Title: Florida Entomologist
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Title: Florida Entomologist
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Creator: Florida Entomological Society
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Place of Publication: Winter Haven, Fla.
Publication Date: 1991
Copyright Date: 1917
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Insects -- Periodicals
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(ISSN 0015-4040)


FLORIDA ENTOMOLOGIST

(An International Journal for the Americas)

Volume 74, No. 2 June, 1991

TABLE OF CONTENTS


Announcement 74th annual meeting ....................................... .............. i
FORUM

HOLLINGSWORTH, R. G.-Balsam Woolly Adelgid (Homoptera: Adelgidae) and
Spruce-fir Decline in the Southern Appalachians: Assessing Pest Relevance
in a Damaged Ecosystem ..................................... ........................ 179

FALL ARMYWORM SYMPOSIUM-'90

PITRE, H N .- Preface ............................................................................ 188
WISEMAN, B. R., AND H. R. GROSS-Dr. John R. Young-Economic En-
tom ologist ...................................................................................... 189
QUISENBERRY, S. S.-Fall Armyworm (Lepidoptera: Noctuidae) Host Strain
Reproductive Compatibility .............................................................. 194
PAIR, S. D., J. R. RAULSTON, J. K. WESTBROOK, W. W. WOLF, AND S. D.
ADAMS-Fall Armyworm (Lepidoptera: Noctuidae) Outbreak Originating
in the Lower Rio Grande Valley, 1989 ............................................... 200
WISEMAN, B. R, AND D. J. ISENHOUR-Development of Fall Armyworm on
Diets Containing Resistant and Susceptible Corn Silks ....................... 214
ISENHOUR, D. J., AND B. R. WISEMAN-Fall Armyworm Resistance in Progeny
of Maize Plants Regenerated Via Tissue Culture ................................ 221
YANG, G., D. J. ISENHOUR, AND K. E. ESPELIE-Activity of Maize LeafCuticu-
lar Lipids in Resistance to Leaf-Feeding by the Fall Armyworm ........... 229
GROSS, H. R., AND S. D. PAIR-Seasonal Distribution, Response to Host De-
velopmental Stage, and Screened-Cage Performance of Archytas mar-
moratus (Diptera: Tachinidae) and Ophion flavidus (Hymenoptera:
Ichneumonidae) on Spodoptera frugiperda (Lepidoptera: Noctuidae) ...... 237
ROGERS, C. E., A. M. SIMMONS, AND O. G. MARTI-Noctuidonema guyanense:
An Ectoparasitic Nematode of Fall Armyworm Adults in the Tropical
A m ericas .................................................................................... 246
GARDNER, W. A.-Ovicidal Properties of Fenoxycarb Against the Fall Ar-
myworm (Lepidoptera: Noctuidae) ................................................... 257
GUILLEBEAU, L. P., AND J. N. ALL-Use of Pyrethroids, Methomyl, and Chlor-
pyrifos to Control Fall Armyworm (Lepidoptera: Noctuidae) in Whorl
Stage Field Corn, Sweet Corn, and Sorghum ..................................... 261
CHANDLER, L. D., AND H. R. SUMNER-Effects of Various Chemigation
Methodologies on Suppression of the Fall Armyworm (Lepidoptera: Noc-
tuidae) in Corn .............................................................................. 270
SUMNER, H. R. R. B. CHALFANT, AND D. COCHRAN-Influence of Chemiga-
tion Parameters on Fall Armyworm Control in Field Corn .................. 280
PORTILLO, H. E., H. N. PITRE, D. H. MECKENSTOCK, AND K. L. ANDREWS-
Langosta: A Lepidopterous Pest Complex on Sorghum and Maize in Hon-
duras ........................................ ......................................... 287

Continued on Back Cover

Published by The Florida Entomological Society









FLORIDA ENTOMOLOGICAL SOCIETY
OFFICERS FOR 1989-90
P resident .............................................................. ..................... J. F Price
President-Elect ........................... ............................................ J. L. Knapp
Vice-President .......................... .......................................... D. F. W illiams
Secretary ..................................................................... ..... J. A Coffelt
Treasurer ........................................... .................... A. C. Knapp
Other Members of the Executive Committee
J. E. Eger J. E. Pefia J. R. Cassani J. H. Frank
J. R. McLaughlin S. Valles M. Lara
PUBLICATIONS COMMITTEE
J. R. McLaughlin, USDA/ARS, Gainesville, FL ....................................... Editor
Associate Editors
Agricultural, Extension, & Regulatory Entomology
Ronald H. Cherry-Everglades Research & Education Center, Belle Glade, FL
Michael G. Waldvogel-North Carolina State University, Raleigh, NC
Apiculture
Stephen B. Bambara-North Carolina State University, Releigh, NC
Biological Control & Pathology
Ronald M. Weseloh-Connecticut Agricultural Experiment Sta., New Haven, CT
Book Reviews
J. Howard Frank-University of Florida, Gainesville
Chemical Ecology, Physiology, Biochemistry
Louis B. Bjostad-Colorado State University, Fort Collins, CO
Ecology & Behavior
John H. Brower-Stored Product Insects Research Laboratory, Savannah GA
Theodore E. Burk-Dept. of Biology, Creighton University, Omaha, NE
Forum & Symposia
Carl S. Barfield-University of Florida, Gainesville
Genetics & Molecular Biology
Sudhir K. Narang-Bioscience Research Laboratory, Fargo, ND
Medical & Veterinary Entomology
Arshad Ali-Central Florida Research & Education Center, Sanford, FL
Resumen
Omelio Sosa, Jr.-USDA Sugar Cane Laboratory, Canal Point, FL
Systematics, Morphology, and Evolution
Michael D. Hubbard-Florida A&M University, Tallahassee
Howard V. Weems, Jr.-Florida State Collection of Arthropods, Gainesville
Willis W. Wirth-Florida State Collection of Arthropods
Business M manager ....................................................................... A. C. Knapp
FLORIDA ENTOMOLOGIST is issued quarterly-March, June, September, and De-
cember. Subscription price to non-members is $30 per year in advance, $7.50 per copy;
institutional rate is $30 per year. Membership in the Florida Entomological Society,
including subscription to Florida Entomologist, is $25 per year for regular membership
and $10 per year for students.
Inquiries regarding membership and subscriptions should be addressed to the Busi-
ness 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 in Winter Haven, FL.
Manuscripts from all areas of the discipline of entomology are accepted for consider-
ation. At least one author must be a member of the Florida Entomological Society.
Please consult "Instructions to Authors" on the inside back cover.
This issue mailed June 28, 1991













ANNOUNCEMENT 74TH ANNUAL MEETING
FLORIDA ENTOMOLOGICAL SOCIETY

The 74th annual meeting of the Florida Entomological Society will be held August
4-7, 1991 at the Ritz Carlton Hotel, 280 Vanderbilt Beach Road, Naples, Florida 33963;
telephone (813 598-3300. Registration forms and information will be mailed to members
and will appear in the Newsletter.

David F. Williams, Chairman
Program Committee, FES
USDA-ARS
Medical and Veterinary Entomology Research Laboratory
Gainesville, Florida 32604
(904) 374-5982 or 374-5903











Hollingsworth & Hain: Balsam Woolly Adelgid 179

FORUM

BALSAM WOOLLY ADELGID (HOMOPTERA: ADELGIDAE)
AND SPRUCE-FIR DECLINE IN THE SOUTHERN
APPALACHIANS: ASSESSING PEST RELEVANCE
IN A DAMAGED ECOSYSTEM

ROBERT G. HOLLINGSWORTH AND FRED P. HAIN
Dept. of Entomology, Box 7626
North Carolina State University
Raleigh, N.C. 27695

ABSTRACT

Research on tree decline has shown that the proportion of sapwood area to heartwood
area is an important measure of tree health. Infestation by the balsam woolly adelgid
(BWA), Adelges piceae (Ratz.), causes the formation of abnormal wood, which is thought
to conduct sap poorly. BWA infestation is also associated with lower (more negative)
xylem pressure potentials and increased areas of heartwood. We hypothesize that lower
pressure potentials (a consequence of abnormal wood production) increase the rate of
cavitation (gas-filling) of sapwood tracheids, thereby accelerating heartwood formation.
If this hypothesis is correct, adelgid attack causes loss of functional sapwood both directly
and indirectly.
There is evidence that the balsam woolly adelgid is an important factor causing the
decline of Fraser fir, Abiesfraseri (Pursh) Poiret, in the southern Appalachians. However
adelgid damage is probably interacting with many other environmental factors to cause
reductions in per cent sapwood area. Determining the relevance of this pest to tree
decline can be accomplished by examing the relationship that exists between adelgid
infestation, increment growth, and per cent sapwood area.

RESUME

En investigaciones se ha demostrado que la proporci6n alburduramen es una media
que se relaciona con la sanidad y vigor de arboles en decadencia. Infestaciones de el
adelgido algodonoso del balsamo (BWA), Adelges piceae (Ratz.), causan la formaci6n de
madera normal y disminuyen la conducci6n de la savia. La infestacion de BWA tambi6n
se asocia con presion potential baja negativea) del xylema y con el incremento del dura-
men. Nosotros sostenemos la hipotesis de que presiones potenciales bajas (a consecuencia
de la producci6n normal de madera) incrementan la tasa de cavitaci6n (llenado de gases)
de las traqueidas del albur, causando la aceleraci6n de formaci6n del duramen. Si esta
hipotesis es correct, el ataque del adelgido causa una perdida direct e indirecta del
albur.
Hay evidencia de que el adelgido algodonoso del balsamo es un factor important
para el declive de pino Fraser, Abiesfraseri (Pursh) Parret, en el sur de los Apalaches.
Probablemente el dano del adelgido esta interactuando con otros factors del medio
ambiente, lo cual causa reducciones en un porcentaje del area de albur. Para determinar
la importancia de esta plaga en el declive del Arbol, se puede examiner la relaci6n que
existe entire las infestaciones de adelgidos, incremento del crecimiento y el porcentaje
del area de albur.










Florida Entomologist 74(2)


There is little doubt that the balsam woolly adelgid (BWA), Adelges piceae (Ratz.),
qualifies as an important pest of Fraser fir, Abies fraseri (Pursh) Poiret. Aerial photo-
graphs taken in 1960 near Mount Mitchell, N.C. revealed that approximately 200,000
fir trees had already been killed just five years after BWA was detected in this area
(Amman & Speers 1965, Amman 1966). By 1966, 90% of all Fraser fir stems over 8 feet
tall in the Mt. Mitchell area had been killed by this insect (Witter & Ragenovich 1986).
Today in the Black Mountains surrounding Mt. Mitchell, an estimated 49% of standing
Fraser fir trees are dead (Dull et al. 1988). Now that BWA has spread throughout the
Black Mountains, it is no longer possible to compare the condition of infested trees with
the condition of nearby trees which have never been infested. Thus it is difficult to
separate the effects of BWA injury from the effects of other environmental factors.
Much research in the southern Appalachians is directed towards assessing the possible
role of atmospheric pollutants in causing a growth decline of both Fraser fir and red
spruce [Picea rubra (Du Roi) Link] (Bruck 1984, Zedaker et al. 1987). Although most
researchers recognize that BWA is an important component of the decline problem, it
is not clear to what degree this insect is continuing to cause decline symptomology. In
order to assess the importance of BWA, we must consider how BWA damage to fir
trees might be interacting with other environmental factors which have been
hypothesized to cause tree decline. This paper reviews some of the factors that might
be important to this interaction.

BACKGROUND AND HISTORY

BWA is thought to be native to the silver fir forests of central Europe (Pschorn-
Walcher & Zwolfer 1958). This insect, in the family Adelgidae, seldom causes serious
injury to fir trees (Abies sp.) within its native range (Varty 1956, p. 39). It was first
discovered in the southern Appalachians in 1955 (Amman 1966). Although BWA attacks
other North American fir species (Abies sp.), Fraser fir is one of the most susceptible
(Mitchell 1966). BWA does not attack spruce.
Fraser fir is thought to represent a glacial remnant from the Pleistocene (Buell 1945,
Cain 1944, Witter & Ragenovich 1986). It occurs in six discrete areas of high altitude
in the southern Appalachians. Although not important as a timber source, Fraser fir
forests are valuable for their recreational use, and also serve as a seed source for the
Christmas tree industry.
Most tree mortality has occurred in the southern portion of Fraser fir's range, from
the Black Mountains surrounding Mount Mitchell to the Great Smoky Mountains. Fraser
fir trees at Mount Rogers, Virginia have suffered considerably less mortality, despite
evidence that BWA has been present at this location since at least 1962 (Haneman et
al. 1981). Individual trees at Mount Rogers do become heavily infested, just as they do
in other areas where Fraser fir grows (personal observation). Therefore the relatively
low mortality of trees in infested areas at Mount Rogers is probably not related to the
degree with which trees become infested.
The life cycle of the BWA is comprised of the egg, three nymphal instars, and the
adult female, which is wingless and parthenogenic. The first nymphal instar is termed
a "crawler." Only this stage is mobile. After it finds a suitable place to feed, it inserts
its stylet into the bark and feeds in that particular spot throughout its life. As an adult
it measures approximately 0.80 mm in length, and is covered with white strands of wax
which make the insect appear "woolly" (Balch 1952). BWA completes two or three
generations per year in North Carolina (Arthur & Hain 1984). The adelgids feed primarily
on the main stem of the tree. Trees that do not recover from infestation generally die
within two to five years after initial attact (Amman & Speers 1965).


June, 1991











Hollingsworth & Hain: Balsam Woolly Adelgid 181

HOST REACTIONS

Adelgid attack causes chemical and structural changes within the bark of susceptible
hosts. Balch (1952) has described these changes in detail for balsam fir (Abies balsamea
[L.] Mill.). Initially the number and size of bark parenchyma cells increase within the
feeding zone (the area surrounding the insect's stylets). Within one year, the feeding
zone becomes surrounded by purplish cork cells. The parenchyma cells within this zone
then disintegrate, and the area becomes infiltrated with resin.
The bark of a Fraser fir tree is bounded exteriorly by a persistent periderm layer.
As a result, the bark of most trees is comprised almost entirely of inner (living) bark
(personal observation; also see Chang 1954). However, beneath areas of bark which are
heavily-infested, a secondary periderm layer is formed at a depth of two or more millimet-
ers. This process leaves behind a superficial layer of dead cells (outer bark) which
physically prevents feeding by future generations of adelgids (Balch 1952). Areas of
bark which are heavily-infested during one insect generation might support few (if any)
insects during the subsequent generation (personal observation).
Although BWA feeds only from the bark of fir trees, infestations on North American
firs typically induce the formation of altered xylem tissue which conducts water very
poorly (Balch 1952, Mitchell 1967). In cross-section this wood is evidenced by enlarged
growth rings which appear to contain a high proportion of latewood. Because of its color,
it is termed "rotholz," a German word meaning "red wood." Microscopic examination
shows that rotholz is anatomically similar to compression wood (Balch 1952), having
thick-walled tracheids which are circular (as opposed to rectangular) in cross-section
(Doerksen & Mitchell 1965, Timell 1986). Rotholz forms only in the vicinity of adelgid
attack (Balch 1952; Doerksen & Mitchell 1965). Even low populations of BWA are
sufficient to cause its occurrence beneath infested bark (Balch 1952, and personal obser-
vation). It has not been reported as occurring in any of the European fir species (Balch
1952, p. 74).


MECHANISM OF INJURY

The bulk of available evidence suggests that the primary damage caused by BWA
infestation to North American firs results from the production of abnormal wood. Mitchell
(1967) injected acid fuchsin dye into the stems of grand and subalpine firs (Abies grandis
(Dougl.) Lindl. and Abies lasiocarpa (Hook.) Nutt., respectively] to investigate the
effect of BWA infestation on water uptake by the sapwood. Compared with uninfested
controls, infested trees absorbed less dye and transported the dye in fewer growth
rings. Dye did not move through areas containing rotholz. Dye uptake experiments have
also been conducted on infested and uninfested balsam fir with similar results (Balch
1952, p. 63).
Figure 1 shows the relative positions of the various wood types discussed above in
a stem section of a Fraser fir Christmas tree which had been lightly infested for three
years.
In general, decline symptoms are similar for all species of North American fir that
are infested primarily on the main stem. Differences which do exist apparently result
from host sensitivity as well as the spatial pattern of BWA colonization (Mitchell 1966).
Symptoms shown by grand and subalpine fir include drooping leaders (Mitchell 1966),
positive sap pressures in mid-summer, and water-soaked appearance of heartwood
(Mitchell 1967). The crown of grand fir usually dies over a period of years, beginning
with the lower limbs and proceeding upwards. Amman (1967) observed a similar pattern
for Fraser fir growing on Mount Mitchell. In contrast, the crown of subalpine fir usually










Florida Entomologist 74(2)


Fig. 1. Cross-section of a previously-infested Fraser fir stem.


begins dying from the top (Mitchell 1966). All of these symptoms are consistent with
the hypothesis that BWA-induced damage impedes water transport in the sapwood.
For some heavily-infested trees, bark and cambial death apparently precede crown
deterioration. This has been observed for balsam fir (Balch 1952) and Fraser fir (personal
observation). In these cases, death of the bark and cambial tissues effectively "girdle"
the trees. Within a year's time, the foliage of the entire crown becomes chlorotic, then
changes to a russet red color. Balch suspected that this rapid tree death was the direct
result of damage to the bark and cambium. To test this hypothesis, he selected four
healthy balsam fir trees and, for each tree, removed a band of bark tissue by cutting
with a scalpel. The depth of the cut and the width (height) of the band was varied
between trees. The tree which received the most bark injury (5-foot-wide band, 3 mm
deep) exhibited symptoms identical to those trees which were naturally "girdled" by
BWA. Considering the rapid nature of decline symptoms, we believe that disturbance
of water transport (not interruption of the phloem) is likely to be the proximal cause of
tree death. Some girdled trees live for many years before dying (Zimmermann 1983, p.
121; Noel 1970). Perhaps in the case of fir, drying out of bark and cambial tissues leads
to cavitation (gas-filling) of sapwood tracheids, thereby increasing resistance to sap
ascent. It is unclear what proportion of Fraser fir succumbing to BWA follow this rapid
pattern of decline.
Although rotholz production is a common occurrence in infested trees of North Amer-
ican fir species (including Fraser fir), not all infested trees produce rotholz. However
the xylem of infested trees can be altered even when rotholz is not produced. Heavily-in-
fested grand fir trees, grown as exotics in Scotland, were found to contain no rotholz,
yet the "sapwood" of these trees (wood adjacent to the cambium) was only one-twentieth
as permeable as sapwood sampled from nearby uninfested trees. This adelgid-altered


June, 1991











Hollingsworth & Hain: Balsam Woolly Adelgid 183

wood stained the same color as heartwood (Puritch 1971). Follow-up studies determined
that the reduced permeability was most likely due to a combination of tracheid pit
membrane encrustation and increased volume of air in the sapwood (a consequence of
accelerated cavitation, or gas-filling of tracheids) (Puritch & Johnson 1971, Puritch &
Petty 1971). A subsequent trial using grand fir from British Columbia found that BWA
infestation was associated with an increase in both heartwood area and number of
heartwood rings. Within an infested tree, the amount of heartwood was greater adjacent
to areas of bark supporting higher BWA populations (Puritch 1977). Based on these
results, Puritch and Johnson (1971) advanced the hypothesis that infestation by BWA
caused the formation of "premature heartwood."
Pressure chamber measurements on cut shoots of Fraser fir add additional evidence
that infestation interferes with water transport through the sapwood. Measurements
taken in June showed that infested trees at Mount Mitchell and Roan Mountain, N.C.,
had lower xylem pressure potentials (an indication of poorer water status) than uninfested
controls, while the infested and uninfested trees at Mt. Rogers, Virginia did not differ
from one another. In mid-summer, there were no significant differences at any site. In
September however, infested trees showed lower water potentials at all locations (Arthur
1985). As September is traditionally a low-rainfall month in the southern Appalachians,
these results indicate that the physiological effects of BWA damage are more severe
during periods of low rainfall.
In summary, the most important consequence of BWA infestation is a reduction of
effective sapwood area leading to increased flow resistance in the sapwood.
Having established the probable mechanism of BWA injury, we can now consider
how other environmental factors suspected to cause tree decline might be interacting
with effects caused by the Balsam Woolly Adelgid. By so doing we hope to devise a
reasonable method for determining the relevance of BWA in the context of a damaged
spruce-fir ecosystem. We will use the Black Mountains of North Carolina as a case in
point.

TREE DECLINE

Approximately 7200 acres of spruce-fir forest are contained within the rugged Black
Mountains of North Carolina. The peaks stretch along a single twelve-mile long ridge
with a north-south orientation. The percentage of Fraser fir in the stand component
increases with elevation, up to 66% at elevations above 6000 feet. Approximately 11%
of the spruce-fir type in the Southeast is within this region (Dull et al. 1987, Dull et al.
1988).
Disturbance by humans has been intense in this area (Pyle & Schafale 1988). Most
notable is the logging and associated slash fires with subsequent erosion and windthrow
problems. The majority of the logging operations occurred between 1912 and 1922, but
salvage logging of windthrown trees continued until at least 1929. Other man-made
disturbances resulted from grazing, tourism, and fires set by hunters prior to commercial
logging.
Within the Black Mountains, both red spruce and Fraser fir are now declining, as
evidenced by crown condition, growth increment, and mortality data. The decline has
been most severe at the higher elevations, which also contain the highest proportion of
fir (Bruck 1984, Bruck & Robarge 1988, Dull et al. 1988, Zedaker et al. 1987). From
Mount Mitchell there is evidence that acidic cloud water is responsible for leaching of
both calcium and magnesium from the forest canopy (Robarge et al. 1987).
The incidence of Fraser fir mortality is highly correlated with the presence of BWA
(Zedaker et al. 1987). However it should be noted that the highest elevations, where
fir dominates over spruce, probably receive greater inputs of atmospheric pollutants










184 Florida Entomologist 74(2) June, 1991

due to higher precipitation and frequent cloud immersion (Dull et al. 1987). In this
context, Hain and Arthur (1985) hypothesized that atmospheric pollutants may either
lower the tolerance of Fraser fir to BWA, or add a final, lethal stress to trees already
heavily stressed by BWA.
There is a growing consensus in Europe that pollution-induced deficiencies of soil
nutrients are responsible for much of the forest decline observed there (Pitelka & Raynal
1989). Blank et al. (1988) summarized current hypotheses regarding pollutant effects in
Europe, and emphasized that no single hypothesis explains all of the observed "decline
types." One common type of decline exhibited by Norway spruce, Picea abies L. Karst,
at high altitudes in Germany is defined by the yellowing and subsequent loss of older,
magnesium-deficient needles. Blank et al. suggested that naturally low levels of mag-
nesium in the soil predispose the spruce to deficiency caused by the leaching action of
excess inputs of nitrogen and sulphur. The loss of needles would be expected to reduce
the growth potential of the cambium.
Shortle & Smith (1988) hypothesized that calcium deficiency, induced by excess
aluminum in the soil solution, is responsible for the red spruce decline in the northeastern
United States. They noted that calcium is incorporated at a constant rate in the production
of sapwood (regardless of tree vigor), and they used this fact to argue that calcium
availability is a limiting factor for cambial growth. Because the demand for calcium per
unit of cambial area is constant, the need for calcium (which is not recovered from the
heartwood) increases exponentially as the tree grows. Calcium-deficient trees will have
reduced sapwood area, leading to crown thinning and susceptibility.
Although the mechanism causing decline differs between these two scenarios, both
scenarios result in reduced annual increment, which is evidenced by narrow growth
rings. These narrow growth rings are associated with reduced sapwood area. Shortle
& Bauch (1986) found this to be the case for declining balsam fir in the U.S. and silver
fir (Abies alba Mill.) in West Germany. Their results indicated that trees with less than
25% basal area of sapwood become highly vulnerable to death from secondary pathogens
and insects. The vulnerability occurs because less sapwood is available for defense, food
storage, and water conduction (Shortle & Bauch 1986, Shortle & Smith 1988).
A reduced proportion of sapwood area results from a reduced rate of sapwood pro-
duction, an accelerated rate heartwood formation. According to Huber, the loss of water
from the tracheids is the "beginning of a chain of events which we call heartwood
formation" (Zimmermann & Brown 1971, p. 212). Loss of water from the tracheids
occurs when the tracheids cavitate. As sapwood ages, the proportion of tracheids which
are cavitated gradually increases (Zimmermann 1983, p. 46). This is a least part of the
reason why inner sapwood is generally less permeable than outer sapwood (Puritch 1971).

INTERACTION OF BWA DAMAGE WITH OTHER ENVIRONMENTAL FACTORS

As previously discussed, trees infested by BWA contain poorly-conducting sapwood
rings and a greater proportion of heartwood. A reduction in effective sapwood area
caused by BWA may lead to a lower (more negative) xylem pressure potential in the
stem of an infested tree. According to Darcy's Law, the flow rate of a liquid through a
porous material is equal to: [cross-sectional conducting area x permeability x pressure
difference] + [viscosity x specimen length] (Puritch 1971). For a given rate of sapwood
flow, loss of sapwood area should cause pressure differences in the main stem to increase,
assuming all other factors are held constant. Thus negative xylem pressures in the stems
may became more negative in response to sapwood loss. Trees might compensate for
lost sapwood area by dropping foliage or reducing transpiration. However there is
experimental evidence (as discussed in the Introduction) that pre-dawn xylem pressure
potentials are in fact lower (more negative) in infested versus uninfested trees. This
indicates that compensation, if it occurs, is incomplete.










Hollingsworth & Hain: Balsam Woolly Adelgid


As pressure in the main stem becomes more negative, the relative frequency of
cavitation (gas-filling) of sapwood tracheids is expected to increase (see Zimmermann
1983, p. 46). As previously mentioned, the loss of water from sapwood tracheids may
initiate the process of heartwood formation (Zimmermann & Brown, 1971, p. 212). Thus
we suggest that BWA damage accelerates heartwood formation by increasing the rate
of cavitation of sapwood tracheids. If BWA attacks a tree whose cambial growth potential
has already been reduced by other environmental factors, then per cent sapwood area
may be reduced to the point that the tree succumbs to insects, disease, or drought.

RESEARCH DIRECTIONS

If BWA interacts with other environmental factors to cause an reduction in per cent
sapwood area, studying the interaction fully will require knowing the infestation history
for each tree. Reasonably accurate infestation histories can be constructed by examining
tree rings for the presence of rotholz.
Rotholz can usually be distinguished from true compression wood because the latter
is seldom formed on both sides of the tree simultaneously. The presence of rotholz in a
tree ring can be determined by examining wood cores collected from opposite sides of
a tree. Unfortunately our experience suggests that heartwood-sapwood boundaries can-
not be reliably determined from Fraser fir wood cores. Apparently the cores do not
provide enough surface area for perceiving the generally slight color differences between
sapwood and heartwood which occur when Fraser fir wood is reacted with 40% perchloric
acid (following the method of Eades 1958). Assessing heartwood/sapwood boundaries
may require cutting down a limited number of sample trees from protected areas. Data
on rotholz histories and per cent sapwood areas could be used for testing the hypothesis
that BWA infestation accelerates the formation of heartwood. In addition, it could be
used to test for an interaction of BWA injury and tree decline (as measured by growth
increment data) for Fraser fir growing in the Black Mountains of North Carolina.

REFERENCES CITED

AMMAN, G. D. 1966. Some new infestations of the balsam woolly aphid in North
Carolin, with possible modes of disperal. J. Econ. Entomol. 59: 508-511.
AMMAN, G. D. 1970. Phenomena of Adelges piceae populations (Homoptera: Phyl-
loxeridae) in North Carolina. Ann. Entomol. Soc. Am. 63: 1727-1734.
AMMAN, G. D., AND R. L. TALERICO. 1967. Symptoms of infestation by the balsam
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AMMAN, G. D., AND C. F. SPEERS. 1965. Balsam woolly aphid in the southern Appalac-
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ARTHUR, F. H. 1985. Physiological characteristics of Fraser fir in relation to mortality
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ARTHUR, F. H., AND F. P. HAIN. 1984. Seasonal history of the Balsam Woolly Adelgid
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its effect on balsam fir, Abies balsamea (L.) Mill. Canadian Dept. Agric. Publ.
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on forest decline. Nature 336(6194): 27-30.
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BRUCK, R. I., AND W. P. ROBARGE. 1988. Change in forest structure in the boreal
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BUELL, M. F. 1945. Late Pleistocene forests of southeastern North Carolina. Torreya
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DOERKSEN, A. H., AND R. G. MITCHELL. 1965. Effects of the balsam woolly aphid
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188 Florida Entomologist 74(2) June, 1991

FALL ARMYWORM SYMPOSIUM

Preface

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

The Fall Armyworm Symposium, held during the annual meetings of the Southeastern
Branch of the Entomological Society of America since 1978, has served as a forum for
scientific exchange of information on this pest of importance in the Americas. The papers
presented have elucidated aspects of fall armyworm systematics, seasonal habitats and
dynamics, migration, host plant resistance, biological and chemical control, to name a few.
The fall armyworm is a serious pest on corn, sorghum, and related grasses but
attacks other crops as well when conditions are favorable. The extensive area of occur-
rence of this pest at damaging levels presents a challenge to entomologists throughout
the Americas in developing practical and economical control measures. Dispersal of this
insect from potential source areas has not been defined clearly. Migration into areas
where it cannot survive is of international importance. Aspects of systematics of the
species, spread of insecticidal resistance, development of resistant crop plants, and
impact of chemical and biological control present a veritable smorgasbordd of research
opportunities for collaborative research among scientists in the Americas. Projects in
these areas provide information essential to the development of integrated pest manage-
ment programs at different levels of crop production technology.
The papers presented here were part of the Fall Armyworm Symposium at the 64th
Annual Meeting of the Southeastern Branch of the Entomological Society of America
in Orlando, Florida, February 8, 1990. As in previous symposia on the fall armyworm,
these papers represent current research on this pest. This symposium is dedicated to
a scientist who has made many valuable contributions to management of this insect: Dr.
John R. Young.

HENRY N. PITRE
Department of Entomology
Mississippi State University
Mississippi State, MS 39762











Fall Armyworm Symposium '90-Wiseman & Gross 189

DR. JOHN R. YOUNG ECONOMIC ENTOMOLOGIST

B. R. WISEMAN AND H. R. GROSS
USDA-ARS-IBPMRL
Tifton, GA 31793-0748

ABSTRACT

Dr. John R. Young, USDA-ARS-IBPMRL (retired), developed chemical and autoc-
idal strategies for controlling the fall armyworm, Spodoptera frugiperda (J. E. Smith)
in corn and sorghum. Dr. Young's career spanned 30+ years with USDA during which
time he published more than 100 articles in professional and/or popular journals. Dr.
Young was one of the founders of the Fall Armyworm Conference, from which 133
recorded presentations and 57 articles by conferees have been published. Dr. Young
pioneered principles and methodologies for the safe, economical, and efficient manage-
ment of economic insect species through "insectigation"-the application of pesticides
in irrigation water. John has been one of the discipline's true "Economic Entomologists."

RESUME

El Dr. John R. Young, jubilado del USDA-ARS-IBPMRL, desarroll6 metodos au-
tocidas y quimicos para control del cogollero del maiz, Spodoptera frugiperda (J. E.
Smith) en maiz y sorgo. La carrera del Dr. Young abarca mas de 30 afios con el USDA.
Durante este tiempo public mas de 100 articulos en revistas profesionales y populares.
El Dr. Young fue uno de los fundadores de la Conferencia del Cogollero, en la cual se
han efectuado 133 presentaciones y se han publicado 57 articulos. El Dr. Young fu6 un
pionero en los principios y metodologias para un manejo seguro, economic y eficiente
de las species de insects a traves de la 'insectigacion'-aplicaci6n de insecticides en el
agua de irrigaci6n. John ha sido un entomologo economic verdadero.



