghum lines for fall armyworm leaf-feeding resistance.











422 Florida Entomologist 63 (4) December, 1980

PEANUTS
Resistance to fall armyworm in peanuts is being studied at Tifton by
another AR plant breeder-entomologist team. Leuck et al. (1967) reported
resistance to a complex of leaf-feeding insects including the fall armyworm
in peanuts. Hammons (1970) registered 'Southeastern Runner 56-15' peanut
cultivar, which exhibits more fall armyworm resistance than any other com-
mercial peanut variety developed in U. S. breeding programs. As a result,
this cultivar was planted on ca. 10-15% of the peanut acreage during the
period (1955-1970) it was grown (Hammons, personal communication).
Leuck and Skinner (1971) showed in laboratory tests that continuous feed-
ing of this insect through 3 successive generations on foliage of 'Southeastern
Runner 56-15' had an adverse effect on the biology of insect because the
larval development period was lengthened and reduced numbers of adults
emerged.

BERMUDAGRASS
Resistance in bermudagrass to the fall armyworm is also being studied
by AR scientists at Tifton, GA. Leuck et al. (1968b) screened 441 bermuda-
grass clones and found 2 to be resistant, 9 to be intermediate in resistance,
and the rest to be susceptible. Leuck and Skinner (1970) compared the de-
velopment and mortality of larvae reared on the susceptible 'Coastal' ber-
mudagrass and on a resistant bermudagrass clone 'Georgia accession No.
239'. They observed higher larval and pupal mortality on the resistance clone.
No releases of fall armyworm resistant bermudagrass cultivars have yet been
made.

RICE
Resistance research concerned with the fall armyworm in rice is now
underway at the Texas Agricultural Experiment Station at Beaumont.
Bowling (1978) simulated feeding by the fall armyworm by artificially re-
moving various portions of the photosynthetic surfaces during the seedling
and tillering stage of growth. Sometime in the future, they plan to begin
screening rice varieties for fall armyworm resistance.
Also, a joint effort by AR scientists at Crowley, LA and scientists at the
Louisiana Agricultural Experiment Station, Baton Rouge has recently been
initiated. These scientists are in the process of greenhouse screening of rice
lines including those that have shown resistance to the rice stalk borer, Chilo
plejadellus Zincken and the sugarcane borer, Diatraea saccharalis.

MILLET

Limited research on resistance in millet to the fall armyworm has been
conducted and is continuing at AR laboratories at Tifton and at Stillwater.
Leuck et al. (1968a) screened 1436 pearl millet inbreds at the seedling stage
for fall armyworm resistance of which 4% were resistant, 28% were inter-
mediate, and 68% were susceptible to larval feeding. Later Leuck (1970)
studied the effect of 1 of these resistant inbreds (No. 240) on the fall army-
worm. He found that the cumulative effects of exposure to the resistant in-
bred resulted in lower pupal weights, longer times to first moth emergence










1980 Fall Armyworm Symposium


and to peak moth emergence, and more days to develop from egg to egg. The
research group in Oklahoma has identified an intermediate resistance source
in Proso millet cultivars (Wilson, personal communication). No releases of
fall armyworm resistant millets have yet been made.

PLANT RESISTANCE PROGRAMS NEEDS AND BENEFITS
Plant resistance researchers asked about their needs or about limiting
factors respond with an array of answers. A major concern among some is
the difficulty in maintaining team continuity when a member is lost because
of retirement, transfer, or resignation. Also concern is expressed about the
need for additional scientists when existing programs become large and
phases of the program must suffer from lack of concentrated attention.
Others have expressed the need for more funds or new funds. There is some-
times need for more rearing capabilities. Infestation and evaluation tech-
niques are mentioned as a limiting factor. Time is another limiting factor
because it takes time to develop new techniques and resistant germplasm.
As most of these comments make plain, plant resistance research is
strictly a team effort, and a given program must extend over many years.
The benefits, however, are great for fellow scientists, farmers and consumers.
New knowledge about the biology of the insect and its interactions with its
host plant (s) (including economic thresholds) is generated. More efficient
techniques of infestation (including artificial rearing) and evaluation are
produced. Most important resistant germplasm is made available that can be
incorporated into cultivars for farmer use.

ACKNOWLEDGEMENTS

The author would like to thank the following scientists who contributed
information about their plant resistance programs:
Corn-W. W. MCMILLIAN, N. W. WIDSTROM, AND B. R. WISEMAN, AR,
SEA, USDA, Tifton, GA; W. P. WILLIAMS, AR, SEA, USDA, Mississippi
State, MS; J. A. MIHM, CIMMYT, Mexico; G. L. BELAND, Funk Seeds In-
ternational, Bloomington, IL; J. E. CAMBELL, Pioneer Hi-Bred, Johnston, IA;
J. L. OVERMAN, DeKalb Ag. Research Inc., Union City, TN.
Sorghum-W. W. MCMILLIAN, N. W. WIDSTROM, AND B. R. WISEMAN, AR,
SEA, USDA, Tifton, GA; R. L. WILSON, AR, SEA, USDA, Stillwater, OK.
Peanuts-R. 0. HAMMONS, AND R. E. LYNCH, AR, SEA, USDA, Tifton,
GA.
Bermudagrass and Millet-G. W. BURTON, AND R. E. LYNCH, AR, SEA,
USDA, Tifton, GA; R. L. WILSON, AR, SEA, USDA, Stillwater, OK.
Rice-C. C. BOWLING, TX Agric. Exp. Sta., Beaumont, TX; C. M. SMITH,
LA Agric. Exp. Sta., Baton Rouge, LA; J. F. ROBINSON, AR, SEA, USDA,
Crowley, LA.

LITERATURE CITED
BOWLING, C. C. 1978. Simulated insect damage to rice: effects of leaf re-
moval. J. Econ. Ent. 71: 377-8.
HAMMONS, R. 0. 1970. Registration of Southeastern Runner 56-15 peanuts.
Crop Sci. 10: 727.
LEUCK, D. B. 1970. The role of resistance in pearl millet in control of the


