Title: Florida Entomologist
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Permanent Link: http://ufdc.ufl.edu/UF00098813/00068
 Material Information
Title: Florida Entomologist
Physical Description: Serial
Creator: Florida Entomological Society
Publisher: Florida Entomological Society
Place of Publication: Winter Haven, Fla.
Publication Date: 1990
Copyright Date: 1917
Subject: Florida Entomological Society
Entomology -- Periodicals
Insects -- Florida
Insects -- Florida -- Periodicals
Insects -- Periodicals
General Note: Eigenfactor: Florida Entomologist: http://www.bioone.org/doi/full/10.1653/024.092.0401
 Record Information
Bibliographic ID: UF00098813
Volume ID: VID00068
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: Open Access

Full Text

(ISSN 0015-4040)


(An International Journal for the Americas)

Volume 73, No. 3 September, 1990


Announcement Forum Section ................................................................. i


WISEMAN, B. R.-Plant Resistance to Insects in the Southeastern United States
A n Overview ................................................................................ 351
SLANSKY, F., JR.-Insect Nutritional Ecology as a Basis for Studying Host
P lant R resistance ............................................................................ 359
JACKSON, D. M.-Plant-Insect Behavioral Studies: Examples with Heliothis and
M anduca Species ............................................................................ 378
PARROTT, W. L.-Plant Resistance to Insects in Cotton .............................. 392
SCHALK, J. M.-Plant Resistance to Insects in Vegetables for the Southeastern
U united States ......................................................... ...................... 396
QUISENBERRY, S. S.-Plant Resistance to Insects and Mites in Forage and Turf
G rasses ......................................................................................... 411
LYNCH, R. E.-Resistance in Peanut to Major Arthropod Pests ................. 422
WISEMAN, B. R., AND F. M. DAVIS-Plant Resistance to Insects Attacking Corn
and Grain Sorghum ........................................................................ 446

Research Reports
ALI, A., AND R. G. LUTTRELL-Survival of Fall Armyworm (Lepidoptera: Noc-
tuidae) Immatures on Cotton .......................................................... 459
HENNESSEY, M. K.-Insect Type Specimens in the Staten Island Institute of
Arts and Sciences, New York .......................................................... 465
CHOATE, P. M.-Checklist of the Ground Beetles of Florida (Coleoptera:
Carabidae), Literature Records ........................................................ 476
Leiophron (Hymenoptera: Braconidae, Euphorinae) From Kenya ......... 492
Trichopria stomoxydis (Hymenoptera: Proctotrupoidae: Diapriidae) a Gre-
garious Endoparasite of Stomoxys calcitrans From Zimbabwe, Africa .... 496

Scientific Notes
ported Fire Ant Infestation of Soybean Fields in the Southern
U united States ...................................................................... 503
ZOEBISCH, T. G., AND D. J. SCHUSTER-Influence of Height of Yellow
Sticky Cards on Captures of Adult Leafminer (Liriomyza trifolii)
(Diptera: Agromyzidae) in Staked Tomatoes ........................... 505
Continued on Back Cover

Published by The Florida Entomological Society

President ......... .......................... ................. J. E. Eger
President-Elect ...................................... .......................... J. F. Price
Vice-President ........................................................ J. L. Knapp
Secretary ......................................... .. ................. J. A. Coffelt
Treasurer ................................. .................. A. C. Knapp
Other Members of the Executive Committee
R. S. Patterson J. E. Pefia F. D. Bennett
M. Camara R. Coler
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
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
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 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 September 1, 1990

A New Type of Article for our Authors and Subscribers

We are proud to announce that scientists may submit articles for publication in a
FORUM section of Florida Entomologist. FORUM articles (1-2 per issue) will appear
at the beginning of each issue in a section marked FORUM.
Articles for the FORUM section must follow the general style guidelines for all
other articles submitted to Florida Entomologist. FORUM articles must be of high
scientific quality, demonstrate acceptable experimental design and analysis, and cite
appropriate sources to support findings. FORUM articles will include "cutting edge"
science, scientifically meritorious but controversial subjects, new methodologies (de-
signed and tested), experimentally-based designs and tests of pedagogical methods, and
documented challenges to existing entomological techniques, philosophies or experimen-
tal paradigms.
Submitted articles should include "Submitted to Florida Entomologist: FORUM"
on the title page. Three or more peer reviews will be acquired by the Associate Editor
for FORUM publications.
We feel the addition of a FORUM section will expand the scope of Florida En-
tomologist and allow readers and publishing scientists an additional creative outlet that
will complement our symposia, research articles, and notes.