Dr. John R. Young was born on August 6, 1932 at Perry, FL where he grew up,
and remained through high school. John's interest in entomology began while he served
in the Armed Forces in Korea as a medical laboratory technician from 1949 to 1951.
After returning from Korea, John began his undergraduate study at the University of
Maryland, where he received his B.S. in Bacteriology Chemistry and Zoology in 1957.
He also completed graduate work at the University of Maryland, receiving his M.S. in
Entomology in 1959 and a Ph.D degree in Entomology, with a minor in Statistics, in 1964.
Following graduation, he relocated to Tifton, GA where he became a research en-
tomologist with the U.S. Department of Agriculture's Agricultural Research Service,
Grain and Forage Insects Branch, at the Southern Grain Insects Laboratory (SGIRL)
(currently Insect Biology and Population Management Research Laboratory [IBPMRL])
under the direction of Dr. H C Cox. During his 30 + year career, Dr. Young served
under two additional laboratory directors, Drs. A. N. Sparks and Charlie Rogers.
Dr. Young is married to the former Ilene Carpenter. They have two children, Jim
and Malinda, and two grandchildren.
Dr. Young first formulated the idea of a conference on the fall armyworm around
1976. He discussed with several colleagues his concepts of an informal conference followed
on alternate years by a formal symposium. The first fall armyworm symposium was
held in January, 1977 as an informal conference at the Francis Marion Hotel in Charleston,
SC, with Dr. Young as moderator. There were 38 participants discussing topics of:
Resistance to Insecticides, Application Methods, Migration, Parasites, Rearing,










Florida Entomologist 74(2)


Pheromones, Light Traps, Host Plant Resistance, Hosts, and Economic Importance.
The beginning of this important conference occurred before the devastating "outbreak"
of fall armyworm in the summer of 1977. The second conference was held in January,
1978 at Gainesville, FL with Dr. E. R. Mitchell as the moderator. There were six
presentations. The second conference had its proceedings published in 1979 in the Florida
Entomologist. Editors of the Florida Entomologist agreed to publish all subsequent
proceedings, which now have abstracts in both English and Spanish.
Since that first meeting of interested participants, there have been seven informal
and five formal fall armyworm conferences, which have resulted in a total of 133 recorded
presentations and 57 published articles. These impressive records must be at least
partially credited to Dr. Young for his vision of developing better management systems
for the fall armyworm through the formal exchange of information among interested
scientists, producers, and industry representatives.
As a research entomologist at the IBPMRL, Dr. Young's mission was to gain new
knowledge on the insect biology/ecology and population dynamics of pest species of field
crops (with emphasis on the fall armyworm) and to apply this information toward the
development of chemical and autocidal strategies for control. Dr. Young pioneered
principles and methodologies for the economical, efficient, and environmentally sound
strategies of management of economic insect species.
To date, Dr. Young's research career spans 30+ years, during which time he has
authored or co-authored over 100 publications and made over 70 presentations, 27 of
which were invitational. The following are but a few of Dr. Young's many accomplish-
ments over the expanse of his career. Dr. Young and coworkers developed the concept
of inducing sterility in the fall armyworm with chemosterilants. Chemosterilant feeders
were designed, effective chemicals were identified, and criteria were developed for
assessing sterility, thus introducing a safe and efficient technology for managing fall
armyworm populations with minimum contamination of the environment.
Dr. Young found that adults of fall armyworm could also be sterilized with gamma
irradiation. He identified the effective radiation dose and established the most susceptible
developmental stage. Dr. Young found that the production of substerility in the F1 fall
armyworm with gamma irradiation was a viable approach for inducing sterility in sub-
sequent generations. Because of reduced somatic damage, substerile fall armyworm
were more competitive in nature than fully sterile insects and, thus, suppressed the
wild population by infusion of deleterious genes.
One of Dr. Young's more important accomplishments was his work on the SGIRL
corn earworm colony. He conceived the criteria for colony characterization, established
the mating regimes to insure retention of heterozygosity, and conducted the trials that
verified the rearing procedures. This colony has been utilized by the entire laboratory
staff for achieving reproducible laboratory and field results.
Dr. Young developed a control strategy for fall armyworm that allowed production
of multiple crops of field and/or sweet corn in the Southeast. He identified plant growth
stages, based on leaf development, where damage by and control of the fall armyworm
had the greatest effect on grain and forage yields. John found that the second crop of
field corn produced its greatest returns for management cost when it was harvested as
silage.
Dr. Young will probably be remembered most for the research conducted during the
last ten years of his USDA career. Dr. Young observed the early expansion of irrigation
usages in the southeastern U.S. and envisioned with it a means for the safe, economical,
and efficient delivery of agricultural chemicals, including pesticides, to their target.
John pioneered the introduction of chemigation, the application of agricultural chemicals
(i.e., pesticides, fertilizers, and growth regulators) in irrigation water and demonstrated
the practicality of this control strategy.


June, 1991











Fall Armyworm Symposium '90-Wiseman & Gross 191

Dr. Young convened a group of interested scientists in Atlanta in 1982 that became
the "Chemigation Information Exchange Group." This group has met annually to ex-
change information on chemigation, insectigation, and fertigation. He has since taken
a lead role in the founding and promotion of this innovative technology, including helping
to organize and serving as editor on "National Symposia on Chemigation" in 1981 and
1982.
Dr. Young successfully integrated irrigation and insect control into a cost-effective
approach for grain production. Early studies with emulsifiable formulations of insec-
ticides revealed that they were diluted to ineffective levels when applied in irrigation
water. Subsequent efforts by Dr. Young revealed that insecticides formulated in oils
(without emulsifiers) would remain intact during transport in irrigation water, but would
penetrate the plant canopy, and separate from the water phase when it impinged upon
the plant or insect surfaces. In studies involving the use of specific insecticides in
non-emulsifiable petroleum or seed oils, control of corn earworm and fall armyworm
was equal or superior to that achieved with conventional methodology.
As we conclude this dedicatory address on Dr. John R. Young, what more befitting
things could be said than those of his peers, as follows:


"Dr. Young was able to put together a truly multidisciplined program aimed
squarely at the limiting factor for corn production in the area, the fall armyworm
Spodoptera frugiperda (J. E. Smith). It was in this regard that we at Dow first
came to work with John and I emphasize work. He is a hard man to keep up
with. John needed a material with excellent fall armyworm activity and low
solubility. Our LORSBAN* product turned out to be well suited to John's uses.
Unfortunately our emulsifiable formulation was not. Thus began a series of studies
on various adjuvants and formulations designed to optimize the activity of the
material. That activity continues to this day; and through it all, John's ideas have
figured prominently in our development and labeling process. In the last few
years John has carried word of this new application technique throughout the
country. As an ambassador for chemigation, he has organized symposia, spoken
at a multitude of crop clinics, and been a tireless inspiration to those trying the
method for the first time. The fact that in 1983 chemigation in corn jumped from
less than 1% to around 10% of the foliar market is a tribute to the fit of the
method. John has acted as a catalyst, especially when he speaks to consultant
organizations and irrigation workshops throughout the country. He gets people
excited by talking about the basic benefits of the method. John most definitely
is an independent thinker. He has pressured us for years to develop a non-emul-
sified LORSBAN formulation for chemigation. Finally, in 1984 we had one for
him to test." (L. L. Larson, Agric. Products Dept., DOW Chemical USA, Midland,
MI).

"I credit Dr. Young's efforts as being the single most important factor in estab-
lishing the credibility, practicality and validity of chemigation as an economically
effective technique for the control of insects, particularly with respect to corn.
At a time a few years ago when practically all scientists discounted chemigation
as a practical means of applying pesticides whose efficacy depended upon their
remaining on the plant foliage, Dr. Young maintained that the technique did have
promise. He intensified his research efforts on chemigation, working diligently
on basic studies of chemical formulations for chemigation, application techniques
and the resulting efficacy in field studies. His diligence in pursuing this research
with industry, other scientists and farmer cooperators was, in my opinion, the










192 Florida Entomologist 74(2) June, 1991

driving force which elevated the application of insecticides via chemigation to the
current level of acceptance. As you know, chemigation is now receiving widespread
interest in not only the scientific community but also in industry and by farmers.
Dr. Young's role in establishing this technology is manifested not only by his
publications but also by the numerous requests which he receives for presentations
to regional, national and international scientific meetings, industry and grower
groups." (E. Dale Threadgill; Prof. and Head, Agric. Engineering Dept., Univer-
sity of GA, Athens, GA).

"During the past several years, Dr. Young, using imaginative and innovative
research approaches, persuasion, and perseverance has become a nationally and
internationally recognized authority on applying chemicals-specifically insec-
ticides-through irrigation systems (chemigation). This research has developed
new parameters on effectiveness of selected insecticides in relationship to formu-
lations, carriers, deposition on target organisms, potential dilution effects, and
safety during application with irrigation systems. Dr. Young's research on chemi-
gation has proven that this technique is a viable and economically sound procedure
that can be used in irrigated agriculture. His research has made late season crops
of field corn and sweet corn feasible by effectively controlling insects with timely
application of insecticides through irrigation. This application technology has a
significant economic advantage over conventional application methods and can be
used in a timely, effective, integrated pest management program." (Clyde C.
Dowler, Res. Agronomist, USDA-ARS, Tifton, GA).

"As a practitioner of IPM in the cropping systems of the central great plains,
where irrigation is a way of life, I know of no single research worker who has
contributed so widely to a practical approach to controlling many insect pests of
corn, milo, field beans, potatoes, soybeans and alfalfa. Dr. Young's insectigation
research, particularly the addition of oil to insecticide application through sprinkler
irrigation, has and is revolutionizing insecticide application to this area. Previous
to his work with vegetable additives, insectigation was limited to applications
using minimal amounts of water. This was frequently impossible due to the neces-
sity to continue irrigating; the crop water needed. With the added oil, farmers
can insectigate with irrigation amounts of water. This does not break the irrigation
cycle nor reduce the insecticide's effectiveness." (Earle S. Raun, Ph.D. R.P.E.,
Pest Management Co., Lincoln, NE).

"Dr. Young has been the leader of several multidiscipline research teams involved
in applying insecticides through overhead sprinkler irrigation systems for control-
ling insects on many crops. This innovative means of applying pesticides resulted
in three National Symposia on Chemigation held at the Rural Development
Center, Tifton, GA in 1981, 1982, and 1985. Dr. Young was a leader in planning
and organizing the symposia. The new technology generated by Dr. Young has
resulted in label amendments for two major insecticides for broader use on many
crops. In addition, he has been active in transferring technology from his research
program to various user groups. For example, with fewer insecticide applications
than required with conventional methods, he has consistently demonstrated
greater than 99% control of the corn earworm on sweet corn, a high value crop
in the United States. Much of Dr. Young's research results in maximizing insect
control, minimizing use of insecticides, and reducing unit production costs." (A.
W. Johnson, Supervisory Res. Plant Pathologist, USDA-ARS, Tifton, GA).











Fall Armyworm Symposium '90-Wiseman & Gross


"My association with John relates to his pioneering research injecting insecticides
through overhead center pivot irrigation systems. Insectigation is a rapidly ad-
vancing new technology of pest control and is a process that is being accepted
by a growing number of producers of irrigated crops. John's foresight in developing
the research program on insectigation and his involvement in disseminating his
research information through public meetings and other media has put him in a
position of being a national leader in economic entomology." (John F. Witkowski,
Ext. Entomol., University of Nebraska, Lincoln, NE).

"I have had the distinct pleasure of working with John for a number of years,
both in small plot testing, lab trials and, of course, chemigation. I found John to
be a very innovative, enthusiastic, dedicated and seemingly tireless researcher.
John's work on fall armyworm, on corn, his work with R. B. Chalfant on vegetable
insects, his work with A. W. Johnson on nematicides, and his numerous other
consultations with researchers and growers have, I feel, played a major role in
the development of insectigation as a viable, practical approach to insect control
that offers the grower a number of advantages over conventional methods includ-
ing ease of application, more uniform coverage, lower application costs, etc. I
feel his discovery that activity of foliar insecticides was significantly enhanced
by the addition of vegetable oil was the most important. This discovery allows
the use of lower rates of insecticides which is beneficial to the grower, the consumer
and the environment. As a result of his discovery and subsequent work to explain
this phenomenon, I believe it will only be a short time before there will be a
significant number of foliar insecticides, herbicides and fungicides formulated
specifically as oil formulations for use in chemigation systems." (William S. Hurt,
Project Manager, Agric. Prod. Res., Rohm and Haas Co., Spring House, PA).

"From having worked with John for the past several years, I know of no other
entomologist more deserving of this recognition than Dr. Young. John has always
shown outstanding enthusiasm and dedication to the field of chemigation for pest
management. I and my colleagues consider Dr. John Young to be the outstanding
researcher and pioneer in this field of research." (J. C. La Prade, Field Develop-
ment Representative, Rhone-Poulenc Ag. Products Co., Dothan, AL).

"Dr. Young has not worked in isolation and through his enthusiasm has attracted
researchers in other agricultural fields to study crop production holistically. John
was instrumental in the direction and success of the R. K. Mellon Foundation ($2
million) Irrigated Crop Production Project." (Richard B. Chalfant, Professor,
Dept. of Entomology, CPES, Univ. of GA, Tifton, GA).

"John is one of those individuals who refuses to take no for an answer. His
concepts and ideas go beyond where others have stopped. John has single-handedly
changed the concepts of the farmer and brought chemigation into a new era."
(James M. [Jim] Rice, M. L. Bull Co., Inc., Norcross, GA).

The aforementioned comments by several of John's peers exemplify his work, his
dedication, and many of his accomplishments. Dr. Young has certainly been interdiscip-
linary in his research. Dr. Young is truly deserving of the recognition by this conference.
Therefore, it is a sincere and distinct pleasure for us to have been able to bring this
dedicatory address to honor "Dr. John R. Young Economic Entomologist."










194 Florida Entomologist 74(2) June, 1991

FALL ARMYWORM (LEPIDOPTERA: NOCTUIDAE)
HOST STRAIN REPRODUCTIVE COMPATIBILITY

S. S. QUISENBERRY
Department of Entomology
Louisiana Agricultural Experiment Station,
Louisiana State University Agricultural Center,
Baton Rouge, Louisiana 70803

ABSTRACT
The reproductive compatibility between fall armyworm, Spodoptera frugiperda (J.
E. Smith), host strains (corn and rice) and the impact of colony age on reproductive
potential were evaluated. Incompatibilities in interstrain matings were not observed
and strains successfully mated in both directions. The number of fertile intrastrain and
interstrain females ranged from 50 to 100% and 80 to 100%, respectively. Egg mass
numbers were greater when colony age of corn females was older (25+ yr). Colony age
of corn or rice males in the intrastrain and interstrain matings was less important in
the number of egg masses produced than colony age of the corn females. In contrast,
the number of egg masses oviposited was greater when colony age of rice females was
younger (< yr and 1 yr). Regardless of strain, the younger the colony age the greater
the number of viable eggs. Fewer viable eggs were produced as the period of colonization
was extended, particularly period of colonization of females.

RESUME

Se evalu6 la compatibilidad reproductive entire el cogollero, Spodotera frugiperda
(J. E. Smith), las lines del hospedero (maiz y arroz), y el impact de la edad de la
colonia en el potential reproductive. No se observaron incompatibilidades en el
apareamiento de razas entrecruzadas, y las razas se aparearon con exito en ambas
direcciones. El numero de entrerazas fertiles y hembras entrerazadas vari6 desde 50 a
el 100% y de 80 al 100% respectivamente. El numero de posturas de huevos ovipositadas
fue mayor cuando la colonia de las hembras criadas en maiz alcanz6 mayor edad (25+
afios). La edad de la colonia de machos criados en maiz o arroz fue menos important
que la edad de las hembras criadas en maiz en los apareamientos entire raciales e inter-
raciales en lo relacionado con el numero de posturas producidas. En contrast, el numero
de posturas fue mayor cuando la edad de la colonia de hembras criadas en arroz, era
mas joven (< afio y 1 afo). Entre mas joven fue la colonia, mas grande fue el ndmero
de huevos producidos, sin que importara la raza. En la misma proporci6n que la edad
de la colonia aumentaba se produjeron menos huevos viables, particularmente en el
period de colonizacion de hembras.



Two strains (corn and rice) of the fall armyworm, Spodoptera frugiperda (J. E.
Smith), have been identified (Pashley et al. 1985, Pashley 1986) that differ at allozyme
loci (Pashley 1986) and in their mitochondrial DNA (mtDNA) restriction enzyme profiles
(Pashley 1989). Numerous biological differences have been detected since their discovery.
Physiological (i.e., development) differences exist between strains reared on each other's
host plants (Pashley 1988a, Whitford et al. 1988), on artificial diets (Quisenberry &
Whitford 1988, Whitford et al. 1988), and on selected bermudagrass genotypes (Lynch
et al. 1983, Pashley et al. 1987a b, Quisenberry & Whitford 1988). Pashley et al. (1987b)
also reported dissimilarity between strains in insecticidal resistance. In addition, ovipos-
itional preferences were found to differ (Whitford et al. 1988).











Fall Armyworm Symposium '90-Quisenberry


Studies of interstrain hybridization and compatibility have been conducted to ascer-
tain the taxonomic status of the strains. Pashley & Martin (1987) reported undirectional
reproductive incompatibilities in interstrain matings. In no choice matings, rice females
mated with corn males but corn females did not mate with rice males. Furthermore, F1
hybrid females did not mate but males did. However, Whitford et al. (1988) found strains
successfully mated in both directions. Pashley (1988) suggested the reproductive com-
patibilities reported by Whitford et al. (1988) may be due to altered behavioral charac-
teristics that accompanies the selection process of colonization. Pashley & Martin (1987)
used first and second or fourth and fifth generation fall armyworm while Whitford et
al. (1988) used colonies at least 3 yr-old.
The objectives of this study were to determine the reproductive compatibility between
fall armyworm host strains and to evaluate the impact of colony age on reproductive
potential.

MATERIALS AND METHODS

Six fall armyworm laboratory colonies were used. Colonies were previously identified
electrophoretically as the corn and rice strains (Mason et al. 1987, Pashley et al. 1987a,
D. P. Pashley unpublished). Corn strain 1 (C1) and corn strain 2 (C2) colonies were field
collected from corn and maintained in the laboratory for 3 generations and 1 yr, respec-
tively. Corn strain 3 (C3) was originally collected on bermudagrass but was supplemented
with larvae from an unidentified (probably corn) source (Burton 1967, Perkins 1979) and
maintained in the laboratory for 25+ yr. Rice strain 1 (R1), rice strain 2 (R2), and rice
strain 3 (R3) colonies were field collected from bermudagrass and maintained in the
laboratory for 2 generations, 1 yr, and 4+ yr, respectively. C2 was obtained from the
USDA-ARS, Crop Science Research Laboratory, Mississippi State, Mississippi, and the
C3 from the USDA-ARS, Insect Biology and Population Management Research Labo-
ratory, Tifton, Georgia. Colonies were maintained individually according to procedures
by Perkins (1979) at 26.7 0.5C, 14:10 (L:D) photoperiod, and > 50% relative humidity.
Larvae were reared on a modified pinto bean diet (Quisenberry & Whitford 1988).
Pupae from the corn and rice strain colonies were sexed and placed individually in
polystyrene cups (29.7 ml) and capped with a waxed lid which had an attached pad of
moistened cellulose wadding (2.54 x 2.54 cm). At emergence, intrastrain and interstrain
pairs of virgin adults were placed in oviposition containers (1.89 liter) containing vermicu-
lite and an ovipositional substrate (cheesecloth top). Each container was provided a
wicked polystyrene cup (29.7 ml) containing adult diet (honey-beer-ascorbic acid). Ovipos-
itional containers were checked daily and egg masses removed when present for a total
of 4 ovipositional days per mated female. Egg masses were held individually until hatch
at 26.7 0.50C, 14:10 (L:D) photoperiod, and > 50% relative humidity. Females were
dissected after successful oviposition or death for the presence of spermatophores to
determine if mating had occurred.
The experiment was arranged in a completely randomized design with 36 total mating
types and 10 replicates per mating type, for a total of 360 individual pairings. All possible
combinations of colony mating types were examined. Data were subjected to analysis
of variance and significant (P < 0.05) means separated by least-squares means (SAS
Institute 1985).

RESULTS

The colonies used in this study were identified electrophoretically as different fall
armyworm strains (corn or rice). The influence of colony age on reproductive compati-
bility (i.e., number of egg masses oviposited and number of females with spermatophores)










196 Florida Entomologist 74(2) June, 1991

varied between strains and according to mating type (significant strain by colony age
interaction; P < 0.003) and required that data be analyzed within each strain by mating
type (Table 1).
The crossing results indicated the strains successfully mated in both directions (Table
1). Dissections of females showed that spermatophores had been transferred in 80-100%
of the matings, except for intrastrain (C2 9 x C2 6) corn matings where only 50% of
the females had spermatophores.
The number of egg masses oviposited by females in corn matings was greater when
the colony age of females was older (25+ yr). Thus, the colony age of corn females was
more important in the number of egg masses produced than colony age of corn or rice


TABLE 1. FALL ARMYWORM INTRASTRAIN AND INTERSTRAIN REPRODUCTIVE
COMPATIBILITY.

Cross No. of No. egg No. with
Strain Colony age 9 T pairs masses Spermatophores

Corn 25+ Yr x 25+ Yr C3 x C3 10 11.4a 10a
25+ Yr x 1 Yr C3 x C2 10 10.9a 10a
1 Yr x 25+ Yr C2 x C3 10 10.0a 10a
25+Yr x 1 Yr x 1Yrx 1Yr C2 x C2 10 1.9c 5c
Corn 25+ Yr x 1Yr C3 x R2 10 13.0a 10a
hybrid 25+ Yr x < Yr C3 x R1 10 12.1 a 10a
25+Yr x 4+Yr C3 x R3 10 11.2 a 9ab
1Yr x 1Yr x 4+Yr C2 x R3 10 4.1b 9ab
1Yrx 1Yr C2 x R2 10 3.9b 9a
Rice 1Yrx 1Yr R2 x R2 9 12.3a 10a
1Yr x 4+Yr R2 x R3 10 9.2ab 10a
1Yr x < Yr R2 x R1 10 8.6ab 10a
4+Yrx Yr R3 x R2 10 5.8b 10a
4+Yrx 4+Yrx4Yr R3 x R3 10 5.3b 10a
Rice 1 Yr x 25+ Yr R2 x C3 10 10.9a 10a
hybrid 1 Yr x 1 Yr R2 x C2 10 9.7ab 10a
1Yrx < Yr x 25+ Yr R1 x C3 10 6.6bc 10a
4+ Yr x 25+Yr R3 x C3 10 4.8c 10a
4+Yr x 4+Yrx 1Yr R3 x C2 10 3.4c 10a

Means within a column (strain or hybrid by length of colonization) followed by the same letter are not significantly
different (P > 0.05); least-squares means test).











Fall Armyworm Symposium '90-Quisenberry


males in matings. In contrast, the number of egg masses produced by rice female matings
was greater when female colony age was younger (< yr and 1 yr).
Colony age significantly influenced the number of viable eggs produced (Table 2).
The younger the colony age, regardless of strain, the greater the number of viable eggs
and thus, reproductive potential. Conversely, the older the colony age of the female the
fewer the number of viable eggs.

DISCUSSION

Incompatibilities reported in interstrain matings by Pashley & Martin (1987) were
not found in this study (Table 1). Results are in agreement with Whitford et al. (1988)
who found strains successfully mated in both directions. Colony age did not affect repro-


TABLE 2. EFFECT OF COLONY AGE ON FALL ARMYWORM EGG VIABILITY.

Cross No. of No. viable
Colony age 9 6 pairs eggs


< Yr x 1 Yr






1Yr x


< Yr x 25+/4+ Yr



1Yr x 25+/4+ Yr



1Yr x 1Yr



25+/4+ Yr x 1Yr



25+/4+ Yr x < Yr



25+/4+ Yr x 25+/4+ Yr


Cl x C2
Cl x R2
R1 x R2
R1 x C2
C1 x C1
C1 x R1
Rl x R1
R1x C1
C2 x C1
C2 x R1
R2 x R1
R2 x Cl
Cl x C3
Cl x R3
R1 x R3
Rl x C3
C2 x C3
C2 x R3
R2 x R3
R2 x C3
C2 x C2
C2 x R2
R2 x R2
R2 x C2
C3 x C2
C3 x R2
R3 x R2
R3 x C2
C3 x C1
C3 x R1
R3 x R1
R3 x C1
C3 x C3
C3 xR3
R3 xR3
R3 x C3


391 a



375 a



331a



310 ab



259 abc



199 bc



169 bc



151 c



121c


Means followed by the same letter are not significantly different (P > 0.05; least-squares means test).










Florida Entomologist 74(2)


June, 1991


ductive compatibility as suggested by Pashley (1988); however, colony age, particularly
of females, had a significant impact on the number of viable eggs produced. Extended
colonization of fall armyworms resulted in production of fewer viable eggs (Table 2).
The corn and rice fall armyworm strains differ in a number of physiological (Lynch
et al. 1983, Pashley et al. 1987a b, Pashley 1988, Quisenberry & Whitford 1988, Whitford
et al. 1988) and behavioral (Whitford et al. 1988) traits; however, the status of reproduc-
tive isolating mechanisms between strains is not clear because matings in both directions
occur (Table 1; Whitford et al. 1988). A prereproductive isolating mechanism between
strains is not strongly fixed. This study and Pashley & Martin (1987) did not give females
a choice between males of the two strains. However, preliminary studies reported by
Pashley (1988b) indicated cross-attraction of strains occurs in the field even though
males are preferentially attracted to females of their own strain. Pashley (unpublished)
also reported that corn females did not mate with rice males but rice females accepted
corn males. Studies must be conducted to further evaluate cross-attraction and mating
in the field. In addition, extensive mate choice experiments should be performed to
determine if mate preference serves as an isolating mechanism between strains.
Pashley (unpublished) suggests that temporal isolation by way of differences in mating
times may be the primary isolating mechanism between strains. Corn strain mating
occurs during the first part of the night while rice strain mate the last third. Thus,
mating behavior and hybrid presence must be evaluated to establish if reproductive
isolating mechanisms between fall armyworm strains exist.
In addition to fall armyworm strain differences influencing reproductive parameters,
colonization of insects may cause changes in phenotypes (Mason et al. 1987). Phenotypic
changes caused by random genetic drift, founder effects, nonrandom mating, or selection
during colonization may influence reproductive behavior, fertility, and rates of reproduc-
tion (Dame et al. 1964, Fye & LaBrecque 1966, Raulston 1975, Economopoulos et al.
1976). Thus, inherent fall armyworm differences and colonization of insects potentially
influenced the differences in reproduction observed in this study.

ACKNOWLEDGMENTS

The author expresses gratitude to F. M. Davis (USDA-ARS, Crop Science Research
Laboratory, Mississippi State, MS), R. E. Lynch (USDA-ARS, Insect Biology and
Population Management Laboratory, Tifton, GA), and D. P. Pashley for supplying fall
armyworm eggs. I wish to thank D. P. Pashley and J. A. Martin for genetic analysis
of the fall armyworm colonies. The manuscript was improved by review from D. P.
Pashley. Approved for publication by the Director of the Louisiana Agricultural Exper-
iment Station as Manuscript Number 90-17-4114.

REFERENCES CITED

BURTON, R. L. 1967. Mass rearing the fall armyworm in the laboratory. USDA-ARS
33-117.
DAME, D. A., D. B. WOODARD, H. R. FORD, AND D. E. WEIDHAAS. 1964. Field
behavior of sexually sterile Anopeheles quadrimaculatus males. Mosquito News
24: 6-14.
ECONOMOPOULOS, A. P., A. V. VOYADJOGLOU, AND A. GIANNAKAKIS. 1976. Repro-
ductive behavior and physiology of Dacus oleae: Fecundity as affected by mating,
adult diet, and artificial rearing. Ann. Entomol. Soc. America 69: 725-729.
FYE, R. L., AND G. C. LABRECQUE. 1966. Sexual acceptability of laboratory strains
of male house flies in competition with wild strains. J. Econ. Entomol. 59: 538-540.
LYNCH, R. E., W. G. MONSON, B. R. WISEMAN, AND G. W. BURTON. 1983. Bermu-
dagrass resistance to fall armyworm (Lepidoptera: Noctuidae). Environ. Entomol.
70: 1837-1840.


198











Fall Armyworm Symposium '90-Quisenberry 199


MASON, L. J., D. P. PASHLEY, AND S. J. JOHNSON. 1987. The laboratory as an
altered habitat: phenotypic and genetic consequences of colonization. Florida En-
tomol. 70: 49-58.
PASHLEY, D. P. 1986. Host associated genetic differentiation in fall armyworm: a
sibling species complex? Ann. Entomol. Soc. America 79: 898-904.
PASHLEY, D. P. 1988a. Quantitative genetics, development and physiological adapta-
tion in sympatric host strains of fall armyworm. Evolution 42: 93-102.
PASHLEY, D. P. 1988b. Current status of fall armyworm host strains. Florida Entomol.
71: 227-234.
PASHLEY, D. P. 1989. Host-associated differentiation in armyworms (Lepidoptera:
Noctuidae): an allozymic and mitochondrial DNA perspective, pp. 103-114 in H.
D. Loxdale and J. den Hollander (eds.). Systematics Association Special Volume
No. 39. Clarendon Press, Oxford.
PASHLEY, D. P., AND J. A. MARTIN. 1987. Reproductive incompatibility between
host strains of fall armyworm (Lepidoptera: Noctuidae). Ann. Entomol. Soc.
America 80: 731-733.
PASHLEY, D. P., S. J. JOHNSON, AND A. N. SPARKS. 1985. Genetic population
structure of migratory moths: the fall armyworm (Lepidoptera: Noctuidae). Ann.
Entomol. Soc. America 78: 756-762.
PASHLEY, D. P., S. S. QUISENBERRY, AND T. JAMJANYA. 1987a. Impact of fall
armyworm (Lepidoptera: Noctuidae) host strain on the evaluation of Bermuda-
grass resistance. J. Econ. Entomol. 80: 1127-1130.
PASHLEY, D. P., T. C. SPARKS, S. S. QUISENBERRY, J. JAMJANYA, AND P. DOWD.
1987b. Two fall armyworm strains feed on corn, rice, and Bermudagrass.
Louisiana Agriculture 30: 8-9.
PERKINS, W. D. 1979. Laboratory rearing of the fall armyworm. Florida Entomol.
62: 87-91.
QUISENBERRY, S. S., AND F. WHITFORD. 1988. Evaluation of bermudagrass resist-
ance to fall armyworm (Lepidoptera: Noctuidae): influence of host strain and
dietary conditioning. J. Econ. Entomol. 81: 1463-1468.
RAULSTON, J. R. 1975. Tobacco budworm: Observation on the laboratory adaptations
of a wild strain. Ann. Entomol. Soc. America 68: 139-142.
SAS INSTITUTE. 1985. SAS user's guide: statistics, version 5. SAS Institute, Cary,
N.C.
WHITFORD, F., S. S. QUISENBERRY, T. J. RILEY, ANDJ. W. LEE. 1988. Oviposition
preference, mating compatibility, and development of two fall armyworm strains.
Florida Entomol. 71: 235-243.