423










424 Florida Entomologist 63 (4) December, 1980

fall armyworm. J. Econ. Ent. 63: 1679-80.
AND J. L. SKINNER. 1970. Resistance in bermudagrass affecting con-
trol of the fall armyworm. Ibid. 63: 1981-2.
AND 1971. Resistance in peanut foliage influencing fall army-
worm control. Ibid. 64: 148-50.
R. 0. HAMMONS, L. W. MORGAN, AND J. E. HARVEY. 1967. Insect
preference for peanut varieties. Ibid. 60: 1546-9.
-- C. M. TALIAFERRO, R. L. BURTON, AND M. C. BOWMAN. 1968a. Fall
armyworm resistance in pearl millet. Ibid. 61: 693-5.
C. M. TALIAFERRO, G. W. BURTON, R. L. BURTON, AND M. C. BOWMAN.
1968b. Resistance in bermudagrass to the fall armyworm. Ibid. 61:
1321-2.
MCMILLIAN, W. W., AND K. J. STARKS. 1967. Greenhouse and laboratory
screening of sorghum lines for resistance to fall armyworm larvae.
Ibid. 60: 1462-3.
MIHM, J. A., F. B. PEAIRS, AND A. ORTEGA. 1978. New procedures for ef-
ficient mass production and artificial infestation with lepidopterous
pests of maise. In CIMMYT Review. CIMMYT. 138 p.
ROBERSON, W. N., B. R. WISEMAN, AND W. W. MCMILLIAN. 1978. Screening
seedling sorghum for resistance to the fall armyworm. Sorghum News-
letter 21: 98.
SCOTT, G. E., F. M. DAVIS, G. L. BELAND, W. P. WILLIAMS, AND S. B. KING.
1977. Host plant resistance is necessary for late-planted corn. Miss.
Agric. Forest. Exp. Stn. Res. Rep. 3: 1-14.
WILLIAMS, W. P., F. M. DAVIS, AND G. E. SCOTT. 1978. Resistance of corn
leaf-feeding damage by the fall armyworm. Crop Sci. 18: 861-3.
WISEMAN, B. R., AND F. M. DAVIS 1979. Plant resistance to the fall army-
worm. Fla. Ent. 62: 123-30.
--, F. M. DAVIS, AND J. E. CAMPBELL. 1980. Mechanical infestation de-
vice used in fall armyworm plant resistance programs. Fla. Ent. (In
press)
---- D. B. LEUCK, AND W. W. MCMILLIAN. 1973. Effects of fertilizers on
resistance of 'Antigua' corn to fall armyworm and corn ear worm. Fla.
Ent. 56: 1-7.
-- W. W. MCMILLIAN, AND N. W. WIDSTROM. 1974. Techniques, ac-
complishments, and future potential of breeding for resistance in corn
to the corn earworm, fall armyworm and maize weevil; and in
sorghum to the sorghum midge. Pages 381-93 In F. G. Maxwell and
F. A. Harris, eds. Proceedings of a summer institute on biological
control of plant insects and diseases. Univ. Press of Mississippi, Jack-
son, MS.










1980 Fall Armyworm Symposium


425


MECHANICAL INFESTATION DEVICE USED IN
FALL ARMYWORM PLANT RESISTANCE PROGRAMS1,2,3

B. R. WISEMAN4, F. M. DAVIS5, AND J. E. CAMPBELL6

ABSTRACT
A mechanical device called the "Bazooka" was developed by an en-
tomologist of the Centro Internacional de Mejoramiemto de Maiz y Trigo
(CIMMYT) for manually dispensing lepidopterous larvae. Modifications
have been made to fit individual plant-resistance programs for infestations
of fall armyworm, Spodoptera frugiperda (J. E. Smith), southwestern corn
borer, Diatraea grandiosella (Dyar), and the European corn borer, Ostrinia
nubilalis (Hiibner). The implementation of this mechanical larval dispenser
allows its use in the laboratory for rearing insects, in the greenhouse for in-
festing seedlings, and in the field for large or small testing purposes.


Programs in plant resistance to insects have been greatly enhanced by
artificial rearing of the insect (Wiseman et al. 1974, Davis 1976). A pre-
requisite to most initial searches for insect-resistant cultivars, but more
especially for breeding programs for insect resistance, is the development
and use of rapid, artificial infestation techniques (Wiseman and Davis
1979a, b).
Early methods of infesting plants for resistance testing with the fall
armyworm, Spodoptera frugiperda (J. E. Smith), were described by Wise-
man et al. (1974). Use of the very laborious camel hair brush technique to
transfer larvae to plants made large-scale, rapid screening impossible. How-
ever, with other insects such as the southwestern corn borer, Diatraea
grandiosella (Dyar), (Davis 1976) and the European corn borer, Ostrinia
nubilalis (Hiibner), (Guthrie et al. 1965), infestations were made rather
easily with pinned egg masses placed into the whorls of corn plants.
However, it was not until recently that a technical breakthrough occurred
and rapid infestations of lepidopterans could be made. Mihm et al. (1978)
developed a manual larval dispenser (Fig. 1) called the "Bazooka" that could
be pre-calibrated to deliver a uniform amount of larvae mixed with corncob
grits. We wish to illustrate, in chronological order, the modifications that
have been made to the Bazooka.
The Southern Grain Insects Research Laboratory (SGIRL) entomologist
received a copy of the original Bazooka from Centro Internacional de
Mejoramiemto de Maiz y Trigo (CIMMYT) in 1977. Roberson et al. (1978)
modified it for use in evaluations of large numbers of sorghum seedlings.
Problems still existed with breakage and poor dispensing until later modifi-
cations were made (Fig. 2). A stainless steel plate was placed below the
slide mechanism and kept under tension by 2 springs. This procedure pro-

'Lepidoptera: Noctuidae.
21n cooperation with the University of Georgia College of Agriculture Experiment Stations,
Coastal Plain Station, Tifton, GA 31793. Accepted for publication 20 August 1980.
3Mention of a proprietary product in this paper does not constitute an endorsement of this
product by the USDA.
4Southern Grain Insects Research Laboratory, AR, SEA, USDA, Tifton.
'AR, SEA, USDA, Mississippi State, MS 39762.
6Pioneer Hi-Bred International, P. 0. Box 85, Johnston, IA 50131.










426 Florida Entomologist 63 (4) December, 1980
























































Fig. 1. Original Bazooka for rapid infestation of plants with insects.

vided an outlet for the grits that would sometimes accumulate between the
slide and the upper plate. A metal cap was used instead of polyethylene
because the summer heat melted the glue that held the polyethylene cap;
thus, as the glue melted, the bottle and cap were easily dislodged from the
dispenser, spilling grits and larvae over the plants. The outlet hole was re-
Y4',.

.;;.6Q.




L..o.