Wiseman: Symposium-Plant Resistance to Insects


USDA, ARS, Insect Biology & Population Management Research Lab,
Tifton, GA 31793


Plant resistance to insects is an effective and ideal method for controlling crop pests.
The development and use of plant cultivars with resistance to insects and their effects
on insect populations is reviewed. Resistant plants may be used as a sole control method
or as an adjunct to other control components of integrated pest management. Although
demand for the use of resistant cultivars for control of insects is anticipated to increase,
graduate training in applied plant resistance is lacking, and only four universities in the
southeastern United States have formal graduate courses. Georgia, Louisiana, and Mis-
sissippi have major programs of plant resistance to insects with lesser amounts in
Florida, North Carolina, and South Carolina. The United States Department of Agricul-
ture's Agricultural Research Service has the largest efforts in plant resistance to insects
in the Southeast.


Un m6todo efectivo e ideal para controlar plagas en cultivos es el uso de plants
resistentes. Se revisa el desarrollo y el uso de variedades resistentes a plaga de insects
y sus efectos en las poblaciones de insects. Plantas resistentes se pueden usar como el
inico m6todo de control o como adjunto a otros components de control en un sistema
integrado de administraci6n de plagas. Aunque se anticipa el aumento en la demand
de variedades resistente a plagas, hay una falta de entrenamiento en el Area de la
aplicaci6n de resistencia de plants al nivel de graduados, y solo cuatro universidades
en el sudeste de los Estados Unidos ofrecen cursos formales para graduados. Los es-
tados de Georgia, Louisiana y Mississippi tiene grandes programs de resistencia de
plants a plagas de insects, y la Florida, Carolina del Norte y Carolina del Sur tienen
programs menores. El Servicio de Investigaci6n Agricola del Departamento de Ag-
ricultura de los Estados Unidos tiene los mayores programs de studios de resistencia
de plants a plagas en el sudeste.

Numerous agricultural leaders over the past 25 years have emphasized the need for
nonchemical control of insect pests. However, Headley (1979) predicted that chemical
control would have a major role in pest management in high value crops until 1992 and
then the trend for nonchemical control methods would increase (Table 1). He also pre-
dicted that resistant cultivars would have a major role in controlling pests in grain crops
until 1992 and that a demand for their use would sharply increase in all crops after that
time. The recent ARS budget increases for biocontrol and ground water quality em-
phasize the need for more nonchemical pest control research to minimize reliance on
chemical pesticides for pest control. Plant resistance to insects, integrated with other
biocontrol strategies, should be one of the principle means of nonchemical control of
The growing of cultivars resistant to insect pests has been acclaimed the most effec-
tive and ideal method of combating pests that attack plants (Luginbill 1969). The use
of resistant cultivars, either alone or in combination with other integrated pest manage-

Florida Entomologist 73(3)


Pest control technique Probable use to 1992 Trend in use

Chemical methods
Insecticides Major Declining
Mechanical methods Minor Declining
Biological methods
Parasites & predators Minor No change
Bacteria Minor Increasing
Viruses Not significant Increasing
Pheromones Not significant No change
Resistant varieties Major Increasing
Pest genetics Minor Declining
Cultural methods
Crop rotation Minor Declining
Trap crops Minor No change

*Modified from Headley 1979.

