Title: Florida Entomologist
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Title: Florida Entomologist
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Place of Publication: Winter Haven, Fla.
Publication Date: 1986
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FLORIDA ENTOMOLOGIST

(An International Journal for the Americas)

Volume 69, No. 3 September, 1986

TABLE OF CONTENTS

1985 FALL ARMYWORM SYMPOSIUM
Hollywood, FL
WISEMAN, B. R., AND W. A. GARDNER-Preface ...................................... 451
MITCHELL, E. R.-USDA Technical Bulletin No. 34-The Legacy of Phillip
Luginbill ............................................................... 452
Migration and Population Dynamics
RAULSTON, J. R., AND COWORKERS-Fall A ,, ...r. Distribution and Popu-
lation Dynamics in the Texas-Mexico Gulf Coast Area ...................... 455
PAIR, S. D., J. R. RAULSTON, A. N. SPARKS, J. K. WESTBROOK, AND G. K.
DoUCE-Fall Armyworm Distribution and Population Dynamics in the
Southeastern States .................................................. .................. 468
LINDUSKA, J. J., AND F. P. HARRISON-Adult Sampling as a Means of Predict-
ing Damage Levels of Fall Armyworm (Lepidoptera: Noctuidae) in Grain
C orn ..................................... .. .... ... .............. .. ................. 487
WESTBROOK, J. K., AND A. N. SPARKS-The Role of Atmospheric Tr,,spoirt in
the Economic Fall Armyworm (Lepidoptera: Noctuidae) Infestations in
the Southeastern United States in 1977 ......................... ................ 492
Biological Control
GROSS, H. R., JR., AND S. D. PAIR-The Fall Armyworm: Status and Expecta-
tions of Biological Control with Parasitiods and Predators .................. 502
ASHLEY, T. R.-Geographical Distributions and Parasitization levels for Para-
sitiods of the Fall Armyworm, Spodoptera frugiperda ........................ 516
HAMM, J. J., S. D. PAIR, AND 0. G. MARTI, JR.-Incidence and Host Range
of a New Ascovirus from Fall Armywomn, Spodoptera frugiperda
Lepidoptera: Noctuidae) .................................................... ........... 524
GARDNER, W. A., A. F. PENDLEY, AND G. K. STOREY-Interactions Between
Bacillus thuringiensis and Its Beta-Exotoxin in Fail Armnyworn (Lep-
idopterra: Noctuidae) Neonate Larvae ....................... ............... 531
Plant Resistance
OVERMAN, J. L.-Resistance in Corn (Zea mays) to the Fall Armi'yorm
(Spodoptera frugiperda): The Impact of Public Research on Commercial
Seed Com panies ........................................................ ............ .. 537
HAMM, J. J., AND B. R. WISEMAN-Plant Resistance and Nuclear Polyhedro-
sis for Suppression of the Fall Armyworn (Lepodcoptera: Noctuidae) .... 341
BUNTIN, G. D.-A Review of Plant Response to Fall ArmUyorm, Spodoptera
frugiperda, Injury in Selected Field and Forage Crops ........................ 49
WISEMAN, B. R., R. E. LYNCH, K. L. MIKOLAJCZAK, AND R. C. GUELDNER-
Advancements in the Use of a Laboratory Bioassay for Basic Host Plant
Resistance Studies ....................................................... .......... .. 559
PAIR, S. D., B. R. WISEMAN, AND A. N. SPARKS-Influe nce of Four Cor,
Cultivars on Fall Armyworm (Lepidoptera: Noctaidae) Establislhmnt
and Parasitization ....................................................... .... 566

Continued on Back Corcr

Published by The Florida Entomological Society













FLORIDA ENTOMOLOGICAL SOCIETY




OFFICERS FOR 1985-86
President .. ................ ......... ........... .... .. ............ D. J. Schuster
P resident-E lect .................................................................... ..... J. L Taylor
V ice-P resident .................................................................... R S. Patterson
Secretary ...... ..................... ................................ E. R. Mitchell
Treasreer ... .......... ............. .................... A. C. Knapp


M. L. Wright, Jr.
J. E. Eger, Jr.
Other Members of the Executive Committee ..................L. S. Osborne
G. Mathurin
A. Gettman
C. G. Witherington
J. R. McLaughlin


PUBLICATIONS COMMITTEE


E editor .... ... .... ..................... ....... ....... ....... ......... J. R M cLaughlin
A associate E ditors ............................................................................. A A li
C. S. Barfield
J. B. Heppner
M. D. Hubbard
O. Sosa, Jr.
H. V. Weems, Jr.
W. W. Wirth
Business Manager ............ ............... .............. A. C. Knapp

FLORIDA ENTOMOLOGIST is issued quarterly-March, June, September, and De-
cember. Subscription price to non-members is $30.00 per year in advance, $7.50 per
copy. Membership in the Florida Entomological Society, including subscription to Flor-
ida Entomologist, is $25 per year for regular membership and $10 per year for students.
Inquires regarding membership, subscriptions, and page charges should be addressed
to the Business Manager, P. O. Box 7326, Winter Haven, FL 33883-7326. Florida
Entomologist is entered as second class matter at the Post Office in DeLeon Springs
and Winter Haven, 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 acknowledged 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. Page charges are assessed for printed articles.
Manuscripts and other editorial matter should be sent to the Editor, JOHN R.
McLAG(;HLIN, 4628 NW 40th Street, Gainesville, FL 32606.


This issue mailed October 10, 1986











Wiseman & Gardner: Preface


PREFACE

NOTE: Reprints of each paper of the Fall Armyworm Symposium are available from
the respective authors.


This symposium on the fall armyworm was the fourth formal conference devoted
entirely to this particularly important polyphagous insect pest. Three previous symposia
were held in conjunction with the 1980, 1982, and 1984 annual meetings of the Southeast-
ern Branch of the Entomological Society of America. In addition, informal conferences
have been held and formal papers presented at the Southeastern Branch meetings on
odd-numbered years.
It is indeed fitting that this fourth symposium be dedicated to Philip Luginbill,
author of USDA Bulletin No. 34 entitled "The Fall Armyworm." We trust that this
symposium, which will include topics of migration, population dynamics, biocontrol,
host plant resistance, and chemical control, honors an agricultural scientist whose early
research on the fall armyworm provides strong basis for much of our present endeavors.
We hope that a precedent has been set to honor a scientist at each of our formal
symposia.
We envision that each future symposium will likewise inspire research scientists to
seek the identity of factors which enabled the fall armyworm to obtain pest status, and
in doing so, to develop new, lasting, environmentally sound management strategies
which will eliminate or at least reduce its impact on production of agricultural crops.
We are indebted to Drs. Tom Helms, Section F Chair, and George Shambaugh,
Program Chair of ESA's National Conference, for the opportunity to arrange this sym-
posium for the national conference at Hollywood, Florida in 1985.
B. R. WISEMAN
W. A. GARDNER










Florida Entomologist 69(3)


USDA TECHNICAL BULLETIN NO. 34-
THE LEGACY OF PHILIP LUGINBILL

EVERETT R. MITCHELL
Insect Attractants, Behavior, and Basic Biology Research Laboratory,
Agricultural Research Service, U. S. Department of Agriculture,
Gainesville, Florida 32604

ABSTRACT

Philip Luginbill's 1928 treatise on the fall armyworm, Spodoptera frugiperda (J. E.
Smith), long has been considered the source for authoritative information on the biology
and dynamics of this pest. What makes Bulletin No. 34 so special? The information
presented on the life history and habits of the fall armyworm is interesting and amaz-
ingly accurate as verified by numerous publications over the past half century. In view
of Bulletin No. 34 and all that has been written on the fall armyworm since 1928, one
cannot help but wonder why we are not further along in our efforts to control or
suppress this pest.

RESUME

La disertacion de Philip Luginbills en 1928 sobre el gusano cogollero, Spodoptera
frugiperda (J. E. Smith), ha sido considerada por much tiempo una fuente autoritativa
de informaci6n sobre la biologia y el dinamismo de esta plaga. i,Que hace al Boletin No.
34 tan especial?. La information presentada sobre la historic de la vida y habitos del
gusano cogollero es interesante y asombrosamente precisa, como se ha verificado en
numerosas publicaciones durante el fltimo medio siglo. En vista del Boletin No. 34 y
todo lo que se ha escrito sobre el gusano cogollero desde 1928, uno no puede evitar
preguntarse el por que no estamos mAs adelantados en nuestro esfuerzo para controlar
o suprimir esta plaga.



Who was Philip Luginbill? In my quest to gather information on the man to whose
memory we dedicate the 1985 Fall Armyworm Symposium, I came across this cryptic
notation in the 1959 edition of American Men of Science:

LUGINBILL, DR. PHILIP, 107 W. Fowler St., West Lafayette, Ind. EN-
TOMOLOGY, Columbus Grove, Ohio, Oct. 16, 84; m. 09; c. 5. B.S.A., Ohio
State, 10; M.A., South Carolina, 17; Ph.D. (biol), George Washington, 24.
Teacher, pub. schs. Ohio 04-06; sr. entomologist, div. cereal & forage insects,
bur. entomol. & plant quarantine, U. S. Dept. Agr., 10-50, in charge research lab;
RETIRED. A.A.; assoc. Asm. Econ. Entom; fel. Entom. Soc. Am; S.C. Acad;
Ohio Acad; Ind. Acad. Life histories of cereal and forage insects; Phyllophaga.

In the original publication, the citation measures approximately 80 x 18 mm-not
much type space for someone who devoted virtually his entire professional career of
40+ years to solving entomological problems of cereal and forage crops.
Although Dr. Luginbill could be cited for his accomplishments in several areas, I


September, 1986











Mitchell: Fall Arm'iyworm Sympiiin i iI


chose to look at the man from the perspective of his most notable contribution insofar
as this symposium is concerned-USDA Technical Bulletin No. 34, The Fall Armyworm
(Luginbill 1928). This bulletin is among the most widely cited of all publications on the
fall armyworm, Spodopterafrugiperda (J. E. Smith), and there are more than 1,300 (T.
R. Ashley, personal communication). What then is so special about Bulletin No. 34?
As I read through the bulletin, it occurred to me that under our present peer review
system and standards for scientific publications, this particular work probably would
be unacceptable to all but the most understanding of editors and liberal reviewers.
Why? First, the work would be considered too broad in scope. It covers the taxonomy,
morphology, origin and distribution, economic importance, causes conducive to out-
breaks, food plants, life history and habits, and control of the fall armyworm. There
also are sections on the parasitoids, hyperparasitoids, predators, and pathogens of the
fall armyworm. Secondly, there is no statistical analyses of the data; and the data given
are in detail uncharacteristic of present-day scientific publications. Third, Dr. Luginbill
had the audacity to sprinkle his discussion of the facts with personal opinions and
speculation. For example, on the origin and distribution of the fall armyworm he said,
"Outbreaks, when general and severe, apparently originate in Mexico and the West
Indies." He made this statement without proof of such movement, i.e, he never saw
fall armyworm moths actually flying across the water from the Caribbean Islands or
Mexico into the United States. To this date, we do not have proof of such movement-
but circumstantial evidence then and now indicates that Dr. Luginbill probably was
correct.
In spite of the rather primitive conditions, by today's standards, under which Dr.
Luginbill and his colleagues had to conduct research, the information presented on the
biology, habits, and distribution of the fall armyworm and its natural enemies are amaz-
ingly accurate. For example, he described the causes conducive to fall armyworm out-
breaks thusly:

The probability of a general invasion of the fall armyworm in the United
States depends to a large extent upon the prevailing weather conditions during
the winter months in the region where the insect is a permanent resident. This
insect thrives best during periods of cool weather, with an abundance of rainfall.
Such conditions are favorable not only for a luxurious growth of grasses and
other closely allied plants, but are known to check the multiplication of natural
enemies, thus permitting the pest to propagate unhampered in enormous num-
bers. By the time conditions become favorable for the multiplication of natural
enemies, the insect has gotten beyond biological control, migrated northward,
and invaded the more northerly regions of the United States. If humid weather
conditions prevail great damage to various crops may result. During seasons
when no general invasion occurs local outbreaks of the insect occur in the South
only following a period of heavy rainfall and humid weather.

Outbreaks also are facilitated by a period of low rainfall or drought followed by
heavy rainfall. Both drought and heavy rainfall are very damaging to parasitoids of the
fall armyworm, and heavy rainfall promotes luxuriant plant growth conducive to rapid
build-up of fall armyworm populations. It is precisely these circumstances that precipi-
tated the devastating fall armyworm outbreak experienced throughout the southeastern
United States in 1975 and again in 1977.
Dr. Luginbill's assessment of the importance of natural enemies on keeping fall
armyworm populations in check is of special interest, especially to those with visions of


453











Florida Entomologist 69(3)


suppressing this pest in its overwintering habitat, i.e., southern Florida, in order to
reduce the numbers of moths migrating northward each spring. According to Dr. Lugin-
bill ". . the abundance or scarcity of natural enemies to a large extent determines
whether or not fall armyworms become abundant enough during a season to cause
destruction to crops. .. It appears that a general outbreak of Laphygma frugiperda
becomes possible only when the natural enemies of the insect have been reduced in its
permanent habitat, thus permitting the insect to develop in enormous numbers in early
spring."
Dr. Luginbill attributed the general outbreak of fall armyworm in 1912, "... unques-
tionably the most severe that had ever occurred in the United States [to that time],"
to a severely reduced level of parasitization in Florida during the winter and spring
that allowed the fall armyworm to increase in great numbers. Although the parasitic
enemies had increased their numbers by midsummer of 1912, the fall armyworm already
had spread practically throughout all areas of the United States east of the Rocky
Mountains. "The caterpillars appeared in destructive numbers in Florida in April and
in southern Alabama the latter part of the same month. In early May, moths began to
issue from this generation and crossed Alabama and other Gulf States, producing
another generation. The moths of the latter generation migrated farther north, repeat-
ing the operation again and again."
Unlike 1912, outbreaks of fall armyworm in 1913 were few in number and local in
distribution, owing to the abundance of natural enemies in southern Florida in February
and March and throughout late spring. Recent research in South Florida (Ashley et al.
1982, 1983, Mitchell et al. 1984) showed that parasitoids, especially Chelonus insularius
Cresson and Temelucha difficilis Dasch., have a tremendous suppressive effect on fall
armyworm populations most years. Moreover, the percentage of fall armyworm larvae
in corn that is parasitized in each of the first four instars is correlated positively with
the percentage of available larvae in a given instar within the total population. In view
of these findings and the observations of Dr. Luginbill and others on the influence of
weather on larval fall armyworm-parasitoid interactions, it is surprising that action
agencies have not seized the opportunity to predict possible outbreaks of the fall ar-
myworm through annual evaluations of the parasitization levels of this pest in its over-
wintering habitat, i.e., South Florida.
In summary, the information presented in Bulletin No. 34 on the life history and
habits of the fall armyworm is interesting and accurate as verified by numerous publi-
cations on the fall armyworm over the past 57 years. Even with respect to control
technology, not much has changed. Pesticides-sprays, dusts and baits-were among
the favored methods for control of the fall armyworm in 1928. The chemicals have
changed, but to this day, spray and bait formulations continue to be the principal method
of controlling this pest.
We will be forever grateful to Dr. Luginbill for his fine contribution. It is unlikely
that anyone will take time to prepare a similar document summarizing information on
the fall armyworm from 1928 to the present. The reasons for this are not lost on those
struggling to gain tenure in academia or to promote his/her professional career in other
research organizations. Thus, publication of the proceedings of this and earlier symposia
(1979, 1980, 1984) provide a means for keeping current of research on the fall ar-
myworm. Still, in view of Dr. Luginbill's treatise and all that has been written on the
fall armyworm over the past half century, one cannot help but wonder why we are not
much further along in our efforts to control or suppress the fall armyworm than we
were in 1928. Such is the legacy of Philip Luginbill.

ENDNOTE

Proceedings of the Fall Armyworm Symposia were published in the Florida En-
tomologist: 1979, 62: 81-133; 1980, 63: 357-480; 1984, 67: 323-367.


454


September, 1986











Mitchell: Fall Armyworm Symposium 455

REFERENCES CITED

ASHLEY, T. R., C. S. BARFIELD, V. H. WADDILL, AND E. R. MITCHELL. 1983.
Parasitization of fall armyworm larvae on volunteer corn, Bermudagrass, and
paragrass. Florida Ent. 66: 267-271.
ASHLEY, T. R., V. H. WADDILL, E. R. MITCHELL, AND J. RYE. 1982. Impact of
native parasites on the fall armyworm, Spodopterafrugiperda (Lepidoptera: Noc-
tuidae), in South Florida and release of the exotic parasite, Epiphosoma vitticole
(Hymenoptera: Ichneumonidae). Environ. Ent. 11: 833-837.
LUGINBILL, P. 1928. The fall armyworm. USDA Tech. Bull. No. 34. 92 pp.
MITCHELL, E. R., V. H. WADDILL, AND T. R. ASHLEY. 1984. Population dynamics
of the fall armyworm (Lepidoptera: Noctuidae) and its larval parasites on whorl
stage corn in pheromone-permeated field environments. Environ. Ent. 13: 1618-
1623.





FALL ARMYWORM DISTRIBUTION AND POPULATION
DYNAMICS IN THE TEXAS-MEXICO GULF COAST AREA

J. R. RAULSTON, Subtropical Crop Insects Research Unit, ARS, USDA, P. 0. Box
1033, Brownsville, TX 78520; S. D. PAIR and A. N. SPARKS, Insect Biology and Pop-
ulation Management Research Lab., ARS, USDA, Tifton, GA 31793; J. LOERA G.,
SARH, INIA, CIAGON, Col. Rio Bravo, Tamps., Mexico; F. A. PEDRAZA M., SARH,
INIA, CIAGON, S. Jimenez, Tamps., Mexico; A. PALAMON T., SARH, INIA, CIAGON,
Tampico, Tamps., Mexico; A. ORTEGA, CIMMYT, 06600 Mexico D.F., Mexico; J. Ruiz
SANCHEZ M., SARH, INIA, CIAGOC, Veracruz, Veracruz, Mexico; P. MARQUEZ C.,
SARH, INIA, CIAPAS, Juchitan, Oaxaca, Mexico; H. RULES A. and JOEL PEREZ M.,
SARH, INIA, CIAPY, Campeche, Camp., Mexico; R. RODRIGUEZ R., SARH, INIA,
CIAPY, Merida, Yucatan, Mexico; H. CARRILLO R., SARH, INIA, CAECHET, Cd.
Chetumal, Q. Roo, Mexico; R. ARCHUNDIA R., SARH, INIA, CIAPAS, Tapachula,
Chiapas, Mexico; and FRANCISCO HERRERA R., SARH, INIA, CAUEX, Uxmal, Yuc.,
Mexico.

ABSTRACT

Fall armyworm, Spodopterafrugiperda J. E. Smith, population trends were studied
along the Mexican Gulf Coast, the Isthmus of Tehuantepec, and the Yucatan Peninsula
using Hartstack pheromone traps. Trap capture generally peaked in November and
December, while the lowest capture period occurred during mid year. A temporal prog-
ression in trap capture was noted during the early part of the year from Veracruz,
Mexico, to the Lower Rio Grande Valley of Texas.
A similar temporal progression in occurrence of larval populations from southern
areas of the State of Tamaulipas to the Rio Grande Valley was also observed. Studies
in an irrigated corn-growing region encompassing the Lower Rio Grande Valley in both
southern Texas and northern Tamaulipas, Mexico (with ca. 200,000 ha of corn) showed
the major fall armyworm emergence from the area occurred in June, resulting in an
adult population of from 6.11X108 to 1.72X10" moths.











Florida Entomologist 69(3)


RESUME

Se estudiaron las tendencies de la poblaci6n del gusano cogollero, Spodoptera
frugiperda (J. E. Smith), a lo largo de la costa del Golfo de Mexico, el Istmo de Tehuan-
tepec, y la peninsula de YucatAn, usando trampas de feromonas Hartstack. General-
mente, las captures en las trampas llegaron a su auge en Noviembre y Diciembre,
mientras que el period de menor capture ocurri6 a mediados de afio. Se not6 una
progresi6n temporal en las captures durante la primera parte del afo, desde Veracruz,
Mexico, a la parte del Bajo Valle del Rio Grande en Texas.
Tambien se observ6 una similar progresi6n temporal en ocurrencia de poblaciones
larvales desde areas del sur del Estado de Tamaulipas, hasta el Valle del Rio Grande.
Estudios en una region productora de maiz bajo riego circundado el Bajo Valle del Rio
Grande en ambos el sur de Texas y el norte de Tamaulipas, Mexico (con ap-
roximadamente 200,000 ha de maiz), indicaron que la emergencia mayor del cogollero
en el Area ocurri6 en Junio, resultando en una poblacion adulta de 6.11X10W a 1.72X10".




In recent years, research efforts have been initiated to determine the role of move-
ment within and between geographical regions on development of populations of pes-
tiferous Noctuidae. Luginbill (1928) concluded that the fall armyworm (FAW), Spodopt-
era frugiperda J. E. Smith, was normally incapable of continuous survival beyond the
subtropical regions of the North American continent. Thus, two regions, south Florida
and south Texas-Mexico, are implicated as sources from which this insect annually
re-invades the temperate zone of the continent. Therefore, we are attempting to deter-
mine general trends in FAW population development along the Mexican Gulf Coast
extending from the Lower Rio Grande Valley (LRGV) of southern Texas and northern
Tamaulipas, Mexico, across the Isthmus of Tehuantepec, and including the Yucatan
Peninsula.
The FAW has been cited as one of the most destructive pests of Mexican agriculture.
Marquez Delgado (1951) reported that of the more than 60 hosts listed for this insect,
agriculturally important damage in Mexico was most often observed in corn, tomatoes,
potatoes, cotton, clover, and vegetables. Sifuentes (1974) stated that over 50% of the
land in Mexico devoted to agriculture was planted in corn, and Villanueva Barradas
(1972) estimated that 10% of this crop was lost as a result of FAW damage. The FAW
is considered a major constraint to corn production in the States of Michoacan, Guerrero,
Morelos, Oaxaca, Veracruz, Chiapas, Tamaulipas, Jalisco, Nayarit, Sinaloa, and Yuca-
tan (Sifuentes et al. 1971, Marquez Delgado 1951). These states include 52% of the 7.5
million ha of corn grown in Mexico (Anon. 1983).

PHEROMONE TRAP STUDY

To study long-term FAW population trends, cone traps (Hartstack et al. 1979) baited
with the FAW lure reported by Sekul and Sparks (1967,1976) or a 4-component lure
supplied by Terochem Laboratories Ltd.' were installed at various locations along the
Mexican Gulf Coast, the Isthmus of Tehuantepec, and LRGV (Fig. 1). Trap data for
College Station, Texas, were also included. Traps (1-6/location) were installed in 1982
and 1983 and have been operated continuously to the present. Exceptions are noted at
Merida, Yucatan; Chetumal, Quintana Roo; and Tapachula, Chiapas, where incomplete
data have resulted in less than one full year of capture observation. Male trap capture


September, 1986


456











Raulston et al.: Fall Armyworm Symposium


Fig. 1. Fall armyworm pheromone trap locations in Mexico.


data were compiled either daily (except for weekends) or 3 times/week throughout the
year.
Corn planting in the region encompassing the trap locations total over 2 million ha
(Table 1) or about 27% of the corn planted in Mexico (Anon. 1983). Only 14% of the corn
in the region is irrigated, and 81.6% of this irrigated corn is located in the State of
Tamaulipas. Chiapas has the largest corn planting at 667,162 ha followed by the states
of Veracruz and Tamaulipas.
Trap captures (Table 2) are expressed as the percent of the yearly total capture/trap
occurring within each of twelve 30-day periods. Yearly total capture/trap was deter-
mined by averaging all captures at each location from the date of trap installation to
the last date of observation listed. The locations are listed in order of descending latitude
from north to south. Also presented in Table 2 are rainfall data for those locations from
which these data were available, expressed in the same manner as the trap capture.
These data indicate the peak 30-dy capture at 42.9% of the locations occurred between
intervals 10 and 12 and an additional 35.7% occurred between intervals 7-9. Only two
locations, Llera and Manuel, both situated in southern Tamaulipas, exhibited their











Florida Entomologist 69(3)


TABLE 1. TOTAL HECTARES OF CORN PLANTED IN STATES OF THE REPUBLIC OF
MEXICO WHERE FALL ARMYWORM TRAPS ARE LOCATED.

No. ha of corn
State Irrigated Dryland Total

Tamaulipas 231,107 109,677 340,784
Veracruz 10,608 437,994 448,602
Oaxaca 27,690 286,241 313,931
Tabasco 0 47,705 47,705
Chiapas 9,365 657,797 667,162
Campeche 832 39,993 40,825
Yucatan 1,723 127,935 129,658
Quintana Roo 1,774 37,513 39,287
Total 283,099 1,744,855 2,027,954


largest capture peak within the initial 3 intervals of the year. Interestingly, this is a
relatively minor corn producing area in comparison with the northern Tamaulipas-
LRGV area. However, much of the corn that is produced in southern Tamaulipas will
be found at various stages of maturity ranging from whorl to fruiting during these initial
3 intervals.
The intervals of lowest and highest capture for each location are shown in Fig. 2.
The lowest capture at the 2 northernmost locations, College Station and LRGV, occur-
red between intervals 1-5 and 1-4, respectively. During the initial 5 intervals at College
Station, capture/trap averaged only 0.07 males/trap/day. In LRGV, capture occurring
in the initial 4 intervals averaged 0.36 males/trap/day. The period of least capture at
locations in Mexico occurred most frequently between intervals 5-9.
Average yearly rainfall for the locations listed in Table 2 ranged from 680.6 mm
(Abasolo, Tamaulipas) to 1438.8 mm (Veracruz, Veracruz). Northeastern Mexico-LRGV
is climatologically classified as semi-arid and receives the least rainfall of the entire
study region. However, the pattern of rainfall at all the locations is quite similar as
indicated by the intervals when the least and highest rainfall occurred. Indeed, at 71.4%
of the locations, the least rainfall occurred during the third 30-dy interval. Conversely,
the highest rainfall occurred during interval 9 at 71.4% of the locations. Also, there was
a trend for peak trap capture intervals to occur from 60-90 dy after the rainfall peaks,
while the intervals of least capture most frequently occurred 60-90 dy after the periods
of least rainfall.
Initial trap captures at locations selected to represent the range of latitudes within
the study region were compared by determining the 10-dy interval when the initial 5%
of the total yearly capture occurred. A 2nd degree polynomial curvilinear regression
analysis was performed using the determined 10-dy interval as the dependent variable
and the latitude of the corresponding locations as the independent variable (Fig. 3).
These data were described by the equation: Y = 485.2 -48.1X + 1.3X2 with an R2 value
of 0.82 indicating 82% of the temporal variation in initial trap capture was explained by
the latitude of the trap location. The initial 5% capture at all locations in Mexico, with
latitudes ranging between 16-24, were clumped within the first 60 dy of the year. The
major temporal hiatus occurred between latitudes 240 and 260 which may implicate this
zone as being the northernmost area where overwintering normally occurs. This would


September, 1986

















Raulston et al.: Fall Armyworm Symposium 459


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Raulston et al.: Fall Armyworm Symposium


LOW CAPTURE


PEAK CAPTURE


COLLEGE STATION k
LRGV
ABASOLO
PADILLA
LLERA
MANUAL
POZA RICA
VERACRUZ
JUCHITAN
UXMAL
CAMPECHE
2 4 6 8 10 12 2 4 6 8 10 12
30 DAY INTERVAL

Fig. 2. Intervals of lowest and highest fall armyworm capture in pheromone traps
at various locations in Mexico.


200-






150-




I> S

<100-






50- C
A E G


I- I g g I I I g I I I I I- I I I 1
15 20 25 30
LATITUDE
Fig. 3. Curvilinear regression analysis (2nd degree polynomial) of latitude (X axis)
vs. date when initial 514 of yearly trap capture occurred (Y axis).