Florida Entomologist 74(2)


FALL ARMYWORM (LEPIDOPTERA: NOCTUIDAE)
OUTBREAK ORIGINATING IN THE LOWER
RIO GRANDE VALLEY, 1989

S. D. PAIR,' J. R. RAULSTON,2 J. K. WESTBROOK,1
W. W. WOLF,' AND S. D. ADAMS1
'Insect Biology and Population Management Research Laboratory Agric.
Res. Serv., USDA, Tifton, GA 31793.
2Subtropical Agricultural Research Laboratory, Subtropical Cotton
Insects Unit, 2413 East Highway 83, Weslaco, TX 78596.

ABSTRACT

Ecological, meteorological, and radar evidence indicated that 200,000 ha of irrigated
corn grown in the Lower Rio Grande Valley (LRGV) of Texas and northeastern Mexico
served as a primary source of migrant fall armyworm (FAW), Spodoptera frugiperda
(J. E. Smith) (Lepidoptera: Noctuidae), that severely impacted crops at Corpus Christi
and on the High Plains of Texas during the summer of 1989. Based on soil samples taken
in 100 corn fields in the region which yielded an average of 3.97 pupae/m2 of soil, an
estimated 7.94 billion FAW adults were available for transport from the LRGV during
late June and early July. A similar study conducted in 40 fields of 16,200 ha of corn
grown 400 km NNW of the LRGV near Uvalde, Texas yielded populations averaging
0.39 pupae/m2 which likely produced approximately 0.06 billion FAW adults. In the
LRGV 15.9% of the adults had emerged during June 5-13 while no FAW adults had
emerged at Uvalde June 19-21, thus indicating that the major FAW emergence events
in the LRGV preceded those at Uvalde. Large numbers of FAW were captured in
pheromone traps at Uvalde on the night of June 21 in the absence of local emergence,
suggesting an influx of migrants from the LRGV.
Concurrently, pheromone traps indicated large influxes of FAW on the Texas High
Plains. Subsequent reports indicated unusually early FAW infestations at Ankeny, Iowa
and at Columbia, Missouri. Ground-based and airborne RADARS detected the maximum
aerial density of insects emanating from the LRGV on the night of June 20. Calculated
trajectories indicated that weather transport systems were available for displacement
of passive objects to the High Plains (1000 km) and to Ankeny, Iowa (1900 km). This
study constitutes the first reported evidence of long-distance FAW migration from a
defined source area to directly impact crops in remote areas. Mature corn in the LRGV
is proposed as a major contributory source of migrant FAW in the Central U.S.

RESUME

Evidencia ecologica y metereologica suministrada por el radar indic6 que 20,000 has.
de maiz de irrigaci6n en el Valle del Rio Grande (LRGV) de Texas y en el noreste de
Mexico, sirvieron como las fuentes primaries para el cogollero migrador (FAW), Spodopt-
era frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), el cual hizo un gran impact en
Corpus Cristi y en High Plain en Texas, durante el verano de 1989. Basados en las
muestreos de suelos tomadas en 100 campos de maiz en esta region, las cuales tenian
un promedio de 3.97 pupas/m2 de suelo, se estim6 que 7.94 billones de adults de FAW
podian estar disponibles para ser transportados desde LRGV durante el final de Junio
y a comienzos de Julio. Un studio similar realizado en 40 campos de 16,200 has de maiz
cultivado a 400 kilometros al norte del LRCV cerca a Uvalde, Texas, brindaron un
promedio poblacional de 0.30 pupas/m2 el cual produjo aproximadamente 0.06 kilos de
adults del FAW. En el LRGV 15.9% de los adults emergieron durante Junio 5-13
mientras que no hubo emergencia de adults en Uvalde en Junio 19-21, indicando que
la mayor emergencia de adults en LRGV precedia a aquella de Uvalde. Tanto el gran
numero de FAW capturados en trampas con feromona localizadas en Uvalde en la noche


June, 1991


200











Fall Armyworm Symposium '90-Pair et al. 201

del 21 de Junio y tanto la ausencia de emergencia en esa localidad, sugiri un influjo de
migradores desde LRGV. Al mismo tiempo, las trampas de feromonas indicaron grandes
migraciones de FAW en Texas, High Plains. Otros reports indicaron unas infestaciones
tempranas de FAW en Ankeny, Iowa y en Columbia, Missouri. Radares terrestres y
aereos detectaron la mayor densidad de insects provenientes desde LRGV en la noche
del 20 de Junio. Las trayectorias calculadas indicaron que el desplazamiento de los
sistemas de transportes de objetos pasivos hacia High Plains (1,000 km) y hacia Ankeny,
Iowa (1900 km). Este studio constitute la primera evidencia de migraci6n a larga
distancia del FAW desde una fuente definida haciendo un impact director en campos
localizados. El maiz pre-cosecha en le LRGV es propuesto como la mayor fuente de
migraci6n del FAW hacia el centro de los Estados Unidos.



The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), is a sporadic but
often severe pest of many row crops and forages throughout much of South and North
America and in the West Indies (Sparks 1979, Mitchell 1979). Because they lack a
diapause mechanism, FAW are unable to survive winter in temperate zones and are
believed to overwinter primarily in the southernmost portions of Florida and Texas
(Luginbill 1928, Hinds & Dew 1915, Vickery 1929, Pair et al. 1986, Raulston et al.
1986b). Each spring, FAW populations (varying in magnitude from year to year) migrate
from overwintering source areas to reinvade more northerly habitats. Luginbill (1928)
noted several reports of FAW outbreaks, with particularly severe devastation occurring
in 1899 and in 1912 when crops were almost completely devastated east of the Rocky
Mountains. Heavy spring floods across the South during each of those years resulted
in late-planted forage and grain crops, which were believed to contribute directly to
subsequent outbreaks of FAW (Hinds & Dew 1915, Vickery 1929). Although other
outbreaks have occurred irregularly, and most are poorly documented, none seem to
match the severity of 1977 when losses due to FAW amounted to $137.5 million in
Georgia alone (Sparks 1979).
The abiotic and biotic processes predisposing outbreaks of FAW are only partially
understood. Luginbill (1928) associated the propagation of FAW populations in overwin-
tering areas with periods of cool weather and abundant rainfall that is believed detrimen-
tal to its natural mortality agents. Under favorable conditions, FAW increase to damag-
ing population levels and migrate before natural enemies can increase and regulate their
populations. Substantial evidence suggests that drought promotes outbreaks of a mul-
titude of insect pests (Mattson & Haack 1987) including FAW (Luginbill 1928). The
outbreak of 1977 was characterized in the Southeast by record-breaking cold winter
temperatures followed by an abnormally warm and dry spring and summer (Westbrook
& Sparks 1986). Pair et al. (1986) suggested that the amounts of corn planted, favorable
production practices, and synchronous FAW emergence from overwintering areas may
largely determine the magnitude of populations arriving at northerly locations from the
Southeastern U.S.
In 1989, the Insect Migration Unit of this laboratory and personnel of the USDA-ARS
Subtropical Cotton Insects Laboratory, Weslaco, TX conducted field studies to document
the production and movement of corn earworm (CEW), Heliothis zea Boddie, populations
from irrigated corn in the Lower Rio Grande Valley (LRGV). Strong circumstantial
evidence indicated this region as a primary source for migrant CEW and FAW popula-
tions capable of impacting more northerly areas (Raulston et al. 1986abc, Sparks et al.
1986, 1989, Pair et al. 1987). Favorable meteorological conditions occur on an interannual
basis during the spring and early summer which are highly conducive to long-range
transport of noctuids (Westbrook et al. 1985). While conducting field studies on the
southern edge of the irrigated corn-growing region located in northeastern Tamaulipas,
Mexico, we observed FAW populations destroying ear stage corn. The severity of the










202 Florida Entomologist 74(2) June, 1991

localized FAW outbreak prompted efforts to document the magnitude and subsequent
dispersal of the emerging population from a known source area. The results of those
studies are reported herein.

DESCRIPTION OF SOURCE AREAS

Raulston et al. (1986b) reported on the seasonal population dynamics of FAW in the
Texas-Mexico Gulf Coast area during 1984-1985. A northerly temporal sequence of FAW
population movement was observed in the state of Tamaulipas, and FAW populations
were generally higher in the southern portions, particularly in irrigated corn grown
near Abasolo (Fig. 1). Raulston and Houghtaling (1986) described the climatological,
geographical, and agricultural characteristics of the LRGV (Fig. 2). The area (ca. 65
km long by 65 km wide centered at N25 30' W98 00') lies in northern Tamaulipas, Mexico
and in southern Texas in a region described by Correll & Johnston (1970) as the Tamauli-
pan brushlands. The area is semi-arid tropical and typically receives ca. 680 mm of
rainfall annually. The LRGV (15,000 km2) is an area of intensive agriculture and ca.
200,000 ha of irrigated corn are planted in late February each year (170,000 in Mexico
and 30,000 in Texas). Non-irrigated areas south of the LRGV are primarily devoted to
dryland sorghum (500,000 ha) and to livestock production on native rangeland. Also, an
additional 15,000 ha of irrigated corn are grown near Abasolo, situated ca 200 km south
of the LRGV. Because of intensive agriculture and its geographical features, the LRGV
is a natural corridor and/or primary source area for several economically important
noctuid pests including FAW, CEW, and tobacco budworm, H. virescens F. (Raulston
et al. 1986a, Sparks et al. 1989) that may impact crops in more northern areas.
A portion of the 1989 study was conducted ca. 470 km NNW and downwind of the
LRGV at the Winter Garden area near Uvalde, TX. This area is at the northern edge
of the Tamaulipan brushlands and ca. 16,200 ha of irrigated corn are planted in March.
This site was selected to delineate the extent of FAW infestations in the proposed source
area because it lies in the route for insects emigrating from the LRGV to more northerly
areas such as the Texas High Plains.

METHODOLOGY

The potential production of FAW was studied in corn fields in the LRGV from June
5-13, 1989. To determine pupal production from maturing corn, two 1-m2 soil samples
were excavated to a depth of 8-10 cm in each of 100 fields in the LRGV (80 in Mexico
and 20 fields in the U.S). On corn rows adjacent to each soil sample, 25 ears (total of
100/field) were inspected and the number of damaged and/or infested ears and the
number of medium and large FAW larvae remaining in the ears were counted and
recorded. At Uvalde, 40 fields were sampled on June 15-19, 1989 in the same manner
as previously described. All noctuid life stages, i.e., prepupae, pupae, and pupal exuviae
recovered from the soil samples were collected and identified to species. Calculations
of the mean number of FAW produced per unit area were based on the total number
of live prepupae and pupae and exuviae encountered in each sample. A portion of the
live FAW pupae collected from the soil samples in the LRGV was held in an insectary
to estimate emergence periods of FAW adults.
Pheromone traps (International Pheromone Systems, Merseyside, England) were
used to index adult FAW populations in the LRGV, Uvalde and Lubbock, TX, and at
Lane, OK. Two traps at each location were positioned at Uvalde (June 21), Lubbock
(June 19), and at Lane, OK (June 18). Pheromone traps were already positioned in the
LRGV (10 locations) and in Crowley, LA as part of an ongoing monitoring system. In
all cases, traps were baited with a synthetic FAW pheromone (Terochem Laboratories
Ltd, Alberta, Canada) that was changed every two weeks.











Fall Armyworm Symposium '90-Pair et al. 203






,r,-le COk)

) *ee O l





%IYA "I 4 I








li ILA 1 iTxs
^*dr^ '*



















Li ele,
/d. a N ee






14










kk
/L a p tr jl



















Fig. 1. Map of the Lower Rio Grande Valley of Texas and the State of Tamaulipas,
Mexico (from Raulston and Houghtaling 1986).
I V~v t/e--.



> ^C. "'"~
^ ^^s .^*^
^^ *^ .r^

. \T*^|A





1> IC

Fig 1 Ma o te Lwe Ro Gane allyo exsadte tt fTaalps
Meic (ro Rulto ndHoghalng196.sJ











Florida Entomologist 74(2)


Fig. 2. Irrigated region of Tamaulipas State in northern Mexico and the Lower Rio
Grande Valley of Texas.


Meteorological and ground-based radar observations were conducted near Donna,
TX during June of 1989. In addition, an airborne radar was operated on the nights of
June 20-21 on flights from Weslaco to San Antonio, TX. Readers are referred to Wolf
et al. 1986a, Hobbs & Wolf (1989), and Wolf et al. (1990), for specific details of these
operations and data collections.

RESULTS AND DISCUSSION

Prior to initiation of soil samples in the LRGV, eight corn fields in Mexico were
sampled weekly to determine infestation levels of both CEW and FAW. Because very
low numbers of FAW were detected in whorl-stage corn, there was no evidence that
local populations were responsible for the subsequent heavy infestations observed on
mature corn during mid-June. Also, pheromone traps positioned in the LRGV did not
indicate the presence of significant FAW activity during May or early June. High FAW
populations often occur on irrigated corn grown in southern Tamaulipas. Raulston et
al. (1986a) determined that corn grown near Abasolo produced an estimated 0.4 billion
FAW adults in 1984. It is unlikely that the 500,000 ha of dryland sorghum normally
grown due south of the irrigated region was a source area for the LRGV since little of
that crop was planted in 1989 due to a severe drought over most of northern Mexico
and south Texas. Hence, we suspect that irrigated crops such as corn at Abasolo or
other hosts not affected by the drought in areas farther south the most likely initial
inocula for the sudden and widespread FAW infestation of ear-stage corn in the LRGV.
All fields in the LRGV and 95% of those at Uvalde had ears infested with FAW
larvae. As might be expected of the FAW, populations were clumped and the most
severely affected fields were located on the southeastern portion of the LRGV. In the
LRGV, 86% of the fields produced FAW pupae while only 35% of the fields at Uvalde


204


June, 1991











Fall Armyworm Symposium '90-Pair et al.


produced pupae (Table 1). In the LRGV, 59% of the fields produced FAW populations
exceeding 1.0/m2 or 10,000/ha. In three fields, populations exceeded 20 pupae/m2 (200,000/
ha). The most heavily infested field averaged 59 pupae/m2 (590,000/ha). This field was
ca. 400 ha in size and potentially produced 236 million FAW. The maximum number of
FAW produced in a single field in the Uvalde area was 3.0/m2 (30,000/ha). These data
do not take into account the potential adult production from medium and large larvae
remaining in the ears at either location.
The resultant adult FAW production from ear stage corn in the LRGV and at Uvalde
was estimated at 3.97 and 0.39/m2, respectively, during June 1989 (Table 2). Adult FAW
emergence had already commenced in the LRGV since 15.9% of the stages recovered
were exuviae. However, FAW exuviae were not recovered at Uvalde, indicating that
no local emergence had yet occurred. Estimates of adult production from 1984-1985
(Raulston et al. 1986a) and 1986-1988 (J. R. Raulston, unpubl.) are included for compara-
tive purposes. Based upon the total hectarage of corn grown in the LRGV and at Uvalde
during 1989, we estimated that 7.94 and 0.06 billion adult FAW, respectively, were
produced at the two locations. The production of FAW during 1989 was 2 x that observed
during the study conducted in 1986, when an estimated 3.27 billion FAW were produced.
Mortality of FAW prepupae and pupae due to nematodes and unidentified pathogens
amounted to 10.2% in the LRGV. No mortality of FAW was observed in the samples
taken at Uvalde.
The 1989 studies in the LRGV probably underestimate the actual FAW production
due to several factors. The soil samples were taken coincidental to when maximum CEW
pupation occurred. FAW are typically secondary invaders where high CEW larval infes-
tation exists, and as a result, many FAW were still completing development when
sampling occurred. Based upon samples of 100 ears in each field, there remained 1.77
billion ( = 0.88/row m) medium larvae and 3.69 billion large FAW larvae (R= 1.84/row
m) yet to complete development in the LRGV. These estimates did not include numerous
large FAW larvae observed feeding on the often dense growth of crabgrass and Amaran-
thus sp. prevalent in many fields. Mexican producers may use little or no herbicides
contributing to weedy conditions within the corn fields. Assuming that only 50% of the
medium and 75% of the large FAW larvae found in the ears completed development,
the total FAW production in the LRGV may have exceeded 11.5 billion adults during
late June and early July 1989. In addition, mature corn in the LRGV also produced an
estimated 6.9 billion CEW adults during June 1989 (J. R. Raulston, unpubl.).
The additional production of FAW adults developing from ears at Uvalde was consid-
erably less than that in the LRGV. At Uvalde, an average of 0.35 medium and 0.69
large FAW larvae/row m still remained in the ears when soil samples were taken. Based


TABLE 1. FREQUENCY OF FALL ARMYWORM PREPUPAE, PUPAE, AND EXUVIAE IN
SOIL SAMPLES' IN LRGV AND AT UVALDE, TX. JUNE 1989.

% of fields

Average FAW/m2 LRGV Uvalde

0.0 14.0 65.0
0.5-1.0 27.0 25.0
1.5-5.0 37.0 10.0
5.5-10.0 15.0 0.0
10.5-20.0 4.0 0.0
> 20.5 3.0 0.0

'Soil samples taken to a depth of 8-10 cm.


205











Florida Entomologist 74(2)


June, 1991


TABLE 2. ESTIMATED FALL ARMYWORM PRODUCTION DEVELOPING IN CORN THE
LRGV AND AT UVALDE, TEXAS, 1984-1989.1

Est. no. adults
No. fields No. m2 soil Avg. no. produced
Year2 Location sampled sampled FAW/m2+SD (billions)

1984 LRGV 9 134 0.8581.16 1.72
1985 LRGV 100 200 0.160+0.53 0.32
1986 LRGV 120 240 1.633 3.27
1987 LRGV 90 180 0.128 0.25
1988 LRGV 90 180 0.117 0.23
1989 LRGV 100 200 3.97 8.50 7.94
1989 Uvalde 40 80 0.39 0.91 0.06

'Based on m2 soil samples taken in 200,000 ha of corn in the LRGV, and 16,200 ha at Uvalde, TX.
'Data for 1984-1985 from J. R. Raulston et al. 1986c; data for 1986-1988 are from J. R. Raulston (unpublished).

on the total hectarage, 55.8 million medium and 110 million large larvae had yet to
complete development at that location. Adults developing from larvae at Uvalde and
the LRGV would likely have emerged through mid-July.
Cumulative emergence of adult FAW from field-collected pupae in the LRGV (not
considering exuviae), surpassed 50% on the night of June 16, and reached 100% by June
23. Pheromone traps positioned throughout the LRGV failed to reflect the expected
dramatic change in local FAW adult populations. From May 1-July 31, avg. capture/trap
night exceeded 10 FAW males only during mid-June and again in mid-July. Based on
total catches over 10 day periods, the highest numbers were captured June 20-June 29
(77/trap) and from July 10-19 (105/trap). Pheromone traps located within the source
areas apparently did not provide evidence of the local emergence of FAW from mature
corn. Pheromone traps detected peaks of CEW emergence from whorl-stage corn in the
LRGV but again failed to detect peaks of CEW emergence from mature corn (Raulston
et al. 1990). Apparently certain physiological cues prompt migration from a decaying
habitat (Hughes 1979), as little oviposition occurred on locally susceptible crops such as
cotton. Similarly, Browne & Swaine (1966) observed that African armyworm, S. exempta
(Wlk.) outbreaks rarely recur in the same vicinity and concluded that long-distance
migration of moths takes place successively from one outbreak to another.
An unusually early appearance of FAW in more northerly areas provided further
evidence that a large proportion of the emerging FAW population in the LRGV migrated
from the region. Large numbers of FAW males were captured in pheromone traps at
Uvalde (400 km NNW) and at Lubbock, TX (1000 km NNW of the LRGV) during June
19-22 (Fig. 3). In the absence of local FAW emergence, captures of FAW males at
Uvalde averaged 414/trap on the night of June 21 and approached or exceeded 200/night
through June 30. Subsequent smaller peaks occurred on July 9. At Lubbock, large
catches of FAW coincided with those observed at Uvalde. The highest average numbers
occurred in traps from June 20-28, with the highest number of males captured on the
nights of June 20 (153/trap) and June 26 (155/trap). Smaller numbers were captured
through the first half of July prior to the first expected generational peak (ca. July 15),
suggesting that additional immigration into the Lubbock area had occurred. Unfortu-
nately, traps were installed at the northern locations too late to fully bracket the initial
emergence and dispersal of FAW from the LRGV. However, these data are indicative
of an en masse migration of FAW from the LRGV to areas where local FAW populations
were either not established or had not developed to the adult stage. The earliest FAW
infestation in 22 years occurred on whorl-stage corn at Ankeny, Iowa during mid-July,
1989. Day-degree analysis of FAW development rates suggested that migrants arrived










Fall Armyworm Symposium '90-Pair et al. 207

800
8 -- Uvalde, Tx

------- Lubbock, Tx
C600
Ssoo



400

LL

> 200



0
18JUN 09JUL 30JUL 20AUG 10SEP 010CT 220CT
1989

Fig. 3. Average number of FAW males captured nightly in pheromone traps at
Uvalde (June 21-July 24) and Lubbock, TX (June 19-Oct 22), 1989.

in the Ankeny area on June 20-25 (W. B. Showers, pers. comm.). Light infestations
were also noted at Columbia, MO during mid-June (Armand Keaster, pers. comm.).
Very low trap captures of FAW were noted at Lane, Oklahoma and at Crowley, LA,
indicating that migrating FAW either did not converge in those areas or overflew them
to more distant locations. FAW populations as indexed by traps, surveys, and pest
reports were low throughout the Southeast during 1989, indicating that migrant FAW
from the LRGV did not contribute significantly to infestations in those states (S. D.
Pair, unpubl.).
Throughout the summer of 1989, FAW populations increased in severity on the Texas
High Plains as evidenced by extremely heavy FAW captures of 775 males/night during
early August. Similar to the pattern of infestations observed in the LRGV, the heaviest
damage was first detected in the southern and southeastern portions of the High Plains
area. Initial infestations in June and subsequent generations occurred primarily on
late-planted grain sorghum, with varying degrees of FAW damage occurring in irrigated
corn in Texas and eastern New Mexico (W. P. Morrison, pers. comm.). Of the 525,000
ha of sorghum produced on the High Plains, ca. 80,000 ha in the more southern counties
of Crosby, Lubbock, Lamb, and Floyd were the most severely affected and required
insecticidal application to control headworms. Corn grown north of these counties did
receive FAW damage, but not to the degree observed in sorghum. FAW damage was
not reported on crops in the Uvalde area, probably because of the advanced stage of
corn maturity and the lack of other preferred hosts in the area. In early July, severe
damage to drought-stressed dryland corn occurred near Corpus Christi, and larval
populations of FAW averaged ca. 130/m2 in hay pastures between Corpus Christi and
San Antonio (Roy Parker, pers. comm.).
Radar and meteorological data (Wolf et al. 1990) provide further evidence of the
LRGV as a source area and for the potential long-distance displacement of FAW from









Florida Entomologist 74(2)


the LRGV to the High Plains and other northern locations. During the emergence events
in the LRGV, several frontal systems crossed the Great Plains which offered optimum
opportunities for long-distance transport of FAW. On June 20, a cold front was located
in the Central Great Plains. By 0600h on June 23 the front was positioned across Central
Texas. Calculated trajectories, based on 500 m altitude (above ground level) wind vel-
ocities measured by the ground-based radar and interpolated twice-daily NWS weather
data, indicated displacement of passive objects to the vicinity of extreme northern Texas
and to western Oklahoma by June 24 (Fig. 4a, b). The displacement of passive insects
from the LRGV on June 22 was calculated to have terminated in the Lubbock, TX
vicinity on July 24 (Fig. 4c). NWS upper-air data typically underestimate the nocturnal
wind speed, especially during episodes of low-level jet formation (Westbrook et al. 1989).
Meteorological soundings near Donna, TX indicated the presence of a low-level wind
jet from 142 to 161 degrees azimuth during the night of June 20. As in previous studies


Successive 500 m altitude nocturnal atmospheric

trajectories starting at 18h on June 20, 1989.


Fig. 4a, b, c. Successive nocturnal atmospheric trajectories at 500 m altitude starting
at 1800 h from Donna, TX on June 20, 21, and 22, 1989.


June, 1991


208










Fall Armyworm Symposium '90-Pair et al. 209

(Sparks et al. 1989), winds from any direction other than southerly resulted in low
densities of airborne insects observed by radar. Due to the emergence peaks of both
FAW and CEW and the accompanying southerly winds, the highest densities of airborne
insects detected by the ground-based radar during this study were recorded on this
date. Initially, the ground-based radar, located at the northern (downwind) edge of the
corn growing area, detected early evening take-off and departure of large numbers of
insects emanating from corn fields. Simultaneously, the airborne radar detected low
numbers of flying insects 50 km downwind of the source area. A large cloud of insects
was detected flying at 200-700 m altitude as the airborne radar approached the LRGV,
and was subsequently tracked from near Weslaco, TX, northward to San Antonio (400
km) on the same night. Interpolated wind vectors during the night of June 20 indicated
displacements toward the 350 degrees azimuth, a heading consistent with the flight path
of the insect cloud tracked by airborne radar from the LRGV. The remains of twelve
insects were collected from the engine cowling following these flights, two were positively


Successive 500 m altitude nocturnal atmospheric

trajectories starting at 18h on June 21, 1989.


Corpus Christi


Fig. 4b. Continued









Florida Entomologist 74(2)


identified as CEW, but it is likely that the insect cloud contained FAW as well. Further
evidence of a simultaneous exodus of FAW and CEW from the LRGV may be inferred
by the simultaneous and unusually early arrival of CEW on cotton on the High Plains
during late June and early July (Leser 1989).
Determining source areas of migrant FAW and their resultant impact on local crops
has been identified as a critical need in developing area-wide suppression programs
(Knipling 1980, Sparks 1986). Our studies clearly demonstrate the need to accurately
delineate source populations on an annual basis when considering potential noctuid
movement in agroecosystems. There are few other instances where sources of immigrant
FAW and their subsequent invasion of crops were specifically documented. Hinds &
Dew (1915) described the successive progression of FAW populations from crops in the
Mobile, AL area northward during the outbreak of 1912. Rose et al. (1975) documented
an en masse arrival of FAW in Sault Ste. Marie, Canada. Backtrack analyses suggested
the flight originated 1600 km to the south in the Lower Mississippi River Valley. An


Successive 500 m altitude nocturnal atmospheric

trajectories starting at 18h on June 22, 1989.


Corpus Christi


Fig. 4c. Continued


210


June, 1991











Fall Armyworm Symposium '90-Pair et al.


analysis of the seasonal phenology of FAW infestations across Mississippi during 1978-
1979 suggested that immigrants arrived via storm systems from unidentified source
areas (Hogg et al. 1982). FAW populations demonstrate a successive progression north
and northwesterly of their overwintering sites in Florida, and the spring arrival of FAW
males in adjacent states appears to be associated with the presence of certain synoptic
weather systems (Pair & Sparks 1986, Pair et al. 1986). Circumstantial evidence also
exists that a reverse FAW migration from the Texas High Plains to the LRGV occurred
during the fall of 1984 (Pair et al. 1987). Research also indicates that FAW may undertake
transoceanic flights across the Gulf of Mexico (Wolf et al. 1986b). However, our study
provides the first combined ecological, meteorological, and radar evidence for migratory
flights of FAW from a defined geographical area to impact crops far removed from the
source.
The outbreak discussed in this paper obviously did not approach the severity of those
described in 1899, 1912, or 1977, but the potential certainly existed. A widespread
outbreak could occur in the presence of favorable conditions if heavy populations existed
simultaneously during the early summer in both northern Mexico and in the southeastern
states. It is conceivable that a similar situation triggered the massive outbreak east of
the Rockies in 1912. The sudden appearance of FAW in the LRGV and at more northerly
locations emphasizes that persistent efforts are needed to identify source areas and
monitor FAW populations via traps and/or within-field scouting. Such endeavors are
requisite for timely prediction of severe infestations (Barfield et al. 1980, Sparks et al.
1985). Indeed, epicenters of extremely severe FAW populations may develop within a
general infestation over a relatively widespread area as demonstrated by the events in
the LRGV in 1989.
The production of CEW from mature corn grown in the LRGV has been identified
as a potentially major threat to cotton and other crops in northern Texas and elsewhere
(Sparks et al. 1986, 1989). Data collected from 1984-1989 indicate that FAW production
on mature corn in the LRGV averaged 2.3 billion adults annually, and assuming a 1:1
sex ratio exists, 1.1 billion were females. If each female then oviposits an average of
500 viable eggs, and if hypothetically 25,000 eggs/ha of crop are needed to create an
economic infestation, then FAW that were produced in the LRGV had the potential for
impacting 22 million ha of susceptible crops. Similarly, the magnitude of FAW populations
produced in the LRGV during 1989 had the potential for infesting 79 million ha of crops.
Thus, mature corn in the LRGV should be considered as a major source of FAW popu-
lations having the potential to migrate and inflict widespread economic damage in much
of the central U.S.

ACKNOWLEDGMENTS

The authors gratefully extend their appreciation to the following individuals for their
assistance in monitoring traps and/or providing information on fall armyworm popula-
tions: W. P. Morrison and Roy Parker, Texas Agricultural Extension Service; Don
Rummel, Ken Neece, and John Benedict, Texas Agricultural Experiment Station; P.
D. Lingren, John Robinson, and W. B. Showers, USDA-ARS.


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Florida Entomologist 74(2)


DEVELOPMENT OF FALL ARMYWORM ON DIETS
CONTAINING RESISTANT AND SUSCEPTIBLE CORN SILKS

B. R. WISEMAN
USDA-ARS-IBPMRL
Tifton, GA 31793

D. J. ISENHOUR
Department of Entomology
Coastal Plain Exp. Stn.
University of Georgia
Tifton, GA 31793

ABSTRACT

Growth and development of fall armyworm, Spodoptera frugiperda (J. E. Smith),
larvae on pinto bean diet containing dry corn, Zea mays L., silks of resistant, 'Zapalote
Chico', or susceptible, 'Stowell's Evergreen', at 0, 18.75, 37.50, and 67.0 mg silk/ml diet
were evaluated at 20, 25 and 300C. Weight of larvae that fed on resistant and susceptible
silk-diets averaged 38 and 205 mg, respectively. At 20C, the weight of larvae that fed
on various concentrations of silk/diet did not differ between the resistant and susceptible
genotypes or among the various concentrations within each corn genotype. However,
at 200C, significant differences were found between the resistant and susceptible for
development time, weight of pupae and time to adult eclosion for larvae that fed on
various concentrations of silk/diet. Significant differences were consistently recorded
for all characters measured (P <0.05) between the resistant 'Zapalote Chico' and suscep-
tible 'Stowell's Evergreen' at 25 and 300C. Larvae failed to develop to pupae at the
highest concentration (67.0 mg/ml) of resistant silks at 20, 25, or 300C.