ment systems, provides crop protection that is biologically, ecologically, economically,
and socially feasible (Teetes 1985). Resistant cultivars are nonpolluting to our environ-
ment and may be grown at no extra expense to the farmer.
The use of insect-resistant plants is usually associated with reduced crop damage by
pests (Painter 1951). Painter attributed resistance to heritable qualities of the plant. A
resistant plant is always resistant to a specific pest species under given environmental
conditions; if the environment changes, the level of resistance may or may not change.
Mutations in a resistant plant genotype may or may not be resistant, but its predecessor
remains resistant to the pest insect. A pest insect species may also form new biotypes
while the original insect biotype remains susceptible to the resistant plant genotype.
Hence, resistance in plants to insects is probably more stable than given credit. Con-
versely, insect pests are genetically diverse, as evidenced by the number of biotypes
in certain crop-insect relationships, i.e., the Hessian fly.
Painter (1968) proposed three mechanisms of resistance: non-preference, antibiosis,
and tolerance. (1) Nonpreference denotes a group of plant characters and insect re-
sponses that lead an insect away from a plant or plant part for oviposition, for food, or
for shelter, or for any combination of the three (Painter 1951, 1968). Painter (1968)
delineated nonpreference into two distinct actions of choice by insects among cultivars:
(a) a choice to oviposit, establish, or feed when several cultivars are grown or (b) a
choice to oviposit, establish, or feed when only one cultivar is present. Owens (1975)
further described these two uses of nonpreference as relative or absolute. (2) Antibiosis
is the mechanism of resistance that produces those adverse effects on the insect life
history which result when a resistant plant is used for food (Painter 1951). The effects
of an insect feeding on a plant with this type resistance may be death of the neonate
larva or nymph, reduced food consumption that results in a smaller size or lower weight,
increased developmental time, low food reserves, death in the prepupal stage, and/or
reduced fecundity (Owens 1975). (3) Tolerance to insect damage is a resistance
mechanism that allows the plant to grow and reproduce or repair injury in spite of
supporting a density of insects approximately equal to what would be damaging to a
susceptible cultivar (Painter 1951).
The basic triad of the mechanisms of resistance proposed by Painter (1951) is usually
delineated by specifically designed experiments to demonstrate the independence of the
three components; however, resistant cultivars often possess combinations of these
resistance mechanisms, especially with regard to nonpreference and antibiosis. With a

September, 1990


Wiseman: Symposium-Plant Resistance to Insects

combination of resistance mechanisms, a cultivar that is nonpreferred does not require
the same level of antibiosis or tolerance that a more preferred cultivar must possess to
have the same level of resistance. Thus, different cultivars may possess the same levels
of resistance with different mechanisms of resistance and/or levels of the resistance
Plant resistance to insects received a lot of attention and support shortly after the
late Rachael Carson published her book, "Silent Spring," even though she did not men-
tion the use of resistant cultivars as a means of nonchemical control of insect pests. This
was probably because the resistant plant's effect is not as dramatic and its effects on
insects are not as visible as those of other control measures (Luginbill 1969). However,
agricultural leaders recognized the importance of resistant cultivars as the most success-
ful and least heralded of all the natural methods of insect control (Holcomb 1970).
Dahms (1972a) reported that more than 100 varieties or inbreds with resistance to
insects have been released, with resistance to more than 25 insect species. Today,
probably more than 500 cultivars with resistance to more than 50 insect species or
biotypes have been developed and released.
The development and use of resistant cultivars should be the foundation or "hub" of
any crop protection scheme. Before 1951, the production of sweet corn was unprofitable
in the Southeast, even with the use of pesticides. However, in 1951 'loana' sweet corn
was released with low to intermediate levels of resistance to corn earworm. This allowed
growers to produce sweet corn without pesticides. Today, higher levels of resistance in
sweet corn are available to growers, as evidenced by the fact that 'loana' is used in our
studies as a susceptible check. Use of resistant cultivars has certainly been profitable
to the grower. Luginbill (1969) quoted a return value to the grower of $300 for each $1
invested in research and development of resistant plants. McMillian & Wiseman (1972)
also estimated that for each $1 invested by the USDA for the period from 1950 through
1970 on research on resistance in corn to Heliothis zea (Boddie), $20 was returned to
the grower in the form of an increase in corn yield.
Historically, insect-resistant cultivars have been more widely used for crops where
plant resistance was the only method of protection from losses caused by insects (Wise-
man 1982). One of the earliest records of the use of an insect resistant variety was that
of Havens (1792) who reported that the wheat variety 'Underhill' was planted to avoid
losses caused by the Hessian fly, Mayetiola destructor (Say). Today, growing resistant
wheat cultivars is the primary method for controlling the Hessian fly worldwide. The
Purdue-USDA small grains improvement program has estimated a $3.4 billion increase
in farm income attributable to improved cultivars with resistance to this insect (Roberts
et al. 1988). The annual return exceeded $4.6 million per scientific year invested, calcu-
lated over a 64-year period of the program. Buntin & Raymer (1989) reported an
economic benefit of using resistant wheat cultivars to control the Hessian fly averaged
$104/ha in Georgia.
Grape stocks resistant to Phylloxera spp. were first grown commercially in Europe
in 1870, and U.S. grape stocks were subsequently shipped to France to save the wine
industry from Phylloxera (Painter 1951). 'Rescue', a resistant wheat cultivar, rescued
the wheat growers of the Northern Plains of the U.S. and Canada from the wheat stem
sawfly, Cephus cinctus (Norton) (Luginbill 1969). In addition, the planting of some 8.6
million hectares of corn hybrids resistant to the European corn borer, Ostrinia nubilalis
(Hiibner), is a present day example of the adoption and wide use of a resistant cultivar
in some crop-insect relationships (Schalk & Ratcliffe 1976).
Dr. R. G. Dahms (personal communication, 1972) stated that in 1951, in the U.S.,
resistant grain and forage cultivars were available only for limiting losses to the corn
earworm in dent corn and to the Hessian fly in wheat (Table 2). By 1971, U.S. growers
had dent corn resistant to corn earworm and European corn borer, alfalfa cultivars
resistant to spotted alfalfa aphid, Therioaphis maculata (Buckton), wheat cultivars