Florida Entomologist 69(3)


confirm data presented by Pair and Sparks (in press) which showed overwintering
larval populations in Florida were restricted below 270 N latitude.
A final comparison of FAW trap capture was made by combining data from closely
associated locations to provide a regional scenario. Thus the study region was divided
into 7 subregions consisting of the following location combinations: A-College Station,
Texas; B-LRGV, Texas; C-Abasolo and Padilla, Tamaulipas; D-Llera and Manuel,
Tamaulipas; E-Poza Rica and Veracruz, Veracruz; F-Campeche, Campeche, and
Uxmal and Merida, Yucatan; G-Juchitan, Oaxaca, and Tapachula, Chiapas.
Subregion A (Fig. 4) exhibited a single capture peak with the highest capture
occurring during interval 10. Subregion G also exhibited a single capture peak with the
highest capture occurring during interval 11. All other subregions exhibited two peak
capture periods. The initial peak in the LRGV (Subregion. B) was associated with
emergence from corn, followed by a subsequent decline, then a 2nd peak in intervals
11-12. This 2nd peak is not associated with a major cropped host, however, it is of a
similar magnitude as the initial peak associated with adult emergence from ca. 200,000
ha of irrigated corn grown in the area. Subregions C and D exhibited initial peaks





















40
30 0






20

A

2 4 6 8 10 12
30-DAY INTERVAL
Fig. 4. Regional capture of fall armyworm in pheromone traps.
A = College Station, Texas
B = Lower Rio Grande Valley of Texas
C = Abasolo and Padilla, Tamaulipas
D = Llera and Manuel, Tamaulipas
E = Poza Rica and Veracruz, Veracruz
F = Campeche, Campeche and Uxmal and Merida, Yucatan
G = Juchitan, Oaxaca, and Tapachula, Chiapas


September, 1986











Raulston et al.: Fall Armyworm Symposium


between intervals 3 and 4 or 60 dy earlier than Subregion B. Concurrently in Subregion
E, although trap capture is declining during the initial intervals, major capture was still
occurring during intervals 1-2. Thus, along the Gulf Coast of mainland Mexico a south
to north temporal progression in trap capture is indicated. The occurrences of such a
temporal progression suggests the possibility of influence between these subregions
from south to north in the development of FAW populations. However, extensive pop-
ulation dynamics studies within these subregions would be necessary for verification
and to determine the impact of such possible movement. The complexity of the problem
of verification of movement becomes evident when one considers the fact that the FAW
is capable of continuous survival in these areas.

LARVAL AND ADULT SURVEYS-LRGV AND TAMAULIPAS, MEXICO

The State of Tamaulipas contains ca. 230,000 ha of irrigated corn. Of this, ca. 170,000
ha are situated immediately south of the Rio Grande River in an irrigation region
extending east and west from Ciudad Camargo to Matamoros and south to El
Moquetito (crosshatched area Fig. 1). An additional 30,000 ha of corn are planted in the
LRGV of south Texas. Another irrigated region is situated along the Rio Soto la Marina
extending from Abasolo to Soto la Marina in central Tamaulipas which contains 15,000
ha of corn. Most of the corn in these regions is planted early to mid February.
FAW larval surveys were conducted in the LRGV and the Abasolo areas during
1984-85 spring corn-growing seasons. Also occasional surveys were made in southern
Tamaulipas near Manuel from January to May. These surveys were performed by ran-
domly selecting 50-100 plants within individual fields and determining the number of
larvae present. Also in LRGV, 7 corn plots (0.4 ha each) were planted in 1984 between
Julian days 48-79, and 3 plots (0.8 ha each) were planted in 1985 between dy 47-74.
These plots were checked biweekly (50-100 plants per plot/observation) for larval infes-
tation until the corn matured.
Emergence cages (0.456 m2; 20/plot) were subsequently installed on dy 113 in 5 plots
(1984) and 1 m2 cages were installed on day 107 in 3 plots (1985). Adult emergence was
monitored biweekly, and the cages were relocated biweekly (1984) or weekly (1985).
Emergence was monitored through dy 194 in 1984 and through dy 184 in 1985. Further,
in 1984, ten 1 m2 soil samples were excavated between dy 178 and 193 in each of the 7
plots to determine the total number of pupae or exuviae/ha as an index of the number
of adults produced. An additional thirty-two 1 m2 samples were excavated in each of 2
fields in the Rio Bravo area of northern Tamaulipas on dy 183-184 and twenty-five 1 m2
samples were excavated in 3 fields near Abasolo on dy 161. In 1985, two 1 m2 soil
samples were excavated in each of 100 fields in the irrigated corn region of northern
Tamaulipas-LRGV between dy 161-164.
In 1984, observations were initiated on day 65 for larvae on corn in the LRGV area
(Table 3). Larvae were first observed at a low rate (0.003/plant) between dy 85-89 and
remained low through dy 109. Then between dy 110 and 114, larval density increased
by a factor of 10 to 0.028/plant. The peak incidence of larvae (0.192/plant) occurred
between dy 130-134 followed by a 2nd peak between dy 160-164. The initial observations
at Abasolo were made also between dy 65-69 when a larval density of 0.014/plant was
observed. The peak density of 0.240/plant occurred between dy 120-124. At Manuel in
southern Tamaulipas, a larval density of 0.46/plant was observed between dy 20-24 from
a single field observation. The highest density observed in this area occurred between
dy 100-104 at 0.847 larvae/plant.
In 1985 at LRGV, an initial larval density of 0.01/plant was observed on dy 75-79,











Florida Entomologist 69(3)


TABLE 3. INCIDENCE OF FALL ARMYWORM LARVAE ON CORN IN LRGV,
ABASOLO, TAMPS., AND MANUEL, TAMPS., AREAS DURING 1984 AVER-
AGED OVER 5-DY PERIODS.

LRGV Abasolo Manuel
Julian No. fields Fall army- No. fields Fall army- No. fields Fall army-
dy observed worm/plant observed worm/plant observed worm/plant

20- 24 1 0.460
50- 54 4 .220
65- 69 1 0 3 0.014
70- 74 1 0 6 .084
75- 79 4 0
80- 84 6 0
85- 89 7 -.003 3 .013
90- 94 11 .007
95- 99 3 0 3 .047
100-104 11 .005 3 .080 5 .847
105-109 17 .002
110-114 12 .028 6 .105
115-119 13 .057
120-124 21 .078 3 .240
125-129 10 .068 5 .208
130-134 12 .192
135-139 6 .073 2 .140
140-144 16 .105 4 .215
145-149 6 .073
150-154 7 .06 5 .144
155-159 10 .122
160-164 4 .135
165-169 4 .15
170-174 2 .03




however, the peak density did not occur until dy 120-125 at 0.127 larvae/plant (Table
4). At Abasolo, initial observations between dy 75-79 indicated a density of 0.370 larvae/
plant. The peak density was observed (0.510 larvae/plant) between dy 90-94. A single
survey was made in southern Tamaulipas and Veracruz between dy 48-54 in 1985. In
four fields surveyed in the Manuel area, an average larval density of 0.47/plant was
observed, while a density of 0.357/plant was noted in Veracruz.
Data listed in Tables 3 and 4 show a temporal succession in developing FAW popu-
lations from south to north in the State of Tamaulipas to the LRGV of Texas. In the
extreme southern part of the state, in the Manuel area, high densities of larvae were
observed on corn between dy 20-24, then in the central area, larvae were noted by dy
65-69, our initial observations in the area. At LRGV, FAW larvae were observed by
dy 75-79, but the population remained low until dy 115-119. The peak larval populations
for 1984-85 at LRGV occurred between dy 120-134. At Abasolo, the peak occurred
between dy 120-129 in 1984, however, in 1985, the peak occurred between dy 90-94 or
25 dy earlier. The delay observed in 1984 at Abasolo may have resulted from the severe
freeze that occurred in the region during the winter of 1983-84, however, the time when
peak larval densities occurred at LRGV was apparently unaffected.


September, 1986











Raulston et al.: Fall Armyworm Symposium


TABLE 4. INCIDENCE OF FALL ARMYWORM LARVAE ON CORN IN THE LRGV AND
ABASOLO AREAS IN 1985 AVERAGED OVER 5-DY PERIODS.

LRGV Abasolo
Julian No. fields Fall armyworm No. fields Fall armyworm
dy observed per plant observed per plant

70- 74 2 0
75- 79 2 .010 4 0.370
80- 84 4 .005
85- 89 2 0 4 .365
90- 94 6 0 .4 .510
95- 99 3 .007
100-104 3 0 4 .340
105-109 12 .019 4 .310
110-114 9 .007
115-119 6 .037
120-124 3 .127
125-129 6 .113
130-134 13 .038
135-139 5 .080
140-144 30 .032
145-149 24 .011 4 .015
150-154 19 .022
155-159 12 .010
160-164 2 .080




Adult FAW energence in corn plots at LRGV averaged 0.43 and 0.60/m2, respec-
tively, for 1984 and 1985 (Table 5). Initial emergence occurred between dy 135-134, then
the peak emergence occurred between dy 160-164 in both years. Emergence continued
through dy 180-189. The period of initial trap capture peak at LRGV (Table 1), which
occurred between dy 150-180, encompassed 75-77% of the total emergence from the corn
plots in both years. Indeed, when the arcsine-transformed percent of emergence/5-dy
period data for 1984-85 were compared by performing a G test analysis (Sokal and Rohlf
1969), no significant difference in the emergence pattern for the 2 years was noted
(P<.05).
When adult emergence (Table 5) is compared to the incidence of FAW larvae (Tables
3 and 4), it is evident that the peak larval density occurred 5 dy prior to initial emergence
in 1984 and 20 dy prior in 1985. Further, in 1984, the larval density peak occurred 30
dy prior to the adult emergence peak, while in 1985, the larval density peak occurred
40 dy prior to the emergence peak. Concomitantly, initial emergence occurred 25 and
20 dy, respectively, prior to the peak emergence period in 1984 and 1985. Thus the
larval density peak did not result from reproduction of adults emerging in local corn.
Further, the emergence peak probably resulted from those insects constituting the
larval density peak and was not indicative of a 2nd generation in local corn.
In 1984, excavations of 1 m2 soil samples in the LRGV area indicated an average of
0.8581.164 pupae and exuviae/m2 (Table 6). At Abasolo, soil samples indicated
2.798+4.072 pupae and exuviae/m2, ca. 3 times the density observed in the northern
area. When comparing the density of larvae in the 2 areas (Table 3) for those time











Florida Entomologist 69(3)


TABLE 5. EMERGENCE OF ADULT FALL ARMYWORM (1984-85) IN CORN PLOTS AT
LRGV. EMERGENCE WAS MONITORED WITH TWENTY 1 m2 CAGES/PLOT
IN EACH OF 5 PLOTS (1984) OR 3 PLOTS (1985).

% of emergence occurring
Emergence/m2 per time interval
Julian
dy 1984 1985 1984 1985

110-114 0 0
115-119 0 0 0 0
120-124 0 0 0 0
125-129 0 0 0. 0
130-134 0 0 0 0
135-139 .01 0 2.3 0
140-144 .01 .07 2.3 11.7
145-149 .02 .03 4.7 5.0
150-154 .01 .05 2.3 8.3
155-159 .08 .07 18.6 11.7
160-164 .15 .12 34.9 20.0
165-169 .02 .08 4.7 13.3
170-174 .05 .05 11.6 8.3
175-179 .02 .08 4.7 13.3
180-184 .02 .05 4.7 8.3
185-189 .04 0 9.3 0
190-194 0 0 0 0
195-199 0 0 -
Total/m2 .43 .60


TABLE 6 No. OF FALL ARMYWORM EXUVIAE OR PUPAE FROM EXCAVATIONS OF 1
m2 SOIL SAMPLES IN 1984 AND 1985.

1984 1985
No. Total no. No. FAW No. Total no. No. FAW
Location fields samples per m' fields samples per m2

LRGV 9 134 0.8581.164 100 200 0.16.53
Abasolo,
Tamps. 3 25 2.798+4.072 -



intervals when both areas were sampled, the LRGV averaged 0.042 larvae per plant/5-
dy interval, while Abasolo averaged 0.121 larvae per plant/5-dy interval, also about 3
times that observed in the northern area. The increase in density of adult emergence
at Abasolo probably resulted then from the earlier occurrence of larval populations on
the corn, as well as the overall higher densities observed over the growing season. Soil
samples were taken during 1985 only in the LRGV area. These data (Table 6) indicated
an average of 0.16+.53 pupae and exuviae/1 m2. Although the average observed in 1985
was only about 19% of that observed in 1984, we feel that this was a more representative
figure for the area considering the samples were taken from 100 commercial corn fields
dispersed throughout the corn-growing area.


466


September, 1986











Raulston et al.: Fall Armyworm Syg,,l,~osii i,,


These data indicate that in 1984, up to 1.72X109-2.33X10' FAW were produced in
LRGV corn (200,000 ha), while 4.20X10" 6.11X10s could have been produced in the
Abasolo area. Further, in 1985, up to 3.2X1081.06X10 could have been produced in
the LRGV area. Then recalling data from Table 5, ca. 75% of these moths in the
northern area would have emerged between dy 150-180. Interestingly, this corresponds
to the period of initial capture at College Station as shown in Fig. 3A.

SUMMARY

Our trap data indicate a general trend along the Mexican Gulf Coast, Isthmus of
Tehuantepec, and Yucatan Peninsula regions of low FAW trap capture during the
mid-portions of the year with the peak captures occurring either early of late in the
year. Further, a temporal succession in initial trap capture was observed from south to
north along the Gulf Coast region. When initial trap capture was regressed on latitude,
a curvilinear pattern was shown which suggested the critical latitude for continual
early- season development of FAW populations to be ca. 26'N.
A temporal progression in developing FAW larval populations from southern to
northern Tamaulipas also was indicated. Further, the capacity of an irrigated area in
the LRGV to produce FAW moths was illustrated to be from 4.20X10" to 1.72X10".
Also, the emergence pattern of moths in this area coincided with the initial captures
occurring farther north at College Station.

ENDNOTE

Mention of a commercial product in this paper does not constitute an endorsement
of this product by the USDA.

REFERENCES CITED

ANONYMOUS. 1983. Information agropecuaria y forestal 1983. Subsecretaria de Agri-
cultura y Operacion Direccion de Economia Agricola. 84 pp.
HARTSTACK, A. W., JR., J. A. WITZ, AND D. R. BUCK. 1979. Moth traps for the
tobacco budworm. J. Econ. Entomol. 97: 1077-1089.
LUGINBILL, P. 1928. The fall armyworm. U. S. Dep. Agric. Tech. Bull. 34. 92 pp.
MARQUEZ DELGADO, A. 1951. Gusano cogollero y gusano medidos del maiz. Fitofilo
2: 14-25.
PAIR, S. D., AND A. N. SPARKS. (In press). Evidence of annual long-distance migra-
tion by the fall armyworm. In (A. N. Sparks, ed.), Long-Range Migration of
Moths of Agronomic Importance to the United States and Canada: Specific
Examples of Occurrence and Synoptic Weather Patterns Conducive to Migration.
U. S. Dep. of Agric. Misc. Publ., accepted 12/83.
SEKUL, A. A., AND A. N. SPARKS. 1967. Sex pheromones of the fall armyworm
moths: Isolation, identification, and synthesis. J. Econ. Entomol. 60: 1270-1272.
SEKUL, A. A., AND A. N. SPARKS. 1976. Sex attractant of the fall armyworm moth.
U. S. Dep. Agric. Tech. Bull. 1542. 6 pp.
SIFUENTES A., J. A. 1974. El gusano cogollero del maiz y su combat en Mexico.
Folleto de Divulgacion 52: 1-6.
SIFUENTES A., J. A., C. MORAN V., AND S. LOPEZ B. 1971. Plaga important. El
gusano cogollero del maiz. Avance Agricola y Ganadero 2: 38-47.
SOKAL, R. R., AND F. J. ROHLF. 1969. Biometry-the principles and practice of
statistics in biological research. W. H. Freeman and Company, San Francisco.
776 pp.


467











468 Florida Entomologist 69(3) September, 1986

VII.ANUEVA BARRADAS, J. 1972. El gusano cogollero del maiz. Pp. 297-300 en
"Memoria del II Simposio Nacional de Parasitologia Agricola y I Reunion Na-
cional Sobre Plagas y Enfermedades de las Hortalizas" (eds. Legunes Tepeda.
A., Saenz Colin, A., and Leon Lopez, R.). 694 pp.







FALL ARMYWORM DISTRIBUTION AND POPULATION
DYNAMICS IN THE SOUTHEASTERN STATES

S. D. PAIR
Insect Biology and Population Management Research Lab, USDA-ARS,
Tifton, GA 31793,
J. R. RAULSTON
Subtropical Crop Insects Research Unit, USDA-ARS,
Brownsville, TX 78520,
A. N. SPARKS and J. K. WESTBROOK
Insect Biology and Population Management Research Laboratory, USDA-ARS,
Tifton, GA 31793
AND
G. K. DOUCE
Extension Service, University of Georgia, Tifton, GA 31793

ABSTRACT

Following the winters of 1983-85, fall armyworm (FAW), Spodoptera frugiperda
(J. E. Smith), populations in the continental United States were restricted to extreme
south Florida. Reinvasion of northerly areas occurred predictably each year with larval
infestations on whorl-stage corn in southwest Georgia by mid- to late April each year.
Pheromone trap catches indicated populations at Dade and Palm Beach Counties, FL,
were greater and peaked earlier than those at more northerly locations during the early
spring, indicating this area as either a major contributor or recipient of migrant FAW.
Initial trap captures of FAW males occurred earlier and higher larval infestations were
observed at Baldwin County, AL, than in locations in south Georgia. The proximity of
weather systems inducing southerly wind components in areas ahead of the front were
associated with initial trap captures of FAW males at northerly locations in all three
years. Pheromone trap captures indicated FAW populations were lower in 1984 than
in 1983 or 1985, probably because of the colder winter and spring temperatures recorded
in 1983 and 1984, respectively. Severe outbreaks of FAW did not occur during the study
although severe winters occurred each year. These data indicate that the conditions
following extremely low winter temperatures may influence FAW populations more
than extreme low temperatures alone. The (a)synchrony of emerging FAW adults at
overwintering sites timed with the availability and amounts of susceptible stages of corn
planted in more northerly areas may be the most important factors determining the
magnitude of FAW populations each year throughout the southeastern states.











Pair et al.: Fall Armyworm Symposium 469


RESUME

A consiguiente de los inviernos de 1983-85, poblaciones del gusano cogollero,
Spodoptera frugiperda (J. E. Smith), fueron restringidas al extreme sur de la Florida
en los Estados Unidos continental. Anualmente se reinvadieron, como era predecible,
las areas del norte, con infestaciones larvales en la etapa del verticilo del maiz, en el
suroeste de Georgia de a mediados a tarde Abril cada afio. Temprano en la primavera,
captures con trampas de feromonas indicaron que poblaciones en los condados de Dade
y Palm Beach fueron mayores y llegaron a su auge mas temprano que quellas en lugares
mas al norte, indicando que estas areas son mayores contribuidoras o recipient de
gusanos cogolleros migrants. Se observ6 captures de gusanos cogolleros machos mas
temprano e infestaciones de larvas mas altas en el condado de Baldwin, Alabama, que
en lugares de sur de Georgia. En los tres anos, la proximidad de sistemas metereol6gicos
induciendo compuestos de vientos surefios en areas delante del frente, fue asociada con
captures iniciales de gusanos cogolleros machos en localidades nortefas. Trampas de
feromonas indicaron que poblaciones de gusanos cogolleros fueron mas bajas en 1984
que en 1983 o 1985, probablemente por los inviernos mas frios, y las temperatures
registradas en las primaveras de 193 y de 1984 respectivamente. Erupciones several
de gusanos cogolleros no ocurrieron durante el studio, aunque inviernos severos ocur-
rieron cada afo. Los datos indican que las condiciones que le siguen a temperatures
extremes bajas en el invierno, pudieran influenciar las poblaciones de gusanos cogolleros
mas que solamente las temperatures extremes bajas. La sincronizaci6n o no sincroniza-
ci6n de gusanos cogolleros adults emergiendo de los lugares donde pasan el invierno,
junto con la disponibilidad y cantidades de etapas susceptibles de maiz sembrado en
areas mas nortefias, pudieran ser los factors mas importantes que determinan la mag-
nitud de las poblaciones de gusanos cogolleros cada afio atrav6s de los estados del
sudeste.




Fall armyworm, Spodoptera frugiperda (J. E. Smith), annually reinvades its host
range from overwintering sites in south Florida and Mex:co. Occasionally, because of
factors still not well understood, outbreak years occur over wide geographic areas of
the U.S. resulting in tremendous economic losses. The outbreak of 1977 serves as our
most recent example of the potential for fall armyworm (FAW) to devastate crops
(Sparks 1979).
The potential source areas for overwintering populations and their seasonal distribu-
tion throughout the United States have been identified (Luginbill 1928, Vickery 1929,
Snow and Copeland 1969). Waddill et al. (1982) documented the seasonal abundance of
FAW populations at 4 sites in Florida. Pair and Sparks (in press) reported on the
northward progression of larval infestations from sites below ca. 28N latitude in south
Florida into adjacent southeastern states.
Prevailing winds during the spring are thought to largely determine the extent and
direction of FAW adult movement; Luginbill (1928) recognized earlier that the prevail-
ing wind vectors in the southeastern U.S. consisted of south-southeasterly components
during the spring months. More recently, Muller (1979) identified several synoptic
weather systems conducive for the northward transport of migratory insects. Pair and
Sparks (in press) associated the initial spring captures of FAW males in pheromone
traps positioned in several Gulf Coast states with those synoptic weather types having
southerly wind components. This phenomenon is consistent with other insect movement
reports in the U.S. and Africa. Frontal systems with their convergent air masses govern
the direction and fallout areas of Spodoptera exempt (Walker) in Africa (Rainey 1979).











470 Florida Entomologist 69(3) September, 1986


Hogg et al. (1982) associated fall armyworm oviposition with southerly winds and frontal
systems producing rain in Mississippi. Standard weather stations, however, may not
report or detect low-level jet systems with different wind vectors which are capable of
transporting insects long distances.
The potential overwintering source areas and migratory aspects of FAW require
more exact definition. Such information requires an accumulation of data on seasonal
distribution trends on a long-term basis in the southeastern states before reliable predic-
tions of potentially damaging FAW populations can be made in any given year or region.
We report seasonal pheromone trap captures at selected locations in several southeast-
ern states during 1983-85 and the extent of larval infestations as they advance north-
ward during the spring. The influences of weather in delineating overwintering popula-
tions and in the aerial transport of FAW adults are discussed.

METHODS AND MATERIALS

WEATHER: Weekly average minimum and maximum temperatures and precipitation
data were collected from National Oceanic and Atmospheric Administration (NOAA)
for the following locations and their respective latitudes and longitudes: Miami FL
(2545'N, 8015'W); Orlando, FL (28030'N, 81050'W); Mobile, AL (30045'N, 8820'W);
and Tifton, GA (3120'N, 8330'W) (Fig. 1). These were selected based on their location
in or near suspected overwintering areas (Miami, Orlando), or in areas where FAW
survival does not normally occur (Mobile, Tifton). In addition, the number of days each
week with 0C or less temperatures for 1983-85 were calculated for each location. These
were used as a relative measure of the potential FAW winter mortality among years
at each location. Hogg et al. (1982) reported 13.8C as the lower limit for FAW develop-
ment and o0C temperatures are known to kill FAW life stages as well as their plant
hosts (Luginbill 1928). Surface weather charts (NOAA) were employed to assess the
transport potential of FAW from suspected source areas during the spring.
ADULT POPULATIONS: Seasonal population trends based on catches of FAW males
in 75-50 cm cone traps (Hartstack et al. 1979) were measured for three years at the
following selected locations: Dade, Palm Beach, Seminole, and Gadsden Counties, FL,
Tift County, GA, Baldwin County, AL, and Acadia County, LA (Fig. 1). In addition,
cone traps were positioned at several locations in Florida, Georgia, Alabama, South
Carolina, and Louisiana, to detect the initial FAW flights during the spring. One to
three traps were operated at each location and were positioned adjacent to corn fields
whenever possible. Traps at most of the locations were in continuous operation since
1982 although the numbers of sites and the seasonal duration of monitoring have varied
from year to year. During 1983 and 1984, traps were baited with 25 mg of a synthetic
pheromone mixture consisting of (Z)-9-dodecen-l-ol acetate (Z9 DDA) and (Z)-9-tetrade-
cen-l-ol acetate (Z9 TDA) in a 10:1 ratio (Mitchell 1979, Jones and Sparks 1979). In
1985, a four-component bait (Terochem") was used in all traps; this new formulation is
at least 5 times more attractive to FAW males than baits containing Z9 DDA and Z9
TDA (S. D. Pair et al. unpublished data). In all cases, pheromone baits were changed
every two weeks.
LARVAL SURVEYS: Host plants (primarily corn) were sampled for the presence of
FAW beginning in early spring each year in south Florida initially and in more northerly
areas as the season progressed. Previous studies had indicated that FAW rarely attack
other hosts when corn or sorghum is available (Pair and Sparks, in press); therefore,
efforts were concentrated on these two crops. Infestation levels were determined by
counting infested plants on 4 m of row at four locations per field. In most instances,











Pair et al.: Fall Armyworm Symposium


Baldwin Co.


[Palm Beach Co.


Fig. 1. Locations of primary weather and FAW trap data collection sites.


two to five fields were sampled for each location. When FAW were not observed in the
counts, a more thorough search of the field was conducted to determine if infestations
were actually present since in many cases these involved larvae hatching from only a
few isolated egg masses. Where volunteer corn was encountered, primarily in south
Florida, 50 plants were selected at random and examined for the presence of FAW
larvae. Infestations in each sampling area were assigned a number on a scale of 0-5 that
reflected the relative degree of infestation in each area as follows: 0 = no detection, 1
= 1-5%, 2 = 6-25%, 3 = 26-50%, 4 = 51-75%, and 5 = 76-100%.

RESULTS AND DISCUSSION

CLIMATIC TRENDS: Figure 2 illustrates the average rainfall, temperature, and
number of days with 0C or colder temperatures at Miami and Orlando, FL, Mobile,
AL, and Tifton, GA, during 1983-85. Highly variable departures from normal rainfall
were recorded during the spring at each location. Rainfall at Miami and Orlando tends
to be least in the spring and winter due to the subtropical climate. Rainfall at Mobile
and Tifton tends to be higher during the spring and fall months.
As expected, average spring and winter temperatures become progressively cooler
with increased latitude. Of the three years, 1985 was one of the coldest on record and
freezing temperatures were recorded as far south as Miami during January. However,
temperatures warmed rapidly and higher than normal average readings were recorded
at the Mobile and Tifton locations. Cold fronts and warming trends may be directly
involved in limiting FAW survival in their early spring movement northward. Prior to
and following cold fronts, adults may be transported northward with prevailing winds.
If suitable host plants are available and temperatures favor development and survival,
















Florida Entomologist 69(3)


September, 1986


FOUR-WEEK PRECIPITATION TOTAL WEEKLY MEAN AIR TEMPERATURE
''AT ION'T ON S ATI ON= T ON

5001


P
H
F
C
I 300-
P

T
A


S `


-__ *



2 3 4 56 7 9 C 2

FOJR-4EEK PtE IOD

LEGENDt YEAR --- NCRMA 0 J s 1983
* 1984 o 0 0 198'


WEEKLY NUMBER OF DAYS 0 C OR BE






6 -










D











]
1 : 4 o 0 9





0 70 o4C 2 0 28C 350
,J I AN DAY

; GFND YE AR 1- D 18j i
o o '985


1, A

Ir !
Ac


SC
r-


ND:


wLOw FOUR-
-


28'1 a .


JUl ;AN A V

EAR ---- ,R'AL [ D 983
A 984 o < 985


WEEK PRECIPITATION TOTAL
2 :- 2' : D 1


C 2 3 6 8 9

FCuR- wEK PFR

EGFND: YEA ORMA
1984


Fig. 2. Climatological records for Miami and Orlando,
GA, 1983-85.