: f,


?
AA: ".,...
..,:2


ft,-'. .

























dispenser, spilling grits and larvae over the plants. The outlet hole was re-










1980 Fall Armyworm Symposium 427

duced to 6.25 mm in diam. because of problems encountered with absorption
of moisture by the grits, which resulted in a scalding effect on the sorghum
leaves. This small hole allowed a delivery of 0.2 ml of #2040 grits and fall
armyworm larvae. The rubber band was retained to return the slide to the
loading position. The end spout was reduced to a 6.25-mm opening, and a
small funnel was used for delivery into the whorls of small plants. The
opening tip was beveled to prevent the grits and larvae from clogging the
spout. This could happen when infestations were made before the dew
evaporated. Wiseman and Widstrom (1980) have reported on a compari-
son of methods of infesting fall armyworm larvae in whorl-stage corn. They
found that the Bazooka was the easiest and most efficient method tested.
Also, they found that corn plants could be infested 3-4 times faster with the
Bazooka than by pinning egg masses into the whorl.







































Fig. 2. Bazooka as modified by Wiseman for fall armyworm infestation.
...... M,

"' 7.!; M" i "










428 Florida Entomologist 63 (4) December, 1980

At about the same time that the Bazooka was being modified at SGIRL,
CIMMYT made a paddle version (Fig. 3) and sent it to the Corn Host Plant
Resistance Research Unit at Mississippi State, MS, where Davis and Oswalt
(1979) modified it as shown in Fig. 4. Davis and Oswalt called their new
device an inoculatorr." The inoculator uses a side-to-side paddle action in-
stead of the slide-through action of the Bazooka. The delivery hole is 12.5
mm in diam. Davis and Oswalt (1979) illustrated the construction of the
inoculator and estimated its cost at ca. $4.00 for materials and 6 hours of
labor. The inoculator was a significant breakthrough for their southwestern
corn borer resistance investigations for both the laboratory rearing (inocu-
lating diet cups) and later for infesting larvae on the whorl and tassel
stages of corn.








































Fig. 3. Original paddle version of the Bazooka used to infest plants with
insects.









1980 Fall Armyworm Symposium


DAVIS

Fig. 4. Inoculator developed by Davis for inoculating diet cups with the
southwestern corn borer.
In 1978, the entomologist at Pioneer Hi-Bred International received the
Bazooka as modified at SGIRL and made additional streamlining modifica-
tions (Fig. 5). The stainless steel plate was eliminated by use of thicker
pieces of plexiglas and the routing out of the slide groove to a close tolerance.


429









430 Florida Entomologist 63 (4) December, 1980

The use of the thicker plexiglas added balance to the dispenser, made
manipulation with 1 hand easy, and simplified construction and cleaning by
reducing the number of pieces of plexiglas and screws. The slide end was
coated with a rubberized material for prevention of blisters on the fingers
after prolonged use. The rubber band was retained to return the slide to
the loading position. This modified Bazooka has been used successfully in
dispensing European corn borers, fall armyworms, and southwestern corn
borers in Pioneer's insect-resistance programs. For infestation of corn with
these insects, the slide-mechanism outlet hole is 9.37 mm in diam., which
allows a delivery of 0.35 ml of #2040 corncob grits. Cost per unit has been
estimated at ca. $6.00 for materials and 2 hours for labor when built in lots
of 50 or more.


Fig. 5. The Bazooka as modified by Campbell to infest corn plants with the
European corn borer and fall armyworm.









1980 Fall Armyworm Symposium


431


Figures 6 and 7 illustrate the various component parts of the inoculator
and modified Bazooka. Dimensions of the various components may vary de-
pending upon individual needs and characteristics. The inoculator will be
commercially available in the near future.
In summary, we have made individual modifications of a mechanical
lepidopteran larval dispenser in several forms that now allows us to expand
insect-resistance programs in at least 3 different locations for 3 different
lepidopteran pests.

ACKNOWLEDGMENT
We thank Johnny Skinner for modification on the SGIRL Bazooka, and
Margie Mertaugh (illustrator) and Frank Benci of the USDA Boll Weevil
Laboratory for the illustrations.

LITERATURE CITED
DAVIS, F. M. 1976. Production and handling of eggs of southwestern corn
borer for host plant resistance studies. USDA-AR Tech. Bull. 74. 11 p.
DAVIS, F. M., AND T. G. OSWALT. 1979. Hand inoculator for dispensing
lepidopterous larvae. USDA-SEA-SR 9. 5 p.
GUTHRIE, W. D., E. S. RAUN, F. F. DICKE, G. R. PESHO, AND S. W. CARTER.
1965. Laboratory production of European corn borer egg masses.
Iowa State J. Sci. 40: 65-83.
MIHM, J. A., F. B. PEAIRS, AND A. ORTEGA. 1978. New procedures for ef-
ficient mass production and artificial infestation with lepidopterous
pests of maize. CIMMYT Review. 138 p.
ROBERSON, W. N., B. R. WISEMAN, AND W. W. MCMILLIAN. 1978. Screening

PIVOT SCREW CAP
AND NUT



INOCULATOR HANDLE
BODY





PADDLE


EXIT TUBE


Fig. 6. Various components of the Inoculator.









Florida Entomologist 63(4)


BAZOOKA
BODY'


METERING
BAR


RUBBEI
BAND


EXIT TUBE


FUNNEL


Fig. 7. Various components of the modified Bazooka.
seedling sorghum for resistance to the fall armyworm. Sorghum News-
letter 21: 98.
WISEMAN, B. R., AND F. M. DAVIS. 1979a. Plant resistance to the fall army-
worm. Fla. Ent. 62: 123-30.
WISEMAN, B. R., AND F. M. DAVIS. 1979b. A flow chart for plant resistance
to insects investigations. Proc. FAO/IAEA Training Course. 1979,
Univ. of Fla.: 194-5.
WISEMAN, B. R., W. W. MCMILLIAN, AND N. W. WIDSTROM. 1974. Tech-
niques, accomplishments, and future potential of breeding for re-
sistance in corn to the corn earworm, fall armyworm, and maize
weevil; and in sorghum to the sorghum midge. Pages 381-93. In Bio-
logical Control of Plant Insects and Diseases. (Eds.) F. G. Maxwell,
and F. A. Harris. Mississippi State Univ.
WISEMAN, B. R., AND N. W. WIDSTROM. 1980. Comparison of methods of
infesting whorl-stage corn with fall armyworm. J. Econ. Ent. 73:
440-2.


432


December, 1980








































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1980 Fall Armyworm Symposium


433


EMPLOYMENT OF PARASITOIDS AND PREDATORS
FOR FALL ARMYWORM CONTROL1'2

W. JOE LEWIS AND DONALD A. NORDLUND
Southern Grain Insects Research Laboratory
Agric. Res., SEA, USDA
Tifton, GA 31793

ABSTRACT
Although fall armyworm, Spodoptera frugiperda (J. E. Smith), has
numerous natural enemies attacking it, the insect remains an important pest
of many annual row crops and pasturage. Attempts to use natural enemies
to control this pest must take into consideration the characteristics of the
annual row crop agroecosystem. Several approaches including importation
of new species, propagation and release, and resource management are sug-
gested and the qualities of each are discussed.



Previous presentations at these conferences have provided information
concerning the frequency and distribution of many species of natural enemies
that attack the fall armyworm, Spodoptera frugiperda (J. E. Smith). Ashley
(1979), in particular, presented detailed information about the classification
and distribution of the parasitoids and noted that 53 species from 43 genera
and 10 families have been reared from fall armyworm larvae. In addition,
there are numerous predators known to attack this pest, though no summary
dealing with them is available. Since there is obviously an abundance of
natural enemies attacking the fall armyworm, the question at hand is how
can we make more effective use of these important beneficial insects. This
discussion will concentrate on exploring various strategies for employing
these entomophages as pest control agents against this important pest insect.
Suggested approaches for using natural enemies in biological control are
listed in Table 1.