Florida Entomologist 73(3)


Insect and Crop Chemical Cultural Res. Var.

Corn earworm
Sweet corn X -
Dent X
European corn borer X X
Southwest. corn borer X X
Corn rootworm X
Fall armyworm X -
Spotted alfalfa aphid X -
Sorghum -
Wheat X X
Barley X X
Hessian fly X X

*From R.G. Dahms (personal communication).

resistant to Hessian fly, and a barley cultivar resistant to the greenbug, Schizaphis
graminum (Rodani) (Table 3). Dahms then made a prediction that by 1981, U.S. farmers
would have grain and forage cultivars resistant to all eight major pests listed in Table
4. This prediction was achieved and surpassed with the release of the first sorghum
hybrid with resistance to the sorghum midge, Contarinia sorghicola (Coquillett), in
July of 1981. However, chemical controls are still needed for second generation Euro-
pean corn borer, Southwestern corn borer, and for control of corn rootworms.
The use of resistant cultivars as a primary control measure has made the use of other
control components unnecessary for the management of some insect pests. The results
have been rather specific, cumulative, and persistent (Dahms 1972b, Wiseman 1982).
Further, Adkisson & Dyck (1980) stated that reduction in pest populations achieved
through the use of resistant plants is constant, cumulative, and practically without cost


Insect and Crop Chemical Cultural Res. Var.

Corn earworm
Sweet corn X X
Dent X X
European corn borer X X
Southwest. corn borer X X
Corn rootworm X X
Fall armyworm X -
Spotted alfalfa aphid X
Sorghum X X
Wheat X X
Barley X X
Hessian fly X X

*From R. G. Dahms (personal communication).


September, 1990

Wiseman: Symposium-Plant Resistance to Insects 355


Insect and Crop Chemical Cultural Res. Var.

Corn earworm
Sweet corn X X X
Dent X X
European corn borer X X
Southwest. corn borer X X
Corn rootworm X X
Fall armyworm X X
Spotted alfalfa aphid X
Hessian fly X X
Sorghum X X
Wheat X X
Barley X X
Sorghum midge
**Sorghum X X X

*From R.G. Dahms (personal communication).
**First resistant hybrid release in July 1981 by Funk Seeds International.