FL, Mobile, AL, and Tifton,

















Pair et al.: Fall Armyworm Symposium


473


WEEKLY MEAN AIR TEMPERATURE WEEKLY NUMBER OF DAYS 0 C OR BELOW
ST;ATIO =" OBI F STAT:3N MOBI F


L*1
A


70 140 c~


61




J




D 3
i O;


0 /C 40 210 28 350
j_ IAN DAY


LEGEND; YFAR


1O8MA
: *o8'A


FOUR-WEEK PRECIPITATION TOTAL WEEKLY MEAN AIR TEMPERATURE
A': N CRL A', O '' T N Di L AND


F
P ID %'-
F 20-] "


i -..jy ~ h

R !5 n


n an





-t *



^;


0 140 2IC 280 J50 4,
K,1 j ) 31


,FND'; F4C


S NORMA
* 5 984


5 '
11,




M
M

;00


r N 41


SA 5 6 7 a 9 0 t

ObUr WFFK PERI OD

NORL [
1' 984


Fig. 2. Continued


1


* :98R
















474 Florida Entomologist 69(3) September, 1986



WEEKLY NUMBER OF DAYS 0 C OR BELOW FOUR-WEEK PRECIPITATION TOTAL
STAT :I OR.ANDO S AT ION MIAMI


A
Y
S 3- 3



2



0 00





0 70 140 210 280 350 420
JULIAN DAY
LEGEND= YEAR o o[ 1983 * 1984
o o o 1985


WEEKLY MEAN AIR TEMPERATURE
STATION MIAMI


7'- -- -


i 2 --I-- -

t ^"* '-















5







JUL I AN DAY
~-1






70 7 140 220 280 350 420


LEGEND: YEAR --- NORMAL 0 0 0 1983
1984 o o o 1985


0 70 140 210 280 350 420
JULIAN DAY
LEGEND: YEAR 0 0o 1983 * 1984
o o 1985


Fig. 2. Continued


500
a0OO

P
R
E
I 300



T
0 200 o








o *


!11 1

0123456789 1234
FOUR-WEEK PERIOD
LEGEND: YEAR -- NORMAL 0 0 0 1983
S* 1984 o o o 1985


WEEKLY NUMBER OF DAYS 0 C OR BELOW
STATION=MIAMI

7


b











Pair et al.: Fall Armyworm Symposium


an FAW infestation may develop. However, subsequent cold fronts with extended
periods of lower than normal temperatures do not favor survival. The degree of warming
following the typical coldest weather recorded in January of each year could determine
the rate of FAW population movement from south Florida. For example, the winter of
1983-84 was not as severe as 1982-83, but produced lower than average spring temper-
atures at all locations. These cooler temperatures prevailed during the spring months
longer during 1984 than in either 1983 or 1985. Further, at Tifton in March 1984, four
days of o0C or below were recorded while no freezing temperatures were recorded in
March, 1983 and 1985. Although the progression of larval infestations was similar in all
3 years, these cooler spring temperatures may account for the observed 3-week delay
in initial FAW adult captures at Mobile, AL, and the lengthy time interval between
second and third captures at Seminole County, FL, during 1984 (Fig. 3).
ADULT POPULATION TRENDS: Captures of FAW males at Dade and Palm Beach
Counties, FL, were similar in that the highest captures tend to occur during the spring
and in the late fall and winter months (Fig. 3). This bimodal occurrence of FAW popu-
lations in south Florida probably results from the distinct wet-dry seasons often as-
sociated with subtropical or tropical areas. A major peak in trap capture in Dade County
occurred between days 75-115 during all 3 years, while those in Palm Beach County
often consisted of several sharp peaks during the spring and thus were less defined in
terms of time. Catches at Palm Beach County were consistently greater in both the
spring and fall months than at Dade County or for any of the other trap locations. For
example, during 1985, a maximum of ca. 450 FAW males per night were captured on
day 60 in Palm Beach County compared with a maximum catch of ca. 240 per night in
Dade County on day 115. This may be explained by the increased availability of host
plants due to the season-long production of vegetables, including sweet corn, in the
more fertile soils in areas adjacent to Lake Okeechobee or these hosts may serve to
concentrate FAW moths migrating from other areas. Conversely, most of the hosts in
Dade County are grown in smaller-sized fields with marl-type soils that are typically
low in fertility, and are usually available to FAW only in the spring, winter, and fall
months.
The effects of winter temperature on FAW survival in more northerly locations in
Florida can best be illustrated through adult captures in Seminole County. FAW males
were captured during January of each year at or prior to the occurrence of subfreezing
temperatures, often in higher numbers than during the summer months. However, cold
January temperatures had the dual effect of destroying the host plants and FAW larvae,
and possibly pupae in the soil. In 1983, following the mid-January freezes, 11 FAW
males were trapped in February, one in March, but additional specimens were not
captured until 12 April. These few adults may have emerged from pupae in the soil that
were not killed by the freeze or may represent migrant adults from the south. In 1984,
following the mid-January freezing temperatures, FAW were not detected at all until
13 March.
Trap captures in Gadsden County, FL, are more indicative of distinct generational
peaks with the maximum numbers occurring in late summer and fall. Similar population
trends, differing only in magnitude of catches, were observed at Baldwin County, AL,
Acadia County, LA, and Tift County, GA. Although not presented, lower trap catches
were recorded at South Carolina locations, probably due to their more northerly location
and/or the relative scarcity of host plants, particularly corn.
Populations observed at Tift County consistently followed similar trends from year
to year and peaked at ca. day 200 each year. At Baldwin County, AL, catches generally
exceeded those observed at Tifton, particularly during the periods from day 100-200.













Florida Entomologist 69(3)


FAW TRAP CAPTURE
LOCATION=DADE CO, FL YEAR=83


100.0-



10.0-



1 .0-



0.1-





I mr r


0 73 146 219 292
JULIAN DATE
FAW TRAP CAPTURE
LOCATION=DADE CO. FL YEAR=85


100.0-



10.0-



1 .0-


100.0-



10.0-



1 .0-



0.1-


September, 1986


FAW TRAP CAPTURE
LOCATION=DADE CO, FL YEAR=84


365 0 73 146 219 292 365
JULIAN DATE
FAW TRAP CAPTURE
LOCATION=PALM BEACH. FL YEAR=83


100.0-



10.0-



1 .0-



0.1-


0 73 146 219 292 365
JULIAN DATE
FAW TRAP CAPTURE
LOCATION-PALM BEACH. FL YEAR-84
0- I


0 73 146 219
JULIAN DATE


100.0-



10.0-



1 .0-



0.1-


0 73 146 219 292
JULIAN DATE
FAW TRAP CAPTURE
LOCATION=PALM BEACH, FL YEAR=B5


292 365 0 73 146 219
JULIAN DATE


292 365


Fig. 3. Seasonal trap catches of FAW males at selected locations, 1983-85.


1000.


100.0-



10.0-



1.0-



0.1-


rA y


-



-



-



-


\N
















Pair et al.: Fall Armyworm Symposium


FAW TRAP CAPTURE
LOCATION=SEMINOLE, FL YEAR-83


1000.0 !


100.0-




10.0-




1.0-




0.1-


ionnn n.


100.0-




10.0-
O.-




1 .0-




0.1-


73 146 219 292
JULIAN DATE

FAW TRAP CAPTURE
LOCATION=SEMINOLE, FL YEAR=85


1000.0 -




100.0-




10.0-




I.0-




0.1-
0 73 146 219 292 365
JULIAN DATE

FAW TRAP CAPTURE
LOCATION=-ADSDEN CO, FL YEAR-84


1000.0-


146 219
JULIAN DATE


n000. 0


100.0-




10.0-




1.0-




0.1-


1 000.0 4


100.0-




10.0-




1.0-




0.1-


FAW TRAP CAPTURE
LOCATION=SEMINOLE. FL YEAR-84


0 73 146 219 292
JULIAN DATE

FAW TRAP CAPTURE
LOCATION-GADSDEN CO. FL YEAR=83


0 73 146 219 292
JULIAN DATE

FAW TRAP CAPTURE
LOCATION=GADSDEN CO. FL YEAR=85


92 365 0 73 146 219
JULIAN DATE

Fig. 3. Continued


292 365


477















Florida Entomologist 69(3)


FAW TRAP CAPTURE
LOCATION=BALDWIN CO. AL YEAR=83


10.0-



1.0-



0.1
0 73 146 219 292 3
JULIAN DATE

FAW TRAP CAPTURE
LOCATION=BALDWIN CO. AL YEAR=85

1000.0 -


100.0-



10.0-



1.0-



0.1-







1000.0-


100.0-



10.0-



1 .0-
S.-


0


-1



0 73 146 219 292 31
JULIAN DATE

FAW TRAP CAPTURE
LOCATION-ACADIA CO, LA YEAR=84


-- --I T
73 146 219 22
JULIAN DATE


100.0-1


1000.C


September, 1986


FAW TRAP CAPTURE
LOCATION=BALDWIN CO. AL YEAR=84


0 73 146 219 292
JULIAN DATE

FAW TRAP CAPTURE
LOCATION=ACADIA CO. LA YEAR=83


0 73 146 219 292 365
JULIAN DATE

FAW TRAP CAPTURE
LOCATION-ACADIA CO, LA YEAR=85


146 219
JULIAN DATE


Fig. 3. Continued













Pair et al.: Fall Armyworm Symposium


FAW TRAP CAPTURE
LOCATION-TIFT CO. GA YEAR=83


0 73 146 219
JULIAN DATE


FAW TRAP CAPTURE
LOCATION=TIFT CO. GA YEAR-B4


1000.0 I


100.0-

io-

10.0-



1.0-



0.1-


365 0 73 146 219 292 365
JULIAN DATE


FAW TRAP CAPTURE
LOCATION=TIFT CO. GA YEAR-85


100.0-



10.0-



1.0-




0 73 146 219 292 365
JULIAN DATE

Fig. 3. Continued

In 1984, unusually high catches occurred in Baldwin County from day 100-120; however,
catches declined thereafter and remained low for the remainder of the year. Indeed,
lower catches of FAW males were recorded in 1984 than in either 1983 or 1985 at all
locations except those in south Florida, possibly because of the cooler spring tempera-
tures occurring in 1984 or due to the increased efficiency of pheromones used in 1985.
SPRING LARVAL INFESTATIONS: During February 1983 and 1985, FAW larval
populations on volunteer or row crop corn were limited to areas below ca. 280N latitude
following the subfreezing temperatures in January of each year (Fig. 4). Highest spring
infestations were observed in extreme south Florida. The progression of infestations
from south Florida throughout peninsular Florida was similar for all 3 years, and larvae
were detected during mid- to late April each year in corn fields located in southwest
Georgia. In February 1983, FAW larvae were abundant on young volunteer corn in
Dade County, FL; however, March larval populations were decimated by heavy rains
(Steve Sims, personal communication). In April, infestations were detected in southwest
Georgia, and FAW were present throughout Florida and south Georgia in May.


479


1000.0 I


100.0-



10.0-



1 .0-



0.1-











Florida Entomologist 69(3)









c)
a,

0) O



C


September, 1986













Pair et al.: Fall Armyworm Symposium 481










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a, o









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ro
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Florida Entomologist 69(3)









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September, 1986











Pair et al.: Fall Armyworm Symposium


In 1983-85, infestations did not approach those observed in 1981-82 (Pair and Sparks,
in press). These earlier surveys and those of the present study indicate that FAW
infestations tend to be higher during May at locations in the Florida panhandle and
Baldwin County, AL, than in south Georgia. Hinds and Dew (1915) reported that FAW
infestations in Alabama were always detected earlier in Baldwin County than other
areas of the state. June infestations of FAW were greater near Charleston, S.C., than
inland locations of the state. Thus, warmer spring temperatures due to the proximity
of both locations to the warming influences of the ocean may advance FAW infestations.
Early appearances of FAW at Baldwin County, AL, could result from the prevailing
southeasterly winds blowing across southern Florida and/or other areas of the Carib-
bean which harbor overwintering populations.
INITIAL OCCURRENCE OF FAW MALES: The first and successive captures of FAW
males are illustrated in Figure 5 for the years 1983-85. Since continuous generations
occur throughout the year in southern Florida, these trap locations are not shown. In
the southernmost study area above the overwintering area (Seminole County, FL)
FAW males were often captured throughout December and January. However, follow-
ing invasion of polar air, no males were captured between 6 January and 13 March. The
influence of a colder than normal spring is reflected in the month delay at most locations
in captures of males during 1984.
A general northward and northwesterly progression of FAW trap captures through
time is indicated for north Georgia and South Carolina. Generally, FAW males were
captured in traps located in South Carolina during May and June. However, no FAW
were captured in Saluda County until 4 August 1983. Males were observed in Charleston
County 2 and 3 months prior to capture in other South Carolina locations in 1983 and
1985, respectively. FAW males often appeared in locations such as Baldwin County,
AL, which is northwest of southern Florida, prior to their capture in south Georgia and
Acadia County, LA, indicating that overwintering FAW populations in southern Florida
could be responsible for the annual reinfestation of crops along the Atlantic Seaboard
and the central Mississipppi Valley states.
Raulston et al. (in press) reported that FAW were not captured until days 150-180
at College Station, TX, in 1984-85 and that quite low FAW larval populations were
present in northeastern Mexico and the Lower Rio Grande Valley. This further suggests
that the southeastern states are a major contributory area to summer FAW populations
in the eastern U.S.
Figure 6 illustrates the typical weather patterns that are conducive to the northward
transport of FAW in the spring of 1983-85. These frontal systems occur at frequent
intervals in the spring across the U.S. The advance of these systems with their warm
southerly and southeasterly wind components ahead of the front may largely determine
the direction and extent of FAW adult movement. Prior to a particular frontal passage,
FAW were recorded at five sites in April 1983 and in 1984, and at eight sites in late
March 1985. After passage of these frontal systems, northerly wind components usually
prevail, and FAW captures are rarely observed until additional systems again move
into position and again produce the southerly winds. When FAW emergence in areas
of overwintering sites coincides with such weather events, long-range movement is
likely.

SUMMARY

These studies were conducted in "off-years" of FAW populations during which wide-
spread outbreaks did not occur. The initial captures of FAW males, coupled with the


483










Florida Entomologist 69(3)


First and Successive Occurrences
of FAW Males, 1983


/6/7

First and Successive Occurrences
of FAW Males,1984


4/
First and Successive Occurrences
of FAW Males, 1985


Fig. 5. First and successive captures of FAW males during 1983-85.


September, 1986











Pair et al.: Fall Armyworm Syttijini,,t


FAW Captures
April 8-11,1983
Prior to Frontal Passage


FAW Captures
April 26-30,1984
Prior to Frontal Passage


FAW Captures
March 26-31,1985
Prior to Frontal Passage


Fig. 6. Frontal systems associated with the capture of FAW males in pheromone
traps during the spring months, 1983-85.

progression of FAW larval infestations in corn, implicate south Florida as a major
contributor of FAW to areas of the eastern U.S. and perhaps southwestern Alabama.
The influence of severe winters as the determining factor for FAW outbreaks in any
one season has not been resolved. Certainly, the conditions that follow particularly
severe influxes of polar air into Florida may play even greater roles on FAW population
dynamics than temperature extremes alone.
Volunteer and commercial seed corn are the primary overwintering host reservoirs
for FAW in south Florida. Production of seed corn requires insecticidal applications to
prevent severe FAW attack and yield losses; thus, FAW mortality due to parasitism
is higher in volunteer corn. However, spraying of seed corn in the latter stages of


485











Florida Entomologist 69(3)


maturity may be terminated, allowing FAW to develop in the ear stages. Similarly,
fields of sweet corn are sometimes abandoned because of low market values, allowing
FAW to develop in the ears. Prior to ca. 1981, most seed-corn was planted during late
fall and winter and matured in January-February (Van Waddill, personal communica-
tion). Corn maturing at these times produced FAW at a time well suited for adult
emergence and movement onto corn in central Florida during March and April. How-
ever, in recent years, planting dates have been changed to August to avoid winter kills
of late fall and winter plantings in extreme south Florida. Corn planted in August
matures by December, and FAW produced at this time emerge prior to the time corn
is available during March and April in more northerly areas of Florida. Furthermore,
migrant FAW moths in December-February, as well as larvae they produce, would
have to contend with the cold weather normally associated with.January and February.
Other important factors often overlooked are the times of planting and extent of
corn hectarage available for FAW colonization each year in north Florida and south
Georgia. For example, during the outbreak of 1977 following a severe winter, 0.9 million
ha of corn were planted in Georgia alone. This situation presented a tremendous poten-
tial for producing overwhelming FAW populations in the absence of mortality factors.
In comparison, greatly reduced acreages (0.3-0.4 million ha/yr) of corn were planted in
Georgia from 1982-85.
The factors determining "normal" and "outbreak" years require additional long-term
studies of FAW population dynamics, particularly the relationship of weather and host
availability during the early spring months. A large hectarage of corn in north Florida
and southern Alabama and Georgia, planted at an opportune time for a synchronous,
massive FAW invasion from overwintering sites, may well determine the magnitude of
FAW densities in northerly areas during summer and fall months.




REFERENCES CITED

HARTSTACK, A. W., JR., J. A. WITZ, AND D. R. BUCK. 1979. Moth traps for the
tobacco budworm. J. Econ. Ent. 72: 519-522.
HINDS, W. E., AND J. W. DEW. 1915. The grass worm or fall armyworm. Alabama
Agric. Exp. Stn. Bull. 186: 61-92.
HOGG, D. B., H. N. PITRE, AND R. E. ANDERSON. 1982. Assessment of early-season
phenology of the fall armyworm (Lepidoptera: Noctuidae) in Mississippi. Envi-
ron. Ent. 11: 705-710.
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: 721-725.
LUGINBILL, P. 1928. The fall armyworm. USDA Tech. Bull. No. 34.
MITCHELL, E. R. 1979. Monitoring adult populations of the fall armyworm. Florida
Ent. 62: 91-98.
MULLER, R. A. 1979. Synoptic weather types along the central Gulf Coast: variability
and predictability. Pages 133-146 In R. L. Rabb and G. G. Kennedy, eds. Move-
ment of highly mobile insects: concepts and methodology in research. North
Carolina State Univ., Raleigh.
PAIR, S. D., AND A. N. SPARKS. 1986. Evidence of annual long distance migration
by the fall armyworm. In A. N. Sparks (ed.), Long-Range Migration of Moths
of Agronomic Importance to the United States and Canada: Specific Examples
of Occurrence and Synoptic Weather Patterns Conducive to Migration (ESA
Symposium, 1982). USDA Misc. Publ. (In press).


September, 1986











Pair et al.: Fall Armyworm Symposium


RAINEY, R. C. 1979. Interactions between weather systems and populations of locusts
and noctuids in Africa. Pages 109-119. In R. L. Rabb and G. G. Kennedy, eds.
Movement of highly mobile insects: concepts and methodology in research. North
Carolina State Univ., Raleigh.
RAULSTON, J. R., S. D. PAIR, A. N. SPARKS, J. LOERA G., F. A. PEDRAZA M., A.
PALAMON, T., A. ORTEGA, J. R. SANCHEZ M., P. MARQUEZ C., H. RULES
A., JOEL PEREZ M., R. RODRIGUEZ R., H. CARILLO R., R. ARCHUNDIA R.,
AND FRANCISCO HUERRERA R. Fall armyworm distribution and population
dynamics in the Texas-Mexico Gulf Coast area. Florida. Ent. 69: 455-468.
SNOW, J. W., AND W. W. COPELAND. 1969. Fall armyworm: use of virgin female
traps to detect males and to determine seasonal distribution. USDA Prod. Res.
Rep. No. 110.
SPARKS, A. N. 1979. A review of the biology of the fall armyworm. Florida Ent. 62:
82-87.
VICKERY, R. A. 1929. Studies of the fall armyworm in the Gulf Coast district of
Texas. USDA Tech. Bull. No. 138.
WADDILL, V. H., E. R. MITCHELL, W. H. DENTON, S. L. POE, AND D. J. SHUSTER.
1982. Seasonal abundance of the fall armyworm and velvetbean caterpillar
(Lepidoptera: Noctuidae) at four locations in Florida. Florida Ent. 65: 350-354.









ADULT SAMPLING AS A MEANS OF PREDICTING DAMAGE
LEVELS OF FALL ARMYWORM
(LEPIDOPTERA: NOCTUIDAE) IN GRAIN CORN

JAMES J. LINDUSKA AND FLOYD P. HARRISON
Department of Entomology
University of Maryland
College Park, MD 20742

ABSTRACT

Any attempt to correlate adult fall armyworm, Spodopterafrugiperda (J. E. Smith)
captures with infestation is complicated because plant maturity at the time migrating
moths arrive in Maryland determines the extent to which larvae infest and damage
corn, Zea mays L. Plants in mid-whorl and older escape injury whereas younger plants
become infested. This work attempts to explain the difference maturity makes in suscep-
tibility to fall armyworm and to correlate moth trap catches in pheromone traps with
percent plants becoming infested. Observations in 4 separate plantings indicated the
number of neonate larvae is reduced when Pioneer 3184 grain corn attained a maturity
level of ca. 40% tassel-height ratio. The time from emergence from the soil to 40% T-H
was hypothesized as a susceptible period. A regression analysis of % plants infested
and moths captured in pheromone traps during this susceptable period resulted in a
significant regression and an r2 of 0.87.











488 Florida Entomologist 69(3) September, 1986

RESUME

Cualquier intent para correlacionar adults capturados del gusano cogollero,
Spodoptera frugiperda (J. E. Smith) con infestaci6n es complicado porque la madurez
de las plants en el tiempo que las alevillas migratorias llegan a Maryland determine la
magnitude a la cual las larvas infestan y dafian el maiz, Zea mays L.. Plantas a medio
verticilo y mas viejas escapan la lesi6n, mientras que las plants jovenes son infestadas.
Este trabajo intent explicar la diferencia que la maduraci6n de las plants hace en la
susceptibilidad al gusano cogollero y de correlacionar la capture de alevillas atrapadas
en trampas de feromonas con el por ciento de plants infestadas. Observaciones en 4
plantaciones separadas indicaron que el numero de larvitas es reducido cuando granos
de maiz Pioneer 3184 alcazan un nivel de maduraci6n aproximado al 40% de la proporcion
espiga-altura. La etapa desde el brote de la plant hasta el 40% de espiga-altura fue
formulada como un period susceptible. Un analisis de regresion del % de plants infes-
tadas y de alevillas capturadas en trampas de feromonas durante este period suscepti-
ble result en una regresi6n significativa y una r2 de 0.87.



The behavior of fall armyworm (FAW), Spodopteraffrugiperda (J. E. Smith), in corn
Zea mays L. complicates estimation of damage. Egg masses are deposited on corn
plants, larvae move into whorls and remain obscure for some time. Foliar feeding is not
always visible until the larvae have attained some size (Harrison, unpublished). As a
result, an economic injury level as defined by Stern (1973) may be reached before visible
evidence of infestation occurs. Internal ampling is time consuming and objectionable to
farmers. A need exists, therefore, for a reliable and practical method of sampling. Adult
sampling may be practical but there are problems inherent to the technique which
complicate interpretation of data. Hunt (1980) and Harrison (1984) have demonstrated
the relationship between age of corn and susceptibility to FAW. Older corn escapes
injury while younger corn is attacked when subjected to the same populations of
ovipositing moths (Table 1).
This work attempts to test the hypothesis that: (a) there is a limited period of plant
development which offers a favorable environment for young larvae and; (b) the number
of adults captured in traps baited with sex attractants during this period correlates with
damage levels.

MATERIALS AND METHODS

This work was conducted from 1983-85 at the University of Maryland Poplar Hill
Research Farm near Quantico, Md. on the lower Eastern Shore and on nearby privately-
owned land. Each year a series of plantings ca. 30 x 15 m of Pioneer 3184 grain corn
was planted at Poplar Hill, the dates are shown in Table 1. In order to provide more
variation for comparison of damage levels with moth captures, a similar planting was
made at each of three privately-owned farms on June 8, 1984. Prior to the presence of
FAW, 10 plots of 10 plants each were randomly established in each planting. Each plot
was examined daily for FAW feeding. The final examination was made in each plot
when the plants were in full tassel. A Pherocon 1C trap (Zoecon Corp., Palo Alto, Calif.)
was suspended 1 m high from a metal rod located within 10 m of each planting. Only 1
trap was established for the contiguous plantings made each year at Poplar Hill. The
traps were baited with a sex attractant produced, purified and furnished by the Organic
Chemical Synthesis Laboratory, Agricultural Environment Quality Institute in


___











Linduska & Harrison: Fall Armyworm Symposium


TABLE 1. THE EFFECT OF PLANTING DATES ON THE PERCENTAGE OF PLANTS
INFESTED BY FALL ARMYWORM, QUANTICO, MD 1983-85.

Year Planting Date % Plants Infested

1983 May 24 6
May 31 1
June 7 20
June 14 41
1984 May 24 6
May 31 5
June 7 52
1985 May 27 3
June 3 12
June 10 28
June 17 46



Beltsville, Md. The attracant was a mixture containing 50 mg (Z)-9-dodecenyl acetate
plus 2.4 mg (Z)-9-tetradecenyl acetate. The compounds had been purified by high pres-
sure liquid chromatography (Jones and Sparks 1979) and were 98% pure according to
gas chromatographic analysis. This binary mixture was placed in a plastic snap top 2/5
dram vial (Olympic Plastics Co., Los Angeles, Calif.) and the closed vial was placed in
the trap. Traps were examined and FAW male moths were counted and removed daily.
Traps were replaced every 14 days.
In 1984, an additional planting ca. 0.1 ha was made on June 8. On July 17 when the
plants were ca. 135 cm high and exhibited a 60% tassel-height ratio (T-H) (Luckman
and Decker 1952), 100 plants were selected at random and examined internally for the
number and instar of larvae which provided an age distribution profile. The T-H is a
ratio of the height of the developing tassel within the plant to the total plant height.
The same observations of larvae were made on July 24 and July 31. In 1985, 3 similar
plantings were made on June 3, 10 and 17. Beginning the 2nd week of July, before any
visible evidence of FAW feeding appeared, and when plants in the 3 plantings ranged
in height from ca. 60 cm to 140 cm and from 0 to 60% T-H, the same observations of
FAW larvae were made as in 1984. These observations were made weekly for 5 weeks.

RESULTS AND DISCUSSIONS

Table 2 summarizes the results of the observations made of the age distribution of
larvae in the plants that were observed in 1984 and 1985. These data show that in each
case the proportion of 1st and 2nd instar larvae dropped abruptly at ca. the same stage
of plant development, independent of planting date. Counts of egg masses were made
daily. Because daily counts of egg masses indicated oviposition continued beyond the
time of these observations, this reduction in the proportion of neonates was not caused
by a reduction of egg laying activity, but is interpreted to indicate that at some time
plants cease to offer a favorable environment for hatching larvae. In each case, the
reduction occurred between 31% and 49% T-H which was concurrent with a period
ranging from 38 to 46 days post planting. This suggests a period of susceptibility for
initial infestation, under our conditions, from emergence from the soil until ca. 40 days
post planting for this variety of corn. The limited period of plant development as stated











Florida Entomologist 69(3)


TABLE 2. THE EFFECT OF PLANT MATURITY ON THE NUMBER AND AGE DISTRI-
BUTION OF FALL ARMYWORM LARVAE IN CORN, QUANTICO, MD 1984-
1985.