TABLE 1. APPROACHES FOR EMPLOYMENT OF ENTOMOPHAGES FOR FALL ARMY-
WORM CONTROL.

1. Importation of new species
2. Propagation and release
(a) Release throughout overwintering zone
(b) Early-season colonization
(c) Direct therapeutic release
S. Resource management
(a) Optimum propagation, conservation, and utilization through compre-
hensive habitat management
(b) Proper integration of entomophages with other plant protection and
production practices


'Lepidoptera: Noctuidae.
2In cooperation with the Univ. of Ga. College of Agric. Exp. Sta., Coastal Plain Sta.,
Tifton, GA 31793. Accepted for publication 20 August 1980.










Florida Entomologist 63 (4)


IMPORTATION OF NEW SPECIES
Importation of new species of natural enemies certainly deserves con-
sideration since this classical approach has been so successful, particularly in
the more stable types of agroecosystems such as citrus groves. Notable suc-
cesses with this approach against pests in annual row crops, however, are few
(DeBach 1974, van den Bosch and Messenger 1973). Therefore, we strongly
disagree with the general proposition put forth by some biological control
specialists (e.g., DeBach 1974, Sailer 1976) that importation should be given
highest priority and we do not concur with their reservations concerning
augmentation and manipulation. Of course, some of the criticisms of aug-
mentation and manipulation are valid; for example, such approaches will
not alter the basic vulnerability of the target crop (Sailer 1976); also, the
repetitive aspects can make these approaches just as or even more costly than
control tactics employing conventional chemical insecticides (DeBach 1974).
However, we emphatically disagree with the idea that augmentation and
manipulation should have the lowest priority in biological control research
and not be resorted to until it has been determined that importation and con-
servation are inadequate. Rather, we believe that in the case of most major
pests of annual row crops, which involves frequent disturbance of the agro-
ecosystem, augmentation and manipulation procedures are essential to the
effective use of entomophages as biological control agents. In the United
States, this includes such major pests as the corn earworm, Heliothis zea
(Boddie); tobacco budworm, Heliothis virescens (F.); cabbage looper, Tri-
choplusia ni (Hiibner); boll weevil, Anthonomus grandis Boheman; sugar-
cane borer, Diatraea saccharalis (F.); European corn borer, Ostrinia
nubilalis (Hiibner) ; and the fall armyworm.
One of the reasons we believe augmentation and manipulation are es-
sential is that a major factor limiting the effectiveness of entomophages in
annual row crops is the rapidly expanding area of available host-plant sur-
face during the early and mid-growing seasons. Take for an example a hypo-
thetical 1,000-acre farm in the southeastern United States (Fig. 1). It would
not be unreasonable to assume that during the early pre-planting season
(i.e., March-April), there would be only ca. 50 acres on which host plants
would be available for a given pest, whether it be the fall armyworm as it
moves in from its overwintering site or diapausing pests such as Heliothis
spp. These 50 acres would consist primarily of wild host plants growing in
scattered patches. If each ft2 of land surface occupied by host plants pro-
vided 1 ft2 of foliage area, there would be a total of 2,178,000 ft2 of host-plant
surface available during this period. However, during the early growing
season (i.e., May-early June), we could assume 250 acres of host plants with
each ft2 of this surface providing 2 ft2 of foliage area. Consequently, the
total available host-plant surface would have expanded to 21,780,000 ft2.:
During the mid-growing season (i.e., late June and July), we could assume
950 acres of host plants with each ft2 of land surface providing 5 ft2 of
foliage area (Knipling and McGuire 1968). Hence, the total host-plant sur-
face available would have expanded to 206,910,000 ft2, dispersed in an
essentially continuous fashion. Thereafter, the plant surface available to the
pest would level off and later decline. However, the great surge in habitable
space during the early and mid-growing seasons contributes tremendously
to the survival of and thus to the total population buildup of highly mobile


434


December, 1980











1980 Fall Armyworm Symposium


PREPLANTING


50 acres
43,560 ft2 foliage/acre
TOTAL : 2,178,000 ft2


MID GROWTH


950 acres
217,800 ft2 foliage/acre
TOTAL: 206,910,000 ft2


EARLY GROWTH











2 50 acres
87,120 ft2 foliage/acre
TOTAL: 21,780,000 ft2


LATE GROWTH


950 acres
217,800 ft2 foliage/acre
TOTAL : 206,910,000 ft2


Fig. 1. Schematic representation of the available host plant materials
(shaded areas) on a hypothetical 1000 A farm in the Southeastern United
States.

and reproductive pests such as those mentioned. Entomophages must, there-
fore, continuously redistribute themselves to associate with their host or prey,
which exaggerates the typical lag phase in host-parasitoid and predator-prey
relationships. The result is a dramatic limitation of the ability of the
entomophages to maintain the pest population below the economic threshold
(Knipling and McGuire 1968). This effect is particularly true with the fall
armyworm since it apparently lacks any diapause mechanisms (Sparks 1979)
and redisperses each growing season from over-wintering locations in south
Florida, Texas, Mexico, the Caribbean Islands, and possibly more southerly
areas (Luginbill 1928, Sparks 1979).
To further illustrate the effect of the expanding area factor, let us assume
a situation wherein the presence of 1,000 pests and 100 parasitoids/acre re-
sults in 30% parasitization. In a stable arena a 5-fold increase in pests and 1
parasitoid produced/parasitized host, there would be a 3-fold increase in the


435










436 Florida Entomologist 63 (4) December, 1980

parasitoid population (300 parasitoids/acre). Therefore, according to the
data of Knipling and McGuire (1968), assuming random search and a Pois-
son distribution for parasitoid oviposition, an increase to 70% parasitization
would occur the next generation. However, in an arena that expanded 5
times, the result would be a 40% decrease in the parasitoid population (60
parasitoids/acre) and a decrease to 20% parasitization.
Obviously, the expanding space factor alone, though there are numerous
other factors, dramatically limits the ability of entomophagous insects to
prevent pests such as the fall armyworm from exceeding economic thresholds
during the early and mid-growing seasons in annual row crop agroecosys-
tems. In other words, it is not the lack of effective natural enemies but rather
the disruptive effects of modern agronomic methods that lead to outbreaks of
pests such as the fall armyworm. We feel that it is probably ecologically im-
possible for an entomophage to keep the pest below the economic threshold in
annual row crops, when other factors favor an outbreak, without some
manipulative intervention. This is not to say that we should not explore for
new and better natural enemies to incorporate into our programs. Certainly
this should be done. Nevertheless, in the annual row-crop situation, we must
employ augmentation and manipulation techniques.