to the growers. In the future, resistant cultivars developed for the sole component of
control for a specific insect will likely possess a high level of resistance, while other
cultivars will be developed with lower levels of resistance and will be integrated with
other IPM components for the control of pests.
Dahms (1972b) illustrated vividly the theoretical effects of antibiosis on insect popu-
lations using four criteria, i.e., rate of reproduction, rate of nymphal development,
mortality of nymphs, and length of productive life. Applying the four antibiotic factors
cumulatively for the spotted alfalfa aphid, he showed that aphids on 'Lahontan', a resis-
tant alfalfa cultivar, reproduced at a rate of 2.5 per day for 13 days and that nymphs
matured in 9 days with 90% mortality, while aphids on 'Chilean', a susceptible alfalfa
cultivar, reproduced at a rate of 4 per day for 13 days and nymphs matured in 6 days
with only 10% mortality. After 10 days there would be 30 times more aphids on 'Chilean'
than on 'Lahontan', and after 50 days 14 million times more aphids would be produced
on 'Chilean' than on 'Lahontan'. Similar documentation on the effects of resistance to
other insects would be of immense benefit in promoting the use of resistant cultivars.
Resistant cultivars also may be used as an adjunct to other control tactics. Resistant
cultivars are, for the most part, compatible with insecticides, biocontrol agents, and
cultural control. However, the levels and mechanisms of resistance must be well under-
stood to effectively combine other control tactics with the resistant cultivar (Wiseman
Researchers in plant resistance have attained a number of goals. However, in the
Southeast the results have not been as striking as results in the mid-west, probably
because of the overwhelming populations of pests that occur in the Southeast each year
that often mask lower levels of resistance to insects or the levels of resistance in the
germplasm collections are low. But since we work with two dynamic, ever-changing
biological systems, we must not and cannot stop in our search for higher levels of
This symposium reported on programs of plant resistance to insects in the Southeast-
ern United States. Studies on insect nutritional ecology, insect behavior, and plant
resistance enhancing biocontrol were discussed. In addition, information was reported

Florida Entomologist 73(3)

STATES, 1980-89.'

Total Number of

Contributions to Germplasm
State2 Publications PRI Newsletter Releases Graduates

Florida 5 7 0 1
Georgia 149 183 16 0
Louisiana3 98 32 0 2
Mississippi 47 5 8 2
N. Carolina 14 8 1 1
S. Carolina 1 6 3 0

'Source: Plant Resistance to Insects Newsletter Vol. 6-15, 1980-89. Graduates were reported beginning in 1984.
2No reports available from Arkansas or Tennessee.
3Most of the publications for 1986-87 originated from the International Rice Research Institute.

on insect rearing and the development and release of resistant germplasm for corn,
cotton, grasses, peanuts, soybeans, sorghum, tobacco, and vegetables. Over the past
10 years, most of the resistant germplasm released has been from Georgia, followed by
Mississippi and South Carolina. Major efforts in plant resistance have been by USDA's
Agriculturel Research Service. Likewise, the most publications and contributions re-
ported via the Plant Resistance to Insects Newsletters came from Georgia, Louisiana,
and Mississippi, respectively (Table 5). In addition to the crops previously mentioned,
plant resistance research and development on forages, forest trees, rice, sugarcane, and
wheat ongoing in the Southeastern States are listed in Table 6. Research on 33 insect
species has been reported over the past 10 years (Table 7) (PRI Newsletter Vols. 6-15).
There is also some commercial research and development in Tennessee on plant resist-
ance to insects attacking corn. And there are a few programs on biotechnology at the
state, federal, and commercial level with its application to plant resistance to insects in
the Southeast.


Crop Fla. Ga. La. Miss. N.C. S.C. Tenn.

Corn X X 2
Cotton X X
Forage X X X X X
Forest X
Peanut X X
Rice X
Sorghum X
Soybean X X X X X X
Sugarcane X X
Tobacco X X X
Vegetable X X X
Wheat X

'Source: Plant Resistance to Insects Newsletter Vols. 6-15. 1980-89.
2No report available but commercial research and development is ongoing.