No. Larvae/instar
Days % in 100 plants
Planting Date of post Tassel-
date Observation plant Height 1&2 3 4 5th Total

6/8/84 7/17 39 28 32 59 10 0 101
7/24 46 42 8 42 28 22 100
7/31 53 68 6 6 44 44 100
6/3/85 7/10 39 47 0 0 0 47
7/17 43 26 9 20 0 0 29
7/23 50 41 3 6 0 0 9
7/31 57 66 0 4 9 10 23
8/6 64 76 0 3 2 8 14
6/10/85 7/10 26 21 15 0 0 36
7/17 33 32 32 27 0 0 59
7/23 39 49 2 18 25 13 58
7/31 47 54 0 1 1 5 7
8/6 53 59 0 2 2 1 5
6/17/85 7/12 25 37 0 0 0 37
7/18 31 36 39 5 0 80
7/25 38 31 1 6 14 32 53
8/1 45 43 0 3 1 4 8
8/8 52 50 0 0 0 2 2


in (a) of the previously stated hypothesis is therefore from emergence to 40 days post
planting. Acceptance of both of these hypothesis, i.e., (a) and (b) is contingent upon a
significant regression of % infested plants and moths captured during this period of
susceptibility.
Fig. 1 shows the regression of the number of captured moths on the percent of
infested plants. The percent plants infested are those percentages in Table 1 as well as
the percentages observed in the 3 plantings on privately-owned land in 1984. The vari-
ables are highly correlated (r2 = .87, P < 0.001) inferring that the trapping system was
adequate to predict the level of infestation that will occur as expressed by % infested
plants. Comparisons of moth captures for periods shorter and longer than the time
period indicated in this study did not result in significant regression. Other trapping
systems and varieties of corn may undoubtedly result in different prediction models,
nevertheless, for our conditions, the use of trap catches may be a reliable index of %
plants that will become infested.

ENDNOTES


Contribution No. 7272 Scientific Article No. A-4287.


490


September, 1986











Linduska & Harrison: Fall Armyworm Symposium


Total No. Moths/ Trap
Fig. 1. The relationship between fall armyworms captured from the time of seedling
emergence to 40 days post planting and the percent plants infested.



REFERENCES CITED

HARRISON, F. P. 1984. Observations on the infestation of corn by fall armyworm
(Lepidoptera: Noctuidae) with reference to plant maturity. Florida Entomol. 67:
333-5.
HUNT, T. N. 1980. Monitoring and predicting fall armyworm infestations in North
Carolina. Florida Entomol. 63: 361-3.
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. Chem. Ecol. 5:
721-5.
LUCKMAN, W. H., AND G. C. DECKER. 1952. A corn maturity index for use in
European corn borer ecological and control investigation. J. Econ. Entomol. 45:
226-32.
STERN, V. M. 1973. Economic thresholds. Ann. Rev. Entomol. 18: 259-80.











Florida Entomologist 69(3)


THE ROLE OF ATMOSPHERIC TRANSPORT IN THE
ECONOMIC FALL ARMYWORM
(LEPIDOPTERA: NOCTUIDAE) INFESTATIONS IN THE
SOUTHEASTERN UNITED STATES IN 1977

J. K. WESTBROOK AND A. N. SPARKS
U.S. Department of Agriculture, Agricultural Research Service,
Insect Biology and Population Management Research Laboratory
Tifton, GA 31793

ABSTRACT

Abnormally cold air penetrated into the southeastern U.S. in January, 1977 for a
duration of time sufficient to virtually eradicate the fall armyworm, Spodoptera
frugiperda (J. E. Smith), populations as far south as Homestead, FL. However, anomal-
ously warm, wet conditions developed in late winter to enhance the host crop environ-
ment for the reintroduction and subsequent development of fall armyworm populations
that caused extreme agricultural losses in the southeastern U.S. in 1977. Atmospheric
data for the southern U.S., Mexico, Central America, and the Caribbean Islands for
the period October 1976-June 1977 revealed atmospheric anomalies which were signific-
antly correlated with the population dynamics and dispersal of the 1977 fall armyworm
populations. Retrogressive atmospheric trajectories targeted probable fall armyworm
overwintering regions which impacted the southeastern U.S.

RESUME

Un frente normal de aire frio penetr6 el sudeste de los Estados Unidos en Enero
de 1977 por un period de tiempo suficiente para virtualmente erradicar al gusano
cogollero, Spodopterafrugiperda (J. E. Smith), hasta tan al sur como Homestead, Flor-
ida. Sin embargo, se desarrollaron condiciones an6malas calientas y humedas tarde en
el invierno, que mejoraron el medio ambiente del cultivo hospedero para la reintroduc-
ci6n y subsequent desarrollo de poblaciones del gusano cogollero que caus6 grandes
perdidas agricolas en el sudeste de los Estados Unidos en 1977. Datos atmosfericos del
sur de los Estados Unidos, M6xico, America Central, y las Islas del Caribe, del period
de Octubre 1976 a Junio 1977, revel6 anomalias atmosf6ricas que estaban sig-
nificativamente correlacionadas con el dinamismo de poblaci6n y dispersion de la pobla-
ci6n del gusano cogollero en 1977. Trayectorias atmosf6ricas retrogresivas sefalaron
posibles regions donde los gusanos cogolleros invernaron y que afectaron el sudeste de
los Estados Unidos.



Agricultural losses and costs for controlling the fall armyworm (FAW), Spodoptera
frugiperda (J. E. Smith), soared to a value of nearly $300 million for the southeastern
U.S. in 1977-an order of magnitude greater than the composite 1975-1976 and 1978-
1980 average (Entomol. Soc. of Amer. 1977, 1978, 1979, 1980, 1982). FAW populations
exhibited extreme interannual variability in densities and subsequent agricultural losses
to FAW in the southeastern U.S. (Fig. 1). The FAW outbreak of 1977 was particularly
severe in Georgia where agricultural losses and costs of control amounted to $135 mil-
lion. The severity of the 1977 FAW outbreak combined with severe summer drought


September, 1986











Westbrook & Sparks: Fall Armyworm Symposium


A
at


LOSSES MILLIONSS OF DOLLARS)


a0 To I
OTO g2 TO I0
2I TTO SO
SI TO 10 100 1 TO 10

Fig. 1. Agricultural losses and costs of control for the fall armyworm in the south-
eastern U.S. (E.S.A. Southeastern Branch Reports, 1975-1980.)


in many areas greatly reduced the agricultural productivity of the southeastern U.S.
Normally, FAW populations progress slowly northward in the spring from more south-
erly overwintering sites (Sparks 1979); however, agriculturists of the southeastern U.S.
were not prepared for the 1977 FAW outbreak. The mobility of the FAW moths enabled
populations to be quickly re-established north of overwintering regions in the spring.
Insecticide efficiency and available insecticide quantities were unable to suppress the
FAW below economic levels in 1977 (J. R. Young, personal communication, 1985).
This extreme interannual variability of FAW populations was noted by Luginbill
(1928) who documented severe FAW outbreaks in the southeastern U.S. in 1899, 1912,
and 1920. Luginbill (1928) stated that outbreaks which were especially broad and severe
apparently originated in Mexico and the West Indies. He suggested that prevailing
winter weather in overwintering habitats governed the probability of a greater invasion
of FAW in the U.S. The FAW reportedly thrived during cool, wet weather; and locally
severe outbreaks in the southern U.S. occurred only after a period of heavy rainfall and
humid weather. Bodkin (1913) reported that an early-season, prolonged, severe drought
followed by rains may have caused the 1912 FAW outbreak in British Guiana. Warm
temperatures were known to accelerate insect development and increase the probability
of multiple generations of FAW within a region.
Avenues of northward FAW transport have not been adequately determined. Lugin-
bill (1928) indicated that the southeastern U.S. is apparently invaded by migrant moths
from Florida northwestward to the Gulf Coast, then northeastward along the Atlantic
Seaboard. Luginbill (1928) speculated that moths from an overwintering source in the
extreme southern region of Texas may have migrated northeastward into Louisiana,
then northward into the central U.S. Franceschini (1954) documented several 610-m










Florida Entomologist 69(3)


altitude atmospheric trajectories which corroborated the trans-Gulf migration pathway
suggested by Luginbill (1928). Young (1979a) suggested a Western Mexico or Central
America to Georgia migratory route based upon 1977 FAW larval infestations. Pair and
Sparks (in press) documented the progression of FAW populations from southern Flor-
ida during 1981-1982 and indicated that initial trap catches of FAW males were often
associated with southerly winds from certain synoptic weather systems.
This research investigated the climatic environment which coincided with the 1977
FAW outbreak in the southeastern U.S. The objectives were to: (1) determine the
potential impact of the 1977 temperatures on the FAW population dynamics, (2) de-
lineate probable sources of overwintering FAW, and (3) determine the potential role of
atmospheric transport on the location and timing of the 1977 FAW outbreak. Ulti-
mately, an FAW infestation alert may be based upon these atmospheric variables with
the knowledge of specific source areas.

MATERIALS AND METHODS

INSECT INFESTATIONS AND CROP LOSSES

Reports of the progression rate and severity of FAW populations were not generally
collected in 1977 until the outbreak developed to extreme proportions. Indeed, Waddill
et al. (1982) studied the seasonal abundance of FAW at four locations in Florida from
1975 to 1977 but did not report unusually high larval populations during the spring of
1977. However, the U.S. Department of Agriculture (USDA) (1977), based upon scout-
ing reports, periodically reported the spread and severity of the FAW infestations
during 1977 for the entire U.S. These USDA reports and Entomological Society of
America (ESA) Southeastern Branch reports (Entomol. Soc. Amer. 1977, 1978, 1979,
1980, 1982) quantified the intensity and duration of the anomalously severe 1977 FAW
outbreak in the southeastern U.S.

SOIL TEMPERATURE AND FAW APPEARANCE

Temperature directly affects insect phenological development from the egg stage
through emergence to an adult moth. The environment in which the insect develops
varies from plant canopies to soil. A single source (5 cm soil depth) for temperature
measurements allows for the development of pupae already in the soil in the winter and
provides a close approximation to air temperature prior to hot summer days beneath a
crop canopy. FAW spring appearance is here determined as the initial emergence date
for first-generation moths.
Soil temperature data (U. S. Dept. of Commerce-NOAA unpublished-a) were avail-
able from the National Climatic Data Center (NCDC). The NCDC recorded daily
maximum, daily minimum, and/or observation time soil temperatures. The daily mean
(Tm) 5 cm soil temperature was calculated as the arithmetic mean of the daily maximum
(Tx) and daily minimum (Tn) 5 cm soil temperatures

Tm = (T, + Tn) / 2. (1)

The daily mean 5 cm soil temperature was assumed to equal the observation time 5 cm
soil temperature (To) for stations which did not report Tx and T,


494


September, 1986











Westbrook & Sparks: Fall Ariinyworm Symposium


Tm = To when Tx and Tn were unavailable. (2)


Initial spring appearance of FAW moths was calculated for numerous sites in the
Southeast from the daily mean 5 cm soil temperature data. The estimated FAW develop-
ment was based upon the accumulation of day-degree (DD) heat units above a threshold
temperature (Tt) of 13.80C. The mean heat units to complete FAW pupal development
were computed according to the method of Hogg et al. (1982)

DD = (Tm Tt) (3)

and adult FAW moth appearance (egg-larva-pupa-moth) occurred at

Sum (DD) = 339.6 day-degrees. (4)

Several stations reported soil temperatures only at the 2.5 cm and 10 cm depths; the 5
cm FAW appearance date (ED2) was here linearly interpolated from the estimated
values at the 2.5 cm (ED1) and 10 cm (ED4) depths.

ED2 = ED, + (ED, ED4) / 3. (5)

The 5 cm FAW appearance date was extrapolated from a single depth (2.5 or 10 cm)
via an appearance-date profile slope of an adjacent station with similar soil characteris-
tics.

ATMOSPHERIC TRAJECTORIES

Twice-daily upper-air profile data were acquired from the NCDC on magnetic tape
(U. S. Dept. of Commerce-NOAA unpublished-b). Data were available for the surface,
1000 mb pressure-height and 50 mb decrements, thereafter. Atmospheric trajectories
were computed for the 950-mb pressure-height (ca. 500-600 m above mean sea level
(MSL)) as a representative flight altitude for the FAW moths (Wolf et al. in press).
Coincidentally, the 950-mb pressure-height closely approximated the 610-m MSL al-
titude chosen by Franceschini (1954) for gradient trajectories across the Gulf of Mexico.
The NCDC upper-air data were commonly reported only at 0000 Greenwich Mean Time
(GMT) and 1200 GMT.
A modified form of the National Weather Service (NWS) trajectory model (Reap
1972) computed retrogressive 24-h trajectories from a selected destination. Rose et al.
(1975) concluded that migratory FAW moths from Mississippi to Sault Ste. Marie,
Ontario, required as much as 30 h of flight time. The trajectory terminus (Tifton, GA)
represented the Coastal Plain agricultural region of Georgia which was heavily infested
by FAW in 1977. The 24-h atmospheric trajectories were initiated at 0000 GMT (approx-
imately sunset) backward in time to 0000 GMT of the previous day. Thus, the start hour
at the trajectory origin closely approximated the initiation of observed FAW flight
activity (shortly after sunset) (Luginbill 1928).
Retrogressive 12-h trajectory points were calculated from the 0000 GMT and 1200
GMT wind velocity data to compose the 24-h trajectory. The first estimate (X1) of the
12-h retrogressive trajectory point x-coordinate was calculated from the terminus point











Florida Entomologist 69(3)


(X0), the x-component wind speed (Uo(t)) at the terminus point and initial time (t), and
the 12-h transport time increment (Dt)

X, = Xo Uo(t) Dt. (6)

The x-component wind speed (Ul(t-Dt)) at point X, and time (t-Dt) was then averaged
with Uo(t) to compute the second estimate (2) of the 12-h trajectory x-coordinate (X2).
An iterative algorithm computed successive estimates (Xn) of the 12-h retrogressive
trajectory x-coordinate

Xn = XO ((Uo(t) + Un(t-Dt)) / 2) Dt for n =' 2, 3, 4, ...N (7)

For this paper a value of N = 5 was selected to reduce the computational instability of
the trajectory point estimates. The 24-h trajectory origin was calculated from the 12-h
trajectory x-coordinate (X5) by resetting the origin (X0 = X5) and following steps (6)
and (7). The computations were repeated to calculate y-coordinate trajectory points
(Yn) using the y-component wind speed (Vn).

RESULTS

CLIMATOLOGY

Climatological records (Taubensee 1977a,b,c, Wagner 1977a,b,c, Dickson 1977a,b,c)
revealed an abnormally cold, wet period from October, 1976 until mid-February, in the
southeastern U.S., caused by persistent atmospheric high pressure over the eastern
U.S. Many low temperature records and record snowfall amounts were reported (Table
1). The global circulation transported cold Arctic air from Alaska and Canada deep into
the southern U.S. where freezing temperatures and snow flurries were reported for
the first time on record at Miami Beach, FL. The persistence of the atmospheric circu-
lation was typified by the extent of the abnormally cold months.
A notable change in the February, 1977 mean temperature distribution of the south-
ern U.S. was evident relative to the 4 previous cold months. A warming trend was
observed in the extreme northwest corner of the southeastern U.S., including Arkansas
and sections of Tennessee, Mississippi, and Louisiana. The warming trend occurred as
a persistent high-pressure ridge progressed eastward to the midwestern U.S. The east-
ward progression of the hig-pressure ridge continued through the spring and caused
abnormally warm temperatures for the majority of the southeastern U.S.

ESTIMATED FAW APPEARANCE DATES

Estimated initial FAW appearance dates were computed for 1977 and the 1967-1980
composite (exclusive of 1977) based on 5 cm soil temperatures. These dates revealed
earlier than normal estimated FAW appearance dates throughout most of the southeast-
ern U.S. despite the abnormally cold temperatures of January-February, 1977 (Fig. 2).
Estimated 1977 FAW appearance occurred prior (R = -11.9 days) to normal estimated
FAW appearance at 39 stations. Only 2 stations showed a delayed (R = +1.5 days)
appearance in 1977. A close examination of the day-degreee accumulations at Tifton,
GA, and Taylor Creek, FL (27.38 North latitude and 80.88 West longitude), exhibited


September, 1986












Westbrook & Sparks: Fall Armyworm Symposium


TABLE 1. RECORD CLIMATIC EVENTS IN THE


NOVEMBER, 1976
SERVICE RECORDS)


THROUGH APRIL,


SOUTHEASTERN U.S. FOR
1977. (NATIONAL WEATHER


Date Station Event Record*


Fort Smith, AR
Tallahassee, FL
Alexandria, LA
Baton Rouge, LA
Shreveport, LA
Meridian, MS
Columbia, SC
Fort Smith, AR
Ft. Meyers, FL
Lakeland, FL
Lakeland, FL
Miami Beach, FL
Pensacola, FL

Tallahassee, FL
Tampa, FL
W. Palm Beach, FL
Athens, GA
Atlanta, GA
Augusta, GA
Rome, GA
Savannah, GA
Baton Rouge, LA
Shreveport, LA
Jackson, MS
Asheville, NC
Cape Hatteras, NC
Greensboro, NC
Charlotte, NC
Chattanooga, TN
Knoxville, TN
Nashville, TN
Columbia, SC
Wilmington, NC


Tn = -13.3C
265 mm rain
Tn = -7.8C
T, = -6.1C
Tn = -8.9C
Tn = -6.1C
1915 mm rain
Tm = -3.1C
Tm = 13.3C
Tm = 11.1C
2.5 cm snow
Snow flurries
6.4 cm snow

Tm= 6.6C
Tm = 10.7C
Tm = 14.7C
Tm = -0.4C
Tm = -1.5C
Tm= 1.9C
Tm = -1.7C
Tm= 4.4C
Tm = 5.4C
Tm= 2.9C
Tm= 1.8C
Tm = -4.0C
Tm,= 2.1C
Tm = -2.9C
Tm = -1.1C
Tm = -1.9C
Tm = -2.7C
Tm = -4.2C
Tm = 2.1C
Tm = 18.8C


Nov. 1976





Dec. 1976
Jan. 1977















Jan. 1977










Apr. 1977


*Coldest for month on record unless otherwise noted.
T, = minimum air temperature.
T,, = average air temperature.




an estimated FAW egg hatch delay (+6 and +35 days, respectively), an estimated
larval completion date anomaly (+7 and -17 days, respectively), and an estimated pupal
emergence date anomaly (+8 and -16 days, respectively). The abrupt transition to ab-
normally warm temperatures in late February, 1977 occurred more than 1 month after
temperatures normally exceeded the 13.80 FAW developmental threshold temperature
at Taylor Creek, FL. The onset of FAW day-degrees occurred 1 week before normal
at Tifton, GA.


3rd wettest for month


3rd coldest for month

'Wettest for month
3rd coldest for month

Coldest
1st measurable snow
First
1st month with measur-
able snow twice
2nd coldest for month

Coldest
Coldest


Coldest


2nd coldest for month
2nd coldest for month





2nd coldest for month
Coldest
2nd coldest for month
3rd warmest for month










Florida Entomologist 69(3)


Fig. 2. Estimated first generation fall armyworm appearance dates for 1977 in days
before (-) or days after (+) normal (1967-1980) estimated first generation fall armyworm
moth appearance dates.


TAYLOR CREEK. FLORIDA


5001


100 150


JULIAN DATE

LEGEND, YEAR


0


Fig. 3. Normal (1971-1981) and 1977 day-degree accumulations (13.8C threshold)
for fall armyworm phenological development at Taylor Creek, FL and Tifton, GA.


500-







0


TIFTON, GEORGIA


50
JUL IAN


100 150
DATE


** 1977
e-a-e NORMAL


September, 1986


498











Westbrook & Sparks: Fall Armyworm Symposium


TRAJECTORIES
Retrogressive atmospheric trajectories from Tifton, GA, were calculated for the 950
mb pressure altitude. These 24-h trajectories revealed likely source regions of migrant
moths in the southeastern U.S. in 1977. The trajectories demonstrated wide scatter in
both direction and displacement. The sole trajectories to exhibit transport potential
from likely source areas during January, 1977 occurred on January 9 from Tampa, FL,
and on January 14 from Key West, FL. However, both of these trajectories occurred
prior to the extremely cold surge of air on January 20 to southern Florida.
Atmospheric trajectories in February demonstrated a quick recovery of the south-
erly atmospheric transport potential. Five trajectories were targeted as probable insect
transport cases. Especially noteworthy were the February 23, 26, and 27 trajectories
that originated near the Bahama Islands, Homestead, FL, and western Cuba, respec-
tively. Almost every other atmospheric trajectory computed for the month of February
entered Tifton from the northwest quadrant.
The March atmospheric trajectories showed pronounced FAW transport potential
from likely overwintering regions in the Caribbean basin. The March 4 atmospheric
trajectory began in central Cuba and curved west of the Florida peninsula to terminate
at Tifton, GA. Atmospheric transport from the Bahama Islands occurred on March 12
and 28. Transport on March 29 and 30 could have displaced FAW moths from areas
near Key West, FL, to Tifton, GA.
Four cases of southerly transport from overwintering areas occurred in April. The
April 2 and 4 trajectories began near Key West, FL and northwestern Cuba. Atmos-
pheric transport began near the Bahama Islands on April 22 and 23. Other April atmos-
pheric trajectories were scattered to the northwest and southeast of Tifton, GA.
A single atmospheric trajectory from a probable source appeared in May. The May
4 trajectory started near east-central Florida and traversed the Florida peninsula to
Tifton, GA. The majority of the retrogressive trajectories to Tifton, GA, were initiated
from the Atlantic Ocean.
No notable southerly transport was documented in June. The majority of the atmos-
pheric trajectories were computed to enter Tifton from the northwest. The atmospheric
transport potential for northward-bound FAW moths effectively ended in June concur-
rent with the westward intrusion of the atmospheric high pressure along the southern
Atlantic Coast, a normal summertime phenomenon.

DISCUSSION AND CONCLUSIONS

The severe FAW infestations of 1977 showed the rapidity with which mobile pest
insect populations can rebound in a favorable environment despite severe environmental
conditions earlier in the year. Specifically, northward atmospheric transport and warm
temperatures were matched with the availability of host crops at the migration destina-
tion.
The calculation of daily atmospheric trajectories for the southeastern U.S.
documented probable aerial displacements leading to the 1977 FAW infestation. The
computed trajectories frequently corroborated the trajectories hypothesized by Lugin-
bill (1928) which originated in Cuba and southern Florida, headed northwestward into
the Gulf of Mexico, then veered northeast along the Atlantic seaboard. The computed
trajectories failed to show atmospheric transport from the Yucatan peninsula to south-
ern Florida or directly to Georgia as proposed by Young (1979). FAW infestations
occurred in March at Homestead, FL, in April at Gainesville, FL, and yet were unde-
termined in Cuba (S. D. Pair, pers. comm. 1985) to serve as possible FAW sources
during the February-May northward transport episodes.











Florida Entomologist 69(3)


Fig. 4. Twenty-four hour atmospheric (950 mb) trajectories terminating at Tifton,
GA in 1977.


Although record cold temperatures inaugurated 1977, abnormally warm tempera-
tures followed and continued through the growing season in the southeastern U.S. Host
crops, such as corn planted in March, would have grown quickly as available food for
immigrant FAW; and the mobility of the FAW moths may have led to their population
surge before parasite and predator populations re-established themselves.
More research of FAW flight behavior and the delineation of overwintering sites is
needed to improve the accuracy of infestation predictions. The physiological and en-
vironmental cues which lead to migratory flight, flight orientation and layering, and


September, 1986











Westbrook & Sparks: Fall Armyworm Symposium


flight termination should be intensively investigated. Knowledge of the aforementioned
cues may lead to the development of accurate numerical models which predict FAW
migration.

REFERENCES CITED

BODKIN, G. E. 1913. The rice caterpillar. Laphygmafrugiperda, S. and A. a rice pest
in British Guiana. J. Bd. Agr. British Guiana 6: 172-183.
DICKSON, R. R. 1977a. Weather and circulation of November 1976. Monthly Wea.
Rev. 105: 239-244.
1977b. Weather and circulation of February 1977. Monthly Wea. Rev. 105:
684-689.
1977c. Weather and circulation of May 1977. Monthly Wea. Rev. 105: 1075-
1080.
ENTOMOL. SOC. AMERICA. 1977. Southeastern Branch of the Entomol. Soc. of
America insect detection, evaluation and prediction report. Vol. 1, p. 3.
1978. Southeastern Branch of the Entomol. Soc. of America insect detection,
evaluation and prediction report. Vol. 2, p. 3.
1979. Southeastern Branch of the Entomol. Soc. of America insect detection,
evaluation and prediction report. Vol. 3, p. 3.
1980. Southeastern Branch of the Entomol. Soc. of America insect detection,
evaluation and prediction report. Vol. 4, p. 3.
S1982. Southeastern Branch of the Entomol. Soc. of America insect detection,
evaluation and prediction report. Vol. 5, p. 1.
FRANCESCHINI, G. A. 1954. Modifications in tropical air crossing the Gulf of Mexico
toward the United States. Texas A&M Research Foundation, Project 44-Con-
tract AF 19(604)-169, Scientific Report No. 3, A&M Reference 54-34T. 12 pp.
HOGG, D. B., H. N. PITRE, AND R. E. ANDERSON. 1982. Assessment of early-season
phenology of the fall armyworm (Lepidoptera: Noctuidae) in Mississippi. Envi-
ron. Entomol. 11: 705-710.
LUGINBILL, P. 1928. The Fall Armyworm. USDA Tech. Bull. No. 34. 91 p.
PAIR, S. D., AND A. N. SPARKS. Evidence of annual long distance migration of the
fall armyworm. In A. N. Sparks (Ed.). Long-Range Migration of Moths of Ag-
ronomic Importance to the United States and Canada: Specific Examples of Oc-
currence and Synoptic Weather Patterns Conducive to Migration. USDA Misc.
Publ. (In press.)
REAP, R. M. 1972. An operational three-dimensional trajectory model. J. Appl.
Meteorol. 11: 1193-1202.
ROSE, A. H., R. H. SILVERSIDES, AND O. H. LINDQUIST. 1975. Migration flight by
an aphid, Rhopalosiphum maidis (Hemiptera: Aphididae), and a noctuid,
Spodoptera frugiperda (Lepidoptera: Noctuidae). Canadian Entomol. 107: 567-
576.
SPARKS, A. N. 1979. A review of the biology of the fall armyworm. Florida Entomol.
62: 82-87.
TAUBENSEE, R. E. 1977a. Weather and circulation of December 1976. Monthly Wea.
Rev. 105: 368-374.
S1977b. Weather and circulation of March 1977. Monthly Wea. Rev. 105: 793-
799.
1977c. Weather and circulation of June 1977. Monthly Wea. Rev. 105: 1202-
1207.
U.S. DEPT. OF AGRICULTURE. 1977. Plant Pest Report. Vol. 2, pp. 181-666.
U.S. DEPT. OF COMMERCE-NOAA. Unpublished-a. U.S. Soil Temperature Data,
1967-1980. TD-9639.
Unpublished-b. Upper-Air Data, Standard Levels, 1976-1978. TD-9735.











Florida Entomologist 69(3)


WADDILL, V. H., E. R. MITCHELL, W. H. DENTON, S. L. POE, AND D. J. SHUSTER.
1982. Seasonal abundance of the fall armyworm and velvetbean caterpillar
(Lepidoptera: Noctuidae) at four locations in Florida. Florida Entomol. 65: 350-
354.
WAGNER, A. J. 1977a. Weather and circulation of October 1976. Monthly Wea. Rev.
105: 121-127.
1977b. Weather and circulation of January 1977. Monthly Wea. Rev. 105:
553-560.
1977c. Weather and circulation of April 1977. Monthly Wea. Rev. 105: 933-
939.
WOLF, W. W., J. K. WESTBROOK, AND A. N. SPARKS. Relationship between radar
entomological measurements and atmospheric structure in south Texas during
March and April, 1982. In A. N. Sparks (Ed.). Long-Range Migration of Moths
of Agronomic Importance to the United States and Canada: Specific Examples
of Occurrence and Synoptic Weather Patterns Conducive to Migration. USDA
Misc. Publ. (In press.) -
YOUNG, J. R. 1979a. Assessing the movement of the fall armyworm (Spodoptera
frugiperda) using insecticide resistance and wind patterns. In: R. L. Rabb and
G. G. Kennedy (Eds.). Movement of Higly Mobile Insects: Concepts and
Methodology in Research. pp. 344-351.
1979b. Fall armyworm: control with insecticides. Florida Ent. 62: 130-133.