RESUME

Se evalu6 a temperatures de 20, 25 y 30 C el crecimmiento y desarrollo de larvas
de cogollero, Spodoptera frugiperda (J. E. Smith), en dieta de frijol prieto, la cual
contenia maiz (Zea mays L.) seco, cabellos de maiz resistente "Zapalote chico," o sus-
ceptible "Stonewell's Evergreen," en concentraciones de 0, 18.75, 37.50 y 67.0 mg de
cabellos/ml de dieta. El peso de la larva alimentada con cabellos de variedades resistentes
o susceptibles di6 un promedio de 38 y 205 mg, respectivamente. A los 200C, el peso de
la larva alimentada de varias concentraciones de dieta con cabellos, no difiri6 entire
genotipos susceptibles o resistentes o entire las concentraciones de cada genotipo. Sinem-
bargo, aquellas larvas alimentadas con dietas de varias concentraciones de cabellos
resistentes y susceptibles, criadas a los 20C, se encontraron diferencias significativas
en el tiempo de desarrollo, peso de pupas y duraci6n de los estados desde larva a
emergencia de adults. La diferencias significativas fueron consistentes para todos los
caracteres (P > 0.05) entire la variedad susceptible "Stonewell's Evergreen" a 25 y 300C.
Las larvas no alcanzaron estado de pupa en las concentraciones mas altas (67.0 mg/ml)
de los cabellos resistentes a 20, 25 y 300C.



The fall armyworm, Spodopterafrugiperda (J. E. Smith), is a serious economic pest
of several grass species in the United States, particularly corn, Zea mays L., in the
Southeast. The use of resistant corn cultivars to manage the fall armyworm appears to
be the most viable alternative to the use of chemicals for its control (Wiseman 1985).


214


June, 1991











Fall Armyworm Symposium '90-Wiseman & Isenhour 215

Numerous studies have shown various levels of resistance in whorl stage corn to the
fall armyworm since the discovery of resistance in the 'Coastal Tropical Flint' corn. In
particular, the whorl stage of the 'Antigua' group of dent corn has a high level of
resistance to the fall armyworm (Anonymous 1965, Wiseman et al. 1966, Wiseman and
Davis 1979). A high level of resistance against the fall armyworm and the corn earworm,
Helicoverpa zea (Boddie), also was found in the silks of an exotic dent corn cultivar,
'Zapalote Chico 2451# (PC3)' (Wiseman & Widstrom 1986, 1987). Zapalote Chico is a
floury dent corn from the state of Oaxaca, Mexico that has little agronomic value in its
present form. However, it has a great genetic potential as a source of resistance for
reducing losses in corn by the fall armyworm and corn earworm.
In recent years, research on the resistance of corn to fall armyworm has provided
new methods and approaches to differentiate resistant and susceptible corn genotypes
(Davis et al. 1989). The development of laboratory bioassays would be beneficial for
determining basic biological effects of the resistant cultivar on the insect and useful in
determining the chemical basis of resistance. We report effects of different concentrations
of resistant and susceptible corn silks mixed in meridic diets on the growth and devel-
opment of fall armyworm under controlled conditions.

MATERIALS AND METHODS

Larvae used in this study were obtained from a colony maintained on pinto bean
diet (Burton 1967) at the Insect Biology and Population Management Research Labora-
tory, Tifton, Ga. Two corn genotypes, 'Stowell's Evergreen' (SEG), a sweet corn suscep-
tible to fall armyworm feeding on silks, and 'Zapalote Chico 2451# (PC3)', (ZC), a dent
corn resistant to fall armyworm silk and ear feeding in the field, were selected for study.
Each cultivar was grown in bulk in single-row plots, 6.1 m long and 0.76 m apart, at
Tifton in 1986, using accepted agronomic practices common to the area.
Silks of each corn genotype were harvested 2 d after emergence from the husk leaves.
The silks were excised at the tip of the ear, bulked, oven dried at 41C for about 10 d,
and ground to pass through a 1.0 mm screen using a Cyclotec TC1093 (Fisher Scientific,
Atlanta) sample mill. Dry silks from each corn genotype were then stored in a freezer
at -100C until needed. Concentrations of 0, 18.75, 37.5, and 67.0 mg silk/ml diet were
mixed into a diluted (300 ml diet:100 ml distilled water) pinto bean diet for bioassay.
The silk-pinto bean diet mixtures were dispensed into 36 30 ml plastic diet cups at a
quantity of ca. 10 ml per cup and allowed to solidify for about 2 h. One neonate larva
was then placed in each cup, and the cup was capped with a paper lid.
The experiment was arranged as a split split-plot design with 11 replications. The
experimental unit was the mean of two cups per replicate for each treatment. Whole
plots were temperature regimes of 20, 25, and 30 20C. Subplots were corn genotypes
and the final split was concentration of silk per ml of diet. Each environmental room
was maintained with a 14:10 (L:D) photoperiod and 70 5% RH.
Data recorded were weight of larvae at 10 d, developmental time in days, weight of
pupae, and time from egg hatch to adult eclosion. Data were analyzed as replicate means
by General Linear Models Procedure, and means were separated with the appropriate
use of Tukey's honest significant differences (HSD) at P < 0.05 or t-test at P < 0.05
(SAS Institute 1985).


RESULTS AND DISCUSSION

Weights of 10-d-old fall armyworm larvae fed varying amounts of silk-diet mixtures
of Zapalote Chico and Stowell's Evergreen at three temperature regimes are presented
in Table 1. The weight of larvae averaged over the three temperatures at 10 d that










Florida Entomologist 74(2)


TABLE 1. MEAN WEIGHT OF 10-D-OLD FALL ARMYWORM LARVAE THAT WERE FED
VARYING CONCENTRATIONS OF RESISTANT OR SUSCEPTIBLE CORN SILKS
IN MERIDIC DIETS.

x weight of larvae (mg) at indicated temperature (C)'

g s/ 20 25 30
Mg silk/
ml diet n SEG ZC SEG ZC SEG ZC

0 11 10a 9a 270a 265a 435b 464a
18.75 11 6a 2a 231 ab 56b 493a 214b
37.50 11 6a la 216b 12 b 511 a 55c
67.00 11 5a 0.3a 96c 2c 280c Id

'Means within a column not followed by the same letter (Tukey's HSD mean separation) or cultivar means within
a temperature separated by (t-tests) are significantly different (P < 0.05) SAS Institute (1985). SEG = Stowell's
Evergreen, susceptible; ZC = Zapalote Chico, resistant, n = Experimental unit is the response of two larvae per
replicate per treatment.

were fed SEG and ZC were 205 and 38 mg, respectively. No larval mortality occurred
by 10 days. A significant three-way interaction occurred; thus, the data are illustrated
accordingly (Table 2). Growth of the fall armyworm larvae was extremely slow at 20C,
and no significant differences in weights of larvae were detected among different concen-
trations of silks or between corn genotypes (Table 1). However, at 25 and 30C, significant
differences were detected in the weights of larvae that were fed various silk concentra-
tions/diet for SEG and ZC. At a given temperature, there was no significant difference
between the weight of larvae that were fed on the standard laboratory diet without
corn silks. The weights of larvae that were fed 18.75, 37.50, and 67.00 mg ZC silk/ml
diet concentrations were significantly less than those larvae that were fed SEG silks at
similar concentrations. Even though there was about a 50% decrease in weight of larvae
that were fed SEG at 67 mg silk/ml diet compared to the weight of the larvae that were
fed the 37.50 mg SEG/ml diet, there was still a 48 and 280-fold difference in weight
between the larvae that were fed on SEG and ZC silk diets at the highest silk concen-
tration (67 mg silk/ml diet) at 25 and 300C, respectively. Significant differences in weight
of larvae between those that were fed on SEG and ZC were found at 25C and 30C for
all concentrations of silk/diet.


TABLE 2. RESULTS OF PROC GLM FOR WEIGHTS OF FAW LARVAE FED RESISTANT
AND SUSCEPTIBLE CORN SILK DIETS FOR 10-D.

Source df ss F'

Replication 10 23421.65 -
Temperature 2 4020570.45 858.58**
Rep* Temp (Error A) 20 46828.25 -
Genotype 1 999067.58 331.82**
Temp Genotype 2 648587.26 144.48 **
Rep Geno (Temp) (Error B) 30 67334.85 144.48 **
Concentration 3 1086236.56 120.26**
Temp* Cone. 6 586042.49 32.44**
Geno* Conc. 3 456719.14 50.56**
Temp Geno Cone. 6 347308.82 19.22 **
(Error C) 180 541964.66 -

'** indicates highly significant 0.01 level of probability.


216


June, 1991











Fall Armyworm Symposium '90-Wiseman & Isenhour


TABLE 3. RESULTS OF PROC GLM FOR DEVELOPMENT TIME OF FAW LARVAE FED
RESISTANT AND SUSCEPTIBLE CORN SILK DIETS.

Source df ss F'

Replication 10 26.83 -
Temperature 2 21171.97 4649.03**
Rep Temp (Error A) 20 45.45 -
Genotype 1 1153.96 345.89**
Temp Genotype 2 69.37 10.40 **
Rep Geno (Temp) (Error B) 30 100.08 -
Concentration 3 2179.16 376.99**
Temp* Cone. 6 379.99 32.87**
Geno* Conc. 2 891.53 231.35**
Temp *Geno* Cone. 4 54.44 7.06**
(Error C) 150 289.02 -

1** indicates highly significant 0.01 level of probability.

A significant three-way interaction also was noted for development time of larvae
(Table 3). Overall, it required about 2.6 times as long for the larvae to develop at 20C
as compared with those tested at 300C for all diet concentrations. Even though no
significant differences (Table 4) were detected among weights of 10-d-old larvae at 20C
(Table 1), significant differences in development time were found between SEG and ZC
for 18.75 and 37.50 mg silk/ml diet. Larvae failed to develop to pupae when fed the 67.0
mg of resistant silk/ml diet at all three temperatures.
There was a significant genotype and silk-concentration/diet interaction for weight
of pupae (Table 5). Pupal weights of larvae fed SEG silk-diets declined less rapidly than
those fed ZC silk-diets with increasing silk concentrations (Table 6). There were signif-
icant differences among weights of pupae for larvae fed silk diet mixtures of SEG and
ZC for the various silk concentrations/diet and between SEG and ZC at the 37.5 mg
silk/diet. The mean weight of pupae from larvae that were fed the various concentrations
of silk-diet mixtures differed significantly among temperatures: 20C (243a), 25C (256b),
and 300C (251b). As mentioned earlier, no larvae developed to pupation when fed on
the highest ZC silk concentration.

TABLE 4. MEAN DEVELOPMENT TIME FOR FALL ARMYWORM LARVAE FED DIFFER-
ENT CONCENTRATIONS OF SILKS OF RESISTANT OR SUSCEPTIBLE CORN
GENOTYPES IN MERIDIC DIETS.

i development time (days)
at indicated temperature (C)'

Mg silk/ 20 25 30
Mgsilk/ ---- ------
mldiet n SEG ZC SEG ZC SEG ZC

0 11 30a 30a 15a 15a 12a 12a
18.75 11 34b 38b 16a 19b 12a 15b
37.50 11 35b 49c 16a 26c 12a 20c
67.00 11 38c -2 19b -2 15b -

'Means within a column not followed by the same letter (Tukey's HSD) or cultivar means within a temperature
separated by (t-tests) are significantly different (P < 0.05). SAS Institute (1985). SEG = Stowell's Evergreen,
susceptible; ZC = Zapalote Chico, resistant. n = Experimental unit is the response of two insects per replicate per
treatment.
'No fall armyworm developed to pupae.


217










Florida Entomologist 74(2)


June, 1991


TABLE 5. RESULTS OF PROC GLM FOR WEIGHTS OF FAW PUPAE FROM LARVAE FED
RESISTANT AND SUSCEPTIBLE CORN SILK DIETS.

Source df ss F'

Replication 10 6712.43 -
Temperature 2 7496.92 7.50 **
Rep Temp (Error A) 20 9992.85 -
Genotype 1 23506.41 41.20**
Temp Genotype 2 1372.84 1.20 ns
Rep Geno (Temp) (Error B) 30 16399.73 -
Concentration 3 122375.16 56.93**
Temp Cone. 6 3507.30 0.82 ns
Geno*Conc. 2 31145.53 21.73**
Temp Geno Cone. 4 5977.05 2.09 ns
(Error C) 147 105336.30 -

'** indicates highly significant 0.01 level of probability.

A significant interaction between genotype and concentration of silk/diet occurred
for the time of egg hatch to adult eclosion (Table 7). Significant differences in the time
required for adult eclosion for larvae fed the various silk concentrations were found both
among SEG and among ZC treatments and between SEG and ZC for the 18.75 and 37.5
mg of silks (Table 8). Mean time to adult eclosion was greater for larvae fed ZC diets
than for those fed SEG diets. Only 22 of 33 insects emerged as adults for those larvae
fed the 37.5 mg ZC/ml diet, indicating some carry-over effects of the resistance, resulting
in lowering the total number that emerged as adults. Furthermore, larvae that were
fed the highest concentrations of ZC silk diets failed to develop beyond the larval stage.
Also, a significant temperature and genotype interaction occurred for the time of
egg hatch to adult eclosion (Table 7). Significant differences in days to adult eclosion
were found between SEG and ZC at all three temperatures for both SEG and ZC (Table
9). The mean time to adult eclosion for the three temperatures were: 200C (52d), 25C
(27.5d), and 30C (21.5d). Again, larvae that were fed the highest concentration of
silk/diet failed to develop beyond the larval stage.
Four separate resistance characteristics were measured in this study: weight of
larvae at 10 d, larval development time, weight of pupae, and days from egg hatch to
adult eclosion. As expected for poikilotherms, fall armyworm growth and development
were the slowest at 20C and the fastest at 30C. Significant differences between the


TABLE 6. MEAN WEIGHT (MG) OF FALL ARMYWORM PUPAE FROM LARVAE THAT
FED ON VARYING CONCENTRATIONS OF CORN SILKS FROM RESISTANT
AND SUSCEPTIBLE GENOTYPES IN MERIDIC DIETS AT 20-300C.

Spupae wt (mg)'
Mg silk/
ml diet n SEG ZC

0 33 274a 275a
18.75 33 265ab 255b
37.50 33 261b 205c
67.00 33 214c 2

'Means within a column not followed by the same letter (Tukey's HSD) or row means separated by are significantly
different (t-test) (P < 0.05) SAS Institute (1985). SEG = Stowell's Evergreen, susceptible; ZC = Zapalote Chico,
resistant. n = experimental unit is the response of two pupae per replicate per treatment.
'No fall armyworm developed to pupae.


218












Fall Armyworm Symposium '90-Wiseman & Isenhour 219


TABLE 7. RESULTS OF PROC GLM FOR DAYS TO ADULT ECLOSION FOR FAW FED
RESISTANT AND SUSCEPTIBLE CORN SILK DIETS.

Source df ss F'

Replication 10 316.27 -
Temperature 2 16645.33 4200.10 **
Rep Temp (Error A) 20 39.63 -
Genotype 1 555.15 198.78**
Temp* Genotype 2 20.99 3.76*
Rep Geno (Temp) (Error B) 30 194.30 3.17 **
Concentration 3 1272.34 207.78 **
Temp* Cone. 6 129.94 10.61**
Geno* Conc. 2 360.76 88.37**
Temp *Geno* Cone. 4 15.57 1.91ns
(Error C) 121 246.98 -

'** indicates highly significant 0.01 level of probability.





TABLE 8. MEAN DAYS TO ADULT ECLOSION FOR FALL ARMYWORM LARVAE THAT
FED ON VARYING CONCENTRATIONS OF SILKS OF RESISTANT OR SUSCEP-
TIBLE CORN GENOTYPES IN MERIDIC DIETS AT 20-30C.

Mg silk/ R days to adult eclosion'
ml diet SEG(n) ZC(n)

0 30b (33) 30a (38)
18.75 32c(32) 36c (33)
37.50 32c (30) 33b (22)
67.00 28a(30) _

'Means within a column not followed by the same letter (Tukey's HSD) or row means separated by (t-tests) are
significantly different (P < 0.05) SAS Institute (1985). SEG = Stowell's Evergreen, susceptible; ZC = Zapalote
Chico, resistant. n = experimental unit in parenthesis is the response of two insects per replicate per treatment.
'No fall armyworm emerged.





TABLE 9. MEAN DAYS TO ADULT ECLOSION FOR FALL ARMYWORM FROM LARVAE
THAT FED ON DIETS WITH SILKS FROM RESISTANT OR SUSCEPTIBLE CORN
GENOTYPES.

k days to adult eclosion at
indicated temperature (C)1

20 (n) 25(n) 30(n)

SEG 51a (39) 26a (42) 20a (44)
ZC 53b (26) 29b (29) 23b (33)

'Means within a column not followed by the same letter (Tukey's HSD mean separation) or row means between
temperatures separated by are significantly different (t-tests) (P < 0.05) SAS Institute (1985). SEG = Stowell's
Evergreen, susceptible; ZC = Zapalote Chico, resistant. Days to eclosion are averaged across concentrations within
SEG or ZC. n = experimental unit in parenthesis is the response of two insects per replicate per treatment.











Florida Entomologist 74(2)


measured characters for ZC and SEG were consistent at 25 and 300C. However, caution
should be made for using 30C for complete development studies because sometimes the
diet tends to dry much faster than at 20 and 25C, and growth of larvae is enhanced on
the lower concentrations of ZC silk/diet at 300C as compared with those fed ZC silks at
250C.
The resistance of the silks of ZC against the fall armyworm was strongly expressed
with as little as 18.75 mg silk/ml diet, but was expressed even greater at 37.5 mg silk/ml
diet. At the 67.0 mg ZC silk/ml diet, the antibiotic effects were specific, cumulative,
and persistent for the recorded measurements of weight at 10 d, development time,
weight of pupae, and for adult eclosion. In fact, the resistance with 67.0 mg ZC silk/ml
diet was so strong that no fall armyworm developed beyond the larval stage.
Resistance measurements should be recorded at the time or under conditions that
permit the greatest separation of the resistant and susceptible treatments or cultivars
(Wiseman et al. 1980). In addition, as many characters as possible should be measured.
The information reported here will enable us to use this bioassay, with the effective
temperature regime and related concentration of silk/diet, to determine the chemical
factors) present in the silks of Zapalote Chico.

ACKNOWLEDGMENTS

We thank J. L. Skinner, Charles Mullis, Peggy Goodman, and David Atkins for their
technical assistance in this study, and B. G. Mullinix for his statistical advice.

REFERENCES CITED

ANONYMOUS. 1965. The Rockefeller Foundation program in the agricultural sciences.
Annu. Rpt., 1964-65. The Rockefeller Foundation, New York. 262 p.
BURTON, R. L. 1967. Mass rearing the fall armyworm in the laboratory. U.S.D.A.
ARS Publ. ARS 33-117. 12 p.
DAVIS, F. M., W. P. WILLIAMS, AND B. R. WISEMAN. 1989. Methods used to screen
maize for resistance and to determine mechanisms of resistance to the southwest-
ern corn borer and fall armyworm, pp. 101-108 in Toward insect resistant maize
for the Third World: Proc. of International Symposium on methodologies for
developing host plant resistance to maize insects. Mexico D.F., CIMMYT. 327 pp.
SAS INSTITUTE INC. 1985. SAS user's guide: statistics, version 5 edition. Cary, N.C.
956 p.
WISEMAN, B. R. 1985. Development of resistance in corn and sorghum to a foliar-
and ear/panicle-feeding worm complex. Proc. 49th Annu. Corn and Soybean Ind.
Res. Conf. 40: 108-124.
WISEMAN, B. R., AND F. M. DAVIS. 1979. Plant resistance to the fall army worm.
Florida Entomol. 63: 425-432.
WISEMAN, B. R., B. G. MULLINIX, AND P. B. MARTIN. 1980. Insect resistance
evaluations: Effect of cultivar position and time of rating. J. Econ. Entomol. 73:
454-457.
WISEMAN, B. R., R. H. PAINTER, AND C. E. WASSOM. 1966. Detecting corn seedling
differences in the greenhouse by visual classification of damage by the fall ar-
myworm. J. Econ. Entomol. 59: 1211-1214.
WISEMAN, B. R., AND N. W. WIDSTROM. 1986. Mechanisms of resistance in 'Zapalote
Chico' corn silks to fall armyworm (Lep.:Noct.) larvae. J. Econ. Entomol. 79:
1390-1393.
WISEMAN, B. R., AND R. L. WILSON. 1987. Corn earworm development on meridic
diets containing pollinated and unpollinated corn silks from two plantings at two
locations. Maydica 32: 201-220.


June, 1991


220











Fall Armyworm Symposium '90-Isenhour & Wiseman


FALL ARMYWORM RESISTANCE IN PROGENY OF
MAIZE PLANTS REGENERATED VIA TISSUE CULTURE

D. J. ISENHOUR
Department of Entomology
Coastal Plain Experiment Station
University of Georgia
Tifton, GA 31793 USA

B. R. WISEMAN
USDA-ARS
Insect Biology and Population
Management Laboratory
Tifton, GA 31793 USA

ABSTRACT

Plant regeneration of maize genotypes known to be resistant to leaf-feeding by the
fall armyworm, Spodoptera frugiperda (J. E. Smith), was attempted via somatic em-
bryogenesis. Successful regeneration from callus tissue cultures was achieved for the
maize genotypes 'Antigua 2D-118', 'MpSWCB-4', 'Mp496', and some selected single
crosses. Progeny from these regenerates were evaluated under laboratory and field
conditions for their levels of resistance to fall armyworm leaf-feeding as compared to
their respective non-regenerated parental lines. Significant differences in resistance to
leaf-feeding by the fall armyworm were observed between the regenerated and non-re-
generated lines. Differences were of a positive as well as a negative nature in regards
to the levels of resistance in the regenerates as compared to their non-regenerated
parental line. This is further evidence of the potential of somaclonal variation for obtaining
agronomically useful traits for crop improvement, in this instance plant resistance to
insect attack.

RESUME

Se intent, por medio de embriogenenesis somaticas, la regeneraci6n de plants de
genotipos de maiz resistentes a el consume de hojas del cogollero Spodopterafrugiperda
(J. E. Smith). La regeneraci6n de calls de cultivos de tejido fue lograda para los
genotipos "Antigua2D-118," "MpSWCB-4," Mp496, y para algunos cruces simples. Bajo
condiciones de laboratorio e invernadero, se compararon los niveles de resistencia a el
cogollero entire la progenie obtenida a partir de plants regeneradas y comparada con
las lines no regeneradas de los padres. Las diferencias fueron de naturaleza positivas
y negative en referencia a los niveles de resistencia en las lines regeneradas y com-
parados con sus lines paternas no regeneradas. Esto se consider como una evidencia
mas del potential de la variacion somaclonal para obtener caracteres de mejoramiento
del cultivo para resistencia de este a el ataque de insects.



The fall armyworm, Spodopterafrugiperda (J. E. Smith), is a serious pest of maize
in the Americas (Horovitz 1960, Sparks 1979, Dicke & Guthrie 1988). Sparks (1979)
reviewed the biology of the fall armyworm and Ashley et al. (1989) provided the most
current bibliography of this pest.
Maize genotypes resistant to leaf-feeding by the fall armyworm have been developed
(Scott & Davis 1981a, b). Several studies have shown the effects of resistant genotypes











222 Florida Entomologist 74(2) June, 1991

on the growth and development of the fall armyworm (Wiseman et al. 1981, Williams
et al. 1983, Isenhour et al. 1985). At the present time the utilization of resistant genotypes
exhibits the greatest potential as an alternative to insecticides for fall armyworm control
in maize. Wiseman (1987) stressed the value of planting resistant cultivars and how
compatible this control strategy was with others.
Continued progress in a crop breeding program is dependent in large part on the
ability to obtain new sources of genetic variation. Traditionally the source of this variation
has been in the form of plant introductions or exotic germplasm. This material was then
incorporated into the breeding program. A new source of genetic variation that is now
being utitlized is that derived from plant tissue culture. Plant tissue culture-induced
variation, or somaclonal variation, has been reported for several agronomic crops (Larkin
& Scowcroft 1981, Earle & Gracen 1985, Evans & Sharp 1986, Lee et al. 1988, Croughan
& Quisenberry 1989). Croughan & Quisenberry (1989) reported the first instance of
somaclonal variation with respect to resistance to insect feeding. They found increased
levels of resistance to fall armyworm in regenerates of bermudagrass, Cynodon dactylon
(L.) Pers.
Herein we report on the regeneration and potential for obtaining increased levels of
resistance in selected maize genotypes known to be resistant to the fall armyworm.

MATERIALS AND METHODS

PLANT REGENERATION

The maize genotypes 'Antigua 2D-118', 'MpSWCB-4', 'Mp496', and Pio. X 304C were
selected as candidate genotypes for their ability to express totipotency in cell culture.
The Fl progeny of a single cross of A188 x Antigua 2D-118 were also evaluated. A188
was used as a parent because of its reported high level of regeneration potential from
cell culture (Earle & Gracen 1985).
Multiple field plantings of the selected maize genotypes were made during the sum-
mers of 1986-1988 at the Coastal Plain Experiment Station, University of Georgia,
Tifton, GA using standard agronomic practices. Plants were selfed by means of hand
pollinations to ensure a uniform source of immature maize embryos.
Callus tissue was initiated from immature embryos using procedures described by
Green et al. (1974) and Duncan et al. (1985). These procedures involve the culturing of
immature maize embryos on agar-based media supplemented with necessary plant inor-
ganic salts, nutrients, vitamins, and plant growth regulators. Callus tissue forms and
can be cultured for several months by transferring it to fresh media. Plant regeneration
is achieved by varying the plant growth regulator concentrations of the medium. Figure
1 provides an overview of the tissue culture procedures used in the initiation of callus
tissue and the subsequent regeneration of plants back from the callus cultures. Regen-
erated, or Ro, plants were transferred from their agar substrate to soil in the greenhouse,
allowed to mature, and then selfed. Seed from these plants, designated as R1 seed, was
then planted in the field.


EVALUATION FOR FALL ARMYWORM RESISTANCE

Field screening at the whole plant level and laboratory bioassays using meridic diets
were the two methods employed to measure the levels of resistance to the fall armyworm
in the progeny of the regenerated plants.
Field testing utilized artificial infestations of laboratory reared fall armyworms. A
randomized complete block design was used with individual plots consisting of a single
row 3 m in length. There were 10 and 6 replications for 1988 and 1989 respectively. A












Fall Armyworm Symposium '90-Isenhour & Wiseman


self, cross


greenhouse


embryo


plantlet formation


plantlet induction

plantlet induction


increase callus


Fig. 1. Procedures for plant regeneration of maize via callus tissue initiated from
immature embryo culture (after Green et al. [1974]).


fall armyworm colony was initiated with feral larvae collected from maize. The colony
was maintained as describe by Mihm (1983) and feral larvae are added every summer.
Infestation procedures were those described by Wiseman et al. (1980) and Mihm (1983)
with an infestation rate of 40 neonates per plant. Leaf-feeding by the fall armyworm
was visually rated using a system with 1= resistant to 9=susceptible developed by Davis


223


oo
i=a
oo











Florida Entomologist 74(2)


(USDA-ARS, Mississippi, MS personnel communication) and reported by (Diawara et
al. 1990).
Meridic diets were made by incorporating oven-dried maize whorl tissue from field
grown plants into a pinto bean diet (Wiseman et al. 1984, Isenhour et al. 1985). Whorl
leaves were manually removed from the plants, cut into 4-6 cm sections and oven-dried
for 72 h at 420C. Leaves were then ground in a Cyclotec 1093 mill (1.0 mm mess screen
size). Powdered foliage was then held at -20C until diets were made.
Powdered maize foliage was incorporated into the pinto bean diet to a final concen-
tration of 45 mg/ml of diet. Diets were dispensed in 10 ml amounts into 30-ml diet cups.
The diet was allowed to solidify and then a single fall armyworm neonate was placed
on the diet surface and the cup was capped with a paper lid. Cups were held at 26C
and a photoperiod of 14L:10D in a growth chamber. A randomized complete block design
was used with 25 replications.
Statistical analysis was the same for the field and laboratory portions of this study.
Analysis of variance was by the least-squares procedures (SAS Institute 1985) and mean
differences were determined by Duncan's multiple range test (Duncan 1955). Significance
was determined at the 0.05 level.

RESULTS

PLANT REGENERATION

We define successful plant regeneration as the attainment of a viable plant capable
of developing to maturity in soil. Plant regeneration was achieved for Antigua 2D-118,
MpSWCB-4, Mp496, and A188 x Antigua 2D-118. No plants were successfully regener-
ated from callus cultures of Pio. X 304C, however this maybe more of a reflection on
our technique rather than on this genotype.
Table 1 lists the number of successful regenerations by genotype for the 1987, 1988,
and 1989 seasons. Also listed are values for "percent efficiency" determined based on
the number of regenerates obtained divided by the total number of immature maize
embryos that had been placed on media to initiate callus formation. The concept of
percent efficiency is perhaps a rather crude measurement of the given genotypes capacity
to form totipotent callus tissue, but it does provide an indication of how the genotypes
used in this study compare with each other in regards to plant regeneration.
Antigua 2D-118 exhibited the highest degree of regeneration efficiency of the
genotypes we evaluated, but we cannot say how the genotypes would compare if other
regeneration procedures were employed (Table 1). Even though the greatest number
of plants were regenerated from MpSWCB-4, it had the poorest efficiencies of regener-
ation. We used this genotype as one of our "standards", and therefore it received more



TABLE 1. PLANTS REGENERATED FROM CALLUS TISSUE CULTURES OF MAIZE
GENOTYPES RESISTANT TO LEAF-FEEDING BY S. FRUGIPERDA, 1987-1989,
TIFTON, GA.

Genotype No. of Plants % Efficiency'

Antigua2D-118 42 53
MpSWCB-4 342 15
Mp496 93 25
(A188 x Ant. 2D-118) 6 13

'Total number of plants obtained divided by the number of immature embryos that were placed on media.


224


June, 1991











Fall Armyworm Symposium '90-Isenhour & Wiseman 225

emphasis in this study than its ability to regenerate might have warranted. The single
cross with A188 as the female parent did not express a higher degree of regeneration
when compared to the parent of interest, Antigua 2D-118. Similar results have been
observed in crosses with A188 and 'Zapalote Chico' (Isenhour and Wiseman unpublish.
data).

EVALUATION FOR FALL ARMYWORM RESISTANCE

Results of the 1988 field evaluation of the progeny of Ro plants (Rl's) and non-regen-
erated parental lines are presented in Table 2. Significant differences in resistance to
leaf-feeding by fall armyworm were observed between the R1 plants and the non-regen-
erated parental plants. However, these difference were found to be both positive as
well as negative in nature in regards to their degree of resistance. Higher levels of
resistance were observed for the Rl's of MpSWCB-4 as compared to the non-regenerated
plants of this genotype. The reverse was observed for A188 x Antigua 2D-118, with
the R1 plants showing a greater degree of susceptibility to leaf-feeding by the fall
armyworm as compare to the F1 of this cross (Table 2).
Table 3 presents the results of the field evaluations for 1989. The R2 plants failed
to exhibit the increased levels of resistance to leaf-feeding by S. frugiperda as compared
to their non-regenerated parents, as was the case in 1988. The difference in resistance
exhibited by the R2 plants of (MpSWCB-4 x Mp496-Ro) as compared to F2's of a
comparable single cross was an encouraging sign. Due to a limited amount of seed this
line was not screened as an R1 in 1988. This line was derived by crossing a female
non-regenerated MpSWCB-4 with pollen from an Ro plant of Mp496. The progeny from
this cross were then selfed and given as "R" designation due to the fact they had a
regenerated parent.
Table 4 provides the results of the laboratory trial utilizing meridic diets to evaluate
for resistance to feeding by the fall armyworm. The differences in resistance between
the R2 and F2 lines of (MpSWCB-4 x Mp496) observed in the field evaluation were
also detected in the diet trial. Significantly lower larval weights and longer time required
for adult eclosion were observed for fall armyworm larvae fed the diet with leaf tissue
from (MpSWCB-4 x Mp496 Ro) R2 as compared to any of the other diet treatments.