September, 1990

Wiseman: Symposium-Plant Resistance to Insects




Aphids, MS
Bean leaf beetle, LA
Beet armyworm, MS
Caribbean fruit fly, FL
Clover head weevil, MS
Colorado potato beetle, NC
Corn earworm, GA, MS, NC
Cowpea curculio, SC
Diabrotica sp., LA, SC
Fall armyworm, GA, LA, MS, TN
Flea beetle, SC
Green cloverworm, GA
Hessian fly, GA
Leaf miner, FL
Least skipper, LA
Maize weevil, GA
Mexican bean beetle, GA, SC
Pickleworm, SC
Potato leafhopper, NC
Pseudoplusia includes, LA

Rice stink bug, LA
Rice water weevil, LA
Sorghum midge, GA
Southern green stink bug, SC
Southwestern corn borer, MS, TN
Soybean looper, GA, LA, MS
Sugarcane borer, FL
Thrips, NC
Tobacco budworm, MS, NC
Tobacco hornworm, NC
Tomato pinworm, FL
Velvetbean caterpillar, GA, LA, MS
Wireworm, SC

'Source: Plant Resistance to Insects Newsletter, Vols. 6-15. 1980-89.

One weak point in our discipline of plant resistance to insects is the training of
graduate students (Table 5). Even though we have numerous plant resistance research
programs and several formal courses taught in the U.S., today more than ever before,
applied graduate student training in plant resistance to insects is lacking. Most of the
training is on the interaction of insects and plants rather than on the development and
use of resistant cultivars. In the southeastern U.S., formal plant resistance courses are
taught only at Louisiana State University, Mississippi State University, North Carolina
State University, and the University of Florida. The University of Florida has the
distinction of offering two formal graduate courses.
There are definite bright spots for the future for plant resistance to insects. Exam-
ples are the development of resistant cultivars for more crops, development of cultivars
with multiple pest resistance such as that reported by Overman (in press), use of resis-
tant cultivars in the management of insect pests on the farm and on an area-wide basis,
and utilization of biotechnology and genetic engineering breakthroughs for the develop-
ment of resistant cultivars. Plant resistance to insects should be the major component
in the future for management of insect pests. Better training of graduate students in
this area and better documentation on the effects of resistant cultivars on insect popu-
lations are two major needs if we are to meet this expectation.


ADKISSON, P. L., AND V. A. DYCK. 1980. Resistant varieties in pest management
systems. pp. 233-251, in F. G. Maxwell and P. R. Jennings, [eds.]. Breeding
plants resistant to insects. Wiley. New York.
BUNTIN, G. D., AND P. L. RAYMER. 1989. Hessian fly (Diptera: Cecidomyiidae)
damage and forage production of winter wheat. J. Econ. Entomol. 82: 301-306.

Florida Entomologist 73(3)