THE FALL ARMYWORM: STATUS AND EXPECTATIONS OF
BIOLOGICAL CONTROL WITH PARASITOIDS
AND PREDATORS

H. R. GROSS, JR., AND S. D. PAIR
Insect Biology and Population Management Research Laboratory, USDA-ARS,
Tifton, GA 31793

ABSTRACT

Biological control of the fall armyworm, Spodoptera frugiperda (J. E. Smith), in
areas of overwintering and throughout its annual geographic distribution, is a highly
desirable alternative to conventional reductionist methods. Fragmented efforts to ad-
vance biocontrol strategies against the fall armyworm have not to date effectively en-
hanced what nature has provided. This review assesses the impact of endemic
parasitoids and predators as regulators of fall armyworm populations and identifies
areas of research and development that must be addressed before significant advances
can be made in importation and augmentation strategies.

RESUME

El control biol6gico del gusano cogollero, Spodoptera frugiperda (J. E. Smith), en
areas donde invernan y toda su distribuci6n annual, es una alternative altamente deseable
a los metodos reduccionistas tradicionales. Esfuerzos fragmentados para promoveer
estrategias de control biol6gico contra el gusano cogollero, hasta la fecha, no han efec-
tivamente mejorado lo que la naturaleza ha proveido. Esta revision evalua el impact
de parasitoides y depredadores end6micos como reguladores de poblaciones del gusano


September, 1986


502











Gross & Pair: Fall Armyworm Symposium 503


cogollero, e identifica areas de investigaci6n y desarrollo que deben ser tomadas en
cuenta antes que avances significantes se puedan hacer en las estrategias de su impor-
taci6n y aumento.



Following the first appearance each year of larvae of the fall armyworm (FAW),
Spodoptera frugiperda (J. E. Smith), in whorl-stage corn during the spring (April in
Tifton, GA), we typically wait in anticipation to see whether its populations will be
regulated by biotic and abiotic mechanisms or whether another 1977 is in store during
which attributable crop losses and cost of control exceeded $300,000,000 in the continen-
tal United States. Unfortunately, our ability to predict seasonal outcomes is limited to
that of the occasional end-of-the-season prognosticator who offers an "I told you so" to
a prediction not recalled by others.
Anyone having collected and observed FAW larvae from whorl-stage corn is readily
aware that there exists an abundance of natural control agents which take a substantial
toll on their numbers (Ashley 1979), and yet our ability to positively influence their
performance by any means of augmentation, conservation, manipulation, etc., in the
continental U.S. has been to date essentially nonexistent. Are we then bound to accept
only what endemic natural agents can provide in the management of the FAW and other
lepidopterous pests of annual cropping systems, or can we improve on and supplement
the given systems to the benefit of integrated pest management? We believe that better
systems can be developed which can substantially enhance the ability to effectively
manage the FAW, but that currently limited resources and personnel will impede rapid
advancement.
Certain known or suspected factors concerning the FAW serve as a base from which
research approaches to biocontrol of the FAW can proceed.

1) The contribution of FAW overwintering areas to the seasonal population
dynamics in the eastern U. S. is unknown.
2) Whorl-stage corn is likely the primary host that contributes most significantly to
the early-season population dynamics.
3) Because of the general absence of insecticides in whorl-stage corn, conservation
of natural control agents is enhanced.
4) Among biotic agents, parasitoids appear to cause the highest mortality among
FAW larvae on host plants.
5) The requisites for the successful colonization of exotic natural enemies in tempo-
rary agroecosystems is essentially unknown.
6) Neither the research base nor the associated rearing technology are currently
available to permit the consistent and/or economical production of parasitoids or
predators of the FAW needed for large-scale augmentation.

This presentation will focus primarily on importation, colonization, and augmentation
strategies of parasitoids and predators. For the first author's thoughts on conservation
and manipulation of entomophagous agents in the southeastern U.S., the reader is
referred to Gross (1986).










Florida Entomologist 69(3)


IMPORTATION AND COLONIZATION

Volumes have been written on the merits of importing new species of parasitoids
and predators to assist and/or even replace endemic natural agents in the management
of target species. Yet the statement by DeBach (1964) that "the possibility of importing
natural control agents has been vigorously explored for only a relatively few species,
and it is doubtful that the last or perhaps best natural enemy has been imported even
in those projects most assiduously attacked by the biological method" is as appropriate
today as it was 21 years ago. This statement is particularly true for efforts involving
the FAW. Clausen (1956) reported the unsuccessful attempt in 1944 to establish the
parasitoid Archytas incertus (Macq.) (Tachinidae) from Argentina by introducing ca.
700 specimens near the Everglades Experiment Station, FL. This importation also
included several thousand adults of the carabid, Calosoma argentinense Csiki, which
also failed to establish. More recent efforts by Waddill and Whitcomb (1982) to establish
Telenomus remus Hixon, a scelionid egg parasitoid of Spodoptera, were unsuccessful
in south Florida despite the release of ca. 663,500 individuals over 2 years. T. remus is
indigenous to Sarawak and New Guinea and has been successfully established on FAW
in Barbados and Montserrat. Ashley et al. (1982) also were unsuccessful in establishing
Eiphosoma vitticole Cresson, an ichneumonid parasite from Bolivia, in south Florida
following the release of ca. 1,000 pairs over 4 months in 1980. Townes (1971) considered
as favorable the opportunities for colonizing exotic Ichneumonidae on endemic insect
pests but saw limited potential for host population regulation with the Ichneumonidae
because their rates of parasitization were seldom high and they move about freely
leaving many hosts unparasitized. Ophion flavidus Brule is an endemic ichneumonid
parasitoid of the FAW which is aptly described by the above statement (personal obser-
vation). Pair and Waddill (unpublished) tried unsuccessfully during 1983-84 to establish
Microplitis rufiventris Kok. (Braconidae) from Egypt on FAW in volunteer corn at
Homestead, FL, by releasing ca. 3,000 individuals, and on FAW' in corn in Tift County,
GA, (July 1984) by releasing 940 mated females. An additional 512 mated females were
also released in alfalfa at Tift County, GA, in August 1984 against FAW, beet ar-
myworm, S. exigua (Hiibner), corn earworm, Heliothis zea (Boddie), and the yellow-
striped armyworm, S. ornithogalli (Guenee), without successful colonization. Ashley et
al. (unpublished) failed to recover Microplitis manila Ashm. and Microplitis spp.
(Australia) following releases against FAW near Homestead, FL in 1982.
The debate is ongoing among biocontrol (BC) theorists over the factors which in-
crease the probability of successful establishment by exotic biocontrol agents. Ehler
(1982) found that "after almost 100 years of practice in classical BC, an adequate theoret-
ical framework for assaying multiple-species introductions is generally lacking."
Strategies regarding single-species introductions against insect pests of annual row
crops are even less clear. Beirne (1962) reported that of the BC successes, over one-half
of those listed by Sweetman (1958) were oceanic or subtropical ecological islands. De-
Bach (1971) countered that no such correlation existed between BC success and geog-
raphical location, but that the number of successes attained would be proportional to
the amount of research and importation work carried out. More recently, Hall and Ehler
(1979) used data from Clausen (1978) in which exotic insect introduction data from 1890
were summarized again to affirm that, indeed, establishment of natural enemies was
higher on islands than on continents. These findings may later be relevant as primary
sources of migrant FAW are identified (Pashley et al. 1985).
Hall and Ehler (1979) also affirmed that the rate of establishment of natural enemies
was significantly higher in stable environments (forests and rangelands) than in unstable


September, 1986











Gross & Pair: Fall Armyworm Symposium


habitats (vegetable and field crops), but that establishment in intermediate habitats
(orchards or other perennial systems) did not differ significantly from that of annual
cropping systems. Data available to date, however, suggest that colonization of exotic
natural enemies on insect pests of annual crops will not proceed with the comparative
ease of that found for coccids and other Homoptera attacking intermediate habitats
wherein colony populations build over a long period of the year in finite locations.
Nevertheless, the higher degree of difficulty is no longer cause for delaying the advance-
ment of this important strategy for improving our ability to manage the FAW.
Also unsettled are the methods by which natural enemies for introduction into
foreign habitats should be selected; and because the predominant research efforts have
been concentrated in the semi-permanent to permanent habitats, many of the standards
in methodology adopted for these systems are likely inappropriate for use in annual
cropping systems. Flanders (1959) appropriately noted that dominant entomophagous
insects obtained from native habitats in which their host(s) exist at low population
densities are likely to be the mbst effective, particularly if they are host specific.
Beirne (1962) pointed out that non-host specific natural enemies are likely to be used
with increasing frequency in future attempts at permanent biological control because
they are easier to colonize and can survive the temporary absence or scarcity of crop
pests by attacking other hosts. Batra (1982) agreed, suggesting that host-specific natu-
ral enemies have not been used effectively against the wide spectrum of opportunistic,
vagile pests that attack hosts temporarily occupying disturbed or unstable crops such
as annual row crops. These statements are particularly true for the dominant endemic
parasitoids of the FAW in the southern U. S. including the tachinid Archytas mar-
moratus (Townsend), the braconids Cotesia marginiventris (Cresson), Chelonus in-
sularis (Cresson), and the ichneumonid Campoletis spp., which are all polyphagous.

REPRODUCTIVE STRATEGIES

The viewing of natural enemies as r (reproductive rate) and K (carrying capacity)
strategists (MacArthur and Wilson 1967) may also assist in selecting those which may
complement others in the endemic guild. Species known as r strategists tend to occupy
unpredictable environments, have high capacity for population increase (high r values),
and are poor competitors; K strategists, on the other hand, tend to exist in more
constant environments, have relatively low capacity for population increase, and are
good competitors (Force 1974). While realizing that r and K selection is a relative
concept and that most parasitoid guilds will usually develop a continue of r to K
strategists, if we examine the early season parasitoid guild of the FAW in Georgia, we
find that the parasitoids A. marmoratus, C. marginiventris, and Campoletis spp. are
typically the earliest attackers of FAW larvae in whorl-stage corn when densities are
relatively low. These species and others which perform in typical fashion are probably
capable, when available in adequate numbers, of preventing pest population buildup,
which should be the goal of biocontrol strategists, rather than seeking to take corrective
action. C. insularis, an egg-larval parasitoid of the FAW, although occasionally present
when host densities are low, is more highly efficient and more highly visible during mid-
and late summer when FAW populations expand and hosts are abundant. Similar find-
ings were reported by Miller (1980) for C. insularis pasrasitizing Spodoptera praefica
(Grote) in alfalfa. Mitchell et al. (1984) reported that C. insularis were consistently high
performers where distributions of FAW hosts were more uniform. Responses by
Chelonus inanitus (L.) to populations of Spodoptera littoralis (Boisd.) in Israel were
also highly density dependent (Rechav 1975). Whether through less efficient foraging











506 Florida Entomologist 69(3) September, 1986


or otherwise, C. insularis apparently does not prevent host population buildups but
rather tends to suppress and/or regulate populations at relatively high host densities.
These statements and prior stated criteria suggest that C. insularis is the more low
r-selected strategist (Miller 1977) compared to the higher r-selected A. marmoratus
(Hughes 1975), C. marginiventris, and Campoletis spp. However, C. insularis would
be the most obvious parasitoid available to collectors at peak or near-peak FAW popu-
lations, despite its apparent limited role in preventing outbreaks.
Recent studies by Pair et al. (1986), for example, showed that A. marmoratus was
the primary parasitoid attacking medium and large FAW larvae in whorl-stage corn
throughout most southern states during the spring of 1981-83 (Table 1). However, in
areas of overwintering where FAW larval populations are more abundant and uniformly
distributed, C. insularis was the dominant parasitoid in all larval-size categories (Table
2). Also, when we examine the frequency distribution of parasitism among larval sizes
at all geographic locations studied, large larvae, without exception, are least parasitized
(Table 3). Thus, the best opportunity for colonization of exotic parasitoids exists for
those insect species utilizing large larvae in areas other than where overwintering
occurs due to the low frequency of competition that occurs therein. Equal or greater
opportunities may also exist for colonization of exotic parasitoids of the prepupae and
pupal stages of the FAW. Pair and Gross (1984) found only the ichneumonid parasitoid
Diapetimorpha introita (Cresson) to attack pupae of the FAW in Georgia. Clearly,
more efforts are needed to explore the role of species which employ similar strategies.
As suggested by Force (1974), natural enemies selected for importation are generally
the most conspicuous within the endemic community and are usually K strategists. The
intent here is certainly not to diminish the importance of a parasitoid such as C. insularis
because it likely plays a vital role in regulating the seasonal dynamics of the FAW; but
it would not likely be the best parasitoid to select for augmentation if the objective was
to prevent early-season buildup.
Pschorn-Walcher (1977) suggested that r-selected species, which are good colonizers,
are able to penetrate into and adapt to new environments, should be given high priority
in any introduction program because they have a chance to demonstrate their full poten-



TABLE 1. PARASITISM OF FALL ARMYWORM LARVAE BY INDICATED PARASITOIDS
IN SEVEN ATLANTIC AND/OR GULF COASTAL STATES AND NORTHEAST-
ERN MEXICO DURING THE SPRINGS OF 1981-8312.

FAW parasitism

% Contributed by indicated species

Small Medium Large

CS: 33.1 AM -37.1 AM 57.6
CM -30.5 CM -11.4 OF -26.4
RL 8.0 RL 9.4 LA 5.8
CI 6.1 CI 3.7 CS 0.9

'Pair et al. 1986.
2Excludes data from south Florida.
ICS Campoletis sonorensis AM Archytas marmoratus
CM Cotesia marginiventris OF Ophion flavidus
RL Rogas laphygmae LA Lespesia archippivora
CI Chelonus insularis


I












Gross & Pair: Fall Armyworm Symposium


TABLE 2. PARASITISM OF FALL ARMYWORM LARVAE BY INDICATED PARASITOII)S
IN SOUTH FLORIDA DURING THE SPRINGS OF 1981-83'

FAW parasitism

% Contributed by indicated species
Small Medium Large

CP -67.1 CI -59.6 CI -56.1
CM -22.5 MA- 8.2 AM- 16.8
TD 6.6 TD 7.9 OF 7.5

'Pair et al. 1986.
'CI Chel- o/is in lari MA Meteorcs atographae
CM Cotesia maargi ivenftris AM Archytas inarfion atts
TD Temelicha a OF Ophion flarvidiis

TABLE 3. PARASITISM OF INDICATED SIZES OF FALL ARMYWORM LARVAE AT
THREE GEOGRAPHIC REGIONS IN THE SOUTHERN U. S. (AND NE
MEXICO) DURING THE SPRINGS OF 1981-83'.

% Parasitism of FAW larvae

Larval Coastal South SW Texas-
size States Florida NE Mexico

Small 22.7 38.3 28.1
Medium 14.8 29.6 23.8
Large 12.1 14.8 17.6

'Pair et al. 1986.

tial before vying for position with the more competitive K-selected natural enemies. In
contrast to the herbivores, which are the true r-strategists, their predators and
parasitoids are generally slower to colonize vacant habitats. There is no selective pres-
sure for them to colonize early as they would encounter a shortage of host/prey (Price
and Waldbauer 1975). The difference in colonizing ability of the herbivores and their
predators and parasitoids, coupled with differences in reproductive rates, frequently
leads to pest outbreaks early in the season or after the application of insecticides. High
r-strategists do not generally depend on population density, and therefore are the ideal
candidates for importation and colonization, and for augmentation when prevention of
host population buildup is the ultimate goal. As suggested by Ehler and Miller (1978),
r-selected pests may well be controlled by r-selected natural enemies.


PREDATORS

Reference thus far has been limited to parasitoids; however, were we to recall the
frequency with which parasitism versus predation of FAW was witnessed in the field,
predation would be declared the easy winner. However, our knowledge of the influence
of predators on the seasonal dynamics of the FAW is almost totally lacking. Predators
of insect herbivores of annual crops other than corn have been studied more extensively
and are ofttimes reported to effectively regulate populations. For example, van den


507











508 Florida Entomologist 69(3) September, 1986

Bosch (1975) reported that predators appeared to have advantages over highly host-spe-
cific natural enemies and that "it is no exaggeration to state that the noctuid's potential
to cause massive damage to a million acres of San Joaquin Valley cotton is virtually
nullified by the generalist predators." Similarly, Whitcomb (1974) reported that the
population level of three lady beetles determined whether there was going to be a
Heliothis zea outbreak in thousands of acres of cotton and cornfields in the U. S. No
similar claims to date have been made for the FAW, although frequent reports of
predation have been cited. Gross et al. (1985) reported the coccinellid Coleomegilla
maculata (DeGeer) and the bigeyed bug, Geocoris punctipes (Say), as frequent diurnal
predators of FAW eggs in south Georgia, while the earwigs Labidura riparia Pallas
and Doru lineare (Eschscholtz) joined C. maculata as nocturnal predators. They also
demonstrated that aqueous larval homogenates of H. zea and.S. frugiperda applied on
whorl-stage corn caused the aggregation of adults of C. maculata and G. punctipes,
and caused increased numbers of C. maculata egg masses to be oviposited in homoge-
nate-treated plots. Predators of FAW eggs and larvae observed by Luginbill (1928)
included Podisus maculiventris Say, Orius insidiosus (Say), C. maculata, Nabis ferus
L., Vespula carolina L., Solenopsis geminata (Fab.), and Pogonomyrmex barbatus
Smith. Painter (1955) recorded the ground beetle, Onypterygia faminia Sobir, from
Guatemala as a predator of FAW larvae, while Young (1985) reported adults of another
ground beetle, Calosoma sayi DeJean, as predators of FAW pupae in the laboratory.
In a south Georgia sorghum field in August 1981, Pair et al. (unpublished) observed
large numbers of C. sayi larvae preying on FAW pre-pupae and pupae. Huis (1981)
reported that the earwig, Doru taeniatum (Dohrn), preys on egg masses and the first
three larval instars of the FAW. Pair and Gross (1984) frequently found larvae and
adults of several species of carabids, and several late instars of the earwig, L. riparia,
in FAW pupation cells containing macerated fragments of FAW pupae. Also, larvae of
the elaterid Conoderus sp. appeared on occasion to attack FAW pupae. While the role
of endemic predators in the management of FAW populations can only be surmised,
based on findings with other lepidopteran pests of row crops, the opportunity to effec-
tively expand the predator guild attacking the FAW appears limitless. However, appro-
priate caution must be taken to assure that exotic predators do not by preference prey
on other primary endemic beneficial species.
Murdoch et al. (1985) suggested that conventional wisdom may be a poor guide to
biological control, even in persistent ecosystems, and that local pest extinction rather
than stable pest equilibrium may be the more appropriate goal, and that general pre-
dators can be good control agents in these and annual cropping systems. They referred
to the use of predators to attempt local extinction of pests by the "lying-in-wait" strat-
egy which requires a more or less continuous presence of the predators in local areas
subject to pest infestation, combined with adequate attack on the pest when it reinvades
or begins to increase.

NUMBERS OF EXOTIC NATURAL ENEMIES RELEASED

Beirne (1975) found that releases of large numbers of exotic natural enemies into
new habitats increased the probability of establishment. Of 159 natural enemies intro-
duced into Canada, species released in mean total numbers under 5,000, 10% became
established; of species released at 5,000-31,200, 40% became established; and of species
in which over 31,200 were released, 78% became established. These analyses also im-
plied that the greater the number of releases per species the greater the possibility of
establishment. About 90% of the forest species that were released more than 20 times











Gross & Pair: Fall Armyworm Symposium 509

became established as compared with about 10% of those released less than 10 times
each. Because some good colonizer likely established during the earliest of multiple
releases, the estimates of numbers normally needed to insure successful establishment
are probably inflated. Also from Beirne (1975), of the mean total 31,500 individuals for
species introduced into forest environments, 23% became established; of a mean total
6,600 individuals for species introduced into orchard and ornamental shrub situations,
43% became established; and of a mean 33,000 individuals per species released into
annual crops, 16% became established. Data of Beirne (1975), at least in part, provided
support for MacKauer's (1972) view that although insectary propagation increased the
total number of individuals available for release, it did not necessarily enhance the
possibility of colonization. The relevance of these data from Canada to future attempts
at colonization of natural enemies on FAW in the southern U. S. is unknown. Generali-
zation, of course, serves only as a guide. Consider the exceptional case of Sailer (1981)
who introduced 57 females and 130 males of the aphilinid wasp, Prospaltella laborensis
Howard, against the white fly, Dialeurodes citri (Ahmed), in Gainesville, FL, and
achieved colonization. Evidence such as this suggests very strongly that factors respon-
sible for the successful colonization of natural enemies in annual, perennial, and perma-
nent habitats are poorly understood.

NATURAL ENEMY RELEASE STRATEGIES

Of the innumerable factors that potentially influence successful colonization and/or
successful performance of natural enemies following augmentation, none seem to receive
less attention than the conditions surrounding the release itself. Typically, natural
enemies are released from captivity into host-bearing habitats that encourage foraging.
Unfortunately, unless care is taken to reorient released species, the primary tendency
is not for foraging but rather for dispersal. Thus, following dispersal, the favorable
opportunities provided by the release site are removed, immediately lowering the prob-
ability of successful colonization. Knipling (1977) noted that for highly mobile species,
the dispersion of either or both the parasitoids and hosts was likely to preclude accurate
measurement of the effect of parasitoid releases in areas consisting of several hundred
or even several thousand acres. The dispersal tendency can be partially overridden by
the pre-release provisioning of the appropriate kairomone(s) (Gross et al. 1975), pre-re-
lease host-parasitization experience (Gross et al. 1981), and/or by the provisioning of
supplemental hosts within the target habitat (Knipling and McGuire 1968, Parker 1971,
Parker and Pinnell 1972, Gross 1981, and Gross et al. 1984). These techniques have been
shown to be effective for increasing rates of retention and parasitization by Trichog-
rain na spp. and would likely afford higher probability of establishment by other natural
enemies. Lewis and Nordlund (1984) reviewed the role of semiochemicals in the perfor-
mance of parasitoids of the FAW and discussed their implications for behavioral manipu-
lation.
The site selected for attempted colonization of exotic natural enemies is of equal
importance. Foremost in importance is the availability of hosts of the appropriate stage
for parasitization. Most releases of exotic natural enemies against the FAW have logi-
cally been made in south Florida where abundant larval populations were available,
particularly on volunteer whorl-stage corn. However, because of the total failure to date
to achieve colonization of any exotic parasitoids introduced at this location, there is now
reason to question the appropriateness of this geographic area for making inoculative
releases. Unfortunately, these habitats are also typically occupied by several low r-
selected endemic parasitoid species-the true competitors for eggs or early instar larvae











Florida Entomologist 69(3)


[i.e., C. insularis and C. marginiventris (Rajapaskse et al. 1986)] which force the
newcomer to immediately compete for survival. A less hostile initial environment in
north Florida or south Georgia might enhance the probability of successful colonization.
Host density of FAW larvae in whorl-stage corn at these locations could be increased
through artificial infestation methods using the Bazooka-applicator method of Wiseman
et al. (1980) wherein ca. 1,000 plants per man hour can be infested. The adaptation of
a similar gravity-flow, tractor-mounted FAW larval applicator for use on larger acreage
is certainly possible. Beirne (1980) suggested that accidentally-introduced exotic
parasitoids can become permanent inhabitants of new areas more readily than deliber-
ately introduced ones because the former are already colonized on their hosts when they
arrive. As a logical alternative, he suggested that imported adult parasitoids be released
in large cages that have been stocked with the target pest species, followed later by
the distribution of parasitized hosts in the field. These strategies, if used in May or June
in south Georgia, would provide the opportunity for introduced parasitoids (particularly
of large larvae) to complete one generation essentially unimpeded before the appearance
of large populations of FAW and their associated low r-selected endemic parasitoids
during July. Also in question is how exotic natural enemies, which are inherently early
colonizers (r-strategists) (capable of foraging at low host densities) likely respond to the
high larval host densities of overwintering habitats. Do they stay and forage, or do they
find this situation unacceptable and disperse in search of more favorable habitats? The
answer obviously is not available; however, numbers of larvae parasitized by an endemic
early-season colonizer, A. marmoratus, near Tifton, GA, are highest in early season
and late season, but generally occur at very low levels during peak host densities
(personal observation).

PLANNING IMPORTATION AND COLONIZATION STRATEGIES

The primary current need is to identify, collect, and import polyphagous, early-sea-
son colonizers (r-strategists) that attack the egg stage, mid- to large larvae or pupae of
the FAW in whorl-stage corn that are capable of overwintering throughout the geog-
raphical range of the host. Emphasis should also be placed on those species that have
potential for mass production.
Most biocontrol strategists generally agree that a plan should be developed before
attempting the introduction of exotic parasitoid species that could permanently alter
the parasitoid guild. They also agree that adequate understanding of the behavior,
ecology, and dynamics of candidate natural enemies should be well understood before
importation and colonization within new ecosystems are attempted. Although the above
proposal is the ideal situation, it has not been a requisite of prior successes, nor will it
likely be a part of future successes (Ehler 1982). As efforts to establish new species of
natural enemies on lepidopterous pests of row crops in the South increase (and they
will as the Stoneville, MS, quarantine facility is joined by new quarantine facilities in
Texas and North Carolina), primary emphasis should be placed on the keeping of precise
records of information associated with the attempted colonization so that as time passes,
a profile of conditions most conducive to successful colonization can be identified so that
the opportunies offered by exotic natural enemies of insect pests can be fully exploited.
Even if exotic natural agents from tropical regions may not survive overwintering in
these areas, studies may allow strategists to develop an introduction profile that may
assist in future releases.


September, 1986











Gross & Pair: Fall Armyworm Symposium


AUGMENTATION

The ideal biological control agent would suppress populations of the FAW in areas
of overwintering to the extent necessary to prevent dispersing populations from reach-
ing economic levels throughout the geographic range. However, it is unreasonable to
expect that any endemic or available exotic natural agent could regulate populations of
a highly mobile pest species with access to a rapidly expanding enemy-reduced habitat
at sub-economic levels without augmentation (Lewis and Nordlund 1980). The authors
generally agree with Price (1981) that attempts at long-term regulation of pest species
in agroeco-systems from an initial release of natural enemies is likely to be ineffective
because of the many factors that interact to reduce their viability and efficiency.
With augmentation of the appropriate parasitoid species during periods of low host
density, opportunities for effectively managing populations of the FAW in areas of
overwintering or in areas of subsequent establishment appear promising. Knipling
(1980) proposed that the production and release of 2,000 larval parasitoids per acre on
50,000 accumulative acres of FAW infestations in the overwintering area would serve
an effective and desirable method of FAW suppression with rates of parasitization
reaching 90%.
Many natural agents of the FAW and other insect pests of annual crops have been
reared in numbers adequate for laboratory, greenhouse, and screened cage studies;
unfortunately, few are capable of being reared in numbers or at costs adequate to
consider sustained augmentative releases. The notable exception, of course, is Trichog-
ramma spp., which have been effectively and economically reared on unnatural hosts
(Morrison et al. 1978) and aerially applied in the fashion of an insecticide (Jones et al.
1979). Trichogramma spp. have, however, only infrequently been cited as parasitoids
of the FAW. Like Trichogramma, and as reported by King and Morrison (1984), without
exception, parasitoids and predators being mass produced for control of arthropods are
being reared on live hosts or host products. Near term advances in augmentation ap-
pear, therefore, to be limited to natural enemies that can be produced economically on
unnatural hosts. C. insularis, for example, has been reared large scale on eggs/larvae
of the meal moth, Ephestia kuhniella (Tardrew 1951, Bedford 1956). Starler and Ridg-
way (1977) listed only C. insularis as a parasitoid of armyworms among those natural
enemies available for use in practical augmentation in the U.S. The larviparous
Tachinidae (e.g., A. marmoratus) are particularly adaptable to large-scale rearing be-
cause in general maggots are deposited on substrates independent of the host, and
alternatively can be mechanically extracted from fecund females and directly applied
against host insects, thus eliminating the numerous chemically and physically mediated
requisites of the host selection process (King et al. 1979, Hartley et al. 1977, Gross and
Johnson 1985). Gross and Johnson (1985) initiated large-scale rearing of A. marmoratus
on its natural hosts, the corn earworm, H. zea, and the FAW, and more recently on
the greater wax moth, Galleria mellonella (L.), (unpublished) using the same methods.
Laboratory-reared females of A. marmoratus (Gross and Young 1984) and mechani-
cally-extracted maggots from fecund females (Gross et al. 1985) have both been em-
ployed against larval populations of the FAW in whorl- stage corn to effectively reduce
the size of the subsequent host generation. The larviparous Tachinidae as primary
attackers of late-instar host larvae offer more immediate opportunity for evaluation in
augmentation strategies than other available groups and should also be considered for
importation.
Studies of Strand and Vinson (1982a, b) suggest that the range of unnatural hosts
available to parasitoid species may be extended by the application of host-recognition











Florida Entomologist 69(3)


kairomones from the natural host onto the unnatural host. Opportunities offered by this
concept could greatly reduce the cost of parasitoid rearing and thus significantly advance
augmentation strategies.
As might be expected, some resolvable problems have arisen from the production
of natural enemies on unnatural hosts. Morrison and King (1977) suggested that reduced
vigor of entomophages reared on unnatural hosts could occur due to inadequate nutri-
tion, but offered that host suitability could be improved through improvements made
in the diet of the host. Vigor of the tachinid Lixophaga diatraea (Townsend) was im-
proved when cereal diet fed the greater wax moth larvae was supplemented with wheat
germ and the protein content increased (King et al. 1979).
As suggested by House (1977), to resort to a host insect to rear parasitoids in the
laboratory is extravagant and parasitoid quality is hardly controllable. Unfortunately,
biocontrol strategists have had little choice. Greany et al. (1984) provide a representa-
tive list of insect parasitoids that have been reared to adults on artificial media. Their
compilation shows that endopirasitoids of eggs and pupae have been the best candidates
for artificial rearing, but that hymenopterous larval endoparasitoids still have not been
successfully reared to the adult stage on artificial media. Even with hymenopterous
larval parasitoids reared on their natural hosts, sex ratios of progeny are typically
skewed in favor of males, thus further limiting their near term use for augmentation.
House (1977) suggested that the use of artificial diets or even a highly chemically defined
synthetic one for the rearing of parasitoids without resorting to an insect host should
not be ignored. Additionally complicating is the more recent find by Stoltz and Vinson
(1979) and Stoltz (1982) that the host physiology may be altered by symbiotic viruses
injected into the host at oviposition by hymenopterous parasitoids which likely influence
successful parasitism.
Opportunities for augmentation of biocontrol agents against the FAW must be taken
as they become available and as natural enemies are capable of being reared in numbers
adequate for testing. Knipling (1977) suggested that until suitable parasitoids are in-
creased by artificial means throughout a pest ecosystem by as much as 10 to 50 times
above normal numbers during the early generation of the pest population cycles, the
potential of the augmentation systems for managing insects will remain unknown.