TABLE 2. DAMAGE RATINGS FOR LEAF-FEEDING BY S. FRUGIPERDA AT 7 AND 14
DAYS AFTER ARTIFICIAL INFESTATION FOR R1 AND NON-REGENERATED
PARENTAL LINES. TIFTON, GA, 1988.

Damage Rating'

Genotype 7 Days 14 Days

Antigua 2D-118 NR-R2 4as 6ab
MpSWCB-4 R1 5abc 5a
MpSWCB-4 NR 4ab 6ab
(A188 x Ant. 2D-118) R1 6c 8c
(A188 x Ant. 2D-118) F1 5ab 7b
Pio. 3369A NR-S2 6abc 7b

'Visual rating scale where 1 is resistant and 9 susceptible (Davis et al. unpublish. data; USDA-ARS, Mississippi
State, MS).
'NR: non-regenerated controls, R: Resistant, S: Susceptible.
'Means within a column followed by the same letter do not differ significantly at the 0.05 level (Duncan [1965]
multiple range test).











Florida Entomologist 74(2)


TABLE 3. DAMAGE RATINGS FOR LEAF-FEEDING BY S. FRUGIPERDA AT 7 AND 14
DAYS AFTER ARTIFICIAL INFESTATION FOR R2 AND NON-REGENERATED
PARENTAL LINES. TIFTON, GA, 1989.

Damage Rating'

Genotype 7 Days 14 Days

MpSWCB-4 R2 7a2 8a
MpSWCB-4 NR-R3 6b 7b
(MpSWCB-4 x Mp496 Ro) R2 6b 7b
(MpSWCB-4 x Mp496) F2 8a 8a
Pio. 304C NR-R3 8a 8a
Pio. 3192 NR-S3 8a 8a

'Visual rating scale where 1 is resistant and 9 susceptible (Davis et al. unpublish. data; USDA-ARS, Mississippi
State, MS).
"Means within a column followed by the same letter do not differ significantly at the 0.05 level (Duncan [1955]
multiple range test).
"NR: non-regenerated controls, R: Resistant, S: Susceptible.


DISCUSSION

We are very encouraged by the results of the field and laboratory evaluations of
(MpSWCB-4 x Mp496) R2. Levels of insect resistance were enhanced to a limited
degree, and no detrimental agronomic characteristics occurred. However, segregation
is still occurring in this line, which also might explain in part the lack of difference found
in 1989 in the level of resistance in the R2's of MpSWCB-4 and the non-regenerated
parents.
The phenomenon of the occurrence of variations in a plant line owing strictly to the
stresses incurred during tissue culture has been termed somaclonal variation (Larkin
& Scowcroft 1981). There is still uncertainty as to the mechanisms involved, but it has
been likened to an "earthquake" within the plant's genome. No foreign DNA has been
added, rather an alteration has occurred. There is evidence that transposable elements,
or "jumping genes", play a role in the genetic mechanisms involved in the expression
of somaclonal variation (Peschke et al. 1987).
While somaclonal variation is now recognized as a viable source of genetic variation,
there are problems for its application in plant resistance to insects. In herbicide resist-

TABLE 4. MEAN LARVAL WEIGHTS AT 8 AND 12 DAYS FOR FALL ARMYWORMS THAT
WERE FED MAIZE LEAF TISSUE FROM REGENERATED AND NON-REGEN-
ERATED MAIZE LINES IN MERIDIC DIETS.

Larval Weight (mg)

Genotype 8d 12 d Adult Eclosion (d)

MpSWCB-4 R2 28a' 172b 31ab
MpSWCB-4 NR-R2 28a 169b 31ab
(MpSWCB-4 x Mp496 Ro) R2 19b 132c 33a
(MpSWCB-4 x Mp496) F2 30a 204ab 30b
Pio. 304C NR-R2 29a 184ab 30b
Pio. 3192 NR-S2 35a 233a 30b

'Means within a column followed by the same letter do not differ significantly at the 0.05 level (Duncan [1955]
multiple range test).
'NR: non-regenerated controls, R: Resistant, S: Susceptible.


226


June, 1991











Fall Armyworm Symposium '90-Isenhour & Wiseman 227

ance/tolerance screening using tissue culture the selection is actually made at the cell
level by adding the herbicide to the medium. Thus, surviving Ro plants have been
challenged by the given herbicide and should process some degree of resistance. This
is not the case for screening for resistance to insects. The Ro plant has not "survived"
a stressing agent during its development. It will be the Ro plant, or its progeny, that
will be stressed with an insect pest at the whole plant level rather than the cell level.
Viewed in this regard, using tissue culture for resistance to insects is not as efficient
as for herbicide tolerance.
Tissue culture is a very labor intensive procedure, expensive in both time and money.
Somaclonal variants are not always of a positive, or desired, nature. In the case of
maize, we observed a high degree of male sterility in our Ro plants. However, even
with the constraints that we have outlined, somaclonal variation can be a valuable tool
for plant breeding.
When this program was first initiated there were concerns regarding the utility of
a regeneration system based on callus tissue. A system using protoplasts was deemed
more valuable from the standpoint of it being more suitable from gene transfer work.
However, the regeneration of maize from protoplasts is still not as efficient as callus
tissue and successful gene transformation has been achieved using the particle gun to
"shoot" a gene into maize callus (Ludwig et al. 1990).
In summary, we are pleased with being able to isolate somaclonal variants from the
lines that have been regenerated which exhibited increased levels of resistance to leaf-
feeding by the fall armyworm as compared to their non-regenerated parental lines.
However, the regenerated lines should be valuable as "acceptor lines" for gene transfer
efforts by means of the particle gun. If a gene for a specific trait is to be placed in a
maize plant, would it not be more reasonable to use a genotype that is already resistant
to a type of stress? We would encourage individuals engaged in gene transfer of maize
to consider using one of the insect resistant maize lines shown in this study to regenerate
via callus culture.


ACKNOWLEDGMENT

We thank Peggy Goodman, David Atkins, Candace Frederick, Bobby Moody, Johnny
Skinner, and Charles Mullis for their technical assistance in this study. Statistical advice
was provided by Richard Layton.


REFERENCES CITED

ASHLEY, T. R., B. R. WISEMAN, F. M. DAVIS, AND K. L. ANDREWS. 1989. The
fall armyworm: a bibliography. Florida Entomol. 72: 152-204.
CROUGHAN, S. S., AND S. S. QUISENBERRY. 1989. Enhancement of fall armyworm
resistance in bermudagrass through cell culture. J. Econ. Entomol. 82: 236-238.
DIAWARA, M. M., B. R. WISEMAN, D. J. ISENHOUR, AND G. R. LOVELL. 1990.
Resistance in converted sorghums to the fall armyworm. Florida Entomol. 73:
112-117.
DICKE, F. F., AND W. D. GUTHRIE. 1988. The most important corn insects. Corn
and Corn Improvement, Agron. Mono. No. 18, Madison, WI.
DUNCAN, D. B. 1955. Multiple range and multiple F tests. Biometric 11: 1-42.
DUNCAN, D. R., M. E. WILLIAMS, B. E. ZEHR, AND J. M. WIDHOLM. 1985. The
production of callus capable of plant regeneration from immature embryos of
numerous Zea mays genotypes. Planta 165: 322-332.
EARLE, E. D., AND V. E. GRACEN. 1985. Somaclonal variation in progeny of plants
from corn tissue cultures, in R. Henke, K. Hughes, and A. Hollaender (eds)
Propagation of higher plants through tissue culture. Plenum Press, New York.










228 Florida Entomologist 74(2) June, 1991

EVANS, D. A., AND W. R. SHARP. 1986. Applications of somaclonal variation. BIO/
TECH. 4: 528-532.
GREEN, C. E., R. L. PHILLIPS, AND R. A. KLEESE. 1974. Tissue cultures of maize:
initiation, maintenance, and organic factors. Crop Sci. 14: 54-58.
HOROVITZ, S. 1960. Trabajosen march sobre resistencia a insects en el maiz. Agron.
Trop. (Venez) 10: 107-114.
ISENHOUR, D. J., B. R. WISEMAN, AND N. W. WIDSTROM. 1985. Fall armyworm
feeding responses on corn foliage and foliage/artificial diet medium mixtures at
different temperatures. J. Econ. Entomol. 78: 328-332.
LARKIN, P. J., AND W. R. SCOWCROFT. 1981. Somaclonal variation a novel source
of variability from cell culture for plant improvement. Theor. Appl. Genet. 60:
197-214.
LEE, M., J. L. GEADELMANN, AND R. L. PHILLIPS. 1988. Agronomic evaluation of
inbred lines derived from tissue cultures of maize.
LUDWIG, S. R., B. BOWEN, L. BEACH, AND S. R. WESSLER. 1990. A regulatory
gene as a novel visible marker for maize transformation. Science 242: 449-450.
MIHM, J. 1983. Efficient mass-rearing and infestation techniques to fall armyworm,
Spodoptera frugiperda. CIMMYT, El Batan, Mexico.
PESCHKE, V. M., R. L. PHILLIPS, AND B. G. GENGENBACH. 1987. Discovery of
transposable element activity among progeny of tissue culture derived maize
plants. Science 238: 804-807.
SAS INSTITUTE. 1985. SAS user's guide: statistics, version 5. SAS Institute. Cary, NC.
SCOTT, G. E., AND F. M. DAVIS. 1981a. Registration of MpSWCB-4 population of
maize. Crop Sci. 21: 148.
SCOTT, G. E., AND F. M. DAVIS. 1981b. Registration of Mp496 inbred of maize. Crop
Sci. 21: 353.
SPARKS, A. N. 1979. A review of the biology of the fall armyworm. Florida Entomol.
62: 82-87.
WILLIAMS, W. P., F. M. DAVIS, AND B. R. WISEMAN. 1983. Fall armyworm resist-
ance in corn and its suppression of larval survival and growth. Agron. J. 75:
831-832.
WISEMAN, B. R. 1987. Host plant resistance in crop protection in the 21st Century.
Proc. Int. Congress of Plant Protect., Manila Phillippines.
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.
WISEMAN, B. R., R. C. GUELDNER, AND R. E. LYNCH. 1984. Fall armyworm resist-
ance bioassays using a modified pinto bean diet. J. Econ. Entomol. 77: 545-549.
WISEMAN, B. R., W. P. WILLIAMS, AND F. M. DAVIS. 1981. Fall armyworm: Resist-
ance mechanisms in selected corns. J. Econ. Entomol. 74: 622-624.











Fall Armyworm Symposium '90-Yang et al.


229


ACTIVITY OF MAIZE LEAF CUTICULAR LIPIDS IN
RESISTANCE TO LEAF-FEEDING BY THE FALL ARMYWORM

GUANG YANG,' DAVID J. ISENHOUR,2
AND KARL E. ESPELIE'
'Department of Entomology
University of Georgia
Athens, GA 30602

2Department of Entomology
Coastal Plain Experiment Station
University of Georgia
Tifton, GA 31793

ABSTRACT

Genotypes of maize, Zea mays L., known to vary in their resistance to fall armyworm
(FAW), Spodoptera frugiperda (J. E. Smith), were utilized in a study designed to
examine the role that cuticular lipids play in host plant resistance. The surface lipids
were extracted from green and yellow whorl foliage of maize genotypes 'MpSWCB-4',
'Cacahuacintle X's', 'Pioneer 3192' and 'Pioneer X304C'. FAW larvae were reared on
meridic diet to which either the extracted foliage or unextracted foliage had been added.
FAW growth was monitored and shown to be enhanced when larvae were reared on
diet containing foliage from which the cuticular lipids had been removed. Additionally,
FAW growth was inhibited when larvae were fed meridic diet containing cuticular lipid
extracts from foliage of the four maize genotypes.

RESUME

En un studio designado a examiner el papel de los tejidos cuticulares en la resistencia
de plants, se examinaron various genotipos del maiz, Zea mays L., conocidos por su
variablidad en su resistencia al cogollero Spodopterafrugiperda (J. E. Smith). Los lipidos
superficiales fueron extraidos de follaje verede y amarillo de los genotipos "MpSWCB-4,"
Cacahuacintle X's', "Pioneer 3192" y "Pioneer X304C." Larvas de FAW fueron criadas
en dietas meridicas a las cuales se les habia afiadido o suprimido extractos de follaje.
Se observe el crecimiento de FAW, y se demostr6 que acrecent6 cuando la larva fue
criada en dieta con follaje al cual se le substrayeron los lipidos cuticulares. Adicional-
mente, el crecimiento de FAW fue inhibido cuando la larva fue alimentada con una dieta
que contenia extractos de lipidos cuticulares provemientes el follaje de 4 genotipos de
maiz.



The fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), is a serious pest
of maize, cotton, sorghum, peanut and other crops in North and Central America, causing
more than $60 million damage in the southeastern United States per year (Sparks 1986).
The development of sources of resistance to the FAW in crop plants is an economical
and environmentally desirable method to control this pest. The effects of resistant plant
varieties on an individual pest insect are generally specific, cumulative and persistent
(Painter 1968). Due to these characteristics, plant resistance to insects is probably the
most useful of all means of integrated pest control (Wiseman et al. 1983).
The identification of sources of FAW resistance in maize is an important aspect in
the development of a control program for this pest. Several maize genotypes have been










230 Florida Entomologist 74(2) June, 1991

reported to be resistant to FAW (Wiseman & Davis 1979, Wiseman et al. 1981, 1984,
Scott & Davis 1981a, b, Williams et al. 1983, Isenhour et al. 1985, Pair et al. 1986). The
identification of the chemical basis for this resistance would better allow for the incorpo-
ration of these characteristics in breeding programs.
The plant surface, with which an insect pest first comes in contact, plays an important
role in plant/insect interactions (Chapman & Bernays 1989). Many herbivorous insects
seem to be attracted to their potential host plants by visual, olfactory or tactile stimulative
cues based on the physical and chemical characteristics of the plant surface. The cuticular
lipids of a plant can affect many aspects of insect behavior, such as orientation, movement,
oviposition and feeding (Bernays et al. 1976, Chapman 1977, Stork 1980, Stadler 1986,
Woodhead & Chapman 1986, Espelie et al. 1990, Eigenbrode et al. 1990).
Variations in the chemical composition of plant cuticular lipids may result in variable
plant resistance to insect attack (Woodhead 1983, Maloney et al. 1988, Woodhead &
Padgham 1988, Tsumuki et al. 1989). In a few instances, individual classes of cuticular
lipid components have been shown to either stimulate or deter insect herbivory (Klingauf
et al. 1978, Mori 1982, Woodhead 1983). In other cases organic solvent extracts of leaf
material, which contain the cuticular lipids, have been shown to affect the feeding
behavior of herbivorous insects (Blaney & Chapman 1970, Bernays & Chapman 1975,
Varela & Bernays 1988, de Boer & Hanson 1988, Quisenberry et al. 1988). In the present
paper we examine the role that the cuticular lipids of maize foliage may play in resistance
to FAW feeding.

MATERIALS AND METHODS

Plant Material

Four maize genotypes ('MpSWCB-4', 'Cacahuacintle X's', 'Pioneer X304C', and
'Pioneer 3192') were planted during the spring and summer of 1989 in Tifton, Georgia,
using agronomic practices common to the area. No soil or foliar insecticides were utilized.
Separate planting sites were employed for both field and laboratory evaluations. Plants
of each genotype were cut at the 10-12 leaf stage, placed in plastic bags and transported
to the laboratory. Foliar tissue was excised, separated into yellow and green whorl
fractions and either processed immediately for use in laboratory tests or else stored at
-200C.

Field Evaluation of Resistance to FAW

The four genotypes of maize were planted in a randomized complete block design
with 10 replications. Individual plots consisted of 1 row x 3 m in length. Middle-whorl
stage maize plants were artificially infested with FAW at a rate of 30 neonates per plant
on 5 June 1989 using procedures described by Wiseman et al. (1980). Damage to maize
foliage was recorded on the 14th day after infestation according to a 1-9 rating score (1
= most resistant; 9 = most susceptible) (Wiseman et al. 1966, Wiseman & Davis 1979,
Diawara et al. 1990).

Growth of FAW on Diet Containing Maize Foliage or Extracted Maize Foliage

Field grown plants of'MpSWCB-4', 'Cacahuacintle X's', 'Pioneer X304C' and 'Pioneer
3192', in the mid-whorl stage, were excised at the soil level and taken to the laboratory.
Approximately 7 to 10 cm of tissue in the middle of each leaf was discarded. The midrib
of each leaf was also excised and discarded. Fresh green whorl and yellow whorl foliage
was cut into 10-15 cm long pieces and divided into two equal fractions. One fraction was











Fall Armyworm Symposium '90-Yang et al. 231

dipped in redistilled chloroform for 1 min. at room temperature to remove the cuticular
lipids and air-dried (Espelie & Bernays 1989). The other fraction of foliage was not
treated with solvent. Each of these foliar fractions (45 g) was ground and blended with
an artificial bean diet (180 ml) and distributed into 20 diet cups (30 ml) (Mihm 1983,
Wiseman et al. 1984). Each diet cup was infested with a single FAW neonate and
maintained at 280C in an environmentally controlled chamber. Tests were arranged as
a split-split-plot (4x2x2 factorial) design with 20 replications plus a diet check. The
following developmental parameters were recorded: 7 d and 14 d larval weights, days
to pupation, pupal weight and days to adult eclosion.

Growth of FAW on Artificial Diet or on Diet Containing Maize Cuticular Lipids

Fresh green whorl and yellow whorl foliage (50 g) of the four maize genotypes,
obtained in the same manner as described above, were sequentially extracted with 250
ml of each of the following redistilled solvents: hexane, chloroform and methanol. Each
extraction was carried out at room temperature for 1 min. Each extract was concentrated
to a volume of 4 ml in a rotary evaporator at 30C and then stored at -20C. Extracts
were absorbed onto "Celufil-hydrolyzed" (1 g), air-dried for 12 hours at room tempera-
ture, blended into artificial diet (100 ml) and distributed into 30 ml diet cups. Each cup
was infested with a single FAW neonate and kept at 290C. Tests were arranged as a
split-split-plot (4x2x3 factorial) design with 15 replicates plus blank solvent and diet
checks. The solvent checks contained artificial diet to which 1 g of Celufil had been
added after 4 ml of the appropriate solvent (hexane, chloroform, or methanol) had been
removed by air drying. Insect growth was monitored as described above.
All data were analyzed by an analysis of variance and significant mean differences
were separated with the use of Least Significant Difference (LSD) or Waller-Duncan k
ratio t test and significance was determined at the 0.05 level (Waller & Duncan 1969,
SAS Institute 1985, Ott 1988).

RESULTS

Field Evaluation of Resistance to FAW

Field tests of FAW feeding on the whorl stage of maize indicated that there were
major differences between the four genotypes in the 14 d damage ratings for FAW
(Table 1). MpSWCB-4 and Pioneer X304C exhibited strong resistance to FAW feeding,
but Cacahuacintle X's and Pioneer 3192 showed susceptibility to FAW.




TABLE 1. RESISTANCE TO FOLIAGE-FEEDING BY FALL ARMYWORM IN SELECTED
MAIZE GENOTYPES'.

Genotype 14 Day Damage2

'MpSWCB-4' 3.0 0.0d
'Pioneer X304C' 4.8 0.4c
'Cacahuacintle X's' 6.2 0.4b
'Pioneer3192' 7.6 0.5a

'Means (n=10) followed by a different letter are significantly different (P s 0.05); Waller-Duncan k ratio t test;
Waller & Duncan 1969; SAS Institute 1985).
'Rating Score: 1 = most resistant; 9 = most susceptible (Wiseman et al. 1966, Wiseman & Davis 1979, Diawara
et al. 1990).













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Fall Armyworm Symposium '90-Yang et al.


233


Growth of FAW on Diet Containing Maize Foliage or Extracted Maize Foliage

FAW larvae reared on artificial diet containing maize foliage from which the cuticular
lipids had been extracted were larger and developed more rapidly than those larvae
which were grown on diet containing unextracted foliage (Table 2). For ten of the forty
pairs of data (developmental parameters of FAW larvae reared on artificial diet contain-
ing either foliage or extracted foliage), FAW larvae developed significantly better on
the diet containing foliage from which the cuticular lipids had been extracted than they
did on the diet containing unextracted foliage. In most of the remaining instances (24
of 30 data pairs) the FAW larvae developed better on diet with extracted foliage than
they did on diet containing unextracted foliage, but the differences were not significant.
None of the larvae developed significantly better on diet containing unextracted foliage
than those reared on diet containing extracted foliage.
The differences between the developmental parameters of FAW reared on diet with
unextracted and extracted foliage of maize genotype MpSWCB-4 were relatively larger
than those observed for the FAW reared on diet containing foliage from the other
genotypes and these differences were significant for 5 of the 10 data pairs (Table 2).
Those pairs for which the differences were significant included the 7 d weights for the
larvae reared on diet containing both green and yellow whorl MpSWCB-4 foliage. Al-
though there were several differences between FAW growth on green vs. yellow whorl
foliage, these differences were not consistent. There were, however, more instances
where the differences in growth parameters were significant between larvae reared on
diet containing extracted or unextracted green whorl foliage (seven out of ten) than
there were for those larvae reared on diet containing yellow whorl foliage (three out of
ten) (Table 2).
The average developmental parameters of FAW larvae reared on artificial diet con-
taining either maize foliage or maize foliage from which the cuticular lipids had been
removed are shown in Table 3. These values were obtained by combining the values for
green and yellow whorl and for each of the four maize genotypes. Each data point,
therefore, has 160 replicates. FAW reared on diet containing extracted foliage developed
significantly better than those larvae reared on diet containing unextracted foliage as
measured by 4 of the 5 growth parameters (Table 3).

Growth of FAW on Artificial Diet or on Diet Containing Maize Cuticular Lipids

Growth of FAW larvae reared on artificial diet containing the cuticular lipid extracts
of maize foliage was significantly reduced compared to those larvae reared on the control
diets (Table 4). There were no consistent significant differences between the growth of
larvae reared on diet containing hexane extracts of maize foliage compared to those


TABLE 3. RESPONSE OF FALL ARMYWORM FED MERIDIC DIET CONTAINING MAIZE
FOLIAGE OR SOLVENT-EXTRACTED MAIZE FOLIAGE.'

Parameter Foliage Extracted Foliage

7 Day Wt (mg) 15.5 + 9.5a 24.0 13.5b
14 Day Wt (mg) 299.9 107.7a 373.0 140.4b
Days to Pupation 19.7 1.7a 18.6 1. lb
PupalWt (mg) 198.4 40.7a 219.0 39.6a
Adult Eclosion (days) 29.0 1.4a 28.4 1.2b

'Means (n=160) followed by the same letter within a row are not significantly different (P 5 0.05). (Least Significant
Difference; Ott 1988).











234 Florida Entomologist 74(2) June, 1991

TABLE 4. MEAN WEIGHTS (MG) OF FALL ARMYWORM LARVAE AFTER 6 AND 9 DAYS
ON MERIDIC DIET CONTAINING SOLVENT EXTRACTS OF MAIZE FOLIAGE.

Genotype 6DayWt 9DayWt

'MpSWCB-4' 27.3 13.7bc 193.8 65.0ab
'Pioneer X304C' 20.3 10.1d 159.5 62.4c
'Cacahuacintle X's' 21.8 13. d 154.5 + 80. c
'Pioneer 3192' 23.5 11.3cd 170.7 50.7bc
Solvent Check 32.7 + 15.7a 211.6 69.3a
Celufil Check 32.0 11.3ab 203.3 29.7ab

'Means (n=90) within a column followed by the same letter are not significantly different (P s 0.05). (Least
Significant Difference; Ott 1988).

reared on diet containing the subsequent chloroform or methanol extracts of the foliage.
For each genotype the 6 d larval weights were significantly less than those of the larvae
reared on the solvent check which was artificial diet containing Celufil from which an
equal volume of solvent (hexane, chloroform, or methanol) had been air-dried prior to
addition to the diet. The larval 9 d weights were also less for FAW reared on diet
containing the solvent extracts (Table 4). The solvent extracts of MpSWCB-4 foliage
caused the least reduction in growth of the four maize genotypes examined. There were
fewer significant differences observed in the FAW developmental parameters of pupal
weight, days to pupation or days to adult eclosion between larvae fed diet containing
the cuticular lipids compared to those reared on the solvent check diets.

DISCUSSION

Our results indicate that the cuticular lipids of maize play a role in FAW feeding
behavior. Larvae reared on diet containing maize foliage from which the cuticular lipids
had been removed had enhanced growth (Tables 2 and 3). Moreover, the addition of the
extracted cuticular lipids to diet resulted in inhibition of larval growth (Table 4). These
results agree with previous studies which have shown that plant surface lipids affect
herbivory by lepidopteran larvae (Mori 1982, de Boer & Hanson 1988, Maloney et al.
1988, Varela & Bernays 1988, Stoner 1990, Eigenbrode et al. 1990). Recently, FAW
larvae were shown to have reduced growth when they were reared on diet containing
solvent extracts of bermudagrass foliage (Quisenberry et al. 1988).
Previous feeding studies have shown that FAW larvae reared on diet containing
green whorl foliage are larger than those reared on diet with yellow whorl foliage
(Wiseman & Isenhour 1988). In the present study, the extraction of the cuticular lipids
from the maize foliage had a more significant effect upon larvae reared on diet containing
green whorl foliage than it did on those larvae fed diet with the yellow whorl foliage
(Table 2).
Of the four genotypes utilized in this study, MpSWCB-4 exhibited the greatest
resistance to FAW feeding in the field evaluation (Table 1). Larvae reared on diet
containing MpSWCB-4 foliage exhibited the largest increase in growth when the cuticular
lipids were removed from the foliage (Table 2). Although these results might indicate
that the cuticular lipids play a role in the resistance of MpSWCB-4 to FAW attack, the
addition of the extracted lipids from this genotype to larval diet resulted in less growth
inhibition than that which resulted from the addition of the extracts of the other three
genotypes examined (Table 4). The cuticular lipids of maize foliage consist of a variety
of classes of plant wax components (Bianchi et al. 1982, Blaker & Greyson 1988). Future
work will examine the effect that variations (between genotypes and between locations
in the same plant) in specific cuticular lipid components have upon FAW feeding behavior.










Fall Armyworm Symposium '90-Yang et al.


ACKNOWLEDGMENTS

We thank Peggy Goodman and David Atkins for excellent technical assistance and
Professor Joe W. Crim for the generous use of his growth chamber facilities. This work
was supported by a grant from Pioneer Hi-Bred International, Inc. and by HATCH
projects no. 446 and no. 610 allocated to The Georgia Agricultural Experiment Station.

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Florida Entomologist 74(2)


PAIR, S. D., B. R. WISEMAN, AND A. N. SPARKS. 1986. Influence of four corn
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SPARKS, A. N. 1986. Fall armyworm (Lepidoptera: Noctuidae): potential for area-wide
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831-832.
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Florida Entomol. 62: 123-130.
WISEMAN, B. R., F. M. DAVIS, AND J. E. CAMPBELL. 1980. Mechanical infestation
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425-432.
WISEMAN, B. R., F. M. DAVIS, AND W. P. WILLIAMS. 1983. Fall armyworm: larval
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WISEMAN, B. R., R. C. GUELDNER, AND R. E. LYNCH. 1984. Fall armyworm resist-
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Exp. Appl. 47: 15-22.


236


June, 1991










Fall Armyworm Symposium '90-Gross & Pair


237


SEASONAL DISTRIBUTION, RESPONSE TO
HOST DEVELOPMENTAL STAGE, AND
SCREENED-CAGE PERFORMANCE OF
ARCHYTAS MARMORATUS (DIPTERA: TACHINIDAE) AND
OPHIONFLAVIDUS (HYMENOPTERA: ICHNEUMONIDAE) ON
SPODOPTERA FRUGIPERDA (LEPIDOPTERA: NOCTUIDAE)

H. R. GROSS AND S. D. PAIR
Insect Biology & Population Management Research Lab,
U.S. Department of Agric., Agric. Res. Serv.
Tifton, GA 31793

ABSTRACT

Laboratory and field studies with Archytas marmoratus (Townsend) and Ophion
flavidus Brulle were designed to provide a better understanding of their individual and
combined impact on the fall armyworm, Spodopterafrugiperda (J. E. Smith). The highest
percentage of natural parasitism by A. marmoratus and 0. flavidus on S. frugiperda
occurred from late April through mid-June during 1985-1986 near Tifton, Georgia. Ophion
flavidus parasitized 4th, 5th, and 6th instars with equal success, but were minimally
successful in completing development on late 6th instars. Archytas marmoratus were
equally successful in completing development on 3rd, 4th, 5th, and 6th instars. When
S. frugiperda were multiply parasitized, A. marmoratus did not successfully compete
with 0. flavidus. When two A. marmoratus and two 0. flavidus females, or four A.
marmoratus and four O.flavidus females were released against 5-6th instar S. frugiperda
in whorl-stage corn within 1.8 x 1.8 x 1.8 m screened cages, the number of emerged
S. frugiperda adults of the subsequent generation was reduced by 50.6 and 92.1%,
respectively. With the development of economical methods for mass propagation of A.
marmoratus and/or 0. flavidus, will come primary opportunities for advancing biolog-
ically based strategies for managing S. frugiperda.


RESUME

Se establecieron experiments en el laboratorio y en el campo con Archytas mar-
moratus (Townsend) y con Ophion flavidus Brull con el fin de entender su impact
individual y combinado con el cogollero Spodoptera frugiperda (J. E. Smith). Cerca a
Tifton, Georgia, el alto porcentaje de parasitismo natural de A. marmoratus y O.flavidus
en S. frugiperda ocurri6 desde finales de Abril hasta mediados de Junio, 1985-1986.
Ophionflavidus parasite en forma exitosa el estado temprano de los intares, 4to, 5to y
el 6to. Pero tuvo un exito minimo en completar su desarrollo en el estado tardio del 6to
instar. Cuando S. frugiperda fue parasitado en forma multiple, A. marmoratus no
compiti6 con 0. flavidus cuando 2 hembras de A. marmoratus y 2 hembras de 0.
flavidus, o 4 hembras de A. marmoratus y 4 de O. flavidus fueron liberadas contra el
5to- 6to instar de S. frugiperda, el numero de adults de S. frugiperda emergentes fu6
reducido en la generaci6n subsiguiente en un 50.6 a el 92.1%, respectivamente. Con el
desarrollo de los metodos economics para la propagaci6n masiva de A. marmoratus o
de 0. flavidus vendran nuevas oportunidades para un advance en las estrategias de
control biologico para manejo de S. frugiperda.










238 Florida Entomologist 74(2) June, 1991

Archytas marmoratus (AM) (Townsend) and Ophionflavidus (OF) Brull6 are primary
parasitoids of the fall armyworm, Spodopterafrugiperda (J. E. Smith) throughout much
of its range (Raulin & Stehr 1984, Ashley 1979, Pair et al. 1986, Gross & Pair 1986).
Opportunities to advance AM and OF into the forefront of biologically based systems
for the management of S. frugiperda will be hastened as we better understand their
inherent roles within targeted agroecosystems, assist in their conservation, and where
possible release mass-cultured parasitoids to augment feral populations. The current
study examines the seasonal distribution of both parasitoids in south Georgia, their
individual and competitive response to a common host, and their individual and combined
performance when released against larvae of S. frugiperda on whorl-stage corn within
field screen cages.