PROPAGATION AND RELEASE
Mass rearing and release technologies have advanced so greatly that at
least 3 "rear and release" approaches to control the fall armyworm seem
promising: (1) release throughout the overwintering zone, (2) early-season
colonization, and (3) direct therapeutic release on target crops. Two candi-
dates for consideration in all these approaches are Apanteles marginiventris
(Cresson) and Chelonus insularis (Cresson).
The first approach would require a large-scale program designed to re-
lease large numbers of the parasitoids throughout the overwintering zone
when the pest has its most limited distribution. Such a program, if effective,
would dramatically reduce the number of fall armyworms that survive the
winter and would also provide a greatly increased reservoir of parasitoids
that might be able to suppress outbreaks as the spring population moves out
of the overwintering zone. Such a program could be integrated with other
area-wide programs involving autocidal and sex pheromone techniques. A
major difficulty is our limited information concerning the seasonal population
dynamics of the fall armyworm. Lacking this fundamental knowledge, it is
difficult to determine whether such an intensive suppression of the total
population would cause a relaxation of the density-dependent control factors
and result in a dramatic mid- to late-season resurgence.
The second approach of early-season colonization of a selected parasitoid
would have many of the same features as release throughout the overwinter-
ing zone. However, it would be designed primarily to lessen the lag phase in
the parasitoid buildup and distribution.
The third approach, direct therapeutic release of entomophages in indi-
vidual fields on an "as needed" basis, is perhaps the most immediately feasi-
ble technique, and A. marginiventris, in our opinion, is an excellent candi-
date. This species is easy and relatively economical to rear in the laboratory;
it kills the fall armyworm in the early larval stage (P. D. Lingren, personal
communication), and it responds strongly to a kairomone (Lewis and Nord-










1980 Fall Armyworm Symposium 437

lund, unpublished data), as does Apanteles glomeratus (L.) (Sato 1979),
that could be utilized to manipulate its behavioral patterns in the target
area. This approach should be explored intensively in the near future.

RESOURCE MANAGEMENT
Resource management has received the least attention in the past, but it
is perhaps the most feasible overall approach. In addition, such an approach
fits well with the recent thrusts in integrated pest management.
One possibility would be conservation of entomophages by comprehensive
management of the agronomic and cultural practices throughout the total
habitat. This would include proper management of nearby fields and other
habitats so as to encourage the buildup of populations of natural enemies, for
example, proper timing of tillage and other cultural practices that would
encourage the growth of weeds supportive to key entomophages (Altieri and
Whitcomb 1979), artificial application of kairomones (Lewis et al. 1976),
and food sprays (Hagen and Hale 1974, Tassan et al. 1979) to encourage the
buildup of populations of important entomophages.
Another possibility is integration of proper consideration of entomophages
in other plant production and protection practices. The research input into
the development of most plant production and protection techniques is pro-
vided by highly regimented programs within defined specialties with very
limited consideration of the interactions of other components of the cropping
system. For example, host plant resistance research generally requires ex-
tensive breeding and screening, but the results are evaluated only on the
basis of interactions between the plant and the phytophage; little, if any
consideration is given to the potential effects on the third trophic level.
Nevertheless, we know that there are numerous ways in which plants can
affect the performance of entomophages (Vinson 1980). Also, as mentioned
earlier, cultural practices such as irrigation may adversely affect the per-
formance of entomophages and thus should be evaluated on more broadly
based criteria than are presently used. Proper considerations of these vari-
ous interactions can greatly enhance our pest management systems, whereas
failure to adequately consider them can result in negative net effects.
Resource management will require a great deal of additional fundamental
information. However, the exciting recent discoveries in such areas as
nutritional augmentation (e.g., food sprays), behavioral manipulation of
entomophages with kairomones, and the use of weeds to manipulate bene-
ficial insects hold tremendous promise for this approach. Indeed, more than
ever, van den Bosch and Messenger (1973) seem to have been correct in
their statement that "natural enemy manipulations is one of the most
neglected areas of biological control, and yet one of the most promising."

SUMMARY
Although the fall armyworm is attacked by an abundance of natural
enemies, it remains a major pest of many annual row crops. In such an agro-
ecosystem, the ability of entomophages to suppress this and other pests is
limited by the rapidly expanding area of available host-plant surface during
the early and mid-growing seasons. This surging increase in habitable space
requires the entomophages to continuously redistribute and greatly exag-











Florida Entomologist 63 (4)


December, 1980


gerates the typical lag phase in the host-parasitoid and predator-prey rela-
tionships (Knipling and McGuire 1968, Need and Burbuts 1979).
A proper balance of importation of new species, propagation and release,
and resource management should be investigated. For example, explorations
for new species could provide benefit, but some manipulative intervention
will be necessary if these agents are to achieve effective suppression. The
many recent advances in mass rearing and release technologies and the im-
proved understanding of factors that affect host-parasitoid interrelationships
provide tremendous encouragement for the propagation and release and re-
source management approaches.

LITERATURE CITED
ALTIERI, M. A., AND W. H. WHITCOMB. 1979. The potential use of weeds in
the manipulation of beneficial insects. Hort. Sci. 14: 12-8.
ASHLEY, T. R. 1979. Classification and distribution of fall armyworm para-
sites. Fla. Ent. 62: 114-23.
DEBACH, P. 1974. Biological Control by Natural Enemies. Cambridge Univ.
Press. London. 323 p.
HAGEN, K. S., AND R. HALE. 1974. Increasing natural enemies through use
of supplementary feeding and non-target prey. Pages 170-81. In F. G.
Maxwell and F. A. Harris, Eds. Proceedings of the Summer Institute
on Biological Control of Plant Insects and Diseases. Univ. Press of
Mississippi, Jackson. 647 p.
KNIPLING, E. F., AND J. U. McGUIRE, JR. 1968. Population models to ap-
praise the limitations and potentialities of Trichogramma in managing
host insect population. USDA Tech. Bull. 1387. 44 p.
LEWIS, W. J., R. L. JONES, H. R. GROSS, JR., AND D. A. NORDLUND. 1976. The
role of kairomones and other behavioral chemicals in host finding by
parasitic insects. Behavi. Biol. 16: 267-98.
LUGINBILL, P. 1928. The fall armyworm. USDA Tech. Bull. 34. 92 p.
NEED, J. T., AND P. P. BURBUTS. 1979. Searching efficiency of Trichogramma
nubilale. Environ. Ent. 8: 224-7.
SAILER, R. I. 1976. Principles and techniques of biological control. Pages
8-14. In P. L. Brezonik and J. L. Fox, Eds. Proceedings of a Sym-
posium on Water Quality Management Through Biological Control.
Rep. NEV 07-75-1. Dept. of Environmental Engineering Sciences,
Univ. Fla., Gainesville, FL.
SATO, Y. 1979. Experimental studies on parasitization by Apanteles
glomeratus. IV. Factors leading a female to the host. Physiol. Ent.
4: 63-70.
SPARKS, A. N. 1979. A review of the biology of the fall armyworm. Fla. Ent.
62: 82-7.
TASSAN, R. L., K. S. HAGEN, AND E. F. SAWALL, JR. 1979. The influence of
field food sprays on the egg production rate of Chrysopa carnea.
Environ. Ent. 8: 81-5.
VAN DEN BOSCH, R., AND P. S. MESSENGER. 1973. Biological Control. Intext
Educational Publishers. New York. 180 p.
VINSON, S. B. 1980. Habitat location. In D. A. Nordlund, R. L. Jones, and
W. J. Lewis, Eds. Semiochemicals: Their Role in Pest Control. Wiley,
New York. (In press)