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GEOGRAPHICAL DISTRIBUTIONS AND PARASITIZATION
LEVELS FOR PARASITOIDS OF THE FALL ARMYWORM,
SPODOPTERA FRUGIPERDA

TOM R. ASHLEY
Insect Attractants, Behavior, and Basic Biology Research Laboratory
Agricultural Research Service, U.S. Department of Agriculture
Gainesvilie, FL 32604

ABSTRACT

Literature citations were used to determine geographical distribution data and
parasitization levels from larva collections from corn, alfalfa, three species of grass,
peanut, and sorghum for the principal parasitoids of the fall armyworm, Spodoptera
frugiperda (J. E. Smith). The highest parasitization levels found for corn, alfalfa, grass,
peanut, and sorghum were 77, 30, 54, 37, and 20%, respectively. Chelonus insularis
(Cresson) had the highest parasitization rates of all the parasitoids for North and Cen-
tral America. This parasitoid was not recovered from South America or the Caribbean.
Cotesia marginiventris (Cresson) had approximately the same geographical distribution
as C. insularis, but attained its highest parasitization levels in grass rather than corn.
None of the parasitoids exerted substantial mortality throughout any major portion of
the fall armyworm's range.

RESUME

Se usaron citaciones de la literature para determinar datos sobre la distribucion
geografica y niveles de parasitismo de colecciones de larvas en maiz, alfalfa, tres es-
pecies de hierbas, mani, y sorgo, de los principles parasitoides del gusano cogollero,
Spodoptera frugiperda (J. E. Smith). Los niveles de parasitismo mas altos encontrados
en maiz, alfalfa, hierbas, mani, y sorgo, fueron de 77, 30, 54, 37, y 20% respectivamente.
Chelonus insularis (Cresson) tuvo el nivel de parasitismo mAs alto de todos los
parasitoides del Norte y Centro America. Este parasitoide no se encontro en
Sudamerica o en el Caribe. Cotesia marginiventris (Cresson) tuvo aproximadamente la
misma distribuci6n geografica que C. insularis, pero obtuvo su nivel mas alto de
parasitismo en hierbas en vez de en maiz. Ninguno de los parasitoides causaron una
mortalidad substantial a trav6s ninguna Area mayor de la esfera del gusano cogollero.


There are over 1300 literature citations referencing the fall armyworm (FAW),
Spodoptera frugiperda (J. E. Smith), starting from its initial discovery up to the end
of 1983 (Davis, per. comm.). Approximately 2% of these citations provide various types
of data relative to the parasitoids of this pest. However, data on parasitoid distributions
as well as parasitization levels on different FAW hosts are scattered. The purpose of
this paper is to synthesize information on the geographical distributions and parasitiza-
tion rates of the major FAW parasitoid species encountered in five of the principal host
plants. This information may provide a basis for understanding the role played by
parasitoids in the population dynamics of the FAW.


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Ashley: Fall Armyworm Symposium 517

MATERIALS AND METHODS

Bibliographic references were not included in the text, but rather have been tabu-
lated by parasitoid species, author, collection location and crop (Table 1) because of the
quantity involved. References utilized were only those that contained information on
parasitization levels with defined locations where FAW larvae were collected. Corn
(Zea mays L.), alfalfa (Medicago sativa L.), grass, peanut (Arachis hypogoea L.), and
sorghum (Sorghum bicolor (L.) Moench.) represented the five major host plants for the
distribution maps (Fig. 1-H) with collections from some additional hosts contained in
Table 1. The three plant species in the grass category were broadleaf signalgrass,
Brachiaria platyphylla (Briseb.) Nash., paragrass, Brachiaria mutica (L.), and Ber-
mudagrass, Cynondon dactylon (L.). Each star on a distribution map represents a
single geographical location where FAW larval collections were made. These distribu-
tion maps were not intended to represent the entire range of a particular parasitoid
since only collections of FAW larvae were utilized. In several instances more than one
paper dealt with collections from the same location. Where necessary, parasitization
rates were recalculated so as to have all rates based upon the total number of FAW
larvae collected. Parasitization levels in the figures are presented as ranges derived
from the highest and lowest levels of parasitization recorded for a particular host plant.
A single value for percent parasitization indicates the results from a single collection.

TABLE 1. PRINCIPAL PARASITOIDS OF THE FALL ARYMWORM WITH ACCOMPANY-
ING REFERENCES INDICATING LARVAL COLLECTIONS IN DIFFERENT
GEOGRAPHIC LOCATIONS AND CROPS.1

Parasitoid Geographic
Reference location Crop

Apanteles sp.
Lacayo 1977 CA C,S
Alam 1979 CR C
Campoletisflavicincta (Ashmead)
Hogg et al. 1982 US C
Soteres et al. 1984 US A
Wall & Berberet 1975 US P
Vickery 1929 US C
Campoletis grioti (Blanchard)
Lucchini & Almeida 1980 SA C
Campoletis sonorensis (Cameron)
Soteres et al. 1984 US A
Chelonus insularis (Cresson)
Ashley et al. 1980, 1982, 1983 US C,G
Lacayo 1977 CA C,S
Luginbill 1928 US C
Mitchell et al. 1984 US C
Rohlfs & Mack 1985 US C,S
Soteres et al. 1984 US A
Vickery 1929 US C
Wall & Berberet 1975 US P
Wheeler 1985 (per. comm.) CA C
Chelonus antillarum (Marshall)
Alam 1979 CR C
Ryder & Pulgar CR C











518 Florida Entomologist 69(3) September, 1986


TABLE 1. (Continued)

Parasitoid Geographic
Reference location Crop

Cotesia marginiventris (Cresson)
Ashley et al. 1980, 1982, 1983 US C
Hogg et al. US C
Lucchini & Almeida 1980 SA C
Mitchell et al. 1984 US C
Nickle 1976 US P
Reed 1980 US C,Ct,G,S
Rohlfs & Mack 1985 US C,S
Soteres et al. 1984 US A
Vickery 1929 US C
Wall & Berberet 1975 US P
Euplectrus platyhypenae Howard
Alam 1979 CR C
Ashley et al. 1980 US C,G
Hogg et al. 1982 US C
Montoya 1979 MX C
Ryder & Pulgar 1969 CR C
Vickery 1929 US C
Wall & Berberet 1974 US P
Euplectrus sp.
Keller 1980 US C
Lacayo 1977 CA C,S
Reed 1980 US G,M
Meteorus autographae Muesebeck
Ashley et al. 1980, 1982, 1983 US C,G
Nickle 1976 US P
Reed 1980 US C,G
Rohlfs & Mack 1985 US S
Soteres et al. 1984 US A
Meteorus laphygmae Viereck
Vickery 1929 US C
Ophionflavidus Brulle
Hogg et al. 1982 US C
Reed 1980 US C,G,M,S
Rohlfs & Mack 1985 US C,S
Ophion sp.
Ashley et al. 1983 US C,G
Nickle 1976 US P
Wheeler 1985 (per. comm.) CA C
Rogas iri./,l'inrj ,,' Viereck
Ashley et al. 1982, 1983 US C,S
Reed 1980 US C,S
Rohlfs & Mack 1985 US C,S
Vickery 1929 US C
Rogas sp.
Lacayo 1977 CA C,S
Soteres et al. 1984 US A
Ryder & Pulgar 1969 CR C
Tachinidae
Alam 1979 CR C











Ashley: Fall Armyworm Symposium


TABLE 1. (Continued)

Parasitoid Geographic
Reference location Crop

Ashley et al 1980, 1982, 1983 US C,G
Bertels 1956 SA C
Campos 1965 SA C
Fuentes 1973 SA C
Hogg et al. 1982 US C
Hynes 1942 CA C
Lacayo 1977 CA C,S
Lucchini & Almeida 1980 SA C
Nickle 1976 US P
Reed 1980 US C,G,M,S
Rohlfs & Mack 1985 US C,S
Ryder & Pulgar 1969 CR C
Soteres et al. 1984 US A
Vickery 1929 US C
Wall & Berberet 1975 US P
Wheeler 1985 (per. comm.) CA C
Temelhcha difficilis Dasch.
Ashley et al. 1980, 1982, 1983 US C,G
Mitchell et al. 1984 US C


'Locations: CA-Central America. CR-Caribbean, MX-Mexico, SA-South America.
Crops: A-Alfalfa, C-Corn, Ct-Cotton, G-Grass. M-Millet, P-Peanut, S-Sorghum.


[IS--llUrted States.


RESULTS AND DISCUSSION

Parasitoids have been collected from most of the range of the FAW (Fig. 1A).
Combined parasitization rates for all the parasitoids collected indicated that the highest
levels occurred in corn followed by grass, peanut, alfalfa, and sorghum. The Braconidae
had the greatest overall impact on FAW populations with Chelonus insularis (Cresson)
having the highest parasitization rates in Central and North America (Fig. 1B). This
braconid had its greatest impact in southern Florida where 63% of FAW larvae were
parasitized. No collection records were found for C. insularis emerging from FAW
larvae from South America. Chelonus antillarum (Marshall) did not overlap in its dis-
tribution with C. insularis and was recorded with parasitization rates of 30 and 13%
from corn on the islands of Barbados and Cuba, respectively. Cotesia marginiventris
(Cresson) has been included with Apanteles sp. because C. marginiventris was a
member of this genus. The Apanteles sp. were collected in Nicaragua and Barbados
(Fig. 1C). The remaining stars indicated the presence of C. marginiventris. Both C.
insularis and C. marginiventris had approximately the same distributions. However,
C. marginiventris appeared to have its greatest impact on FAW populations in grass,
whereas C. insularis was more prevalent in corn. All of the parasitoid recoveries for
the genus Meteorus occurred within the continental United States (Fig 1D). Meteorus
laphygmae Viereck was collected only in Texas. These parasitoids had their greatest
impact on the FAW in grass. The genus Rogas had the least impact on FAW populations
(Fig. 1E). The distribution of Rogas laphygmae (Viereck) appeared to be confined to
the continental United States. Other members of this genus have been collected in Cuba
and Nicaragua. The highest parasitization rates occurred in grass.











Florida Entomologist 69(3)


Meteorug Cau phe Muesebec,

Fig. 1. Geographical distributions and parasitization ranges of the principal
parasitoids (A-J) of the fall armyworm, Spodopterafrugiperda. Stars indicate parasitoid
recoveries from larval collections and the dashed line defines the known range of the
fall armyworm.



The ichneumonids were represented by three genera. Three species were collected
from the genus Campoletis (Fig. 1F). Campoletis grioti (Blanchard) was collected in
Brazil from FAW larvae feeding on corn. The remaining two species, C. flavicincta
(Ashmead) and C. sonorensis (Cameron), occurred within tne United States. The major
impact of this genus on FAW occurred in corn and no collections were made from grass,


520


September, 1986














Ashley: Fall Ar ,rimro,, Symposium


or sorghum. Members of the genus Ophion were recovered principally from the south-
eastern United States with one collection of an Ophion sp. occurring in Honduras (Fig.
1G). The greatest impact of the ophions occurred on grass, followed by corn. No mem-
bers of this genus have been found parasitizing the FAW in alfalfa. The remaining
iclmeumonid attacking FAW was Temelucha difficilis Dasch. (Fig. 1H). This parasitoid
has been recovered only from larval collections in Florida with the highest parasitization
rates being recorded from corn.


E 2






Range of Parastizathon
by Crop "


Peanutl 1- 3
Sorghum t1 3%


n G


0v


Range of Parasitzation .
by Crop
Corn 1 10% .
Allalla
Grass 1 27%
Peanut 5%
Sorghum 1 3%








and Oohon sla












Florida Entomologist 69(3)


September, 1986


Euplectrus platyhypenae Howard was the only Eulophidae found attacking the
FAW (Fig. 11). Its greatest impact occurred on corn and it was recovered also from
FAW larvae feeding on grass and peanuts. Euplectrus sp., not identified as E. pal-
tyhypenae, was collected from the United States in Alabama and Florida and in Central
America from Nicaragua.
Members of the family Tachinidae, having been collected from North, Central, and
South America as well as the Caribbean, had a greater geographical distribution than
any of the other parasitoid families (Fig. 1J). Even though the tachinids did not have
the highest parasitization rates in any of the individual crops, they parasitized more
FAW larvae over a greater range of crops than any of the other parasitoids.
Parasitoids of the FAW occurred throughout its range and exerted substantial mor-
tality on larval populations. The data indicated that the FAW was parasitized in various
agricultural crops and geographic locations by different complexes of parasitoids. There
did not appear to be a single parasitoid species that exerted significant mortality
throughout any major portion of the FAW's range. This condition may be one of the
principal reasons why the FAW continues to be a serious agricultural pest.


ACKNOWLEDGEMENT

Sincere appreciation is expressed to Ms. Pamela Wilkening for her efforts in gather-
ing and organizing this information.


REFERENCES CITED

ALAM, M. M. 1979. Attempts at the biological control of major insect pests of maize
in Barbados, W. I. Proc. Caribbean Food Crops Soc., Symp. on Maize and
Peanut, Paramaribo, November 13-18, 1978, pp. 127-135.


- -~.-h..


, f I


Range of Paras tlzaton
by Crop

era s 15
Peanut 14%
Sorghm 1 8- 8


' Ta chinl dae


i N>


12_











Ashley: Fall Armyworm Symposium


ASHLEY, T. R., E. R. MITCHELL, N. C. LEPPLA, AND E. E. GRISSELL. 1980.
Parasites attacking fall armyworm larvae, Spodopterafrugiperda in late planted
field corn. Florida Ent. 63: 136-142.
-- V. H. WADDILL, E. R. MITCHELL, AND J. RYE. 1982. Impact of native
parasites on the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noc-
tuidae), in South Florida and release of the exotic parasite, Eiphosoma vitticole
(Hymenoptera: Ichneumonidae). Environ. Ent. 11(4): 833-37.
---, C. S. BARFIELD, V. H. WADDILL, AND E. R. MITCHELL. 1983. Parasitiza-
tion of fall armyworm larvae on volunteer corn, Bermudagrass, and paragrass.
Florida Ent. 66(2): 267-271.
BERTELS, A. 1956. Pragas do milho, metodos de defesa. Boletin Technico do Instituto
Agronomico do Sul. 16: 1-18.
CAMPOS P., J. 1965. Investigaciones sobre el control biologico del "colgollero" del
maiz, Spodoptra frugiperda (J. E. Smith) y otros noctuideos. Revista Peruana
de Ent. 8: 126-131.
FUENTES J., R. 1973. Dipteros parasites de larvas de lepidopteros en algunos
municipios del valle del Cauca. Acta Agronomica 23: 7-50.
HOGG, D. B., R. E. ANDERSON, AND H. N. PITRE. 1982. Early-season parasitization
of fall armyworm (Lepidoptera: Noctuidae) larvae in Mississippi. Florida Ent.
65: 584-585.
HYNES, H. B. N. 1942. Lepidopterous pests of maize in Trinidad. Tropical Agric. 29:
194-202.
KELLER, M. A. 1980. Effects of Temperature and Corn Phenology on Fall Armyworm
Biology. Masters Thesis, University of Florida, 83 pp.
LACAYO, L. 1977. Especies parasiticas de Spodoptera frugiperda Smith, Diatrae
lineolata (Wer) y Trichoplusia ni (Hbn) en zonas de Managua y Masatepe. XXIII
Reunion Anual del PCCMCA, Panama 1977, 28 pp.
LUCCHINI, F., AND A. A. ALMEIDA. 1980. Parasital da Spodoptera frugiperda
(Smith & Abbot, 1797) (Lep., Noctuidae), lagarta do cartucho do MI LHO encon-
trodo em pnota grossa. An. Soc. Ent. Bras. (Brazil) 9: 115-122.
LUGINBILL, P. 1928. The fall armyworm. U.S. Dept. Agric. Tech. Bull. 34, 91 pp.
MITCHELL, E. R., V. H. WADDILL, AND T. R. ASHLEY. 1984. Population dynamics
of the fall armyworm (Lepidoptera: Noctuidae) and its larval parasites on whorl
stage corn in pheromone-permeated field environments. Environ. Ent. 13: 1618-
1623.
MONTOYA, J. A. 1979. Estudio preliminary del ectoparasito del genero Euplectrus del
gusano cogollero Spodoptera frugiperda. VII Reunion Nacional de Control
Biologico, Veracruz, Ver. pp. 81-84.
MOREY, C. S. 1971. Biologia de Campoletis grioti (Blanchard) (Hymen.:
Ichneumonidae) parasite de la "lagarta cogollera del maiz" Spodopterafrugiperda
(J. E. Smith). Rev. Per. Ent. 14: 263-271.
NICKLE, D. A. 1976. The peanut agroecosystem in Central Florida. Ph.D. Disserta-
tion, University of Florida, Gainesville, 131 pp.
NOTZ, A. 1972. Parasitismo de Diptera e Hymenoptera sobre larvas de Spodoptra
frugiperda (Smith) (Lepidoptera: Noctuidae) recolectadas en maiz, Maracay,
Venezuela. Rev. Fac. Agron. 6: 5-16.
PARKER, H. L. 1953. Miscellaneous notes on South American dipterous parasites.
Lab. de Ent. Agric. "Felippo Silvestri" May-Aug, pp. 45-73.
PAIR, S. D., AND H. R. GROSS, JR. 1984. Field mortality of pupae of the fall ar-
myworm, Spodopterafrugiperda (J. E. Smith), by predators and a newly discov-
ered parasitoid, Diapetimorpha introita. J. Georgia Ent. Soc. 19: 22-26.
REED, D. J. 1980. Toxicological and parasitological studies on the fall armyworm,
Spodopterafrugiperda (J. E. Smith), in Alabama. M.S. Thesis, Auburn Univer-
sity, Auburn, Alabama, 55 pp.


523











Florida Entomologist 69(3)


ROHLFS, W. M., AND T. P. MACK. 1985. Seasonal parasitism rates, host size, and
adult emergence pattern of parasitoids of the fall armyworm, Spodoptera
frugiperda (J. E. Smith), with emphasis on Ophion flavidus Brulle (Hymenop-
tera: Ichneumonidae). Ann. Ent. Soc. America 78: 217-220.
RYDER, W. D., AND N. PULGAR. 1969. A note on parasitism of the fall armyworm,
Spodoptera frugiperda, on maize. Rev. Cubana Cienc. Agric. (English ed.) 3:
267-271.
SMITH, R. C. 1921. Observations on the fall armyworm (Laphygmafrugiperda Smith
& Abbott) and some control experiments. J. Econ. Ent. 14: 300-305.
SOTERES, K. M., R. C. BERBERET, AND R. W. Mc NEW. 1984. Parasitic insects
associated with lepidopterous herbivores on alfalfa in Oklahoma. Environ. Ent.
13: 787-793.
VICKERY, R. A. 1929. Studies on the fall armyworm in the Gulf Coast district of
Texas. U.S. Dept. Agric. Tech. Bull. 138, 63 pp.
WALL R., AND R. C. BERBERET. 1975. Parasitoids associated with lepidopterous
pests on peanuts; Oklahoma fauna. Environ. Ent. 4: 877-882.
WALTON, W. R. 1913. Efficiency of tachinid parasite on the last instar of Laphygma.
Proc. Ent. Soc. Washington 15: 128-131.












INCIDENCE AND HOST RANGE OF A NEW ASCOVIRUS
ISOLATED FROM FALL ARMYWORM,
SPODOPTERA FRUGIPERDA (LEPIDOPTERA: NOCTUIDAE)

J. J. HAMM, S. D. PAIR, AND O. G. MARTI, JR.
Insect Biology and Population Management Research Laboratory, USDA-ARS,
Tifton, GA 31793-0748

ABSTRACT

A new virus disease caused by an ascovirus was found in larvae of the fall armyworm,
Spodoptera frugiperda (J. E. Smith), collected in south Florida and Georgia. The host
range of the ascovirus from S. frugiperda was compared to ascoviruses from Trichop-
lusia ni (Hiibner), Autographa precationis (Gn.), Heliothis zea (Boddie), and H. vires-
cens (F.) by hemocoelic inoculation of the following species, S. frugiperda, S. exigua
(Hiibner), S. eridania (Cramer), S. ornithogalli, (Guenee), Heliothis zea (Boddie), and
Feltia subterranea (F.). The ascovirus from S. frugiperda infected only the four species
of Spodoptera. The ascoviruses from T. ni, H. zea, and H. virescens infected all of the
species tested. The ascovirus from A. precationis infected S. frugiperda, S. exigua, S.
ornithogalli, and F. subterranea but not S. eridania or H. zea. Eleven passages per os
in fall armyworm failed to produce a persistently high rate of infection by this route.
Moths from the surviving larvae in the eleventh passage per os did not transmit the
ascovirus to their progeny.


September, 1986











Hamm et al.: Fall Armyworm Symposium


RESUME

Se encontro una enfermedad viral causada por un ascovirus en larvas del gusano
cogollero, Spodoptera frugiperda (J. E. Smith), colectados en el sur de la Florida y
Georgia. La esfera de hospederos del ascovirus de S. frugiperda se compare con as-
covirus de Trichoplusia ni (Hubner), Autographa precationis (Gn), Heliothis zea (Bod-
die), y H. virescens (F.), por inoculaciones hemocelicas de las siguientes species, S.
frugiperda, S. exigua (Hubner), S. eridania (Cramer), S. ornithogalli (Guenee),
Heliothis zea (Boddies), y Feltia subterranea (F.). El ascovirus de S. frugiperda infect
solamente las cuatro species de Spodoptera. Los ascovirus de T. ni, H. zea y H.
virescens infectaron todas las species probadas. El ascovirus de A. precatioris infecta-
ron S. frugiperda, S. exigua, S. ornithogalli, y F. subterranea, pero no a S. eridania
o a H. zea Once pases per os en el gusano cogollero, fall en roducir un persistent grado
alto de infecciofi por este medio. Alevillas de las larvas sobrevivientes en el pase once
per os no trasmiti6 el ascovirus a sus progenitores.




Federici (1983) proposed the name "ascovirus" for a new type of double-stranded
DNA virus pathogenic to certain Lepidoptera in the family Noctuidae. The disease
caused by this virus is characterized by stunting of infected larvae and production of
virus-containing vesicles. These vesicles are released from infected tissues into the
hemolymph, causing the hemolymph to become opaque white. This disease has been
described in larvae of the cabbage looper, Trichoplusia ni (Hiibner), by Browning et
al. (1982), the clover cutworm, Scotogramma trifolii (Hufnagel), by Federici (1982), and
Heliothis spp. by Carner and Hudson (1983). Similar symptoms were observed in larvae
of the fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), collected in south
Florida and Georgia in 1982. The purpose of this paper is to report the level of natural
occurrence of an ascovirus in the FAW, to describe its host range in comparison to other
ascoviruses, and to report tests on per os infectivity and transovarial transmission of
the virus.


MATERIALS AND METHODS

In field surveys for parasitoids, FAW larvae were collected and isolated in 30-ml
cups of bean diet (Burton 1969). Larvae which neither pupated nor produced parasitoids
but remained stunted and pale were suspected of having the ascovirus. Hemolymph
from these larvae was examined using phase-contrast microscopy. If the hemolymph
was cloudy or opaque-white with many vesicles containing refractile inclusions, it was
considered diagnostic for the ascovirus. Infections in a few specimens were confirmed
by electron microscopy.
Two isolates of ascovirus from FAW larvae, collected in Dade County, Fla., were
used in the host-range studies. Isolate 82-126 was collected 7 April 1982 and isolate
84-36 was collected 19 March 1984. The ascovirus from T. ni (82-266) was obtained from
Dr. Brian Federici, Dept. of Entomology, Division of Biological Control, University of
California, Riverside, Cal. Ascoviruses were isolated from Autographa precationis
(Gn.) (isolate 83-30) collected from cardinal flower, Lobelia cardinalis L., in Tifton, Ga.,
30 May 1983; from an H. zea larva (isolate 84-271) collected from peanuts near Tifton,
Ga., 10 August 1984; and from an H. virescens (F.) larva (isolate 85-2) collected from
either Desmodium sp. or tobacco in a tobacco field near Tifton, Ga., 18 October 1985.


525










526 Florida Entomologist 69(3) September, 1986


Certain viral isolates were maintained by passage in alternate hosts because colonies
of the species from which they were originally isolated were not available. The isolate
from H. virescens was maintained in H. zea the isolate from T. ni in FAW, and the
isolate from A. precationis in FAW and later in F. subterranea. Test larvae were from
laboratory colonies at the Insect Biology and Population Management Research Labora-
tory.
A simple but highly effective method of hemocoelic inoculation was developed. The
integument of an infected larva was clipped with small dissecting scissors and the result-
ing drop of infective hemolymph was collected in a 1.5-1.8-mm diameter capillary tube.
A small drop of infective hemolymph was applied to each test larva by touching the end
of the capillary tube to the dorsal surface of the larva. A fine-pointed cactus spine taped
to the end of another capillary tube was used to penetrate the infective hemolymph and
puncture the integument of the test larva for inoculating first and second instars. Stout
cactus spines were used to inoculate larger larvae. Third-instar larvae were used with
the hemocoelic inoculation technique for host-range studies and any tests with negative
results were repeated. Larvae were held individually on bean diet at 20+2C and 50-70%
RH with 14:10 h light:dark photophase.
Because preliminary tests on per os infectivity of the ascovirus from FAW resulted
in low rates of infectivity, a series of per os passages of isolate 84-36 was made in FAW
larvae in an effort to increase the rate of per os infectivity. Inoculum was prepared by
grinding infected larvae with 0.1 M phosphate buffer, pH 7, 1 ml buffer per larva. The
original suspension was assigned a value of 1 and was diluted in the buffer to obtain
relative concentrations of 0.5, 0.05, and 0.005. No effort was made to quantitate the
number of vesicles or virus particles present. The viral suspensions were applied to the
surface of bean diet, without formalin, at the rate of 0. -ml/cup of diet. Neonate, 4-dy-
old or 6-dy-old larvae were allowed to feed on the treated diet for 24 h, then placed
individually in cups of bean diet with formalin. Larvae were held under fluctuating
conditions with a 14:10 h light:dark photophase, 290C dy, 24C night and 70-90% RH.
At the 11th passage of isolate 84-36, surviving larvae treated when 6 and 10 dy old
with 0.5 relative concentration of virus were used in a test for adult to larva transmission
of the virus. Eleven pairs of moths from larvae treated when 6 dy old, 12 pairs of moths
from larvae treated when 10 dy old, and equal numbers of pairs of control moths were
held individually in 473-ml cups for mating and oviposition. Samples of 36 larvae were
taken from the first oviposition of each female. The larvae were held individually on
bean diet under conditions described for the per os passage tests.