MATERIALS AND METHODS

The AM colony used in all studies has been maintained in culture since 1981, with
intermittent introductions of adults emerged from larvae of Heliothis zea (Boddie) and
S. frugiperda collected from whorl-stage corn in south Georgia and north Florida. Since
1984, AM has been cultured according to methods of Gross & Young (1984) and Gross
& Johnson (1985) except that sugar cubes and free water were independently provided
to adult flies instead of a sucrose solution. The OF colony was established during 1984
from field collected larvae of S. frugiperda, and has been maintained under conditions
described for AM, except that a 50% honey solution was provided as a food source. S.
frugiperda larvae used in all studies were obtained from a colony housed at the Insect
Biology and Population Management Research Laboratory which was established from
collections near Tifton, Georgia.
Following both naturally occurring field and laboratory induced parasitism of S.
frugiperda larvae by AM and OF, larvae were placed on pinto bean diet (Burton 1969)
within 30 ml plastic diet cups, and allowed to complete development at 27 1C and
13:11; L:D photoperiod. After sufficient time had passed to permit the emergence of
moths and parasitoids, the percentage of parasitism by AM and OF in all studies was
determined from the number of adult parasitoids emerged (and in the case of OF, larvae
that emerged from the host) versus the number of available hosts. No attempt was
made to determine the cause of death of hosts that did not yield adult parasitoids or moths.


Seasonal Distribution

The frequency with which AM and OF attacked naturally occurring, and/or artificially
introduced populations of S. frugiperda in whorl-stage corn was determined weekly at
an experimental farm near Tifton, Georgia from late April through September, 1985
and 1986. 'Pioneer-3192' dent corn was planted on ca. 3-week intervals to assure an
adequate supply of host plants on which S. frugiperda larvae could establish and develop.
During times when heavy natural populations of S. frugiperda were present, seedling
plants were protected from destruction by intermittent application of methomyl insec-
ticide applied at recommended rates. Four 20-m single row plots were infested weekly
starting in mid-April each year with 10-15 newly closed S. frugiperda larvae per plant.
Larvae were applied from a "Bazooka" insect applicator in accordance with methods of
Wiseman et al. (1980). Artificial introductions of larvae were ceased whenever natural
populations reached adequate levels for testing. When larvae reached late 5th-6th instars,
they were recollected, placed on diet, and allowed to complete development. Whenever
possible, 36 larvae per plot or a total of 144 larvae per sampling date were recollected.










Fall Armyworm Symposium '90-Gross & Pair 239

Host/Parasite Responses

The responses of AM and OF were measured following single and/or multiple
parasitism of S. frugiperda larvae. Except where otherwise indicated, S. frugiperda
larvae were exposed to 1 OF sting and/or 2 AM maggots, and then were returned to
cups containing diet to complete development. (Two AM maggots per host larva were
used to increase the probability of successful parasitism). Newly deposited AM maggots
were transferred with a camel's hair brush from a larviposition substrate, onto the body
of the host larvae. All studies involved 6 replications of 12 S. frugiperda larvae each.
In tests 1 and 2, the responses of AM and OF, respectively, to 3rd, 4th, 5th, and 6th
instar S. frugiperda were measured. Tests 3 through 5 were designed to measure the
specific and interspecific responses of AM and OF when exposed to selected developmen-
tal stages of S. frugiperda larvae. In test 3 the responses of AM and OF were measured
following individual and multiple parasitism of 5th instar S. frugiperda. In test 4, the
responses of the subject parasitoids were measured following AM parasitism of 5th
instar S. frugiperda and subsequent OF parasitism of the same larvae when they reached
1-day 6th instar. In test 5, the responses of AM and OF were measured following
individual and/or multiple parasitism of late 6th instar S. frugiperda. Unlike previous
tests wherein 2 AM maggots were provided per host, S. frugiperda larvae in test 5
were exposed to 10-15 AM maggots applied in suspension onto the inside paper cap
covering the 30 ml larvae bearing diet cup, in accordance with methods of Gross &
Johnson (1985). Paired t-tests were used to determine mean differences (P=0.05) among
treatments (Snedecor & Cochran 1967).

Parasite Performance

The screened-cage performance of AM and OF was measured against 5th-6th instar
S. frugiperda in whorl-stage corn during 2 independent trials during 1985. The following
treatments (no. of parasitoids/cage) were replicated 8 times within 1.8 x 1.8 x 1.8-m
screened cages (Chicopee Manufacturing Company, Gainesville, Georgia 30503-2587)
during May and June 1985: 1) 4 AM females, 2) 4 pairs of OF, 3) 4 AM females plus 4
pairs of OF, and 4) control-no parasitoids released. The same treatment arrangements
were evaluated during August and September 1985, but with 2 instead of 4 parasitoids
used in each case. Three to 4 days before plants were artificially infested, the interior
of all cages was sprayed with methomyl insecticide from a 11.4 liter compressed air
sprayer at recommended rates, to remove naturally occurring parasitoids, predators,
and host larvae. Approximately 10 newly closed S. frugiperda larvae were introduced
per plant with a 'Bazooka' applicator when the 'Silver Queen' sweet corn was 6-8 leaf
stage (May trial) and the 'Pioneer-3369A' dent corn was 8-9 leaf stage (August trial).
Plants averaged 23.3 and 19.1 per cage, respectively, in the May and August trials.
Female parasitoids were reproductively mature when released within cages between
8-900 h. Male OF were released concurrently with females because the laboratory mating
of OF is not as assured as that of AM. (Unmated female OF produce only male progeny.)
During the period when parasitoids and host larvae were present, a 12 x 12 cm square
of cotton batting placed at the top northwest corner of each cage was maintained moist
with a 10% sucrose solution to serve as a food source for parasitoids.
S. frugiperda larvae were allowed to complete development and pupate within the
cages without further intervention. Beginning ca. 10 days after larvae had begun to
leave the plants to pupate, cages were examined 2-3 times weekly for the presence of
S. frugiperda, AM and OF adults. Cages were examined until no moths or parasitoids
were found on 2 successive sampling dates. ANOVA and Waller-Duncan k-ratio t-test
were used to separate mean differences (P= 0.05) among treatments (SAS Institute 1985).










Florida Entomologist 74(2)


RESULTS AND DISCUSSION

Seasonal Distribution

The mean percentage AM and OF parasitism of S. frugiperda larvae recovered from
whorl stage corn near Tifton, GA during 1985 and 1986 is presented in Figure 1. Mean
percentage of parasitism for both parasitoids peaked during late April through mid-June,
generally when naturally occurring populations of S. frugiperda in south Georgia are
typically at their seasonal lows. It seems probable, therefore, that the early season
survival of both parasitoid species is dependent on their access to alternate hosts. AM
has been reported from 10 other hosts (Arnaud 1978) and is a well known early season
parasitoid of H. zea (Gross et al. 1976). Krombein et al. (1979) cite 3 other hosts of OF,
also including H. zea. Two primary, apparently generational peaks of AM parasitism
occurred during April/early May, and during the 3rd week of June when the mean
percentage of parasitism reached the seasonal high of 29.2%. Three primary peaks of
OF parasitism occurred from late April through mid-June, with two occurring in syn-
chrony with those of AM. The highest mean percentage parasitism (19.5%) by OF also
occurred during the 3rd week of June.
Laboratory and field efforts to induce diapause in the larval and pupal stages of AM
have been unsuccessful (H. R. Gross, unpublished). Therefore, early season parasitism
by AM likely results from migrants originating further south, or from adults which have
successfully overwintered in south Georgia. Mean longevity of AM females was reported
to be 72.8 days at 21C (Hughes 1975). It is therefore not improbable that AM adults
are capable of overwintering. No data are available to suggest the strategy used by OF
to overwinter.


19JUN


1v# Iv,1 I avluuj
Archytas marmol














-I
]----


08AUG


ratus


27SEP


16NOV


rrkiM flNaiLI m


Fig. 1. Seasonal distribution of Archytas marmoratus and Ophion flavidus on
Spodoptera frugiperda in whorl stage corn near Tifton, Georgia, 1985-1986.


30


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June, 1991











Fall Armyworm Symposium '90-Gross & Pair


Percentage parasitism of S. frugiperda by AM and OF from July through September
was generally below 10%, and was comparable to that reported by Rohlfs and Mack
(1985) for southern Alabama. A late season (September and October) resurgence in
parasitism by AM has been frequently observed (H.R.G. and S.D.P.) in south Georgia
and may contribute to an overwintering adult generation.

Host/Parasite Responses

The mean percentage AM parasitism did not differ significantly among 3rd, 4th, or
5th instars of S. frugiperda in test 1 (Table 1). Rohlfs & Mack (1985) similarly reported
that AM was recovered from field collections of small, medium and large larvae of S.
frugiperda in ca. equal percentages. Hughes (1975), however, found that although sur-
vival of AM maggots penetrating 2nd, 3rd, and 4th instar H. virescens (F.) was compar-
able, the survival of maggots penetrating 5th instars was significantly higher.
The mean number of OF adults emerged following parasitism of S. frugiperda larvae
was significantly higher from 4th and 5th instars than from 3rd or late 6th instars (test
2, Table 2). However, when based on the number of emerged OF larvae (from 6th instar
S. frugiperda) that failed to pupate, the rates of parasitism of 4th, 5th, and 6th instars
did not differ significantly. The late 6th instars used in the study may have provided
inadequate time and nutrition for OF larvae to complete development before host pupa-
tion. Subsequent independent studies conducted as described for Test 2 revealed that
the mean percentage emergence of OF adults following parasitism of 1 and 2 day 6th
instars was 77.8 and 66.3 (n=144), respectively, thus affirming that early to mid 6th
instars were also highly susceptible for parasitism and allowed complete development
by OF.
Because the primary development in AM larvae was delayed until after host pupation
(Hughes 1975), they were not able to compete with OF either when both parasitized


TABLE 1. RESPONSE OF A. MARMORATUS TO SELECTED INSTARS OF S. FRUGIPERDA.

Mean Percentage Adult A. marmoratus Emergence"

Instar Parasitized

3rd 4th 5th 6th

58.3 75.0 65.3 76.4

'Two newly deposited A. marmoratus maggots were transferred onto the body of each larva.
2Means are not significantly different (P > 0.05) by ANOVA (SAS Institute, 1985).


TABLE 2. RESPONSE OF 0. FLAVIDUS TO SELECTED INSTARS OF S. FRUGIPERDA. .2

Instar Parasitized

Late
3rd 4th 5th 6th

R % Parasitized8 20.8a 87.5b 88.9b 75.0b
x% Adult Emergence 20.8a 86. b 84.7b 25.0a

'Larvae were exposed to 1 0. flavidus sting.
'Means followed by letters in common across columns are not significantly different (P 0.05) according to
Waller-Duncan k-ratio t-test (SAS Institute, 1985).
"Data based on emergence of 0. flavidus larvae from host larvae.











Florida Entomologist 74(2)


5th instar S. frugiperda (test 3, Table 3A), or when OF parasitism was delayed until
larvae reached 1 day 6th instar (test 4, Table 3B). The only apparent opportunity that
AM had to survive in appreciable numbers following multiple parasitism of S. frugiperda
larvae occurred when OF parasitized larvae were nearing pupation (test 5, Table 3C).
These data suggest that AM and OF are, in general, independent, complementary
mortality agents of S. frugiperda and that AM provides the final opportunity for a larval

TABLE 3. MEAN PERCENTAGE EMERGENCE OF A. MARMORATUS AND O. FLAVIDUS
ADULTS FOLLOWING SINGLE AND/OR MULTIPLE PARASITISM OF
SELECTED INSTARS OF S. FRUGIPERDA.

A Percentage of Emerged Adults'

A. marmoratus O.flavidus

Single Multiple Single Multiple
parasitism parasitism parasitism parasitism

70.8 8.3 84.7 84.7

2 diff. = -62.5 SEM 4.69 2 diff. = 0.03 SEM 4.31
t = -13.312 t = 0.01NS

'5th instar S. frugiperda exposed to 1 0. flavidus sting and/or 2 A. marmoratus maggots.
'Mean difference between treatments is significant (P s 0.05) according to paired t-test (Snedecor and Cochran
1967).


B Percentage of Emerged Adults'

A. marmoratus O.flavidus

Single Multiple Single Multiple
parasitism parasitism parasitism parasitism

62.5 12.5 70.8 72.7

x diff. = -58.3 SEM 6.81 diff. = 9.70 SEM 10.64
t = -8.562 t = 0.91 NS

'5th instar S. frugiperda exposed to 2 A. marmoratus maggots and/or 1 day 6th instar exposed to 1 0.flavidus sting.
'Mean difference between treatments is significant (P 0.05) according to paired t-test (Snedecor and Cochran
1967).


C Percentage of Emerged Adults'

A. marmoratus O.flavidus

Single Multiple Single Multiple
parasitism parasitism parasitism parasitism

94.4 41.7 55.5 38.9

x diff. = -52.7 SEM 6.35 2 diff. = -16.7 SEM 9.62
t =-8.312 t = 1.73NS

'Late 6th instar S. frugiperda exposed to 1 0. flavidus and/or 10-15 A. marmoratus maggots.
'Mean difference between treatments is significant (P s 0.05) according to paired t-test (Snedecor and Cochran
1967).


June, 1991










Fall Armyworm Symposium '90-Gross & Pair 243

parasitoid to stay the development of the subsequent generation. An additional oppor-
tunity to reduce pupal populations of S. frugiperda is provided by the parasitoid
Diapetimorpha introita (Cresson), and an array of vertebrate and invertebrate predators
(Pair & Gross 1984, 1989).

Parasite Efficiency
The mean percentage reduction in the cumulative emergence of S. frugiperda adults
following larval exposure in whorl stage sweet corn to 4 pairs of OF, 4 AM females,
and 4 AM females plus 4 pairs of OF per screened cage was 78.9, 81.6, and 92.1%,
respectively (Figure 2). Although all treatment means were significantly lower than
that of the control, they did not differ significantly from one another. The mean percent-
age reduction in the cumulative emergence of S. frugiperda adults following larval
exposure in whorl stage dent corn to 2 pairs of OF, 2 AM females, and 2 AM females
plus 2 pairs of OF per screen cage was 15.2, 38.0, and 50.6%, respectively (Figure 3).
The same pattern of response was common to both tests, with the combined effect of
both parasitoids yielding the greatest impact on S. frugiperda populations, thus support-
ing laboratory observations that AM and OF are complementary mortality agents.
Although differences in percentage reduction in S. frugiperda adults caused by OF and
AM were not significant, in each trial the effect of AM tended to be greater. Although
attempts were made to find and record parasitoids emerging within cages, in neither
test did adequate numbers emerge to provide meaningful data. The reasons) for the
limited parasitoid emergence is unknown, but the lower percentage of natural parasitism

5 4 AM a
4 OF 4 OF c
-- 4 AM 4 OF & 4 OF 3 /
4 Control
4


E3
a> /

2 /

b
El


01' I br
29MAY 08JUN 18JUN 28JUN

DATE

Fig. 2. Mean cumulative emergence of S. frugiperda adults following a single release
of A. marmoratus and/or 0. flavidus at indicated rates against 5th and 6th instar S.
frugiperda in 'Silver Queen' sweet corn, Tifton, Georgia, May-June, 1985. Mean total
numbers of moths emerged followed by letters in common are not significantly different,
by Waller-Duncan k-ratio t-test (P S 0.05), (SAS Institute 1985).









Florida Entomologist 74(2)


10

o
C8


E6
w5


S3



0 1
0 -27
27AUG


- 2 AM 9
S2 OF 9, 2 OF c
2 AM 9, 2 OF & 2 OF c
control


06SEP


16SEP


DATE


Fig. 3. Mean cumulative emergence of S. frugiperda adults following a single release
of A. marmoratus and/or 0. flavidus at indicated rates against 5th and 6th instar S.
frugiperda in 'Pioneer 3369A' dent corn, Tifton, Georgia, August-September, 1985. Mean
total numbers of moths emerged followed by letters in common are not significantly
different by Waller-Duncan k-ratio t-test (P < 0.05) (SAS Institute 1985).

by AM and OF that occurred from mid-June through mid-September (Figure 1) may
reflect lowered adult parasitoid emergence due to the influence of these same mortality
factors.
The mass propagation and release ofparasitoids against incipient seasonal populations
of lepidopterous pests may provide the greatest opportunity to delay, if not stop, the
geometric expansion of subsequent generations that insure economic crop damage and
massive intervention with chemical pesticides. With the development of economical
methods for mass-propagating quality A. marmoratus and/or 0. flavidus will come
primary opportunities for advancing biological strategies for managing S. frugiperda.

ACKNOWLEDGMENTS
The authors gratefully acknowledge the assistance of biological technician Raydene
Johnson.
This article reports the results of research only. Mention of a proprietary product
does not constitute an endorsement or the recommendation for its use by the USDA.

REFERENCES CITED
ARNAUD, PAUL H., JR. 1978. A host-parasite catalog of North American Tachinidae
(Diptera). USDA Misc. Publ. No. 1319, 860 p.
ASHLEY, T. R. 1979. Classification and distribution of fall armyworm parasites. Florida
Entomol. 62: 114-123.


26SEP


June, 1991











Fall Armyworm Symposium '90-Gross & Pair 245

BURTON, R. L. 1969. Mass rearing of the corn earworm in the laboratory. USDA-ARS-
33-134.
GROSS, H. R., AND R. JOHNSON. 1985. Archytas marmoratus (Diptera: Tachinidae):
Advances in large-scale rearing and associated biological studies. J. Econ. En-
tomol. 78: 1350-1353.
GROSS, H. R., AND 0. P. YOUNG. 1984. Archytas marmoratus (Diptera: Tachinidae):
Screened-cage evaluations of selected densities of adults against larval populations
of Heliothis zea and Spodoptera frugiperda (Lepidoptera: Noctuidae) on whorl
and tassel stage corn. Environ. Entomol. 13: 157-161.
GROSS, H. R., AND S. D. PAIR. 1986. The fall armyworm: Status and expectations
of biological control with parasitoids and predators. Florida Entomol. 69: 502-515.
GROSS, H. R., JR., B. R. WISEMAN, AND W. W. MCMILLIAN. 1976. Comparative
suitability of whorl stages of sweet corn for establishment by larvae of the corn
earworm. Environ. Entomol. 5: 955-958.
HUGHES, P. S. 1975. The biology ofArchytas marmoratus (Townsend). Ann. Entomol.
Soc. Am. 68: 759-767.
KROMBEIN, K. V., P. D. HURD, JR., D. R. SMITH, AND B. D. BURKS. 1979. Catalog
of Hymenoptera in America North of Mexico. Vol. 1 Symphyta and Apocrita
(Parasitica). (p. 698). Smithsonian Institution Press, Washington, D.C. 1198 pp.
PAIR, S. D., AND H. R. GROSS. 1984. Field mortality of pupae of the fall armyworm,
Spodoptera frugiperda (J. E. Smith), by predators and newly discovered
parasitoid, Diapetimorpha introita. J. Georgia Entomol. Soc. 19: 22-26.
PAIR, S. D., AND H. R. GROSS. 1989. Seasonal incidence of fall armyworm (Lepidopt-
era: Noctuidae) pupal parasitism in corn by Diapetimorpha introita and Cryptus
albitarsis (Hymenoptera: Ichneumonidae). J. Entomol. Sci. 24: 339-343.
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 southern United States and northeastern
Mexico. Environ. Entomol. 15: 342-348.
RAULIN, F. W., AND F. W. STEHR. 1984. Revision of the genus Archytas (Diptera:
Tachinidae) for America North of Mexico. Entomol. Soc. Am. Misc. Pub. No. 58.
73 pp.
ROHLFS, W. M. III, AND T. P. MACK. 1985. Seasonal parasitism rates, host size and
adult emergence patterns of parasitoids of the fall armyworm, Spodoptera
frugiperda (J. E. Smith) with emphasis on Ophionflavidus Brull6 (Hymenoptera:
Ichneumonidae). Ann. Entomol. Soc. Am. 78: 217-220.
SAS INSTITUTE. 1985. SAS User's Guide. SAS Institute, Cary, North Carolina.
SNEDECOR, G. W., AND W. G. COCHRAN. 1967. Statistical Methods. pp. 93-99. Iowa
State Univ. Press, Ames, Iowa.
WISEMAN, B. R., F. M. DAVIS, AND J. E. CAMPBELL. 1980. Mechanical device used
in fall armyworm plant resistance programs. Florida Entomol. 63: 425-432.










246 Florida Entomologist 74(2) June, 1991

NOCTUIDONEMA GUYANENSE: AN ECTOPARASITIC
NEMATODE OF FALL ARMYWORM ADULTS
IN THE TROPICAL AMERICAS

C. E. ROGERS, A. M. SIMMONS, AND 0. G. MARTI
Insect Biology & Population Management Research Lab,
U.S. Department of Agric., Agric. Res. Serv.
Tifton, GA 31793

ABSTRACT

Noctuidonema guyanense Remillet and Silvain is an ectoparasitic nematode that
attacks the adult stage of Spodopterafrugiperda (J. E. Smith) and a few other species
of Noctuidae. The nematode is widely distributed in the neotropics from French Guiana
to Florida through the Caribbean Basin, and from Colombia, South America to Texas,
North America through mainland countries. Both incidence and intensity of host infes-
tation by N. guyanense are greater in Caribbean Basin countries than in the mainland
countries. Low relative humidity and low and high temperature adversely impact N.
guyanense population dynamics in the laboratory. Infestation by N. guyanense exhibits
an insidious, chronic pathogenicity in hosts. The biology of N. guyanense and its acute
pathogenicity and mechanics of transmission among hosts remain virtually unknown.

RESUME

Noctuidonema quyanense Remillet y Silvain es un nematodo ectoparasitico que ataca
el estado adulto de Spodoptera frugiperda (J. E. Smith) y otras pocas species de la
familiar Noctuidae. Este nematodo esta ampliamente distribuido en los neotropicos desde
la Guyana Francesa hasta Florida, a traves de la Cuenca del Caribe y desde los paises
continentales desde Colombia, America del Sur, hasta Texas, America del Norte. Tanto
la incidencia como la intensidad de la infestaci6n del hospedero por N. guyanense son
mayores en los paises de la Cuenca del Caribe que en paises continentales. La baja
humedad relative y las temperatures bajas y altas afectan adversamente la dinamica de
poblaciones de N. guyanenense en el laboratorio. N. guyanense exhibe una patogenicidad
cronica e insidiosa en sus hospederos. Se desconoce la biologia de N. guyanense y su
patogenicidad aguda asf como los mecanismos de transmisi6n entire hospederos.




Noctuidonema guyanense Remillet and Silvain (Nematoda: Aphelenchoididae), dis-
covered attacking Spodoptera androgea (Cramer) in French Guiana in 1982 (Silvain
1984), was recently described as a new genus and species of insect-parasitic nematode
(Remillet & Silvain 1988). In French Guiana, N. guyanense is most commonly found on
adults of the fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noc-
tuidae), a few other Spodoptera species, Anicla infecta (Ochsenheimer), and Leucania
spp. (Remillet and Silvain 1988). Although several species of parasitic and predaceous
arthropods and a species of nematode are known to attack the larval stages of the fall
armyworm (Ashley 1979, Andrews 1988), N. guyanense is the first known metazoan
parasite of the moth stage. A closely related species of nematode, Acugutturus
parasiticus Hunt, has been reported from the adult stage of the American cockroach,
Periplaneta americana (L.), in St. Lucia, West Indies (Hunt 1980).
The economic importance of the fall armyworm to agriculture in the tropical Americas
necessitates that N. guyanense be investigated as a potential biological control agent
for inclusion in management strategies. This paper reports the results of preliminary











Fall Armyworm Symposium '90-Rogers et al.


research designed to delineate the host-range, distribution, bionomics, and pathogenicity
of N. guyanense.

MATERIALS AND METHODS

Host-Range

Insects to be examined for infestation by N. guyanense were collected by sweeping
vegetation in a variety of habitats, from pheromone traps, and from a 1.5 x 2.0 m white
sheet illuminated by UV light at night. Non-lepidopterous arthropods were placed after
collection into individual vials containing 10% formalin for preservation, storage, and
subsequent microscopic examination. Specimens were identified to family by consulting
keys and descriptions in Borror & DeLong (1964) and Jacques (1947).
Collected Lepidoptera were killed immediately by placing them in a kill jar charged
with ethyl acetate. Abdomens of dead moths were excised at their juncture with the
metathorax and placed into individual vials containing 10% formalin for fixing, preserva-
tion, storage, and subsequent microscopic examination. Abdomens ofmacro-Lepidoptera
(notably, large sphingids) were excised approximately 1/3 from the posterior end and
handled as stated above. Adult Lepidoptera minus their abdomens were pinned and
identified with numbered labels corresponding with their respective abdomens.
Most noctuids collected in French Guiana were identified by comparing adults with
reference specimens that have been identified at the British Museum of Natural History,
London, and maintained at ORSTOM Center, Cayenne, French Guiana. Other Lepidopt-
era were identified by comparing collected specimens with voucher specimens housed
in the U.S. National Museum, Washington, DC, and from descriptions provided in
Borror & DeLong (1964), Covell (1984), Hodges (1983), Howe (1975), Kimball (1965),
and Watson & Whalley (1975). Infrequently collected non-hosts of N. guyanense were
identified only to family.
Collections were made daily in northeastern French Guiana from July 16 through
August 11, 1987. Collections also were made periodically from March-September, 1988,
near Belle Glade, Brooksville, Homestead, and northern Everglades Park in Florida,
and near Tifton, Georgia.
The identity of Noctuidonema was determined initially by comparing collected speci-
mens with voucher specimens on file at ORSTOM, French Guiana, and subsequently
from descriptions in Remillet & Silvain 1988.


Distribution

Male fall armyworm moths were collected in pheromone traps (International
Pheromone Systems, Merseyside, England) from late Fall 1987 through Summer 1988
in several locations from Suriname to Belle Glade, Florida in the Caribbean Basin, and
from Bogota, Colombia to Weslaco, Texas through the mainland tropics (Hartstack cone
traps were used in Texas). Pheromone traps were baited with a commercial pheromone
(Terochem Laboratories, Ltd., Alberta, Canada) to attract males, and contained dichlor-
vos to quickly kill entrapped moths. The abdomen from about 100 moths captured at
each location was separated from the thorax and each placed into a separate vial contain-
ing 10% formalin. The vials with abdomens from each location were shipped to Tifton,
Georgia for subsequent examination for nematodes. The number of juvenile and adult
N. guyanense infesting moths and percent of moths infested were recorded for each of
the 22 locations.
The incidence and intensity of fall armyworm parasitization by N. guyanense at each
location were recorded. Data were analyzed by an analysis of variance test, and signif-


247











Florida Entomologist 74(2)


June, 1991


icantly different means (P < 0.05) were separated by the Waller-Duncan k-ratio t-test
(SAS Institute 1985).

Laboratory Biology

Laboratory studies were conducted to measure the effects of temperature and relative
humidity on N. guyanense populations infesting the fall armyworm. To determine the
effects of relative humidity on population changes of N. guyanense, 70 infested fall
armyworm males were caged and held at 27 1.5C in darkness at either 20% RH or
80% RH. After being held for 24 and 48 h, nematode populations were subsampled by
removing and examining 10 and 5 moths from the cages, respectively. Abdomens from
the moths were removed and placed in 10% formalin to kill and preserve the nematodes
until they could be counted with the aid of a dissecting microscope. As each moth
abdomen was examined, the number and stage of the nematode were recorded.
The effect of temperature on population processes of N. guyanense was studied by
caging 70 infested males of the fall armyworm in darkness at 80% RH and a constant
temperature of 7, 12, 17, 22, 27, 32, or 37 1.50C for 24 h. After 24 h, the abdomens
from 15 randomly selected moths from each temperature were preserved in 10% formalin
and examined via a microscope to count the number of juvenile and adult nematodes
infecting each moth.
The success of nematode transfer during host mating was studied by pairing field-col-
lected male fall armyworms with laboratory-reared, virgin females in 3.8-liter cartons.
Fall armyworm pairs were held at 220C and 80% RH in darkness for 24 h. After 24 h,
the abdomens from 10 male and 10 female moths were excised and preserved in 10%
formalin for microscopic examination. The number of juvenile and adult nematodes
recovered from the 10 male and female moths was compared with the number recovered
from 5 pairs of moths sacrificed at the beginning of the test. Data for the population
dynamics study were analyzed by an analysis of variance, with significantly different
means being separated by the Waller-Duncan k-ratio t-test (SAS Institute 1985).

Pathogenicity

Abdomens from freshly collected moths were removed, fixed in 10% formalin, and
stored for subsequent examination. Male S. frugiperda obtained from the Insect Biology
and Population Management Research Laboratory (IBPMRL) colony were used as nonin-
fested controls. Abdomens selected for sectioning were dehydrated through ethanol
(30-100%) and infiltrated, oriented, and embedded in Sorvall embedding medium. Trans-
verse and longitudinal sections were cut at 2-6 um with hand-broken glass Ralph knives.
Sections were stained in borate-buffered 0.5% Toluidine blue for 1-3 min, rinsed in
water, cleared in xylene, and mounted in Permount. In some specimens, portions of
the posterior cuticle were dissected, dehydrated, cleared, and mounted without staining
directly into Permount as whole mounts. Slides of sections or whole mounts were
examined with a Nikon Optiphot photomicroscope using brightfield illumination or
Nomarski differential interference contest optics and photographed with Kodak Tech-
nical Pan film.

RESULTS AND DISCUSSION

Host-Range

Lepidoptera abdomens examined for N. guyanense included 1,859 specimens repre-
senting 150 species in 21 families from Florida, and 1,279 specimens representing 189














Fall Armyworm Symposium '90-Rogers et al.


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Florida Entomologist 74(2)


June, 1991


species and 19 families from French Guiana. In French Guiana, moths from 5 families
of Lepidoptera harbored N. guyanense, although parasitization in Lasiocampidae,
Notodontidae, Pyralidae, and Sphingidae occurred in only a single species of each family
(Rogers et al. 1990a). Twenty-five species among 20 genera of Noctuidae harbored N.
guyanense in French Guiana, with the incidence of infestation ranging from 10 to 51%.
The intensity of infestation in French Guiana ranged from 7 to 43 nematodes per host.
In Florida, infestation of Lepidoptera by N. guyanense was confined to 6 species of
Noctuidae, in which 19% of the species had an average infestation rate of 32%, harboring
an average of 8 adult and 46 juvenile nematodes per host (Rogers et al. 1990b).
Spodoptera frugiperda, Spodoptera latifascia (Walker), Mocis latipes (Guenee), A.
infecta, and Argyrogramma verucca (F.) were infested by N. guyanense in both French
Guiana and in the southeastern United States (Table 1). Also, in both continents, N.
guyanense infested multiple species of Spodoptera and Mocis. Within Noctuidae, infes-
tation was limited to species of subfamilies Amphipyrinae, Catocalinae, Noctuinae, and
Plusiinae in the United States, and to subfamilies Amphipyrinae, Catocalinae,
Hadeninae, Noctuinae, Plusiinae, and Sarrothripinae in French Guiana. A more detailed
discussion of the N. guyanense-host relationships may be found in Rogers et al. (1990a,
1990b).
Of extreme importance when contemplating possible augmentative activities with
an entomophagous agent of unknown host range is its impact on non-target and/or
beneficial arthropods. Consequently, we identified as many of the non-infested Lepidopt-
era as possible to species, and non-lepidopteran arthropods to family. Lepidoptera not
harboring N. guyanense included 121 species among 22 families in southeastern United
States, and 150 species among 19 families in French Guiana (Table 2). Moths of Noctuidae
were the most common representatives among the Lepidoptera collected in both coun-
tries. However, only 15% and 19% of the noctuid species harbored N. guyanense in
French Guiana and southeastern United States, respectively. Recently, N. guyanense
has been collected from the black cutworm, Agrotis ipsilon (Hufnagel) in Vera Cruz,
Mexico, and Agrotis subterranea (F.) in the southeastern United States (Simmons &
Rogers 1990a).
Noctuidonema guyanense was not found on any of the 466 non-lepidopterous speci-
mens among 171 species of 72 families of Insecta or Arachnida examined from southeast-
ern United States (Rogers et al. 1990b), nor from the 514 non-lepidopterous specimens
among 171 species of 78 families of Insecta, Arachnida, and Diplopoda from French
Guiana (Rogers et al. 1990a) (Table 3). Hence, it appears that hosts ofN. guyanense are
limited to Lepidoptera, among which a few species of Noctuidae serve as the predominant
hosts. No known beneficial species of either Lepidopera or non-lepidopterous arthropods
harbored N. guyanense in either French Guiana or southeastern United States.