438










1980 Fall Armyworm Symposium 439

PATHOGENS FOR THE SUPPRESSION OF THE
FALL ARMYWORM1

WAYNE A. GARDNER2 AND JAMES R. FUXA3

ABSTRACT
The fall armyworm, Spodoptera frugiperda (J. E. Smith), is susceptible
to at least 16 species of entomogenous pathogens including viruses, fungi,
protozoa, nematodes, and a bacterium. Many of these occur naturally in fall
armyworm populations. Some cause natural epizootics. The few attempts to
suppress fall armyworm populations on agricultural crops by application of
pathogens have had various degrees of success.


Entomogenous pathogens may be used to suppress insect populations in
at least 3 ways: (1) optimization of naturally-occurring diseases, (2) intro-
duction and colonization of pathogens into insect populations as natural regu-
latory agents, and (3) repeated applications of pathogens as microbial in-
secticides. Attempts to suppress fall armyworm, Spodoptera frugiperda
(J. E. Smith), populations thus far have been restricted to the use of
microbial insecticides.
This paper summarizes published data on known pathogens of the fall
armyworm (FAW) and their use in minimizing FAW damage. Any omis-
sions are our responsibility and are unintentional. A major portion of the
available literature deals with host susceptibility to various pathogens and
the natural occurrence of pathogens. Relatively few attempts to apply
pathogens for FAW control are recorded.

SUSCEPTIBILITY
The FAW is reported to be susceptible to viruses, fungi, protozoa, nema-
todes, and 2 strains of the bacterium Bacillus thuringiensis Berliner (Table
1). The pathogens vary in their occurrence, distribution, and pathogenicity.
Some, like the nuclear polyhedrosis virus, are quite common and frequently
cause natural epizootics. Others have been observed only as infections in-
duced in the laboratory. Pathogenicity may range from very high with high
mortality rates to the production of only chronic effects. The spectrum of
pathogens to which the FAW is susceptible likely will grow as new investiga-
tions are published.

NATURAL OCCURRENCE

Several pathogens have been observed as natural regulatory agents in
FAW populations. A "polyhedrosis," presumably S. frugiperda nuclear poly-
hedrosis virus (SFNPV), was reported as early as 1915 (Chapman and
Glaser 1915, Allen 1921, Luginbull 1928). Harned (1920/21) stated that the

'Lepidoptera: Noctuidae. Received for publication 20 August 1980.
'Assistant Professor, Department of Entomology, Georgia Experiment Station, University
of Georgia, Experiment 30212.
'Assistant Professor, Department of Entomology, Agr. Exp. Sta., Center for Agr. Sciences
and Rural Development, Louisiana State University, Baton Rouge 70803.












Florida Entomologist 63 (4)


December, 1980


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Florida Entomologist 63 (4)


disease helped prevent a FAW outbreak in Mississippi in 1920. Other reports
are from South America (Steinhaus and Marsh 1962) and Puerto Rico
(Kuno 1979).
A granulosis virus of FAW (SFGV) was first identified by Steinhaus
(1957) from larvae collected on corn in Colombia, South America. Incidences
of natural double infections with SFGV and either SFNPV or microsporidia
have been reported (Weiser 1959, Steinhaus and Marsh 1962).
Recent observations indicate the incidences of SFNPV and SFGV to be
as high as 38% and 16%, respectively, in FAW attacking sorghum in
Georgia (R. D. Schwehr and W. A. Gardner, unpubl.) and 80.6% and 4.5%,
respectively, in Louisiana pastures (J. R. Fuxa, unpubl.).
Fungi also are important natural mortality factors in FAW populations.
Three species have occurred in FAW attacking sugarcane and other crops in
Puerto Rico. These are Entomophthora sphaerosperma Fresenius (Charles
1941), Nomuraea (Botrytis or Spicaria) rileyi (Farlow) Sampson (Lugin-
bill 1928, Wolcott 1955), and Empusa sp. (probably Entomophthora sp.)
(Luginbill 1928).
Entomophthora aulicae (Reich.) Sorok. recently was observed causing
19-40% mortality levels in FAW and other noctuids on grain sorghum in
southern Georgia (Hamm 1980). Nomuraea rileyi also causes FAW mortal-
ity in small grains, bermudagrass (P. B. Martin, personal communication4)
and sorghum (Schwehr and Gardner, unpubl.) in Georgia.
The natural occurrence of 1 nematode, Hexamermis sp., in FAW larvae
was reported from Venezuela (Guagliumi 1962). The only protozoan reported
to occur naturally in FAW is Nosema laphygmae Weiser, a microsporidium
from Colombia (Weiser 1959).
The effect of naturally-occurring pathogens is most evident in epizootics
of diseases. Natural epizootics in FAW populations have been caused by
SFNPV, E. sphaerosperma, E. aulicae, and N. rileyi. Initiation and develop-
ment of such epizootics are governed by a complex of factors such as host
population density, host behavior, pathogen inoculum quantity, and environ-
mental conditions. The effect of pathogens in the enzootic stage is less ob-
vious, but they may cause mortality, interference with development and re-
production, or lowered resistance to insecticides or other mortality factors
(Falcon 1971). Utilization and manipulation of naturally-occurring path-
ogens represent viable FAW control tactics.


FIELD APPLICATIONS

Four entomogenous pathogens have been applied to cabbage or corn for
the control of FAW (Table 2). Their effectiveness in suppressing damage
appears dependent on timing of the pathogen application because the larvae
begin to burrow and feed within plant structures as they grow older and as
the host plant develops. Thus coverage, contact of the target pest with an
effective inoculum, and larval size (age) become limiting factors to effective
control.


4Assistant Professor, Department of Entomology-Fisheries, Coastal Plain Experiment Sta-
tion, University of Georgia, Tifton 21794.


442


December, 1980P










1980 Fall Armyworm Symposium


TABLE 2. RESULTS OF FIELD APPLICATIONS OF ENTOMOGENOUS PATHOGENS TO
SUPPRESS FALL ARMYWORM.