RESULTS AND DISCUSSION

Ascovirus was originally found in FAW larvae in south Florida in 1982 and has been
found repeatedly there and in Georgia. It generally infected only 1-10% of the FAW
larvae collected from populations where it was found (Table 1). This is consistent with
reports of Browning et al. (1982) that more than 12% of the second- and third instar
larvae of T. ni were infected with ascovirus in their studies in southern California.
Carner and Hudson (1983) reported that ascovirus infection in Heliothis spp. was quite
common and widespread in South Carolina, and although the incidence of infection in
the population sometimes reached 25%, it was usually lower.
In host-range studies using the hemocoelic inoculation technique (Table 2), both
ascovirus isolates from S. frugiperda infected S. exigua (HUbner), S. ornithogalli
(Guenee), and S. eridania (Cramer) but did not infect H. zea or F. subterranea (F.).
The ascovirus from A. precationis infected S. frugiperda, S. exigua, S. ornithogalli,











Hamm et al.: Fall Arimylrir'mi Symposium


TABLE 1. NATURAL INCIDENCE OF ASCOVIRUS IN FALL
RELATION TO LOCATION AND DATE OF COLLECTION.


ARMYWORM IN


No. larvae % larvae infected
Location Date collected with ascovirus

Dade County, Fla. 3/10/82 284* 2.5
4/7/82 247* 2.8
2/23/83 32 9.4
2/8/84 591* 6.4
3/13/84 424* 3.1
3/14/84 142* 5.6
4/16/84 432*. 1.8
Collier Co., Fla. 3/11/82 95 4.2
Hendry Co., Fla. 3/12/82 140 1.4
5/5/82 72 1.4
Highlands Co., Fla. 5/4/82 33 3.0
Tift Co., Ga. 8/19/82 455 2.0
8/23/82 357 7.8
8/26/82 529 2.5
8/8/84 134 0.7
8/10/84 142 0.7
8/16/84 117 2.6
8/15/85 139 5.8
8/28/85 134 5.2
9/3/85 383 2.3
9/10/85 213 6.1

*Composite of collections from more than one field in the area.



and F. subterranea but not S. eridania or H. zea. The ascoviruses from T. ni, H. zea
and H. virescens infected all of the species tested. Thus, the ascovirus of FAW was
distinguishable from the other isolates tested on the basis of differences in host range.
When the infective hemolymph was very cloudy or milky, the hemocoelic inoculation
technique infected all or nearly all of the challenged larvae of susceptible species. How-
ever, some infected larvae were stunted, yet the hemolymph was only slightly cloudy
and apparently contained fewer vesicles than when the hemolymph was milky. For that
reason, tests with negative results were repeated. The 51% infection in S. eridania
treated with the ascovirus isolate from H. virescens resulted from the combination of
two tests where there was no infectivity in the first test. The failure of the isolate from
A. precationis to infect S. eridania and H. zea is based on two tests, one using inoculum
produced in FAW and one using inoculum produced in F. subterranea.
Federici (1983) reported that the ascovirus of T. ni was infective for H. zea, H.
virescens, S exigua, and Peridroma saucia (Htbner) in the Noctuidae and Estigmene
acrea (Drury) in the Arctiidae, but did not infect Sabulodes aegrotata (Gn.) in the
Geometridae.
Per os infection of neonate FAW stunted the infected larvae while in the second and
third instar (Fig. 1) which was similar to what was observed in field-collected larvae.
However, the rates of infection in the per os passage tests were erratic (Table 3). This
was due, in part, to a lack of quantification of infective particles. Although passages 3
and 9 showed high rates of infection, the increase was not persistent.
Tests with moths from the surviving larvae in the llth passage of 84-36 failed to















Florida Entonuologist 69(3)


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Hamm et al.: Fall Armyworm Symposium 529



















Fig. 1. Normal fall armyworm larva, 13 dy old, and pale, stunted fall armyworm
larva, 13 dy after feeding on ascovirus isolate 84-36.


demonstrate transmission of the virus to the next generation. Although 28% of the
larvae treated when 6 dy old died of ascovirus, none of the 396 larvae reared from 11
pairs of surviving moths developed the disease. There was no mortality due to ascovirus
in the larvae treated at 10 dy of age, and none of the 432 larvae from the 12 pairs of
moths developed the disease.
Hamm et al. (1985) showed that the braconid parasitoid Cotesia marginiventris
(Cresson) could transmit the ascovirus of FAW from infected to noninfected larvae.
However, the progeny of the parasitoid failed to complete development in host larvae
that were inoculated with the ascovirus during parasitization.
The ascovirus of FAW apparently is only a minor factor in the suppression of FAW
populations overwintering in south Florida and in the larger populations of FAW in
south Georgia late in the summer. Parasitism was a more important mortality factor in
both areas (Pair et al. 1986). What potential the ascovirus may have for microbial
control of FAW is uncertain. We do not know how the pathogen is transmitted in the
field or how important parasitoids may be in its transmission. Since FAW larvae were
susceptible to all of the isolates of ascovirus by hemocoelic inoculation, the isolates
should be compared for infectivity per os. An isolate which has a large host range, at
least within the Noctuidae, and is highly infectious per os should have more potential
for microbial control than an isolate which is restricted to Spodoptera and is poorly
infectious per os.

REFERENCES CITED

BROWNING, H. W., B. A. FEDERICI, AND E. R. OATMAN. 1982. Occurrence of a
disease caused by a rickettsia-like organism in a larval population of the cabbage
looper, Trichoplusia ni in southern California. Environ. Ent. 11: 550-4.
BURTON, R. L. 1969. Mass rearing corn earworm in the laboratory. U. S. Dep.
Agric., Agric. Res. Serv. Tech. Bull. 33-134.
CARNER, G. R., AND J. S. HUDSON. 1983. Histopathology of virus-like particles in
Heliothis spp. J. Invertebr. Pathol. 41: 238-49.














Florida Entomologist 69(3)


September, 1986


0


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Hamm et al.: Fall Ann'ywornl Symposium 531

FEDERICI, B. A. 1982. A new type of insect pathogen in larvae of the clover cutworm,
Scotogramma trifolii. J. Invertebr. Pathol. 40: 41-54.
1983. Enveloped double-stranded DNA insect virus with novel structure and
cytopathology. Proc. Natl. Acad. Sci. USA 80: 7664-8.
HAMM, J. J., D. A. NORDLUND, AND O. G. MARTI. 1985. Effects of a nonoccluded
virus of Spodoptera frugiperda (Lepidoptera: Noctuidae) on the development of
a parasitoid, Cotesia marginiventris (Hymenoptera: Braconidae). Environ. Ent.
14: 258-61.
PAIR, S. D., J. R. RAULSTON, A. N. SPARKS, AND P. B. MARTIN. 1986. Fall ar-
myworm (Lepidoptera: Noctuidae) parasitoids: Differential spring distribution
and incidence on corn and sorghum in the southeastern United States and north-
eastern Mexico. Environ. Ent. 15: 342-8.





INTERACTIONS BETWEEN BACILLUS THURINGIENSIS
AND ITS BETA-EXOTOXIN IN FALL ARMYWORM
(LEPIDOPTERA: NOCTUIDAE) NEONATE LARVAE

WAYNE A. GARDNER, ANDREW F. PENDLEY.
and GREGGORY K. STOREY
Department of Entomology
University of Georgia
College of Agriculture Experiment Stations
Georgia Station
Experiment, Georgia 30212

ABSTRACT

Interactions between Bacillus thuringiensis Berliner and its beta-exotoxin, thurin-
giensin, were evaluated in neonate larvae of Spodoptera frugiperda (J. E. Smith). The
median lethal concentration of B. thuringiensis (Dipel) was 113.8 ug/ml of diet. Test
larvae were continuously fed on diet incorporated with one-half of this concentration
(56.9 ug/ml) in combination with various concentrations of the exotoxin. Potentiation
was the prevalent type of interaction observed between 2 and 10 days after initial
exposure. Treatments with B. thuringiensis in combination with 1, 15, 20, and 100 ppm
of exotoxin yielded higher mortality levels and lower median lethal times than treat-
ments with the individual agents alone. The combination of B. thuringiensis with 10
ppm of exotoxin was additive after 3 days postexposure. Antagonism occurred in com-
binations of B. thuringiensis with 1 and 10 ppm of exotoxin prior to 7 and 4 dy postex-
posure, respectively. This might be attributed to a previously-observed feeding deter-
rent factor in the beta-exotoxin.


RESUME

La interacciofi entire Bacillus thuringiensis Berliner, y su beta-exotoxina, fueron
evaluadas en larvas neonatales de Spodopterafrugiperda (J. E. Smith). La concentra-
cioni letal median de B. thuringiensis (Dipel), fue de 113.8 gg/ml de dieta. Larvas en
las pruebas fueron continuamente alimentadas con dietas donde se incorpor6 la mitad
de esta concentraci6n (56.9 ag/ml) en combinaci6n con varias concentraciones de la











532 Florida Entomologist 69(3) September, 1986

endotoxina. La potencialidad fue el tipo prevalente de interacci6n observado entire 2 y
10 dias despu6s de la exposici6n inicial. Tratmientos de B. thuringiensis en combinaci6n
con 1, 15, 20, y 100 ppm de exotoxina rindieron mayores niveles de mortalidad y tiempos
letales medianos mas bajos que los tratamientos con solamente los agents individuals.
La combinaci6n de B. thuringiensis con 10 ppm de exotoxina despues de 3 dias de estar
expuestos fue aditiva. Antagonismo ocurri6 en combinaciones de B. thuringiensis con
1 y 10 ppm de exotoxina antes de 7 y 14 dias de estar expuestos respectivamente. Esto
pudiera atribuirse a un factor previamente observado en la exotoxina-beta que inhibe
el comer.


Bacillus thuringiensis Berliner (B.t.) is currently the most used pathogen for micro-
bial control of insect pests. Although larvae of the fall armyworm (FAW), Spodoptera
frugiperda (J. E. Smith), are susceptible to commercial formulations of B.t., field tests
quantifying its efficacy against FAW have produced variable results (Krieg and Langen-
bruch 1981). B.t. provides good control of only those lepidopteran species whose larvae
feed on open leaves and, thus, can ingest enough B.t. to cause mortality. Therefore,
FAW control has been achieved with foliar sprays of B.t. when timing of application
was scheduled to contaminate leaf surfaces before larvae began to burrow and feed
within plant structures (Gardner and Fuxa 1980).
FAW also is susceptible to the beta-exotoxin ( = thermostabile exotoxin or thurin-
giensin) of B.t. (Mohd-Salleh and Lewis 1982). This toxin is produced only by some
isolates of certain serotypes of B.t. It is heat stable and water soluble. Beta-exotoxin
is a nucleotidic ATP analog which inhibits protein synthesis through interference of the
production of DNA-dependent RNA polymerase and the subsequent production of
ribosomal RNA (Sebesta et al. 1981). Toxic effects on lepidopteran larvae include mor-
tality or problems associated with molting processes. Reduced fecundity and teratolog-
ical abnormalities can occur in adults exposed to exotoxin as larvae (Ignoffo and Gregory
1972).
At present, most commercial formulations of B.t. contain only spores and the paras-
poral crystals of the delta-endotoxin. Incorporation of beta-exotoxin in commercial prep-
arations of B.t. might enhance effectiveness of both agents against selected target
species and extend the host range of the preparation. For example, Hitchings (1967)
reported that the water-soluble toxin in a commercial product of B.t. spores and crystals
inhibited the reproductive potential of southern armyworms, S. eridania (Cramer),
pupating in treated soil. In addition, synergistic combinations of B.t. and beta-exotoxin
might be discovered for more efficaceous control of susceptible larvae.
Consequently, this study was undertaken to assess the activity of B.t. and beta-
exotoxin against FAW neonate larvae and to search for synergistic B.t.-exotoxin in-
teractions.

MATERIALS AND METHODS

FAW larvae used in this study were obtained from a laboratory colony and were
reared on a semisynthetic diet (Burton and Perkins 1972). Only larvae that were 1 to
4 h old were used in these tests. The sources of the B.t. and beta-exotoxin preparations
were Dipel (16,000 IU/mg) and ABG-6162A, respectively (Abbott Laboratories, North
Chicago, Ill.).
The median lethal concentration (LC5o) of the B.t. preparation was determined by
individually placing test larvae into 30-ml clear-plastic creamer cups, each containing
ca. 9 ml of diet incorporated with B.t.-water dilutions. Ten concentrations of B.t. rang-











Gardner et al.: Fall Armyworm Symposium 533


ing from 20 to 1,600 ug/ml of diet with 30 larvae each were tested. Each concentration
plus a check diet treated only with water were replicated four times. Mortality was
assessed 7 and 14 dy after initial exposure of the larvae. Data were analyzed utilizing
the probit analysis procedure of the Statistical Analysis System (SAS Institute, Inc.
1982).
For tests of interactions, one-half of the LCso of B.t. was combined with five concen-
trations of beta-exotoxin ranging from 1 to 100 ppm (mg [AI]/liter of diet). Test larvae
were placed individually into 30-ml cups, each containing ca. 9 ml of diet incorporated
with water dilutions of either B.t. at one-half of the LCo5, beta-exotoxin at the respec-
tive concentrations, or both. Control larvae were placed on diet treated only with water.
Thirty larvae were tested for each of the four replicates per treatment. Larval mortality
was recorded daily until all test larvae either died or successfully pupated. Larval
weights were determined 10 dy after exposure in those treatments with at least five
living larvae per replicate.
The formula Oa + Ob(l-Oa) was used to calculate expected mortality, where Oa was
the observed percentage of mortality for the first agent alone and Ob was the observed
percentage of mortality for the second agent alone (McVay et al. 1977). Chi-square tests
were used to compare expected observed percentages of mortality. When the observed
mortality was not significantly different from the expected mortality, the combined
effect of the interaction was classed as additive, an interaction in which the combined
mortality level is similar to the sum of the mortality levels of the individual agents
acting alone. Significant deviations of the observed mortality from the expected mortal-
ity were classified as either potentiation (positive chi-square value) or antagonism (nega-
tive chi-square value). Potentiation (synergism) is an interaction in which the combined
effect of the agents is greater than the sum of their individual effects. Antagonism
occurs when the combined effect is less than the sum of the individual effects.
Median lethal times from exposure until mortality (LT5o) also were determined for
each treatment in the interaction tests.

RESULTS AND DISCUSSION

The test to determine the LC5o of the B.t. preparation for FAW neonate larvae
yielded a concentration of 113.8 ug/ml of diet with lower and upper 95% fiducial limits
of 78.4 and 173.5 ug/ml, respectively. Therefore, a concentration of 56.9 ug/ml was used
in the subsequent interaction tests. Total mortality of FAW larvae continuously exposed
to this concentration of B.t. was 29.3%. Cumulative mortality caused by the beta-
exotoxin ranged from 89.7% at 1 ppm to 100% for the remaining four concentrations.
However, at 7 dy after exposure, mortality had not exceeded 50% for all but one of the
concentrations of beta-exotoxin (Fig. 1).
Interactions between B.t. and beta-exotoxin were assessed at 2, 3, 4, 7, 10, and 14
dy after exposure. Assessments at 3, 7, and 10 dy postexposure are presented in Table
1 as examples. Three types of interactions were observed at these times: additivity,
potentiation, and antagonism.
Antagonism occurred soon after exposure only in the combinations of B.t. with 1
and 10 ppm of beta-exotoxin. By 7 dy after exposure, these combinations were either
synergistic or additive. The antagonistic effect might be attributed to a feeding deter-
rent factor in the beta-exotoxin which caused test larvae to slow or cease feeding
thereby slowing consumption of the lethal dose of either agent. Feeding inhibition and
the phenomenon of low mortality at high exotoxin concentrations were first observed
by Mohd-Salleh and Lewis (1982) in lepidopteran larvae continuously fed on diet incor-










Florida Entomologist 69(3)


September, 1986


B.t. (57 pg/ml)
1 ppm EXOTOXIN
10 ppm
15 ppm
20 ppm
100 ppm "


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DAYS POSTEXPOSURE
Fig. 1. Cumulative percent mortality of Spodopterafrugiperda larvae continuously
fed on diet incorporated with Bacillus thuringiensis or five concentrations of the beta-
exotoxin of B. thuringiensis.

porated with exotoxin. Feeding inhibition might be at least partially responsible for the
observed differences in weights of 10-dy-old FAW larvae in response to selected treat-
ments. Mean (-SE) individual larval weights of 65.1 (- 5.6) mg, 16.7 (- 3.8) mg, 2.1
( 0.2) mg, and 170.4 ( 6.8) mg differed significantly (P > 0.05) among the four
respective treatments of B.t. alone, 1 ppm exotoxin alone, B.t. + 1 ppm exotoxin, and
the untreated check.
The combination of B.t. and 10 ppm beta-exotoxin was additive after 3 days postex-
posure. All other combinations were synergistic until mortality due to the exotoxin
approached 100%, thereby producing similar observed and expected mortality values
(additivity). By 14 days after exposure, all combinations were additive.
Median lethal times (LTo5) further demonstrated these interactions (Table 2). LT5o's
of those combinations producing potentiation by 7 dy postexposure (1, 15, 20, and 100
ppm) were at least 4 dy shorter than the LTo's of treatments with the corresponding
concentrations of exotoxin alone. The LTso of the additive combination of B.t. and 10
ppm exotoxin was only 1.6 dy shorter than the LTo5 of the treatment with 10 ppm
exotoxin alone.


100-

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Gardner et al.: Fall Armyworm Symposium


TABLE 1. INTERACTIONS OF BACILLUS THURINGIENSIS AND
SPODOPTERA FRUGIPERDA NEONATE LARVAE.


BETA-EXOTOXIN IN


Days Combinations Observed Chi-square
postexposure tested' % mortality2 value Conclusion

3 Bt + 1 ppm 12.1 -6.12 Antagonism
Bt + 10 ppm 16.1 -10.52 Antagonism
Bt + 15ppm 35.7 1.30 Additivity
Bt + 20ppm 47.4 9.65 Potentiation
Bt + 100 ppm 88.9 39.96 Potentiation
7 Bt + 1 ppm 67.3 11.43 Potentiation
Bt + 10 ppm 61.9 0.81 Additivity
Bt + 15ppm 94.8 52.75 Potentiation
Bt + 20.ppm 98.2 60.31 Potentiation
Bt + 100 ppm 100.0 13.93 Potentiation
10 Bt + 1 ppm 89.7 14.46 Potentiation
Bt + 10 ppm 94.9 2.78 Additivity
Bt + 15ppm 100.0 16.01 Potentiation
Bt + 20ppm 100.0 16.88 Potentiation
Bt + 100ppm 100.0 0.61 Additivity

'B. thuringiensis (Bt) was tested at 56.7 ug of Dipel per ml of diet; beta-exotoxin
was tested at indicated ppm (mg [AI]/ml of diet).
2For all interactions, n = 120 (four replicates).
'Chi-square value = (Observed % mortality expected % mortality)/expected %
mortality (x2 = 3.84, df = 1, a = 0.05).

TABLE 2. MEDIAN LETHAL TIMES FOR SPODOPTERA FRUGIPERDA NEONATE LAR-
VAE EXPOSED TO THE BETA-EXOTOXIN OF BACILLUS THURINGIENSIS
AND COMBINATION OF B. THURINGIENSIS WITH BETA-EXOTOXIN.

B. thuringiensis Beta-exotoxin LT"5 95% fiducial
concn. (ug/ml) concn. (ppm) (days) limits

0 1 10.0 9.2-10.8
56.9 1 6.1 5.2- 6.9
0 10 6.6 6.2- 7.1
56.9 10 5.0 4.7- 5.2
0 15 7.9 7.4- 8.4
56.9 15 3.5 3.3- 3.7
0 20 7.8 7.3- 8.4
56.9 20 3.2 3.0- 3.4
0 100 5.9 5.6- 6.1
56.9 100 1.9 1.6- 2.1



Potentiation occurs in combinations of selected concentrations of B.t. and beta-
exotoxin in FAW neonate larvae. Combinations of these agents can increase mortality
while reducing the time between exposure and death. Causes for the potentiation re-
main unclear but may be due to physiological stress or reduction of the host defense
system.


535











Florida Entomologist 69(3)


Incorporation of beta-exotoxin into commercial products of B.t. could improve the
efficacy of B.t. preparations against lepidopteran larvae, shorten the time between
application and larval death, broaden the host range of the preparation (Krieg and
Langenbruch 1981), and provide a compatible use of multi-functional agents against
target insects thereby minimizing favorable selection conditions for development of
resistance to either agent (Boman 1981). Further development of this concept for use
in insect pest management must include additional laboratory bioassays followed by
greenhouse or field evaluations.

ACKNOWLEDGMENTS

We thank J. M. Cheshire, Jr., J. 0. Howell, and R. D. Getting for critical reviews
of this manuscript.

REFERENCES CITED

BOMAN, H. G. 1981. Insect responses to microbial infections. Pages 769-84. In H. D.
Burges, ed. Microbial control of pests and plant diseases 1970-1980. Academic
Press, London.
BURTON, R. L., AND W. D. PERKINS. 1972. WSB, a new laboratory diet for the corn
earworm and the fall armyworm. J. Econ. Ent. 65: 385-6.
GARDNER, W. A., AND J. R. FUXA. 1980. Pathogens for the suppression of the fall
armyworm. Florida Ent. 63: 439-47.
HITCHINGS, D. L. 1967. Bacillus thuringiensis: a reproductive inhibitor for southern
armyworm. J. Econ. Ent. 60: 596-7.
IGNOFFO, C. M., AND B. GREGORY. 1972. Effects of Bacillus thuringiensis
b-exotoxin on larval maturation, adult longevity, fecundity, and egg viability in
several species of Lepidoptera. Env. Ent. 1: 269-72.
KRIEG, A., AND G. A. LANGENBRUCH. 1981. Susceptibility of arthropod species to
Bacillus thuringiensis. Pages 837-96. In H. D. Burges, ed. Microbial control of
pests and plant diseases 1970-1980. Academic Press, London.
McVAY, J. R., R. T. GOUDAUSKAS, AND J. D. HARPER. 1977. Effects of Bacillus
thuringiensis-nuclear poiyhedrosis virus mixtures on Trichoplusia ni larvae. J.
Invert. Path. 29: 367-72.
MOHD-SALLEH, M. B., AND L. C. LEWIS. 1982. Feeding deterrent response of corn
insects to B-exotoxin of Bacillus thuringiensis. J. Invert. Path. 39: 323-8.
SAS INSTITUTE INC. 1982. SAS user's guide: basics. SAS Institute, Inc., Cary, North
Carolina.
SEBESTA, K., J. FARKAS, K. HORSKA, AND J. VANKOVA. 1981. Thuringiensin, the
beta-exotoxin of Bacillus thuringiensis, pages 249-77. In H. D. Burges, ed.
Microbial control of pests and plant diseases 1970-1980. Academic Press, London.


536


September, 1986











Overman: Fall Arny,,wnrin-i Symposium 537


RESISTANCE IN CORN (ZEA MAYS) TO THE
FALL ARMYWORM SPODOPTERA FRUGIPERDA:
THE IMPACT OF PUBLIC RESEARCH ON
COMMERCIAL SEED COMPANIES

J. L. OVERMAN
Dekalb-Pfizer Genetics, Inc.
Union City, Tennessee 38261

ABSTRACT

The fall armyworm, Spodoptera frugiperda (J. E. Smith), is an economic pest of
late-planted corn, Zea mays L., in the southern United States and it reduces the market
potential for the currently available commercial hybrids. Commercial hybrid seed com-
panies are responsible for developing and marketing the majority of the commercial
corn hybrids. These companies are still dependent on public institutions to identify and
release resistant germplasm, develop insect rearing methods and to design efficient
breeding techniques for developing resistant elite lines. This paper discusses the major
discoveries from the public sector and their impact on commercial seed research.

RESUME

El gusano cogollero, Spodoptera frugiperda (J. E. Smith), es una plaga que causa
perdidas econ6micas en el maiz, Zea mays L., que es sembrado tarde en el sur de los
Estados Unidos y que reduce el mercado potential de los hibridos hoy dia disponibles.
Compafiias comerciales de semillas hibridas son responsables del desarrollo y mercado
de la mayoria del maiz hibrido commercial. Estas compafifas todavia dependent de in-
stituciones pfiblicas para identificar y hacer disponible germplasmas resistentes, desar-
rollar metodos para criar insects, y para disefiar eficientes t6cnicas de fitomejoramiento
para desarrollar las mejores selecciones de variedades. Este trabajo discute los descub-
rimientos mAs important del sector pfblico y de su impact en investigaciones comer-
ciales.


Wiseman and Davis (1979) provided a historical review of plant resistance to the fall
armyworm (FAW), Spodoptera frugiperda (J. E. Smith). Davis (1980a) reviewed the
current public plant resistance programs on corn, Zea Mays L.; sorghum, Sorghum
bicolor (L.) Moench; peanuts, Arachis hypogeae L.; bermudagrass, Cynodon dactylon
(L.) Pers.; rice, Oryza sativa L.; and millet, Pennisetum glaucum L. Their discussions
included comments on factors limiting advancement in FAW research. Concerns in-
cluded a need for team research involving entomologists and plant breeders, improve-
ments in insect rearing, and better plant-infesting techniques. Equally important is the
need for transfer of research information from the USDA/ARS, universities, and inter-
national institutes to private institutions such as commercial seed companies. This link-
age is essential because commercial U.S. seed companies are the primary employers of
corn breeders. These breeders are currently responsible for developing the majority of
elite inbred lines and testing and deploying new hybrids. The remainder of the paper
reviews the potential impact of public FAW research on corn seed companies.











538 Florida Entomologist 69(3) September, 1986


INSECT REARING

Efficient programs for developing FAW resistant cultivars depend on an adequate
supply of the proper larval stage applied at the appropriate plant growth stage. The
following techniques, derived from public research, are being used in commercial seed
research.
FAW are reared in 28.4-ml plastic cups which are 1/3 filled with southwestern corn
borer diet (Davis 1976). The cups are stacked on 11" x 17" cookie sheets. A 15-liter batch
of diet is prepared in a 20-liter steam jacketed kettle. The diet is poured using 1000-ml
plastic beakers. Three people routinely fill about 1500 cups (1/3 full) in 10 minutes.
Alternatively, the diet can be dispensed with the insect-diet dispenser (Davis et al.
1978). Egg masses are surface-sterilized and hatched in 3.8 liter glass jars. After hatch-
ing the first-instar larvae are mixed with autoclaved 20-40-mesh corncob grits (Davis
1980b). The hand operated larval dispenser (bazooka) (Wiseman et al. 1980) is used to
infest each cup with 2-3 larvae. The cups are then hand-capped with plain paper
cardboard lids. Alternatively, a larval dispenser-capper machine can be used for these
two operations (Davis 1980b). Larvae are incubated for about three weeks at 27C at
the end of which time the pupae are removed by hand or with a mechanical pupal
harvester (Davis 1982).
Pupae are placed inn oviposition cages for adult emergence and egg laying. Adults
and eggs are handled according to Davis et al. (1985a). Potential production with this
system is about 10 million eggs per day. Production costs are nominal and most of the
facilities can also be used for rearing the southwestern corn borer, Diatraea grand-
iosella Dyar; European corn borer, Ostrinia nubilalis Hiibner; sugarcane borer, Diat-
raea saccharalis F.; and corn earworm, Heliothis zea Boddie.