Distribution

Noctuidonema guyanense infested fall armyworm males wherever they were col-
lected in the American tropics from November 1987-August 1988. Moths collected in
Caribbean Basin countries usually had a greater incidence of infestation by a higher
number of nematodes than moths collected in mainland countries (Table 4). More than
80% of the fall armyworm males collected in Martinique and Suriname were infected.
Within the Caribbean Basin, low populations of N. guyanense were found in the Virgin
Islands and Bahama. The incidence of moth infestation in the mainland countries was
low in Colombia, South America and south Texas, North America. From 20 to 47% of
S. frugiperda males collected from Mexico through Central America harbored N.
guyanense. Infested moths from mainland countries harbored an average of 26 N.
guyanense per host, while infected moths from the Caribbean Basin harbored an average











Fall Armyworm Symposium '90-Rogers et al. 251

TABLE 2. NON-INFESTED LEPIDOPTERA EXAMINED FOR NOCTUIDONEMA
GUYANENSE.1

No. species examined No. specimens examined

French Southeast French Southeast
Family Guiana U.S. Guiana U.S.

Apatelodidae 1 14 -
Arctiidae 4 8 83 99
Ctenuchidae 7 3 31 28
Danaidae 1 5
Drepanidae 1 10 -
Geometridae 8 9 35 34
Hesperiidae 2 6 4 9
Lasiocampidae ? 1 13 3
Limacodidae 2 7
Lycaenidae 1 1 1 1
Lymantriidae ? ? 32 2
Megalopygidae ? 1 4 2
Noctuidae 121 64 446 684
Notodontidae 5 5 104 8
Nymphalidae 2 2 13 7
Papilionidae 1 1
Pieridae 5 11
Pseudosphingidae 1 2 -
Pterophoridae 1 1 -
Pyralidae 12 10 150 69
Saturniidae 1 3 16 4
Satyridae 1 1
Sphingidae 4 11 11 27
Tineidae 2 8
Tortricidae 2 1 2 2
Yponomeutidae 1 2

'A listing of species examined is available on request.


of 56 N. guyanense per host. Across all collection sites, nematode populations were
greatest in April 1988, when 80% of S. frugiperda males were infested with an average
of 191.4 N. guyanense per host.

Laboratory Biology

As a Pan-neotropical ectoparasite of Lepidoptera adults, N. guyanense populations
should be impacted by extremes in temperature and relative humidity; laboratory exper-
iments illustrated this to be the case. At 27C, populations of N. guyanense infecting
S. frugiperda males increased significantly at 80% RH but changed little at 20% RH
(Table 5). Also, the juvenile to adult ratio was significantly higher (P < 0.05) at 80%
than at 20% RH. Even a short period of low RH may have a detrimental affect on N.
guyanense populations.
A temperature of less than 170C or greater than 370C severely impacted populations
of N. guyanense held at 80% RH (Table 6). A temperature of 32C seemed to be optimum
for N. guyanense development, with a juvenile to adult female ratio of 14 to 1.
Pairing of infested, field-collected S. frugiperda males with non-infested, laboratory-
reared females indicated a significant population shift of N. guyanense during host














June, 1991


Florida Entomologist 74(2)


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Fall Armyworm Symposium '90-Rogers et al.


TABLE 4. DISTRIBUTION AND PARASITIZATION OF THE FALL ARMYWORM BY NOC-
TUIDONEMA GUYANENSE IN THE TROPICAL AMERICAS

% FAW X No. nematodes
Country infested per host

Caribbean Basin
Suriname 88.0 215
Trinidad 41.6 36
Grenada 68.4 44
Martinique 82.8 52
Commonwealth of Dominica 71.3 40
Virgin Islands 1.0 34
Puerto Rico 35.0* 38*
Cayman Island 71.4 110
Bahama 10.1 13
Bermuda 26.0 12
Mainland
Colombia 3.0 12
Panama 46.8 39
Costa Rica 47.4 38
El Salvador 39.8 17
Honduras 31.4* 28*
Belize 36.0 35
Mexico 20.1* 20*
Southeast U.S. 41.8 21
South Texas 8.7 17

*Data from two locations within country.


mating. Pre-copulatory populations of N. guyanense on infested male moths was com-
prised of 63% juveniles and 37% adults. Following a single copulation of its host, N.
guyanense populations on a newly infested female averaged 63% adults and 37%
juveniles. Juvenile transfer during host mating averaged 11%, compared with 31%
transferral of adult nematodes (Simmons & Rogers 1990b).

Pathogenicity

Noctuidonema guyanense may be found around host genitalia, intersegmental areas
between abdominal segments, and in tympanic cavities. Most commonly, the nematode


TABLE 5. INFLUENCE OF RELATIVE HUMIDITY ON NOCTUIDONEMA GUYANENSE
POPULATIONS IN THE LABORATORY AT 27C.

X No. nematodes per moth
Relative Juveniles/
Humidity Total % Juvenile Y nematode

24 hrs.
20% 19a 67 5a
80% 238 b 74 9b
48 hrs.
20% 25a 84 4a
80% 392b 84 11b










Florida Entomologist 74(2)


TABLE 6. INFLUENCE OF TEMPERATURE ON NOCTUIDONEMA GUYANENSE POPU-
LATIONS IN THE LABORATORY AT 80% RELATIVE HUMIDITY.

X No. nematodes per moth
Juveniles/
Temperature C Total Adult % Juvenile 9 nematode

7 18 9 51 1
12 29 10 67 5
17 25 11 56 3
22 52 15 72 7
27 104 21 80 7
32 239 81 66 14
37 8 5 34 <1


is observed on the anterior margin of the eighth abdominal segment and its associated
intersegmental membrane. Microscopic examination of stained sections and whole
mounts of infested S. frugiperda suggests several insiduous, chronic pathologies as-
sociated with infestation by N. guyanense (Marti et al. 1990). Infested moths frequently
exhibit external, irregular dark spots on the cuticle, indicating oxidation of an exudate
from probable stylet penetration sites (Fig. 1). Within the intersegmental spaces of
infested hosts, the cuticle is frequently furrowed adjacent to nematodes, and branched


Fig. 1. External view of cuticle on abdomen of fall armyworm with holes (arrows)
produced by stylets of N. guyanense (X 3,150). (S = scale sockets). (Electron micrograph,
courtesy of William Wergin, ARS, Beltsville, MD).


June, 1991










Fall Armyworm Symposium '90-Rogers et al. 255









/ imr a a i f d in infested m Ii m
I









,r

.. -- ....







Fig. 2. Cross section of intersegmental area of Anomis oedema abdomen showing
N. guyanense (N) and deterioration of muscles (M) beneath proliferating cuticle (P)(X
590).

cuticular proliferations tend to surround the nematodes. Cuticular erosion in the inter-
segmental membrane also is found in infested moths. In heavily infested moths, the
intersegmental spaces may be hypertrophied at the expense of the homocoel. Also,
muscular deterioration beneath intersegmental membranes has been found in heavily
infested moths of Anomis oedema Guen&e (Fig. 2). Infrequent capture of heavily infested
male moths in pheromone traps indicates that at some population threshold, N.
guyanense may interfere with flight by its host.
Virtually nothing is known about the field biology of N. guyanense, nor about its
acute pathogenicity to moths. Visual evidence suggests that the stylet of the nematode
penetrates the cuticle of its host to feed on internal fluids and/or tissue. Nematodes
from wild male hosts are characteristically yellow, whereas nematodes from totally
laboratory-reared females hosts are frequently blue-green, particularly if infested female
moths lay bluish-green eggs. The coloration shift in the nematodes from hosts using
different food sources suggest that N. guyanense may feed on the hemolymph or repro-
ductive system of its host.

ACKNOWLEDGMENTS

We are grateful to the following individuals who helped with the collection of fall
armyworm moths for this study: K. U. Buckmire (St. Georges, Grenada), R. D. Cave
(Tegucigalpa, Honduras), J. L. Despinos (St. Croix, Virgin Island), H. Espinoza (La
Lima, Honduras), P. J. Fitzgerald (Grand Cayman, Cayman Island), R. E. Foster
(formerly Belle Glade, Florida; currently Lafayette, Indiana), B. Gray (Panama City,
Panama), D. J. Hilburn (Hamilton, Bermuda), J. Larios (San Salvador, El Salvador),










256 Florida Entomologist 74(2) June, 1991

L. Palcy (Fort de France, Martinique), A. Pantoja (formerly Rio Piedras, Puerto Rico;
currently Cali, Colombia), B. K. Rai (Belopan, Belize), J. R. Raulston (Weslaco, Texas),
A. van Sauers-Muller (Paramaribo, Suriname), P. Shannon (Turrialba, Costa Rica), E.
T. Wallace (Nassau, Bahamas), A. Whitwell (Roseau, Commonwealth of Dominica), W.
G. des Vignes (Carapichaima, Trinidad), and I. Zenner-Polania (Bogota, Colombia).
We also thank J. F. Silvain, ORSTOM Center, Cayenne, French Guiana; and R. W.
Poole and M. A. Solis, USDA, ARS, U.S. National Museum, Washington, D.C., for
their taxonomic assistance in identifying Lepidoptera species.
This article reports the results of research only. Mention of a proprietary product
does not constitute an endorsement or the recommendation for its use by the USDA.

REFERENCES CITED

ANDREWS, K. L. 1988. Latin American research on Spodopterafrugiperda (Lepidopt-
era: Noctuidae). Florida Ent. 71: 630-653.
ASHLEY, T. R. 1979. Classification and distribution of fall armyworm parasites. Florida
Ent. 62: 114-123.
BORROR, D. J., AND D. M. DELONG. 1964. An introduction to the study of insects.
Rev. Ed. Holt, Rinehart and Wenston, New York. 819 pp.
COVELL, C. V., JR. 1984. A field guide to the moths of eastern North America.
Houghton Mifflin, Boston. 496 pp.
HODGES, R. W. 1983. Checklist of Lepidoptera of North America north of Mexico.
E. W. Classey Lim., and Wedge Ent. Res. Foundation. 284 pp.
HOWE, W. H. 1975. The butterflies of North America. Doubleday, Garden City, NY.
633 pp.
HUNT, D. J. 1980. Acugutturus parasiticus n.g., n.sp., a remarkable ectoparasitic
aphelenchoid nematode from Periplaneta americana (L.), with a proposal of
Acugutturinae N. Subf. Syst. Parasitol. 1: 167-170.
JAQUES, H. E. 1947. How to know the insects. Brown, Dubuque, Iowa. 205 pp.
KIMBALL, C. P. 1965. The Lepidoptera of Florida. Div. Plant Ind., State of Florida,
Dep. of Agric., Gainesville, Florida. 363 pp.
MARTI, 0. G., C. E. ROGERS, J. F. SILVAIN, AND A. M. SIMMONS. 1990. Pathological
effects of an ectoparasitic nematode Noctuidonema guyanense Remillet and Sil-
vain (Nematoda: Aphelenchoididae) on adults of the fall armyworm, Spodoptera
frugiperda (J. E. Smith). Ann. Ent. Soc. Am. 83: 956-960.
REMILLET, M., AND J. F. SILVAIN. 1988. Noctuidonema guyanense n.g., n.sp.
(Nematoda: Aphelenchoididae) ectoparasite de noctuelles du genre Spodoptera
(Lepidoptera: Noctuidae). Rev. Nematol. 11: 21-24.
ROGERS, C. E., O. G. MARTI, A. M. SIMMONS, AND J. F. SILVAIN. 1990a. Host
range of Noctuidonema guyanense (Nematoda: Aphelenchoididae): An ectopara-
site of moths in French Guiana. Environ. Ent. 19: 795-798.
ROGERS, C. E., A. M. SIMMONS, AND O. G. MARTI. 1990b. Parasitism of Lepidoptera
adults by Noctuidonema guyanense Remillet and Silvain (Nematoda: Aphelen-
choididae) in southeastern United States. J. Agric. Entomol. 7: 241-245.
SAS INSTITUTE. 1985. SAS user's guide: statistics. SAS Institute, Cary, North
Carolina. 956 pp.
SILVAIN, J. F. 1984. Premieres observations sur 1'ecologie de Spodopterafrugiperda
(J. E. Smith) et Mocis latipes (Guenee), noctuelles depredatrices des graminees
fourageres en Guyane Francaise, Prairies guyanaises et elevage bovine. Colloques
INRA 24: 253-272.
SIMMONS, A. M., AND C. E. ROGERS. 1990a. Distribution and prevalence of an
ectoparasitic nematode, Noctuidonema guyanense, on moths of fall armyworm
(Lepidoptera: Noctuidae) in the tropical Americas. J. Ent. Sci. 25: 510-518.











Fall Armyworm Symposium '90-Gardner 257

SIMMONS, A. M., AND C. E. ROGERS. 1990b. Temperature and humidity effects on
Noctuidonema (Nematoda: Aphelenchoididae), an ectoparasite of adult Spodopt-
erafrugiperda (Lepidoptera: Noctuidae), and transfer success during host mating.
Ann. Ent. Soc. Am. 83: 1084-1087.
WATSON, A., AND P. E. S. WHALLEY. 1975. The dictionary of butterflies and moths
in color. Exeter Books, New York. 296 pp.





OVICIDAL PROPERTIES OF FENOXYCARB AGAINST
THE FALL ARMYWORM (LEPIDOPTERA: NOCTUIDAE)

WAYNE A. GARDNER
Department of Entomology, College of Agriculture Experiment Stations,
Georgia Station, Griffin, Georgia 30223 U.S.A.

ABSTRACT

Ovicidal effects of fenoxycarb, ethyl[2-phenoxyphenoxyethyl] carbamate, against the
fall armyworm (FAW), Spodoptera frugiperda (J. E. Smith), egg masses of different
ages were investigated in laboratory studies. Egg mass age was a critical factor in the
activity of the juvenoid against FAW eggs. Percent eclosion was significantly (P < 0.05)
lower in egg masses treated on Day 1 of oviposition than in masses treated on either
Day 2 or Day 3 postoviposition. Mean ( SE) percent eclosion of eggs treated on Day
1 was 86.9 (- 12.1), 30.5 ( 1.2), 10.8 ( 0.7), and 17.4 ( 2.7) following application of
fenoxycarb at 0, 50, 100, and 200 gm AI/ha, respectively. Mean percent eclosion of eggs
treated with fenoxycarb on Day 2 or Day 3 ranged from 76.1 to 89.0 and did not differ
significantly (P 0.05) from the untreated checks (83.4% and 93.5%). No delayed
developmental effects in either developmental rate, prepupal weight, or adult fecundity
were noted in the fenoxycarb treatments.

RESUME

Se estudi6 en el laboratorio los efectos ovicidas de fenoxycarb ethyl [2-
phonoxyphenoxyethyl] carbamato, en contra de posturas de huevos de diversas edades
de cogollero (FAW) Spodoptera frugiperda (J. E. Smith). La edad de las posturas de
huevos fu4 un factor critic en la actividad de este juvenoide contra los huevos de FAW.
El porcentaje de eclosi6n fue significativamente (P < 0.05) mas bajo en aquellos huevos
tratados el dia de oviposici6n comparado con aquellos huevos tratados el dia 2 o el dia
3 despues de la oviposici6n. El procentaje promedio ( SE) de eclosi6n de huevos
tratados en el dia fue de 86.9 ( 12.1), 30.5 ( 1.2), 10.8 ( 0.7) y 17.4 ( 2.7) despues
de una aplicaci6n de fonxycarb al 0, 50, 100 y 200 gramos IA/ha, respectivamente. El
porcentaje promedio de eclosi6n de huevos tratados con fenoxycarb en el dia 2 o el dia
3 fluctu6 entire el 76.1 a el 89.0% pero no difiri6 significativamente (P < 0.05) de los
controls tratados (83.4% y 93.5%). No se observaron efectos tardios de fenoxycarb en
la tasa de desarrollo, el peso de prepupas o la fecundidad de los adults.



The fall armyworm (FAW), Spodopterafrugiperda (J. E. Smith), is a persistent pest
of agricultural crops in the southeastern United States and other areas of the Western
Hemisphere. FAW immatures are polyphagous but reportedly prefer grasses (Luginbill





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Florida Entomologist 74(2)


1928). Insecticidal control is often necessary to protect forage and grain crops (Young
1979, Andrews 1980). Conventional chemical insecticides have proven effective against
immatures when formulations and application techniques were appropriate for the host
crop and its stage of development (Young 1979, Pitre 1986).
Development of resistance to selected insecticides has been reported. Carbaryl,
trichlorfon, methyl parathion, and ethyl parathion have been reported to be ineffective
against FAW (Bass 1978, Young 1979, Andrews 1980, Pitre 1986). Other insecticides
including diazinon and certain synthetic pyrethroids provide erratic or poor control in
selected crops and locations (Harrell et al. 1977, Bass 1978, All et al. 1983). Commercial
formulations of Bacillus thuringiensis Berliner also have proven ineffective against
FAW (Gardner & Fuxa 1980, Gardner et al. 1986, Gardner 1988).
Insect growth regulators (IGRs) based on juvenile hormone analogs have not been
thoroughly evaluated against FAW. Recent studies with fenoxycarb, ethyl [2-(p-
phenoxyphenoxy)ethyl]carbamate (Dorn et al. 1981), have demonstrated morphogenetic
(Gancey et al. 1989, Mulye & Gordon 1989) and chemosterilant (King & Bennett 1989,
Chen & Borden 1989) effects. Some IGRs also are ovicidal (Staal 1975). The objective
of this study was to determine the ovicidal effects of fenoxycarb against FAW.

METHODS

Fall armyworm eggs were obtained from a laboratory colony. Larvae were maintained
on a semisynthetic diet (Burton & Perkins 1972). The fenoxycarb used in the study was
ABG-6231 (Lot No. 06-063-BR) provided by Abbott Laboratories (North Chicago, IL).
This chemical is a proprietary product of Maag Agrochemicals Inc. (Vero Beach, FL).
Egg masses were collected at 0800 h for 3 consecutive days. Individual masses were
separated by cutting the underlying cheesecloth which served as an ovipositional sub-
strate. Masses were individually weighed to determine the approximate number of eggs
and transferred to 30-ml clear plastic creamer cups. The cups were labelled with the
egg mass weight and oviposition date and stored at 25C.
On Day 3 egg masses were grouped according to the ovipositional date. Only masses
with weights correlating with 150 to 250 eggs per mass (Lynch et al. 1983) were used
for the study. Within each age category, egg masses were randomly assigned to 1 of 5
treatment groups. The treatments were: fenoxycarb at 50, 100, and 200 gm AI/ha;
chlordimeform at 140 gm AI/ha; and an untreated control. The chlordimeform was
formulated as Galecron 4E. Treatments were applied as an aqueous spray with Potter
Precision Laboratory Spray Tower (Burkard Manufacturing Co. Ltd., Rickmansworth,
Hertfordshire, England). Each treatment for days 1-3 was replicated 5X in 2 consecutive
generations. Each replicate contained 3 to 5 egg masses.
After treatment the egg masses were air dried and returned to their plastic cups
and rearing chamber. Larval eclosion was monitored twice daily. When hatching had
ceased for a minimum of 3 consecutive days, egg masses were examined microscopically
to determine numbers of eggs per mass and the corresponding percentage eclosion.
Neonates were individually transferred to 30-ml clear plastic creamer cups each contain-
ing 10 ml of semisynthetic diet and were checked daily until death or pupation. In those
treatments with at least 10 male and 10 female survivors, 20 pupae (10 female: 10 male)
were placed in a 3-liter container. Emerging moths were fed on stale beer. All egg
masses oviposited from these adults were collected, weighed, and percent eclosion deter-
mined.
The analysis of variance procedure of the Statistical Analysis System (SAS Institute
1985) was used to compare percent eclosion of treated and control egg masses. Larval
mortality and fecundity of survivors in response to ovicidal treatment also were analyzed.
Means were separated by Duncan's (1951) multiple range test when significant (P s
0.05) F-ratios occurred within a comparison.


258


June, 1991











Fall Armyworm Symposium '90-Gardner


TABLE 1. PERCENT ECLOSION OF FALL ARMYWORM EGGS RECEIVING OVICIDAL
SPRAYS AT DIFFERENT EGG MASS AGES.'

Ovicide2 % eclosion of eggs treated on egg mass age
(gm AI/ha) Day 1 Day 2 Day 3

Fenoxycarb(50) 30.5 +12.3a 84.7 + 7.4b 88.2 + 7.1b
Fenoxycarb(100) 10.8 6.6a 85.8 5.6b 87.3 6.3b
Fenoxycarb(200) 17.4+ 6.9a 76.1 8.1b 89.0 3.8b
Chlordimeform (140) 17.6 + 11.9 a 51.6 13.5 a 66.3 10.3 a
Untreated check 86.9 + 12.1a 83.4 6.0 a 93.5 5.2a

'Means (- SE) within a row followed by the same letter are not significantly different (P s 0.05; Duncan's [1951]
multiple range test).
0Ovicides applied as aqueous sprays through Potter Precision Laboratory Spray Tower with 5 replicates/treatment
and 3 to 5 egg masses/replicate.

RESULTS AND DISCUSSION

Egg mass age was a critical factor in the activity of fenoxycarb as an ovicide against
FAW. Percent eclosion was significantly (P 0.05) lower in egg masses treated on Day
1 of oviposition (10.8% to 30.5%) than in masses treated on either Day 2 (76.1% to 85.8%)
or Day 3 (87.3% to 89%) postoviposition (Table 1). Reduced eclosion also occurred
following application of chlordimeform, a conventional insecticide/ovicide; however, per-
cent eclosion for this treatment did not differ significantly (P 0.05) with respect to
egg mass age.
Sensitivity of lepidopteran eggs to IGRs was initially reported by Riddiford & Wil-
liams (1967). Staal (1975) noted that IGRs disrupt embryonic development resulting in
nonemergence only when applied to insect eggs prior to the blastokinesis phase of
development. The activity of fenoxycarb against FAW eggs also appears restricted to
these early phases of embryogenesis.
While delayed larval development and mortality following eclosion from IGR-treated
eggs has been reported (Staal 1975), no discernable effects were observed among larvae
closed from egg masses treated in this study. Numbers of larvae totalled 1520, 1037,
1229, 916, and 1150 for the untreated checks, chlordimeform, fenoxycarb (50 gm AI/ha),
fenoxycarb (100 gm AI/ha), and fenoxycarb (200 gm AI/ha), respectively. Mean ( SE)
larval mortality for the untreated checks was 17.6% ( 4.3). Larval mortality in the
ovicide treatments did not deviate significantly (P 0.05) from that level. Larval
developmental rates were consistent across all treatments with mean prepupal weights
of 252.8 ( 1.9) mg for the untreated checks, 260.4 ( 1.9) mg for the chlordimeform
treatment, and 253.9 ( 2.2), 251.9 ( 2.2), and 252.0 ( 2.5) mg for the respective 50,


TABLE 2. PERCENT ECLOSION OF FALL ARMYWORM EGGS IN RESPONSE TO OVICI-
DAL SPRAYS WHEN SUMMED OVER EFFECTS OF EGG MASS AGE.

Ovicide
(gm AI/ha) % eclosion'

Fenoxycarb (50) 67.8 8.6
Fenoxycarb (100) 61.3 10.1
Fenoxycarb (200) 60.9 9.0
Chlordimeform (140) 45.2 8.4
Untreated check 81.3 5.3

'No significant differences among treatment means (- SE) as determined by analysis of variance (F = 1.59, df = 8).


259










260 Florida Entomologist 74(2) June, 1991

100, and 200 gm AI/ha rates of fenoxycarb. Fecundity and percent eclosion of eggs
produced by adults developing from the treated egg masses also did not differ significant-
ly. Delayed developmental effects in larvae hatching from fenoxycarb-treated eggs did
not occur in this study. These data are supported by Riddiford (1972) who noted that
the IGR dose required to illicit delayed developmental effects may be 3X to 10X higher
than the dose required to prevent eclosion.
Fenoxycarb disrupts the embryonic development of FAW eggs as evidenced by
reduced eclosion. Unfortunately, practical utility is restricted because only young eggs
are sensitive to the fenoxycarb. Table 2 presents mean (- SE) percent eclosion in
response to the ovicide treatments when summed over the effects of egg mass age.
Assuming an equal distribution of 1 to 3-day-old egg masses within a crop field, a single
fenoxycarb application at either of the three test rates will not significantly reduce
eclosion of FAW eggs in that field. Daily applications of fenoxycarb at 50 to 200 gm
AI/ha beginning when oviposition is first detected in the field could potentially reduce
eclosion by approximately 55 to 75% (Table 1).

ACKNOWLEDGMENTS

Technical assistance in this study was provided by D. J. Kinard, A. F. Pendley, and
R. D. Harrison. R. L. Nichols critically reviewed the manuscript during its preparation.

REFERENCES CITED

ALL, J. N., A. JAVID, AND D. E. Dix. 1983. Sweetcorn, control of a mixed infestation
of corn earworm and fall armyworm, 1982. Insect. and Acar. Tests 8: 108.
ANDREWS, K. L. 1980. The whorlworm, Spodoptera frugiperda, in Central America
and neighboring areas. Florida Ent. 63: 456-67.
BASS, M. H. 1978. Fall armyworm: evaluation of insecticides for control. Agric. Exp.
Stn. Auburn Univ. Leaflet 93: 7.
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.
CHEN, N.-M., AND J. H. BORDEN. 1989. Adverse effect of fenoxycarb on reproduction
by the California fivespined ips, Ips paraconfusvs Lanier (Coleoptera: Scolytidae).
Canadian Ent. 121: 1059-68.
DORN, S., M. L. FRISCHNECHT, V. MARTINEZ, R. ZURFLUH, AND F. FISHER.
1981. A novel non-neurotoxic insecticide with a broad activity spectrum. A.
Pflanzenkr. Pflanzenschutz. 88: 269-75.
DUNCAN, D. B. 1951. A significance test for differences between ranked treatments
in an analysis of variance. Virginia J. Sci. 2: 171-89.
GARDNER, W. A. 1988. Enhanced activity of selected combinations of Bacillus thurin-
giensis and beta-exotoxin against fall armyworm (Lepidoptera: Noctuidae) larvae.
J. Econ. Ent. 81: 463-9.
GARDNER, W. A., AND J. R. FUXA. 1980. Pathogens for the suppression of the fall
armyworm. Florida Ent. 63: 439-47.
GARDNER, W. A., A. F. PENDLEY, AND G. K. STOREY. 1986. Interactions between
Bacillus thuringiensis and its beta-exotoxin in fall armyworm (Lepidoptera: Noc-
tuidae) neonate larvae. Florida Ent. 69: 531-6.
GLANCEY, B. M., W. A. BANKS, AND M. S. OBIN. 1989. The effect of fenoxycarb on
alates of the red imported fire ant. J. Ent. Soc. 24: 290-7.
HARRELL, E. A., J. R. YOUNG, AND W. W. HARE. 1977. Insect control on late-planted
sweet corn. J. Econ. Ent. 70: 129-31.
KING, J. E., AND G. W. BENNETT. 1989. Comparative activity of fenoxycarb and
hydroprene in sterilizing the German cockroach (Dictyoptera: Blattellidae). J.
Econ. Ent. 82: 833-8.
LUGINBILL, P. A. 1928. The fall armyworm. USDA Tech. Bull. No. 34. 92 pp.











Fall Armyworm Symposium '90-Guillebeau & All 261

LYNCH, R. E., S. D. PAIR, AND R. JOHNSON. 1983. Fall armyworm fecundity: relation-
ship of egg mass weight to number of eggs. J. Georgia Ent. Soc. 18: 507-13.
MULYE, H., AND R. GORDON. 1989. Effects of selected juvenile hormone analogs on
sixth-instar larvae of the eastern spruce budworm, Choristoneura fumiferana
Clemens (Lepidoptera: Tortricidae). Canadian Ent. 121: 1111-6.
PITRE, H. N. 1986. Chemical control of the fall armyworm (Lepidoptera: Noctuidae):
an update. Florida Ent. 69: 570-8.
RIDDIFORD, L. M. 1972. Juvenile hormone and insect embryonic development: its
potential role as an ovicide, pp. 95-11 in J. J. Menn and M. Beroza [eds.] Insect
juvenile hormones. Academic Press, N.Y.
RIDDIFORD, L. M., AND C. M. WILLIAMS. 1967. The effects of juvenile hormone
analogues on the embryonic development of silkworms. Proc. Nat. Acad. Sci.
USA 57: 595-601.
SAS INSTITUTE. 1985. SAS user's guide: basics, version 5 ed. SAS Institute, Cary, NC.
STAAL, G. B. 1975. Insect growth regulators with juvenile hormone activity. Ann.
Rev. Ent. 20: 417-60.
YOUNG, J. R. 1979. Fall armyworm: control with insecticides. Florida Ent. 62: 130-3.





USE OF PYRETHROIDS, METHOMYL, AND CHLORPYRIFOS
TO CONTROL FALL ARMYWORM (LEPIDOPTERA:
NOCTUIDAE) IN WHORL STAGE FIELD CORN,
SWEET CORN, AND SORGHUM

L. P. GUILLEBEAU AND J. N. ALL
Department of Entomology
University of Georgia
Athens, Ga. 30602

ABSTRACT

It is important to identify new insecticides with efficacy for the fall armyworm,
Spodopterafrugiperda Smith, to allow greater flexibility in management programs and
to retard the development of resistance. Field trials showed all rates tested of the
pyrethroid insecticides tralomethrin, flucythrinate, and cyhalothrin to be as effective
as manufacturers' recommended rates of chlorpyrifos and methomyl against fall ar-
myworm in whorl stage sweet corn, field corn, and sorghum. Permethrin, cypermethrin,
fenvalerate, esfenvalerate, fluvalinate, and cyfluthrin gave erratic control of fall ar-
myworm injury in field corn and sweet corn compared with chlorpyrifos and methomyl;
these insecticides were comparable with other treatments against fall armyworm in
whorl stage sorghum.