Formu-
Pathogen lation* Crop Results** Citations

Spodoptera frugiperda
NPV S corn Young and Hamm
1966
S corn + + Hamm and Young
1971
Metarrhizium anisopliae
(Metch.) Sorok. G corn + + Villacorta 1976
Bacillus thuringiensis
Berliner S cabbage + Creighton et al.
1964
S corn Janes and Greene
1969
S,D cabbage -,+ + Creighton et al.
1970
S corn Greene and Janes
1970a
S corn + Greene and Janes
1970b
S cabbage + + Creighton et al.
1972
S corn + Janes 1973
Neoaplectana carpocapsae
Weiser S corn + + Landazabal et al.
1973

*S spray, G = granular, D = dust.
**- = ineffective control, + effective control only with additional oils or chemical in-
secticides, + + effective control.

FUTURE RESEARCH

Research into microbial control of FAW should initially concentrate on
field and laboratory development of candidate pathogens including
Autograph NPV, N. rileyi, and Vairimorpha necatrix (Kramer) among
others. Further efficacy experiments are needed for the agents that have al-
ready been tested. Bacillus thuringiensis var. kurstaki, the variety now used
in commercial formulations because of its great virulence, apparently has
not yet been field tested against FAW. Searches in foreign countries as well
as the U.S.A. should continue for pathogens and strains with great virulence
for FAW.
Formulation and application will undoubtedly be important in improving
efficacy of microbial control agents. Oils and spreading agents have already
enhanced efficacy against FAW (Creighton et al. 1964, Janes 1973). Current
research is concerned with application equipment, baits, and adjuvants.
Granules probably will be given greater consideration due to the ease with
which they may be formulated with baits or other adjuvants (Yearian 1978).
Additionally, granules or dusts may carry the pathogen more deeply into the
plant structure where FAW tends to feed. It will be necessary to develop


443










444 Florida Entomologist 63 (4) December, 1980

adjuvants for protection of microbial control agents because entomopathogens
from all the major groups of microorganisms are sensitive to environmental
factors, particularly sunlight and humidity (Ignoffo and Hostetter 1977).
In addition to evaluation and enhancement of field efficacy, other research
will be required if FAW pathogens other than B. thuringiensis are to be
registered for insect control (Ignoffo 1973, Falcon 1976). To assure quality
control the microbial agent must be identified and characterized by morpho-
logical, biochemical, serological, or bioassay techniques. Methods must be
developed for mass production. Safety for non-target organisms, particularly
mammals, must be demonstrated. At present no FAW pathogen other than
B. thuringiensis is near registration though some, like N. rileyi and V.
necatrix, are subjects of current research for control of other pests (Ignoffo
1980, Maddox et al. 1980). Some of the necessary laboratory work with
pathogens specific for FAW has begun and should be continued. For example,
SFNPV and SFGV can be mass-produced in live hosts (Ignoffo 1966, Ignoffo
and Hink 1971), and the NPV has the potential to be produced in cell cul-
tures (Goodwin et al. 1970, Goodwin et al. 1973, Gardiner and Stockdale
1975). Characterization of SFNPV and SFGV DNA and of SFNPV in-
clusion bodies has begun (Dougherty and Faust 1969, Summers and Ander-
son 1972, Faust et al. 1973). Initial tests indicate that the SFNPV is safe
to mammals (Heimpel 1971). Differential susceptibility to SFNPV has been
observed between 2 strains of FAW (Reichelderfer and Benton 1974).
Finally, as pathogens are developed for FAW control, further research
will be necessary to efficiently integrate them with other crop-production
practices and pest management systems. Further research into the biology
of FAW, particularly behavior and population dynamics, will help pinpoint
timing and placement of control applications. Efforts should be made to
predict and manipulate natural epizootics and to attempt classical, long-term
biocontrol with entomopathogens.

LITERATURE CITED
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1980 Fall Armyworm Symposium 445

---- T. L. MCFADDEN, AND J. V. BELL. 1970. Pathogens and chemicals
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control. Ann. Rev. Ent. 21: 305-24.
FAUST, R. M. 1974. Bacterial diseases. Pages 87-183 In G. E. Cantwell, ed.,
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Spodoptera eridania, and S. frugiperda to Beauveria bassiana. J. Ga.
Ent. Soc. 13: 214-22.
-- R. M. SUTTON, AND R. NOBLET. 1977. Persistence of Beauveria
bassiana, Nomuraea rileyi, and Nosema necatrix on soybean foliage.
Environ. Ent. 6: 616-8.
GOODWIN, R. H., J. L. VAUGHN, J. R. ADAMS, AND S. J. LOULOUDES. 1970.
Replication of a nuclear polyhedrosis virus in an established insect cell
line. J. Invert. Path. 16: 284-8.
- --- AND 1973. The influence of insect cell lines
and tissue culture media on baculovirus polyhedra production. Ent.
Soc. Amer. Misc. Publ. 9: 66-72.
GREENE, G. L., AND M. J. JANES. 1970a. Insecticides for budworm control in
central and south Florida. Proc. Fla. St. Hort. Soc. 83: 168-70.
--, AND 1970b. Control of budworms on sweet corn in central
and south Florida. J. Econ. Ent. 63: 579-82.
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Sorokin no control "cigarrinha de folha", Mahanarva posticata
(Stal.) no Nordeste de Brasil. Bol. Teen. CODECAP, Recife 3. 45 p.
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of sorghum. J. Invert. Path. In Press.
AND J. R. YOUNG. 1971. Value of presilk treatment for corn earworm
and fall armyworm in sweet corn. J. Econ. Ent. 64: 144-6.
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Florida Entomologist 63 (4)


trol of Insects and Mites. Academic Press, N.Y.
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sect Colonization and Mass Production. Academic Press, N.Y.
1973. Toward registration of a viral insecticide. Ent. Soc. Amer.
Misc. Publ. 9: 57-61.
1980. The fungus Nomuraea rileyi as a microbial insecticide. In
H. D. Burges, ed., Microbial Control of Pests and Plant Diseases 1970-
1980. Academic Press, N.Y. In Press.
AND W. F. HINK. 1971. Propagation of arthropod pathogens in
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AND D. L. HOSTETTER, eds. 1977. Environmental stability of micro-
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BIEVER, AND W. A. DICKERSON. 1976. Natural biotic agents controlling
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on sweet corn ears in south Florida. J. Econ. Ent. 66: 973-4.
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Pseudaletia unipuncta (Haworth). Unpubl. Ph.D. Diss., Dept. of
Entomology, Univ. of Illinois, Urbana.
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446


December, 1980










1980 Fall Armyworm Symposium 447

Soc. Ent. Bras. 5: 102-4.
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of corn earworm and fall armyworm in sweet corn. J. Econ. Ent. 59:
382-4.