FIELD TECHNIQUES

Infestation methods were developed by Wiseman and Widstrom (1984) and Davis
and Williams (1980). FAW egg masses are hatched in the dark in 3.8 liter glass jars.
The first-instar larvae are mixed with 20-40-mesh corncob grits. The mixture is calib-
rated for delivering 20 larvae per shot with the bazooka. Plants are infested with two
applications in the whorl at the 6-to-10-leaf stage. Ten to 14 days later the plants are
rated on a leaf feeding scale as follows: 1-2 highly resistant, 3-4 resistant, 5-6 inter-
mediate, 7-8 susceptible, 9 highly susceptible. In breeder's segregating nurseries, insec-
ticides are applied after evaluation to prevent migration of the larvae from susceptible
onto resistant plants. Resistant plants are then tagged for pollination and identification
at harvest.

SOURCES OF RESISTANCE

All elite corn belt lines and germplasm tested were rated susceptible for FAW. All
resistance currently being used can be traced to coastal tropical flints and Carribean
area germplasm. Resistant germplasm available from public research is as follows:
Antigua 2D (Wiseman et al. 1981) from the Tifton, GA, research group; resistant
germplasm MpSWCB-4, Mp701, Mp702, Mp703, Mp704, Mp705, Mp706, and Mp707
from the Mississippi State research team (Scott and Davis 1981, Scott et al. 1982,
Williams and Davis 1980, 1982, 1984). The Mississippi germplasm has leaf-feeding resis-
tance to FAW and southwestern corn borer. Recently this germplasm was shown to
have leaf-feeding resistance to the European corn borer; Asian corn borer, O. furnacalis











Overman: Fall Airmywivorni Symposium 539


Guenee; African maize stem borer, Chilo partellus Swinh.; and the sugarcane borer (F.
Davis, personal communication). The presence of multiple resistance should make this
germplasm a more attractive breeding material for U.S. and foreign commercial breed-
ing programs.

MECHANISMS OF RESISTANCE

Several investigators have examined the mechanisms of resistance in corn to FAW.
In laboratory choice and no-choice experiments, Wiseman et al. (1981) determined that
nonpreference was the primary cause of resistance in Antigua 2D-118. Resistance in
MpSWCB-4 was mainly antibiosis with low levels of larval nonpreference. In field and
cage studies Wiseman et al. (1983) showed significantly more larvae crawling off Anti-
gua 2D-118 to surrounding uninfested plants than off the resistant MpSWCB-4 or the
susceptible check. These results supported their earlier findings of antibiosis in
MpSWCB-4 and nonpreference in Antigua 2D-118.
Ng et al. (1985) further examined the antibiosis effect of resistant vs. susceptible
hybrids. The survival, growth, and reproduction for FAW larvae were studied in field
and laboratory tests. Larvae reared on resistant vs. susceptible genotypes had higher
mortality, longer larval-development time, smaller larvae, and smaller female pupae.
Under laboratory conditions the reproductive rates were 34-50% less for FAW reared
on resistant genotypes.
In a novel approach, Williams et al. (1985) examined larval growth and behavior of
FAW on callus initiated from susceptible and resistant corn hybrids. Mean weights of
larvae reared for 1 week on callus of resistant and susceptible genotypes were 29.5 and
50.0 mg, respectively. In choice tests, newly-hatched larvae preferred callus from sus-
ceptible genotypes over resistant. Williams et al. (1985) suggest that callus may be used
to study the basis of resistance and its chemical nature, and to evaluate genotypes in
environments where the the whole plant is not adapted.

COMMERCIAL VALUE

In the final analysis, the value of FAW resistance must be demonstrated in the
farmer's field. As a general rule, resistant hybrids must be competitive with other
commercial hybrids in the absence of the pest, and demonstrate a significant yield
advantage under infestation. Resistant germplasm is more likely to be used by breeders
if resistance is additive or dominant in gene action.
Scott et al. (1977) found single-cross hybrids containing one resistant parent yielded
twice as much under FAW infestation as susceptible commercial hybrids. In a corn-fol-
lowing-wheat double-cropping system, Williams and Sanford (1983) showed an esti-
mated profit from FAW and rust-resistant hybrids, but not for commercial hybrids.
Studies by Widstrom et al. (1972) and Williams et al. (1978) showed general combin-
ing ability for leaf-feeding resistance to be highly significant. Thus, all resistant inbreds
in hybrids tested had significant negative effects on FAW as measured by reduced leaf
feeding. Williams et al. (1978) speculate that resistance would be expressed in combina-
tion with other susceptible lines.

SUMMARY

The FAW is an economic pest of late-planted corn in the South and reduces the
market potential for currently available commercial hybrids. Resistant hybrids would











540 Florida Entomologist 69(3) September, 1986


have a significant marketing advantage over the present susceptible hybrids. Commer-
cial seed companies depend on public institutions (USDA/ARS, universities, etc.) to
identify and release resistant germplasm, and develop insect-rearing methods and field
techniques. In the past, deficiencies in these areas have restricted commercial develop-
ment of FAW hybrids resistant to FAW. Major innovations and releases in the areas
of resistant germplasm, FAW rearing methods, and field and laboratory techniques
from USDA/ARS, universities and international research groups should enhance FAW
research in commercial companies.

REFERENCES CITED

DAVIS, F. M. 1976. Production and handling of eggs of southwestern corn borer for
host plant resistance studies. USDA/ARS Tech. Bull. 77. 11 pp.
- T. G. OSWALT, AND J. C. BOYKIN. 1978. Insect diet dispenser for medium-size
rearing programs. U.S. Agri. Res. Serv. [Rep.] ARS-S-1982, 3 pp.
1982. Mechanically removing southwestern corn borer pupae from plastic rear-
ing cups. J.Econ. Entomol. 75: 393-395.
---. 1980a. Fall armyworm plant resistance programs. Florida Entomol. 63: 420-
424.
- 1980b. A larval dispenser-capper machine for mass rearing the southwestern
corn borer. J. Econ. Ent. 73: 692-693.
--, T. G. OSWALT, AND S. NG. 1985a. Improved oviposition and egg collection
system for the fall armyworm (Lepidoptera:Noctuidae). J. Econ. Ent. 78: 725-
729.
--, AND W. P. WILLIAMS. 1980. Southwestern corn borer: Comparison of
techniques for infesting corn for plant resistance studies. J. Econ. Ent. 73: 704-
706.
NG, S., F. M. DAVIS, AND W. P. WILLIAMS. 1985b. Survival, growth and reproduc-
tion of the fall armyworm (Lepidoptera:Noctuidae) as affected by resistant corn
genotypes. J. Econ. Ent. 78: 967-971.
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. Mississippi Agric.
Forest. Exp. Sta. Res. Rep. 3: 1-4.
-- AND 1981. Registration of Mp496 inbred of maize (Zea mays L.). Crop
Sci. 21: 353
SCOTT, G. E., F. M. DAVIS, AND W. P. WILLIAMS. 1982. Registration of Mp701 and
Mp702 germplasm lines of maize. Crop Sci. 22: 1270.
WIDSTROM, N. W., B. R. WISEMAN, AND W. W. MCMILLIAN. 1972. Resistance among
some maize inbreds and single crosses to fall armyworm injury. Crop Sci. 12: 290-
292.
WILLIAMS, W. P., P. M. BUCKLEY, AND F. M. DAVIS. 1985. Larval growth and
behavior of the fall armyworm (Lepidoptera:Noctuidae) on callus initiated from
susceptible and resistant corn hybrids. J. Econ. Ent. 78: 951-954.
---, AND F. M. DAVIS. 1980. Registration of Mp703 germplasm line of maize. Crop
Sci. 20: 418.
--, AND -- 1982. Registration of Mp704 germplasm line of maize. Crop Sci.
22: 1269-1270.
--- AND 1984. Registration of Mp705, Mp706, Mp707 germplasm lines of
maize. Crop Sci. 24: 1217.
- AND J. O. SANFORD. 1983. Corn and wheat in a double-cropping system.
Mississippi Agric. Forest. Exp. Sta. Res. Rep. 8: 11.
- F. M. DAVIS, AND G. E. SCOTT. 1978. Resistance of corn to leaf-feeding dam-
age by the fall armyworm. Crop Sci. 18: 861-863.











Overman: Fall Armityworwt Symposium


WISEMAN, B. R., F. M. DAVIS, AND J. E. CAMPBELL. 1980. Mechanical infestation
device used in fall armyworm plant resistance programs. Florida Entomol. 63:
425-432.
W. P. WILLIAMS, AND F. M. DAVIS. 1981. Fall armyworm: resistance
mechanisms in selected corns. J. Econ. Ent. 74: 622-624.
- F. M. DAVIS, AND W. P. WILLIAMS. 1983. Fall armyworm: larval density and
movement as an indication of nonpreference in resistant corn. Protection Ecol.
5: 135-141.
- I, AND F. M. DAVIS. 1979. Plant resistance to the fall armyworm. Florida En-
tomol. 62: 123-130.
-- AND N. W. WIDSTROM. 1984. Fall armyworm damage ratings on corn at vari-
ous infestation levels and plant development stages. J. Agric. Entomol. 1: 115-
119.







PLANT RESISTANCE AND NUCLEAR POLYHEDROSIS
VIRUS FOR SUPPRESSION OF THE FALL ARMYWORM
(LEPIDOPTERA: NOCTUIDAE)

J. J. HAMM AND B. R. WISEMAN
U.S. Department of Agriculture,
Agricultural Research Service,
Insect Biology and Population Management
Research Laboratory,
P. O. Box 748,
Tifton, Georgia 31793

ABSTRACT

The susceptibility of fall armyworm, Spodoptera frugiperda (J. E. Smith), larvae to
nuclear polyhedrosis virus (NPV) was studied in relation to host plant resistance in
corn, Zea mays L. In laboratory tests, freeze-dried silks of resistant (Zapalote Chico)
and susceptible (Stowell's Evergreen) corn lines were incorporated into artificial diets.
Larvae treated with the virus before they were held individually on the test diets
showed significantly higher mortality due to NPV on the diet containing resistant silks
than on the diet containing susceptible silks. When larvae were fed on test diets for 6
days before they were treated with the virus, the larvae grew larger and were less
susceptible to the NPV on the diet containing susceptible silks than on the diet contain-
ing resistant silks. In a field test comparing five lines of corn with a spectrum of leaf-
feeding resistance to fall armyworm, larvae growing on the most susceptible line had
the lowest mortality due to NPV. Thus, the susceptibility of fall armyworm larvae to
NPV was inversely related to the growth and vigor of the larvae, which was directly
related to the susceptibility of the host plant. Therefore, the fall armyworm NPV should
be more effective when used on resistant lines of corn than on susceptible lines.











Florida Entomologist 69(3)


RESUME

Se estudi6 la susceptibilidad de larvas del gusano cogollero, Spodoptera frugiperda
(J. E. Smith), al virus polyhedrosis nuclear (VPN) en relaci6n a la resistencia del maiz
Zea mays L. En pruebas de laboratorio, sedas secadas por el metodo de congelaci6n
de las variedades resistentes (Zapalote Chico) y la susceptibilidad (Stowell's Evergreen)
fueron incorporadas en una dieta artificial. Larvas tratadas con el virus antes de que se
mantuvieran individualmente en las dietas de prueba, demostraron significativamente
una mortalidad mas alta debido al VPN en la dieta conteniend sedas resistentes que en
la dieta con sedas susceptibles. Cuando las larvas se alimentaron con las dietas de
prueba por 6 dias antes de ser tratadas con el virus, las larvas crecieron mas grande y
fueron menos susceptible al VPN en la dieta con sedas susceptibles que en la dieta con
sedas resistentes. En una prueba de campo donde se compar.aron cinco variedades de
maiz con various niveles de resistencia foliar al gusano cogollero, las larvas desarrollan-
dose en la variedad mas susceptible tuvo la menor mortalidad debido al VPN. En este
caso, la susceptibilidad de larvas del gusano cogollero al VPN fue inversamente propor-
cional al crecimiento y vigor de la larva, que estaba directamente relacionado a la
susceptibilidad de la plant hospedera. De aqui que el VPN del gusano cogollero debe
de ser mas efectivo cuando se use en variedades resistentes de mais que en variedades
susceptibles.


Host plant resistance and microbial control are two tools which can be used in pest
management schemes (Wiseman 1985, Hall 1964). Bergman and Tingey (1979) reviewed
aspects of interactions between plant genotypes and parasites and predators. More
recently, Obrycki and Tauber (1985) reported that highly pubescent clones of potato
plants had the highest percentage of predator eggs (Coleoptera: Coccinellidae) while
clones with the lowest trichome densities had the highest percentages of immature and
adult predators. A high number of aphid parasitoid mummies occurred on clones with
moderate to high densities of glandular pubescence. Treacy et al. (1985) found an inverse
relationship between plant trichome density in cotton and the level of successful attacks
on Heliothis zea (Boddie) eggs by the parasite, Trichogramma pretiosum (Riley), and
the predator, Chrysopa rufilabris (Burmeister). A deleterious interaction between host
plant resistance and a parasitoid was reported by Powell and Lambert (1984). They
found significant reductions in successful development of Microplitis croceipes (Cress.)
in Heliothis larvae that were fed leaves of resistant vs. susceptible soybeans.
Very little research has been done on the interaction between microbial control
agents and host plant resistance to determine how they may be combined most effec-
tively in integrated pest management. Lewis and Lynch (1976) and Lynch and Lewis
(1976) showed that both plant resistance factors in corn and the protozoan, Nosema
pyrausta Paillot, infection reduced the number of European corn borer, Ostrinia
nubilalis (Hiibner), larvae per plant. In these experiments, the larvae were infected
transovarially; therefore, there was no effect of host plant on the incidence of infection.
However, in some tests, the level of infection was dependent on both the egg mass
source and inbred line of corn.
Bell (1978) compared development and mortality in H. zea larvae fed resistant and
susceptible soybean cultivars treated with the fungus Nomuraea rileyi (Farlow) Samson
and the bacterium Bacillus ii, ritgieinsi. (Berliner). The combined effects of the patho-
gen and antibiosis usually caused higher larval mortality in a shorter time than single
factors alone. Hare and Andreadis (1983) showed that host plants more suitable for
growth and survival of the Colorado potato beetle, Lepinotarsa decemlineata (Say),
produced larvae least susceptible to the fungus Beauveria bassiana (Balsamo). They


September, 1986











Hamm & Wiseman: Fall A rni'my11.1 Symposium


hypothesized that the physiological and metabolic stresses imposed on L. decemlineata
larvae feeding on suboptimal hosts may interfere with the efficacy of the defensive
reaction of L. decemlineata to overcome infection by B. bassiana.
On the other hand, Ramoska and Todd (1985) showed that fungal inhibitors produced
by host plants fortuitously protected the insects feeding on them. Mortality of adult
chinch bugs, Blissus leucopterous leucopterous (Say), due to B. bassiana was reduced
in populations fed on sorghum and corn. Fungal development in cadavers of insects fed
on sorghum and corn also was reduced.
In a field test with Elcar, the Heliothis nuclear polyhedrosis virus, Hamm et al.
(1986) found a greater reduction in number of H. zea larvae on a corn hybrid with an
extended tight husk than on a hybrid with a loose husk. However, the virus treatment
saved more kernels of corn on the hybrid with the loose husk than on the hybrid with
the tight husk.
This paper reports two laboratory tests on the effects of incorporating corn silks
from resistant and susceptible lines on the survival of fall armyworm (FAW), Spodopt-
era frugiperda (J. E. Smith), larvae treated with nuclear polyhedrosis virus (NPV). It
also reports one field test comparing the effects of treating FAW larvae with NPV while
on seedling corn of resistant and susceptible lines.

MATERIALS AND METHODS

LABORATORY TESTS

Silks of 'Zapalote Chico 2451#' (resistant) and 'Stowell's Evergreen' (susceptible)
sweet corn were harvested from bulk plantings, freeze dried, and mixed into pinto bean
diet (Burton 1969) for assaying. Four or 8 g (dry weight) of each silk type were blended
into 350 ml of pinto bean diet with an additional 40 or 80 ml of distilled water. Diets
were dispensed into 30 ml plastic diet cups and allowed to solidify for 2 h. The treated
larvae were placed individually in the cups, and held at 26.7 2C and 75 5% RH
with 14:10 h light:dark photophase. The FAW larvae were from a laboratory colony at
the Insect Biology and Population Management Laboratory.
The Georgia strain of the S. frugiperda NPV (Hamm 1968, Loh et al. 1982) was
produced in FAW larvae. The polyhedral inclusion bodies (PIB) were partially purified
by centrifugation five times in 0.1 Mm phosphate buffer, pH 7 and stored at -20C. The
PIB were counted using a Petroff-Hauser bacterial counter.
Two methods for treating larvae were used. A modification of the droplet method
described by Hughes and Wood (1981) was used to treat neonate FAW larvae with NPV
before they were isolated on the test diets. Numerous small droplets of virus suspension
were applied to a 15x15 cm square of 16 mm Teflon sheet. Neonate FAW larvae were
placed on the sheet. Larvae were picked up with a small artist's brush and placed
individually in cups of test diet as they were observed to drink from the droplets and
move away.
In the diet incorporation method, the virus was diluted 1:9 with the test diets without
formalin to produce the desired concentration of PIB/ml of diet. Twenty neonate larvae
per cup were fed on the treated diets for 24 h, then isolated on test diets without virus.
Experiment 1 was designed to compare 2 methods of treating FAW larvae with
NPV to evaluate interaction of the virus and corn silks on mortality due to the virus.
In this split-split-plot design, the main plots were the virus treatments (0 or 1 x 104
PIB/ml). The sub-plots were the treatment methods (droplet method or incorporation
of virus into the diet). The final split consisted of the corn silks (8 g/350 ml diet, resistant,


543











Florida Entomologist 69(3)


susceptible, or check, which was bean diet with no corn silks). There were 72 replica-
tions, each consisting of 1 FAW larva. The percent mortality due to NPV at 9 days post
treatment was transformed to arcsin V % and statistically analyzed by the analysis of
variance method, and means were separated by LSD or Waller-Duncan (SAS 1982).
Significance was determined at P < 0.05 for all levels of this study.
Experiment 2 was designed to determine the effects of feeding on diets containing
susceptible or resistant corn silks for various times before virus treatment on the sus-
ceptibility of FAW larvae to the NPV. In the split-split-plot design, the main plots were
concentration of silks (4 or 8 g/350 ml diet plus 40 or 80 ml of distilled water, respec-
tively). The sub-plots were time on test diets before virus treatment (0, 3, or 6 days).
The final split consisted of the types of silks (susceptible, resistant, and bean diet with
no silks). The virus treatments were 0 or 4 x 104 PIB/ml of diet for neonate FAW, 0 or
4 x 10r PIB/ml of diet for 3-day-old larvae, and 0 or 4 x 106 PIB/ml of diet for 6-day-old
larvae. The neonates were treated as described for the virus incorporation method in
the previous test. The 3-day-old larvae were held, 2 per cup, for 24 h on test diets
incorporated with the virus, before they were placed individually on the original test
diets without virus. The 6-day-old larvae were weighed before they were placed indi-
vidually on test diets containing virus for 24 h, then reisolated on test diets without
virus. Larvae were examined daily until pupation and data were analyzed as described
previously.

FIELD TEST

A field test was designed to determine the interaction between host plant resistance
in whorl-stage corn and treatment with NPV on the damage to corn leaves and the
mortality of FAW larvae due to NPV. The Ohio strain of S. frugiperda NPV (Loh et
al. 1982) was used in the field test. The virus was freshly produced in FAW larvae,
purified by centrifugation, and quantitated as in the previous experiment. Whorl-stage
resistant cultivars 'Antigua 2-D 118', 'MpSWCB-4', and 'Pioneer X304C' and susceptible
cultivars 'Cacahuacintle X's' and 'DeKalb 1214' were selected in accordance with the
results of previous studies (Wiseman et al. 1981 and Gross et al. 1982). In this split plot
design with 8 replications, the main plots were the virus treatments (0 or 1012 PIB/ha)
and the sub-plots were the 5 corn cultivars.
The corn plots were 6.1 m long rows, ca. 25 plants/row, with rows 0.9 m apart.
Agronomic practices common to the area were applied to the experiment At ca. 1
month after emergence, the whorl-stage corn was artificially infested with ca. 25 neon-
ate FAW larvae/plant using the modified bazooka described by Wiseman et al. (1980).
The FAW larvae were applied in the morning and the plots were sprayed with virus
the same afternoon (May 3, 1985). Ca. 5 ml of aqueous virus suspension was sprayed
into the whorl of each corn plant (ca. 1.1 x 10" PIB/plant) with a hand-held, all-purpose
pressure sprayer. Three days after infestation and treatment, 10 plants per plot were
cut near the ground and transported to the laboratory in plastic bags. Up to 18 larvae
were collected from each sample and isolated on bean diet to determine percent mortal-
ity due to NPV. Eleven days after infestation, the remaining plants were visually rated
for leaf-feeding damage using a scale of 0-9 (Wiseman and Davis 1979). Data were
analyzed as in the previous tests.


544


September, 1986











Hamm & Wiseman: Fall A rm.,,iijr'II Symposium


RESULTS AND DISCUSSION

LABORATORY TESTS

Overall, there was no significant difference between the two treatment methods in
percent mortality due to NPV (Table 1). However, there was significantly higher mor-
tality due to NPV in larvae held on diet containing resistant silks (Zapalote Chico) than
in larvae held on diet containing susceptible silks (Stowell's Evergreen). The mortality
on the bean diet check was intermediate and not significantly different from either of
the silk diets.
In the test comparing the effects of feeding on diets containing susceptible or resis-
tant silks before virus treatment, there was no significant difference between the
twoconcentrations of silks and thus the data (Table 2) are averaged across the two
concentrations. There was no significant difference in mortality between diets for larvae
treated with NPV after 0 or 3 days on the test diets. However, after 6 days on the test
diets before treatment, the diet with resistant silks (Zapalote Chico) produced signific-
antly higher mortality due to NPV than the other diets. The weight of 6-day-old larvae
before they were put on the virus-treated diets was significantly lower when grown on
diet containing resistant silks than on the check diet or the diet containing susceptible
silks (Table 3), and the differences were greater at the higher concentration of silks.
There are many reports of increasing resistance to viral infection with larval matura-
tion (Stairs 1965, Ignoffo 1966, Boucias and Nordin 1977, Whitlock 1977). Apparently,
in this test the increase in virus concentration with increased larval age at time of
treatment was sufficient to produce a high rate of mortality for the smaller larvae that
were held on diet containing resistant silks. However, the larvae that were held on diet
containing susceptible silks or the bean diet for 6 days were so much larger at time of
exposure to NPV that the increased virus concentration did not compensate for their
increase in size.





TABLE 1. COMPARISON OF 2 METHODS OF TREATING NEONATE FALL ARMYWORM
WITH NPV (1x0l PIB/ML) TO EVALUATE INTERACTION WITH CORN SILKS
INCORPORATED INTO THE DIET.

Percent mortality due to NPV2
Variety of
silks in diet Droplet In diet Mean

Stowell's Evergreen 19.4 13.9 16.6 a2
Check (bean diet) 25.0 15.3 20.1 ab
Zapalote Chico 33.3 33.3 33.3 b
Mean 25.9 NS 20.8

'There was no mortality due to NPV in the controls.
2Means followed by the same letter are not significantly different (P > .05) according
to LSD test. Overall means separated by NS are not significantly different (P > 0.05)
according to LSD test.











546 Florida Entomologist 69(3) September, 1986


TABLE 2. PERCENT MORTALITY' DUE TO NPV OF FALL ARMYWORM TREATED WITH
VIRUS AFTER FEEDING ON TEST DIETS.

Days on test diets before virus
treatment and concentration of
virus in PIB/ml
0 3 6
Variety of corn -
silks in diet 4X104 4X105 4X106

Stowell's Evergreen 68.1 a 75.0 a 25.0 a
Check (bean diet) 75.0 a 62.5 a 30.6 a
Zapalote Chico 63.9 a 69.4 a 68.1 b


'Means in the same column followed by the same letter are not significantly different
(P > .05) according to LSD test. Means underscored by the same line are not signific-
antly different (P > .05) according to LSD test.
"Values presented are means for combined concentrations of silks (4 g and 8 g).
There was no significant difference due to concentration.



TABLE 3. MEAN WEIGHT (MG) OF FALL ARMYWORM LARVAE FED 6 DAYS ON 2 CON-
CENTRATIONS OF SILKS IN DIETS'.

Concentration of silks
Variety of
silks in diets 4 gm 8 gm

Stowell's Evergreen 75.3 a 84.2 a
Check (Bean diet) 70.8 a 72.9 b
Zapalote Chico 51.1 b 21.6 c

'Means in the same column followed by the same letter are not significantly different
(P > .05) according to LSD test.


FIELD TESTS

The NPV treatment significantly reduced damage to all of the corn lines (Table 4).
Only the most susceptible line, Cacahuacintle, had a significantly higher damage rating
than the others when treated with virus. It also had the lowest percent mortality of
FAW larvae due to NPV (Table 5).
In both laboratory and field tests there was generally less mortality due to NPV
when the FAW larvae were growing more vigorously. Larvae that were treated with
the virus before they were isolated on test diets containing corn silks showed higher
mortality due to NPV on the diet containing resistant silks than on the diet containing
susceptible silks. When larvae were held on the test diets for 6 days before they were
treated with the virus, the larvae grew larger and were less susceptible to the NPV on
diet containing susceptible silks than on the diet containing resistant silks. In field tests


~^^^











Hamm & Wiseman: Fall Armyworm Symposium


TABLE 4. MEAN DAMAGE RATING' FOR 5 CORN LINES 11 DAYS AFTER INFESTA-
TION WITH FAW AND TREATMENT WITH NPV @ 5X1012 PIB/HA

Corn lines Treated Control

Cacahuacintle 1.61 a' 4.44 a
Pioneer X304C 1.17 b 3.54 b
DeKalb 1214 1.15 b 3.42 b
Antigua 2D 1.05 b 2.55 c
Mp SWCB-4 1.01 b 1.59 d
Mean 1.2 3.1

'Damage rating 0-9 with 0 = no damage and 9 = plant destroyed.
2Means in the same column followed by the same letter are not significantly different
(P > .05) according to Wallef-Duncan k-ratio t-test. Overall means separated by are
significantly different (P < .05) according to LSD test.


TABLE 5. PERCENT MORTALITY DUE TO NPV OF FALL ARMYWORM LARVAE COL-
LECTED FROM 5 CORN LINES 3 DAYS AFTER TREATMENT WITH 5X10'2
PIB/HA.

% mortality
Corn lines Treated Control

Pioneer X304C 100.0 a' 0 a
Antigua 2D 97.9 ab 0.79 a
Mp SWCB-4 97.2 ab 0.70 a
DeKalb 1214 93.0 b 0 a
Cacahuacintle 89.6 c 0 a

'Means in the same column followed by the same letter are not significantly different
(P > .05) according to Waller-Duncan k-ratio t-test.

involving leaf resistance to insect feeding, larvae growing on the most susceptible line
had the lowest mortality due to NPV.
There are potentially many different types of interactions between insect resistant
plants and insect pathogens. Thus, it is necessary to study each combination of host
plant resistance and pathogens to determine their actual interactions and implications
for integrated pest management. In the system studied in these experiments, the sus-
ceptibility of FAW larvae to NPV was inversely related to the growth and vigor of the
larvae, which was directly related to the susceptibility of the host plant. Therefore, the
FAW NPV was more effective when used on the resistant line of corn, which exhibited
antibiosis, than on the susceptible line of corn.

REFERENCES CITED

BELL, J. V. 1978. Development and mortality in bollworms fed resistant and suscepti-
ble soybean cultivars treated with Nomuraea rileyi or Bacillus thuringiensis.
J. Georgia Ent. Soc. 13: 50-5.


547




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