September, 1990

DAHMS, R. G. 1972a. Development of crop resistance to insects. J. Environ. Qual. 1:
DAHMS, R. G. 1972b. The role of host plant resistance in integrated insect control.
pp. 152-167, in M. G. Jotwani and W. R. Young [eds.]. The control of sorghum
shoot fly. New Delhi, India. Oxford and IBH.
FOSTER, J. E., AND E. E. ORTMAN. 1987. Annual Plant Resistance to Insects News-
letter. 13. 78 pp.
FOSTER, J.E., AND E. E. ORTMAN. 1988. Annual Plant Resistance to Insects News-
letter. 14. 76 pp.
FOSTER, J. E., AND E. E. ORTMAN. 1989. Annual Plant Resistance to Insects News-
letter. 15. 77 pp.
GALLUN, R. L., AND E. E. ORTMAN. 1980. Annual Plant Resistance to Insects
Newsletter. 6. 85 pp.
GALLUN, R. L., AND E. E. ORTMAN. 1981. Annual Plant Resistance to Insects
Newsletter. 7. 88 pp.
GALLUN, R. L., AND E. E. ORTMAN. 1982. Annual Plant Resistance to Insects
Newsletter. 8. 75 pp.
GALLUN, R. L., AND E. E. ORTMAN. 1983. Annual Plant Resistance to Insects
Newsletter. 9. 84 pp.
GALLUN, R. L., AND E. E. ORTMAN. 1984. Annual Plant Resistance to Insects
Newsletter. 10. 81 pp.
GALLUN, R. L., AND E. E. ORTMAN. 1985. Annual Plant Resistance to Insects
Newsletter. 11. 62 pp.
GALLUN, R. L., AND E. E. ORTMAN. 1986. Annual Plant Resistance to Insects
Newsletter. 12. 72 pp.
HAVENS, J. N. 1792. Observations on the Hessian fly. N. Y. Society of Agric. Trans.,
Arts, and Manufacturing 1: 89-107.
HEADLEY, J. C. 1979. Economics of pest control: have priorities changed? Farm
Chemicals 142: 55-57.
HOLCOMB, R. W. 1970. Insect control: alternatives to use of conventional pesticides.
Science 168: 456-460.
LUGINBILL, P., JR. 1969. Developing resistant plants the ideal method of controlling
insects. USDA. ARS Prod. Res. Rpt. 111. 14 pp.
MCMILLIAN, W. W., AND B. R. WISEMAN. 1972. Host plant resistance: a twentieth
century look at the relationship between Zea mays L. and Heliothis zea (Boddie).
Florida Agric. Exp. Sta. Monograph Ser. 2. 131 pp.
OVERMAN, J. L. In press. A maize breeding program for developing hybrids with
resistance to multiple species of leaf-feeding and stalk-boring Lepidoptera, in
Methodologies used for determining resistance in corn to insects.
OWENS, J. 1975. An explanation of terms used in insect resistance to plants. Iowa
State J. of Res. 49: 513-517.
PAINTER, R. H. 1951. Insect resistance in crop plants. The MacMillan Co.
PAINTER, R. H. 1968. Crops that resist insects provide a way to increase world food
supply. Kansas Agric. Exp. Sta. Bull. 520. 22 pp.
small grain improvement program a model of research productivity. J. Prod.
Agric. 1: 239-241.
SCHALK, J. M., AND R. H. RATCLIFFE. 1976. Evaluation of ARS programs on alter-
native methods of insect control: host plant resistance to insects. Bull. Entomol.
Soc. Amer. 22: 7-10.
TEETES, G. L. 1985. Insect resistant sorghums in pest management. Insect Science
and Its Application 6: 443-451.
WISEMAN, B. R. 1982. The importance of Heliothis-crop interactions in the manage-
ment of the pest. International Crops Research Institute for the Semi-Arid
Tropics. Proc. of the International Workshop in Heliothis Management. 15-20
Nov. 1981. Patancheru, A.P. India. pp. 209-222.
WISEMAN, B. R. 1985. Types and mechanism of host plant resistance to insect attack.
Insect Science and Its Application 6: 239-242.


Slansky: Symposium-Plant Resistance to Insects 359


Department of Entomology and Nematology,
Institute of Food and Agricultural Sciences,
University of Florida, Gainesville, FL 32611 USA


The links between food attributes, food consumption and utilization, and subsequent
insect performance are a primary focus of insect nutritional ecology. Development of
effective host plant resistance (HPR) tactics requires an understanding of these links
to successfully manipulate insect pest performance. Thus, the principles of insect nutri-
tional ecology provide a logical basis for research in HPR. Nutritional, allelochemical
and morphological attributes of crop plants may be altered through selective breeding,
biotechnology and cultural practices to affect target pest biochemistry, physiology and
behavior, including food consumption, digestion and absorption, conversion to biomass,
metabolism, detoxication, sequestration and excretion. These actions are designed to
reduce crop damage by deleteriously affecting insect performance; lowered consump-
tion, slowed growth and reduced weight gain increase mortality and decrease reproduc-
tion in survivors. Responses by the target pest (e.g., detoxication enzyme induction
and increased food consumption) may act to counter certain HPR tactics, but additional
tactics may derive from manipulating these responses. Use of a single plant attribute
to cause heavy mortality associated with a genetically simple mechanism in the target
insect (e.g., an allelochemical toxin in the plant acting analogous to a synthetic insec-
ticide applied to the crop), is likely to lead to relatively rapid evolution of resistance in
the pest population to the HPR tactic. A better strategy for maintaining long-term
effectiveness of resistant crop varieties (i.e., slowing the development of resistance in
the target pests to our HPR efforts) should probably involve multiple HPR tactics,
especially if deployed within a genetically diverse crop variety (such that the plants in
a crop field differ in the extent of expression of the various attributes serving as resist-
ance factors) and/or by alternating in subsequent plantings crop varieties manifesting
different resistance factors. Also, HPR tactics should be used which require genetically
complex alterations in physiology and behavior for an insect to evolve resistance.