SUPPRESSION OF FALL ARMYWORM1 POPULATIONS
BY INCORPORATION OF INSECTICIDES
INTO IRRIGATION WATER2

J. R. YOUNG
Southern Grain Insects Research Laboratory,
Agric Res., SEA, USDA, Tifton, GA 31793

ABSTRACT
Larvae of the fall armyworm, Spodoptera frugiperda (J. E. Smith), in-
festing corn were controlled when chlorpyrifos + oil was applied in irrigation
water with a center-pivot irrigation system. Control was achieved with 0.1
and 0.3 in (2700 and 8100 gal) water/acre.


Control of the fall armyworm, Spodoptera frugiperda (J. E. Smith), on
corn is difficult with ground or aerial application techniques now available
(Young 1979). Applications are currently made with the maximum amounts
of water (aerial 2-5 and ground 10-50 gal/acre) that can be applied eco-
nomically. This quantity of water gives poor penetration through the plant
canopies of mature corn, soybeans, etc., and thus does not give adequate con-
trol without multiple applications (Deonier 1955). This inability to eco-
nomically control the fall armyworm has resulted in major losses in late-
planted corn, sorghum, and other susceptible crops, when high populations of
the fall armyworm are present.
Since irrigation is used increasingly in the Southeast, Young et al. (in
press) suggested that irrigation water be used as a carrier for the insecti-
cide, thereby supplying the volume of liquid needed to penetrate all recesses
of the plant or sites where fall armyworm feed.
Initially, a water-soluble insecticide, methomyl, was used with a set irriga-
tion system (Young et al. in press, Hare et al. 1979). Fall armyworm control,
as measured by the percentage decrease in numbers of infested plants, was

'Lepidoptera: Noctuidae.
21n cooperation with the University of Georgia College of Agric. Exper. Stn., Coastal Plain
Stn., Tifton, GA 31793. Received for publication 20 August 1980.










448 Florida Entomologist 63 (4) December, 1980

only 47% in experiments with methomyl applied at a rate of 0.5 lb AI/acre in
0.0625-0.5 in water/acre and 90% with the same rate of methomyl applied
with ground equipment in 50 gal water. Earlier researchers found that oil
formulations gave better insect control (English 1928, Hoskins and Ben-
Amotz 1938, Pierce et al. 1948). Therefore, we used oil formulations in the
irrigation applications so that the insecticide solution would have a high
affinity for the insect and plant and a minimum affinity for the water.
Young et al. (in press) evaluated control of the corn earworm in spring-
planted sweet corn by means of a formulation of carbaryl in oil (Sevin-4-oil)
without an emulsifier. The carbaryl was metered into either a center-pivot or
cable-tow irrigation system. Results of this study indicated that significant
control could be obtained with either system with water-insoluble formula-
tions applied in irrigation water.
Reported herein are results of 2 sets of experiments conducted to evaluate
the potential of this concept to control the fall armyworm.


EXPERIMENTS AND RESULTS

Experiment 1.-To determine whether chlorpyrifos would control the fall
armyworm through applications with irrigation water, treatments were ap-
plied to corn at various times during the growing season. Pioneer 'X-304C'
field corn was planted in late July in test fields (near Tifton, GA). Chlor-
pyrifos (as Lorsban 4EC) was added to a non-emulsified paraffinic crop
spray oil (Cropspray 7N, Suntec, Inc., Marcus Hook, PA 19061) to give 0.5
lb AI in 1 pint of oil/acre. This formulation was applied at 10, 21, 35, and 40
days post-planting so that applications coincided with infestation counts dur-
ing the vegetative stage and at tasseling. The chlorpyrifos was metered into
a 16-acre center-pivot irrigation system, calibrated to deliver 0.1 in of water/
acre. A control was not used in this experiment since corn planted in July
will be destroyed without insecticide treatments.
Results of this experiment indicated that corn was protected from eco-
nomic damage with only 4 applications of chlorpyrifos during the growing
season (Fig. 1). The fall armyworm population, though relatively light in
1979 (personal observation), was held to less than 30% infested plants by
timing the applications to the plant growth and infestation levels. With
larger populations (50% or more plants infested), additional applications
probably would be needed for equal control levels.
Experiment 2.-To determine the role of oil and/or non-emulsified formu-
lations in insect control, we conducted a trial with a 200+ acre irrigation
system that applied 0.3 in (8100 gal) water/acre. 'Pioneer X-304C' field corn,
which had been planted 8 August, was treated with chlorpyrifos formulated
as Lorsban 4E + water, Lorsban 4E + oil (Cropspray 7N), or Lorsban Tech
+ oil. Rates of 0.5 lb/acre, plus sufficient carrier to equal 2 pints/acre, were
applied to pie-slice-shaped portions of ca. 10 acres/treatment plot, with 2
replications of each treatment. Each solution was metered into the water
stream continuously during the passage of the center-pivot over each treat-
ment area. For a check, ca. 15 acres were left untreated except for irrigation
with water only. We determined control by choosing 4 areas at random from
each replication within each treatment and counting larvae on consecutive
plants until at least 100 larvae, either dead or alive, were encountered. Ten











1980 Fall Armyworm Symposium


FAW


7-10. 7-20
JULY


T TI_ T T


849 8-19
AUGUST


Fig. 1. Mean percentage infested corn plants ('Pioneer X-304C') following
treatments (T) of 0.5 lbs AI of chlorpyrifos (Lorsban 4E) plus 1 pint crop
spray oil.

days after the 1st application and 2 days after a 2nd application, 100 con-
secutive plants in 4 areas of each replication within each treatment were ex-
amined for damage, which was indicated by fresh feeding in the whorl.
Results of this experiment appear in Table 1. Two factors need to be
considered in evaluations of these results: 1) the corn had been treated previ-
ously with methomyl by use of ground equipment, which had left primarily
large larvae that produced extreme damage and caused leaves to fold over,
encasing the larvae within the plant tissues and effectively protecting them
from insecticides, and 2) fall armyworm populations had already begun to


TABLE 1.


CONTROL OF FALL ARMYWORMS INFESTING PIONEER 'X-304C' FIELD
CORN WITH 3 SOLUTIONS OF CHLORPYRIFOS APPLIED IN 0.3 IN IRRI-
GATION WATER WITH A 200+ A CENTER-PIVOT IRRIGATION SYSTEM.
CORN AT PRETASSEL STAGE OF GROWTH (IX-11-79).


Mean % Mean %
mortality reduction in
Treatment (24 hr) infested plants*


Chlorpyrifos EC + water 50 b 95 a
Chlorpyrifos EC + oil (1 pt/A) 63 b 90 a
Chlorpyrifos Tech + oil (1.3 pt/A) 94 a 97 a
Check 0 c 29 b

*Following application of a 2nd treatment (IX-18-79) of 0.5 lb Tech + oil to all treatment
areas except control on IX-20-79, or 10 days following the first application.


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