RESUME

Para una mejor flexibilidad en los programs de manejo del cogollero, Spodoptera
frugiperda (J. E. Smith), es important identificar nuevos insecticides eficaces. Ensayos
de campo demostraron que las dosis de los insecticides piretroides, tralomethrin, flucyt-
hrinate, y cyhalothrin fue tan efectiva en el control del cogollero en el maiz dulce, maiz
de campo y sorgo, como las dosis recomendadas por los fabricantes de chlorpyrifos y
methomyl. Permethrin, cypermethrin, fenvalerate, esfenvalerate, fluvalinate y cyflut-
hrin dieron un control erratic del cogollero en maiz de campo y en maiz dulce comparado









Florida Entomologist 74(2)


June, 1991


con chlorpyrifos y methomyl; estos insecticides son comparable con otros tratamientos
contra el cogollero en sorgo en estado de panoja.


Chemical controls are often necessary to suppress damaging populations of the fall
armyworm (FAW), Spodoptera frugiperda Smith. However, FAW populations have
shown tolerance or resistance to a number of insecticides, including methomyl, carbaryl,
and methyl parathion (Bass 1978, Young 1979). To manage resistance, it is important
to identify suitable alternatives (Metcalf 1980).
Effective chemical options need to be identified to allow greater flexibility in FAW
management. A number of synthetic pyrethroid insecticides such as fenvalerate and
permethrin are registered for control of miscellaneous noctuid pests but generally provide
erratic control of FAW (Harrell et al. 1977). All et al. (1983) found that only high rates
of pyrethroids available at that time controlled FAW in sweet corn; by 1985, pyrethroids
with greater efficacy against FAW had been registered (All et al. 1986).
Heavy FAW infestations occurring in whorl stages of corn and sorghum may be
difficult to control with insecticides. This paper reviews five years of field studies with
synthetic pyrethroids, chlorpyrifos, and methomyl for control of FAW in whorl stage
corn and sorghum.

MATERIALS AND METHODS

Field corn (Dekalb XL 394), sorghum (Dekalb BR83 or BR84), and/or sweet corn
(Funk's G80) were planted each July/August 1983-1987. Standard agronomic practices
of fertilization, irrigation, and weed control were followed. All experiments utilized a
randomized complete block design with plots of 2 rows x 6 m long x 1 m row width x
1.5 m alleys separating 4-5 replicates. Each test had 6-23 treatments. All tests were
conducted at the University of Georgia Experiment Station farm near Athens in the
north Georgia Piedmont region.
Insecticide treatments began 11-19 days after planting when the plants reached the
fourth leaf stage, and 50% of the plants showed leaf feeding symptoms of FAW larvae.
Full cone sprays directed over the whorl were applied 2-4 times at weekly intervals.
Applications were made with hand-held sprayers at 2460.8 g/cm2 (35 psi) in 1983-85 or
2109.3 g/cm2 (30 psi) in 1986-87. A final volume of 467.7 1/ha was applied in 1985 and
233.8 1/ha in other years. One to three weeks after completion of the spray program,
plots were rated for fall armyworm damage on a 0-7 scale. A rating of 0, 1, 2, or 3
indicates < 5%, 5-10%, 10-20%, and > 20% leaf damage, respectively, with no feeding
in the whorl. The values 4, 5, and 6 denote < 20%, 20-40%, and > 40% leaf injury,
respectively, with progressively greater feeding in the whorl. A rating of 7 designates
plants that are completely destroyed. In most tests individual plants were visually
assessed, and a rating for the plot was determined by averaging the data from individual
plants. In other tests an overall plot rating was recorded. Evaluations were conducted
once or twice with a 7-10 day interval. In 1983 and 1985 all plants in the center 5 m of
each plot of the sorghum tests were cut at ground level and weighed to determine silage
yield. Data were subjected to analysis of variance and Duncan's new multiple range
test; P < 0.05 (SAS 1989).

RESULTS AND DISCUSSION

In five years' testing, the pyrethroid insecticides cyhalothrin, tralomethrin, and
flucythrinate provided control of FAW injury comparable with manufacturers' suggested
rates of chlorpyrifos and methomyl in whorl stage field corn, sorghum, and sweet corn.


262










Fall Armyworm Symposium '90-Guillebeau & All


Fenvalerate, esfenvalerate, cypermethrin, fluvalinate, cyfluthrin, and permethrin pro-
vided erratic control in whorl stage field corn and sweet corn at the rates tested, but
compared with other chemical treatments in whorl stage sorghum.

Field Corn

In the first damage ratings of 1983 (Table 1), plots treated with cypermethrin (0.044,
0.075, 0.084, and 0.11 kg [AI]/ha), fluvalinate (0.084 and 0.11 kg [AI]/ha), the higher
rate of permethrin (0.11 kg [AI]/ha), or methomyl (0.56 and 0.84 kg [AI]/ha) had signif-
icantly less FAW damage than untreated plots. Efficacy of both rates of methomyl was
significantly greater than the efficacy of any other compound except cypermethrin at
0.11 kg (AI)/ha. The highest rate of cypermethrin (0.11 kg [AI]/ha) performed signifi-
cantly better than fenvalerate (0.084 and 0.11 kg [AI]/ha) and the lower rate of permethrin
(0.084 kg [AI]/ha). Neither rate of fenvalerate nor the lower rate of permethrin provided
a significant level of control of FAW damage relative to untreated plots.
In the second 1983 damage rating, only plots treated with cypermethrin (0.11 kg
[AI]/ha) or methomyl (0.84 kg [AI]/ha) had significantly less FAW injury than control
plots (Table 1). No other statistical separation occurred among the treatments.
In 1984, all treated plots had significantly less FAW damage than control plots (Table
1). Cyhalothrin (0.017 kg [AI]/ha) had significantly greater efficacy than fenvalerate
(0.11 kg [AI]/ha); all other chemical treatments performed significantly better than
esfenvalerate at 0.017 kg (AI)/ha. No other statistical separation occurred among the
treatments.
In 1985, all insecticide treated plots had significantly lower levels of FAW damage
relative to untreated plots in two injury evaluations (Table 1). In the first rating, there
were no significant differences among the insecticide treatments. In the second assess-
ment, fluvalinate (0.062 kg [AI]/ha), tralomethrin (0.017 kg [AI]/ha), cyhalothrin (0.017
kg [AI]/ha), flucythrinate (0.056 kg [AI]/ha), and cyfluthrin (0.067 kg [AI]/ha) controlled
FAW injury significantly better than methomyl (0.56 kg [AI]/ha).
In both FAW injury ratings taken in 1986, all insecticide treated plots had significantly
less FAW damage than control plots (Table 1). There was no statistical separation among
the insecticide treatments in the initial assessment; in the second evaluation, every
other chemical treatment performed significantly better than esfenvalerate at 0.042 kg
(AI)/ha in control of FAW damage.

Sorghum

In 1983, every insecticide treatment provided significant levels of control of FAW
injury (Table 2). Fluvalinate (0.084 kg [AI]/ha) had significantly greater efficacy than
either rate of methomyl (0.084 and 0.11 kg [AI]/ha); no other statistical separation
occurred among the chemical treatments.
All insecticide treatments significantly increased silage yields relative to untreated
plots (Table 2) in 1983 except fenvalerate (0.11 kg [AI]/ha); silage yields from all treated
plots were statistically comparable. There was a trend for more effective treatments to
yield the greatest amounts of silage with two exceptions; silage yields from fenvalerate
(0.084 kg [AI]/ha) and permethrin (0.084 kg [AI]/ha) were higher than yields from any
other treatment except fluvalinate (0.084 kg [AI]/ha) although these rates of fenvalerate
and permethrin did not provide the highest level of protection from FAW injury.
In the initial rating of 1985, cypermethrin (0.067 kg [AI]/ha), cyhalothrin (0.017 kg
[AI]/ha), flucythrinate (0.056 kg [AI]/ha), and cyfluthrin (0.067 kg [AI]/ha) provided
significant levels of control of FAW damage compared with untreated plots (Table 2).
The remaining treatments (fluvalinate [0.062 kg [AI]/ha], esfenvalerate [0.028 kg [AI]/


263














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ha], tralomethrin [0.017 kg [AI]/ha], methomyl [0.56 kg [AI]/ha], and chlorpyrifos [0.56
kg [AI]/ha]) did not significantly reduce FAW injury relative to the control. Additionally,
cypermethrin (0.067 kg [AI]/ha), cyhalothrin (0.017 kg [AI]/ha), and flucythrinate (0.056
kg [AI]/ha) performed significantly better than esfenvalerate (0.28 kg [AI]/ha) and
tralomethrin (0.017 kg [AI]/ha). FAW damage in plots treated with cypermethrin (0.067
kg [AI]/ha) and cyhalothrin (0.017 kg [AI]ha) had significantly less FAW injury than
chlorpyrifos (0.56 kg [AI]/ha); cyfluthrin (0.067 kg [AI]/ha) had significantly greater
efficacy than tralomethrin (0.017 kg [AI]/ha).
Analysis of second 1985 data set was similar; only plots treated with cypermethrin
(0.067 kg [AI]/ha), cyhalothrin (0.017 kg [AI]/ha), flucythrinate (0.056 kg [AI]/ha), and
cyfluthrin (0.067 kg [AI]/ha) had significantly less FAW injury than control plots.
Cyhalothrin (0.017 kg [AI]/ha) performed significantly better than fluvalinate (0.062 kg
[AI]/ha), esfenvalerate (0.017 kg [AI]/ha), methomyl (0.56 kg [AI]/ha), and chlorpyrifos
(0.56 kg [AI]/ha); efficacy of cypermethrin (0.067 kg [AI]/ha) was statistically greater
than the efficacy of esfenvalerate (0.017 kg [AI]/ha) and methomyl (0.56 kg [AI]/ha).
Differences among silage yields in 1985 were not significant (Table 2). Yields generally
did not correlate with efficacy. Silage yields from methomyl (0.56 kg [AI]/ha) and esfen-
valerate (0.028 kg [AI]/ha) plots ranked 1st and 2nd, respectively, among ten treatments,
while yields from plots treated with cyfluthrin (0.067 kg [AI]/ha), cypermethrin (0.067
kg [AI]/ha), and cyhalothrin (0.017 kg [AI]/ha) ranked 5th, 6th, and 7th, respectively.
In the two injury ratings of 1987, all chemical treatments provided significant levels
of control of FAW damage relative to untreated plots (Table 2). No other statistical
differences occurred among the treatments in either of the two ratings.


Sweet Corn

Two sweet corn tests were conducted in 1986. In the first test, mean (fi S.D.) FAW
injury in untreated plots rated 5.2 fi 0.54 in the initial assessment. All chemical treatments
provided significant levels of protection against FAW damage, relative to untreated
plots (F = 11.3; P = 0.05; DMRT, SAS User's Guide 1990). Mean (fi S.D.) percent
control by tralomethrin at 0.028 kg (AI)/ha (100.0 f 0.0%) and by chlorpyrifos at 0.84
kg (AI)/ha (97.4 f 4.7%) was significantly higher than control by esfenvalerate at 0.028
kg (AI)/ha (63.9 fi 36.5%), cyhalothrin at 0.028 kg (AI)/ha (86.5 f 13.9%), and cyfluthrin
at 0.028 kg (AI)/ha (67.0 fi 27.4%). Efficacy of chlorpyrifos at 0.56 kg (AI)/ha (93.8 fi
10.6%) was significantly greater than efficacy of cyhalothrin at 0.028 kg (AI)/ha and
esfenvalerate at 0.028 kg (AI)/ha. Percent FAW control in the remaining treatments
did not differ significantly from any other chemical treatment: methomyl at 0.56 kg
(AI)/ha and at 0.84 kg (AI)/ha (75.3 ft 19.5% and 87.4 ft 16.8%, respectively), flucythrinate
at 0.067 kg (AI)/ha (87.9 f 13.4%) and cypermethrin at 0.067 kg (AI)/ha (74.3 fi 25.1%).
Greater separation occurred among the chemical treatments in the second rating of
the first 1986 test (F = 12.7, P = 0.05). All chemical treatments significantly controlled
FAW injury, compared with untreated plots (mean injury rating [f S.D.], 5.5 fi 0.50).
Percent control of FAW damage by tralomethrin at 0.028 kg (AI)/ha (97.0 fi 4.1%), by
flucythrinate at 0.067 kg (AI)/ha (97.4 fi 2.3%), and by methomyl at 0.084 kg (AI)/ha
(96.8 f 3.1%) was significantly greater than control by all other treatments, except
chlorpyrifos at 0.56 kg (AI)/ha and 0.085 kg (AI)/ha (94.0 ft 6.4% and 88.8 fi 21.7%,
respectively) and methomyl at 0.56 kg (AI)/ha (77.9 ft 20.9%). Chlorpyrifos at either
rate was significantly more effective than cyfluthrin at 0.028 kg (AI)/ha (53.6 fi 35.0%);
efficacy of chlorpyrifos at 0.56 kg (AI)/ha was significantly greater than the efficacy of
esfenvalerate at 0.028 kg (AI)/ha (67.2 f 24.0%) and the efficacy of cyhalothrin at 0.028
kg (AI)/ha (89.2 fi 18.9%). No additional statistical separation occurred; cypermethrin
(0.067 kg [AI]/ha) provided 69.2 f 22.7% control of FAW injury.


268


June, 1991











Fall Armyworm Symposium '90-Guillebeau & All 269

In a single rating, FAW injury in the untreated plots averaged (f S.D.) 3.7 f 0.31
in the second test of 1986. Every chemical treatment provided significant levels of
protection (F = 24.4, P = 0.05). Mean percent control by tralomethrin at 0.028 kg
(AI)/ha (98.3 f 1.6%), by cyfluthrin at 0.028 kg (AI)/ha (97.9 f 2.2%), by methomyl at
0.56 kg (AI)/ha (96.8 f 2.1%), and by cyhalothrin at 0.011 kg (AI)/ha and at 0.028 kg
(AI)/ha (each with 98.9 fi 1.5% control) was significantly greater than control by esfen-
valerate at 0.011 kg (AI)/ha and at 0.028 kg (AI)/ha (70.1 f 18.5% and 83.0 f 20.0%,
respectively). Additionally, the efficacy of tralomethrin at 0.011 kg (AI)/ha (94.6 f 2.6%),
of cyfluthrin at 0.011 kg (AI)/ha (88.0 f 6.3%), and of methomyl at 0.17 kg (AI)/ha (87.2
f 10.3%) was significantly greater than the efficacy the lower rate of esfenvalerate (0.011
kg [AI]/ha).
In the first evaluation of the 1987 test, FAW injury in untreated plots averaged (f
S.D.) 5.4 f 0.43. Cyfluthrin at 0.028 kg (AI)/ha (27.8 f 25.1% control), chlorpyrifos at
0.28 kg (AI)/ha (36.7 f 33.9%), chlorpyrifos at 0.56 kg (AI)/ha (44.2 f 26.3%), cypermet-
hrin at 0.067 kg (AI)/ha (49.2 f 18.9%), tralomethrin at 0.017 kg (AI)/ha (58.4 f 30.2%),
methomyl at 0.56 kg (AI)/ha (66.9 f 11.3%), methomyl at 0.28 kg (AI)/ha (70.5 f 16.5%),
methomyl at 0.84 kg (AI)/ha (87.1 f 9.0%), and cyhalothrin at 0.028 kg (AI)/ha (76.9 f
24.6%) provided significant levels of control of FAW injury (F = 14.5, P = 0.05);
esfenvalerate at 0.028 kg (AI)/ha (12.2 fi 13.8%) did not. Additionally, methomyl (0.84
kg [AI]/ha) was significantly more effective than any non-methomyl treatment, except
cyhalothrin. Cyhalothrin was significantly more effective than cypermethrin, both rates
of chlorpyrifos, cyfluthrin, and esfenvalerate. The efficacy of methomyl at 0.28 kg (AI)/ha
was significantly greater than the efficacy of chlorpyrifos, of cyfluthrin, and of esfenval-
erate. With the exception of cyfluthrin, every other chemical treatment was significantly
more effective than esfenvalerate.
In the second assessment of the 1987 experiment, FAW damage in untreated plots
rated a mean (f S.D.) 5.5 f 0.94; all chemical treatments significantly reduced FAW
injury (F = 4.6, P = 0.05. Mean percent control of FAW injury by cyhalothrin at 0.028
kg (AI)/ha (88.8 f 6.6%) was significantly greater than control by any other treatment,
except tralomethrin at 0.017 kg (AI)/ha (71.1 fi 18.5%). Tralomethrin and methomyl at
0.84 kg (AI)/ha (64.7 f 23.0%) had significantly greater efficacy than any other treatment,
except cyhalothrin and methomyl at 0.56 kg (AI)/ha (60.6 f 9.2%).Methomyl at 0.56 kg
(AI)/ha was significantly more effective than cyfluthrin at 0.028 kg (AI)/ha (30.6 f 10.8%),
methomyl at 0.28 kg (AI)/ha (40.6 f 24.6%), and esfenvalerate at 0.028 kg (AI)/ha (19.2
fi 34.3%). Additionally, the efficacy of chlorpyrifos at 0.28 kg (AI)/ha and 0.56 kg (AI)/ha
(46.0 f 22.0% and 43.5 f 30.3% control, respectively) and the efficacy of cypermethrin
at 0.028 kg (AI)/ha (40.3 fi 24.6%) were significantly greater than the efficacy of esfen-
valerate. Methomyl at 0.28 kg (AI)/ha (40.6 f 31.4%) and cyfluthrin at 0.028 kg (AI)/ha
(30.6 fi 10.8%) were statistically comparable with esfenvalerate, cypermethrin, and
chlorpyrifos (0.56 and at 0.28 kg [AI]/ha).
In summary, these tests indicate that control of FAW damage in whorl stage field
corn, sweet corn, and sorghum provided by the pyrethroid insecticides tralomethrin,
flucythrinate, and cyhalothrin is comparable with recommended rates of methomyl and
chlorpyrifos. The other pyrethroids tested; fluvalinate, fenvalerate, esfenvalerate, per-
methrin, cypermethrin, and cyfluthrin; were relatively less effective in the corn exper-
iments. However, they were comparable with other treatments in control of FAW injury
in whorl stage sorghum.
Many pyrethroid insecticides have shown activity against noctuid larvae, but often
failed to provide adequate control of FAW (Harrell et al. 1977). More recently developed
pyrethroids, including tralomethrin, flucythrinate, and cyhalothrin have been shown to
control FAW attacking sweet corn ears (All et al. 1986). Our results indicate that these
pyrethroids and others now available are also effective against FAW populations in
whorl stage corn and sorghum.










Florida Entomologist 74(2)


Since the late 1970's, FAW populations have shown resistance to a number of insec-
ticides including methomyl (Bass 1978, Young 1979). Identification of suitable alterna-
tives is basic for the management of resistance (Metcalf 1980). Our results indicate that
a number of pyrethroids can be substituted for methomyl or chlorpyrifos in FAW man-
agement programs.

REFERENCES CITED

ALL, J. N., A. JAVID, AND D. E. Dix. 1983. Sweet corn, control of a mixed infestation
of corn earworm and fall armyworm. Insect. and Acar. Tests. 8: 108.
ALL, J. N., A. JAVID, AND L. P. GUILLEBEAU. 1986. Control of fall armyworm with
insecticides in north Georgia sweet corn. Florida Entomol. 69: 598-602.
BASS, M. H. 1978. Fall armyworm: Evaluation of insecticides for control. Agric. Exp.
Stn. Auburn Univ. Leaflet 93: 7.
DUNCAN, D. B. 1955. Multiple range and multiple F tests. Biometrics. 11: 1-42.
HARRELL, E. A., J. R. YOUNG, AND W. W. HARE. 1977. Insect control on late-planted
sweet corn. J. Econ. Entomol. 70: 129-131.
METCALF, R. L. 1980. Changing role of insecticides in crop protection. Annu. Rev.
Entomol. 25: 219-256.
SAS user's guide: statistics. 1989. SAS Institute, Cary, North Carolina.
YOUNG, J. R. 1979. Assessing the movement of the fall armyworm (Spodoptera
frugiperda) using insecticide resistance and wind patterns, pp. 344-351 in R. L.
Rabb and G. G. Kennedy [eds.]. Movement of highly mobile insects: concepts
and methodology in research. North Carolina State University, Raleigh. 456 pp.









EFFECT OF VARIOUS CHEMIGATION METHODOLOGIES
ON SUPPRESSION OF THE FALL ARMYWORM
(LEPIDOPTERA: NOCTUIDAE) IN CORN

L. D. CHANDLER AND H. R. SUMNER
Insect Biology and Population Management Research Laboratory
USDA-ARS, Tifton, GA 31793

ABSTRACT

Studies were conducted in Tifton, Georgia during 1989 to compare the effectiveness
of center-pivot irrigation sprinkler packages and various formulations of insecticides for
the control of fall armyworm, Spodoptera frugiperda (J. E. Smith), infesting corn.
Chemigation with Whirl-jet (E53) sprinklers provided better control of the pest than
impact sprinklers or a Pass system. Chemigation with whirl-jet sprinklers controlled
fall armyworm as well as a conventional hi-clearance sprayer. Asana XL 0.66 EC + oil
chemigated with an irrigation simulator provided the most consistent control of fall
armyworm larvae in whorl stage corn when compared with Asana XL + water, Lorsban
4E + oil, Lorsban 4E + water, Lorsban 6 (tech.) + oil, Larvin 3.2 + oil, and Larvin
3.2 + water. All tested materials resulted in significant reductions in fall armyworm
damage to the whorls of corn.


June, 1991


270











Fall Armyworm Symposium '90-Chandler & Sumner 271

RESUME

En studios realizados en Tifton, Georgia en 1989, se compare la efectividad de
varias formulaciones de insecticides al ser usadas en el sistema de riego por aspersi6n
contra el cogollero, Spodoptera frugiperda (J. E. Smith) en mAz. La quimigaci6n con
aspersorios tipo Whirl-jet (E53) brind6 un mejor control de la plaga que los aspersorios
de impact o el sistema Pass. La chemigaci6n con los aspersorios tipo Whirl-jet control
el cogollero tan bien como un equipo conventional de aspersi6n. Asana XL 0.66 EC +
aceite usado en el riego por aspersi6n brind6 el control mas consistent del cogollero
cuando el mafz estaba en estado de mazorca, comparado con Asana XL + agua, Lorsban
4E + aceite, Lorsban 4E + agua, Lorsban 6 (tech.) + aceite, Larvin 3.2 + aceite y
Larvin 3.2 + agua. Todos los materials dieron resultados significativos en la reducci6n
de dafo del cogollero a la mazorca del maiz.




Fall armyworm (FAW), Spodopterafrugiperda (J. E. Smith), is a major pest of corn
throughout the southeastern United States. Typically, sweet corn is double-cropped
throughout the region with the second crop planted late in the growing season when
populations of FAW are largest (Harrell et al. 1977). Insecticides are the primary
mechanism for control of the FAW. Recent studies conducted in Florida indicate that
maintaining the sweet corn crop relatively free of FAW prior to the silk stage can reduce
the total number of conventionally applied insecticide treatments needed to protect the
ears (Foster 1989). However, more than 10 applications during silking are still needed
to provide control in late summer and fall crops. Young (1980) suggested that insectigation
(application of insecticides in irrigation water) was the best method available for the
application of insecticides to control FAW larvae, especially when late planted corn
became infested. Insectigation allows maximum insecticide coverage without limitation
of water volume as in conventional sprayer operations. Greater volumes of water aid
insecticide penetration into corn whorls. Later studies suggested that FAW larvae could
better be controlled with technical chlorpyrifos (Lorsban) formulated in oil (as opposed
to EC formulation) and applied on an established schedule through a center-pivot irriga-
tion system (Young 1986). This method requires 12-14 insecticide applications during
the spring growing season and 21-26 applications during the summer-fall season (Young
1986) in order to produce 97+% worm free ears of sweet corn. Technical chlorpyrifos
presently is not commercially available or labeled for use in center-pivot systems, thus
alternative formulations and insecticides are needed.
Chemigation has economic advantages over conventional application methods. Chemi-
gation costs are estimated to be $1.70/ha when applied with 10 mm of irrigation compared
to $5.60/ha for conventional treatments (Threadgill 1981). The dollar savings should
make chemigation attractive. However, widespread adoption of chemigation has been
slow. In 1983, growers of an estimated 200,000+ ha, or about 2% of the total sprinkler-ir-
rigated area in the United States, were using insectigation (Threadgill 1985). This
hectarage has since increased, but the safety of insectigation and improvement of insec-
tigation application technology are concerns of growers and researchers. Additional
studies related to insectigation application technology are necessary to optimize the
efficiency of the chemigation system and to compare insectigation with conventional
control methods. This paper reports studies designed to evaluate and improve FAW
control in sweet corn using insectigation technology. The objectives of the studies were
1) to study FAW control variability following insecticide application with various irriga-
tion sprinkler packages, 2) to compare insectigation techniques with conventional appli-
cation methods for FAW control, and 3) to evaluate various insecticide formulations and
carriers for use in insectigation to manage FAW.










272 Florida Entomologist 74(2) June, 1991

MATERIALS AND METHODS

Evaluation of Irrigation Sprinkler Packages

'Merit' variety sweet corn was direct-seeded on 5 July, 1989 in three quadrants (0.15
ha/quadrant) of two center-pivot irrigation systems located on the Coastal Plains Exper-
iment Station in Tifton, Georgia. The corn was grown using established agronomic
practices except for the insecticide applications. Insecticides were applied in a single
quadrant with one of the following irrigation sprinkler packages: a) the Spraying System
Whirl-jet nozzle (E53) calibrated to deliver 17,770 liters/ha of water applied at 69 kPa
(kilopascals); b) the Pass system (Whirl-jet E2-E20 nozzles) designed to put insecticides
into the system at the outer edge of the pivot and calibrated to deliver 1683 liters/ha
of water applied at 69 kPa; and c) the low angle impact sprinkler system calibrated to
apply 17,770 liters/ha of water at 310 kPa. Insecticides formulated with non-EC oil for
a total formulation volume of 4.9 liters/ha were direct-injected with the injection nozzle
pointed downstream into the irrigation mainline. The water velocities at the injection
site were 2.1, 2.8, and 1.1 m/sec for Whirl-jet, Pass and impact systems, respectively.
Applications of chlorpyrifos (Lorsban) and cypermethrin (Cymbush) combinations
were initiated just prior to tasseling (Table 1) and continued through corn ear maturity
following a treatment schedule devised by Young (1986). Treatments were made prior
to tasseling and then every day for five days (beginning at 5% silk), followed by every
other day for four applications and then every third day until harvest. Six 3.8 m long
double row (91-cm spacing) plots/quadrant were established during the whorl plant
growth stage to evaluate effectiveness of sprinkler packages for FAW control. The plot
mid-points were 18, 24, 27, 31, 33, and 39 m from the pivot point in each quadrant.
Each pivot system was 48 m in length from pivot point to wheel track. During whorl
stage, 20 plants per plot were randomly selected and examined for presence of FAW
larvae and new feeding damage following the fourth insecticide application. Mature ears
were harvested on 7 Sept. All ears in each plot were collected and the total number of
marketable size ears was determined. The number of worm-free ears/plot was noted
and an insect damage index (Widstrom 1967) calculated from 15 randomly selected ears
from each plot sample. The damage index was based on a 0 (no damage) to n scale,
where n = the total depth of larval feeding in 1 cm units. The total number of larvae
found in ears in each plot was noted and species of each determined.


Evaluation of Conventional vs Insectigation Treatments

'Merit' variety sweet corn was direct-seeded on 11 July, 1989 in two quadrants (0.15
ha each) of a single center-pivot irrigation system at Tifton, Georgia. Established ag-
ronomic practices for corn production were followed except for the application of insec-
ticides in irrigation water. Insecticides were applied in one quadrant using the Spraying
System Whirl-jet (E53) sprinkler package described in the above test. The main line
water velocity was 1.1 m/sec at the point of insecticide injection. The additional quadrant
was treated during the whorl stage of plant growth with a Ford 400 hi-clearance tractor
equipped with a Johnson PTO mounted sprayer and during the period from silk to
harvest with a John Deere 600 Hi-cycle sprayer. Both sprayers were calibrated to deliver
281 liters/ha of total spray volume. Chlorpyrifos and cypermethrin applications were
initiated just prior to tasseling and continued through harvest as noted in the above
test. An untreated control area was provided at the outer edge of the conventionally
treated quadrant wherein six 3.8 m-long double-row plots were established at the same
time that plots were established within the treated quadrants. Mature ears were har-
vested on 14 Sept., and insect damage evaluations were conducted as above.











Fall Armyworm Symposium '90-Chandler & Sumner 273

Evaluation of Insecticide Formulations and Carriers

A 0.8-ha field was direct-seeded to 'Pioneer 3320' variety field corn on 23 Aug. 1989
at Tifton, Georgia. The field was divided into 32 plots, each 5 rows wide (91-cm spacing)
by 12.2 m long. Each plot was separated by 0.9 m alleys on the same rows. Plots were
arranged in a randomized complete block design with four replications. Seven different
insecticide treatments were applied on whorl stage (4-10 leaf stage) plants with an
irrigation simulator (Sumner et al. 1989) calibrated to deliver 25,400 liters of water per
ha through four E53 Whirl-jet nozzles at 69 kPa. Desired insecticide concentrations
were mixed in either vegetable oil or water and applied, at a rate of 4.9 liters of total
material per ha, following injection into the main line which carried a water velocity of
2.4 m/sec. Thirty plants per plot were randomly selected from the center three rows of
each plot, and the number of freshly damaged plants and lepidopterous larvae noted.
Larvae were identified by species. Insect damage evaluations were performed prior to
each application date and again 48 hours after treatment. Three applications were made.

Statistical Analyses

Means and standard deviations were calculated for all data. Analysis of variance
procedures were performed and treatment means separated by Duncan's multiple range
test (Duncan 1955). Regression analyses of the effects of distance from the pivot point
on ear damage ratings were conducted on both center-pivot irrigation tests.


RESULTS AND DISCUSSION

Evaluation of Irrigation Sprinkler Packages

Whirl-jet (E53) sprinklers provided FAW control in whorl-stage sweet corn that was
statistically superior (P < 0.05) to that noted with impact sprinklers and the Pass system
(Table 1). The number of infested whorl stage corn plants in the quadrant treated with
Whirl-jet sprinklers was ca. 1/2 the infestation noted in the quadrant treated with impact
sprinklers and ca. 1/10 the infestation in the Pass system quadrants. As the corn prog-
ressed into the tassel/silk stage the number of FAW within the plots increased dramat-
ically. The percentage of larvae identified as FAW on ears at harvest ranged from 63
to 95%. Scheduled applications of insecticides did not decrease the FAW population or
resulting damage to a level acceptable for fresh market production. This phenomenon
was likely caused by the low rates of insecticides used, which were less than the recom-
mended label rates. The lower rates were intentionally used to provide less than 100%
insect control to better distinguish insect control levels among the three application
systems. The number of damaged ears harvested was similar (P > 0.05) in the Whirl-jet
and impact sprinkler treated quadrants (Table 1). However, insect damage indices per
quadrant were significantly less (P s 0.05) in the Whirl-jet treated quadrant compared
with the impact and Pass system treated plots.
Table 2 presents results of regression analyses conducted to determine the effective-
ness of insect control as influenced by the distance from the center point of the center-
pivot system. The analyses show that in plots treated with either Whirl-jet or impact
sprinklers insect control decreased with distance from the pivot point, indicating that
the insecticide is not effectively reaching the target at distances over 30 m from the
center. It is probable that this phenomenon is related to the velocity of water flowing
through the mainline at the insecticide injection point. Insecticides were injected into
the system with a main-line velocity of ca. 1.1 and 2.1 m/sec for impact and Whirl-jet
sprinklers, respectively. These velocities may not allow for sufficient break-up of oil




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