El eslab6n entire los atributos de alimentos, consume de comida y utilizaci6n, y el
subsequent comportamiento del insecto, son el foco principal de la ecologia nutricional
del insecto. El desarrollo de tActicas efectivas de un program de resistencia de plants
hospederas require un entendimiento de estos eslabones para manipular con 6xito el
comportamiento de la plaga de insecto. De aqui que los principios de la ecologia nutri-
cional de insects provee una base l6gica para hacer investigaciones sobre resistencia
de plants hospederas. Atributos nutricionales, aleloquimicos y morfol6gicos de plants
de cultivo pueden ser alterados por fitomejoramiento selective, la biotecnologia o por
prActicas culturales que afectan la bioquimica, la fisiologia y el comportamiento, in-
cluyendo el consume de alimentos, la digestion, y la absorci6n, la conversion a masa
biol6gica, el metabolismo, detoxificaci6n, reclusi6n y excreci6n, de la plaga sefalada.
Estas accions estAn disefadas para reducir los dafios al cuitivo por la acci6n dafina al
comportamiento del insecto; el consume menor, el crecimiento retardado y el reducido
aumento de peso, aumenta la mortandad y disminuye la reproducci6n en los sob-
revivientes. La reacci6n de la plaga escogida (tal como la inducci6n de enzimas deto-
xicantes y el aumento del consume de alimentos) pueden actuar para contrarrestar
ciertas tActicas de resistencia de plants hospederas, pero se pudieran derivar otras

Florida Entomologist 73(3)

tacticas manipulando esas reacciones. El uso de un solo atributo de la plant que cause
una gran mortandad asociada con un mecanismo gen6tico simple en el insecto escogido
(tal como una toxina aleloquimica en la plant que actue anAloga a un insecticide sintetico
aplicado al cultivo), es probable que lleve a una evoluci6n rapida el desarrollo de resis-
tencia en la poblaci6n de la plaga hacia la tactica de resistencia de plant hospedera.
Una estrategia mejor para mantener una efectividad mas duradera de las variedades
resistentes (tal como demorando el desarrollo de resistencia de la plaga escogida como
blanco de nuestros esfuerzos en la resistencia de plants hospderas) probablemente
deben de incluir varias tActicas de resistencia de plants hospederas, especialmente si
es desplegada dentro de una variedad geneticamente diverse (tal como que las. plantaa
en el campo difieren en la expresi6n de los various atributos que sirven como factors de
resistencia) y/o alternando la siembra de variedades que manifiestan distintos factors
de resistencia. Tambirn deben de usarse taticas de resistencia de plants hospederas
que requieran complejas alteraciones gen6ticas fisiol6gicas y de comportamiento para
impedir que el insecto desarrolle resistencia.

"A study of the resistance of crop plants to insect attack has served to emphasize
the great importance offood habits in the biology and evolution of plant-feeding insects"
(Painter 1936)
With the above quoted sentence, Reginald Painter began his seminal 1936 paper
"The Food of Insects and its Relation to Resistance of Plants to Insect Attack". The
ideas expressed in that paper were the seeds for his classic book "Insect Resistance in
Crop Plants", in which, 15 years later (Painter 1951), he formulated the basic principles
of host plant resistance (HPR) that continue to provide the foundation underlying our
current HPR research and application efforts. As indicated by the above quote, Painter
also was one of the pioneer insect nutritional ecologists, for he early recognized the
importance of the interactions of food attributes and other environmental factors with
food consumption and subsequent post-ingestive performance. Understanding these in-
teractions is a primary goal of nutritional ecology, because the consumption of food is
a necessity for all other aspects of insect performance (i.e., growth and development,
reproduction, defense, movement and survival; Slansky & Rodriguez 1987). Food con-
sumption is also the main cause of crop injury due to pest insects, either directly through
feeding damage or indirectly through vectoring of disease agents during feeding. At-
tempts to reduce such damage by manipulating insect performance through alteration
of crop plant characteristics form the crux of research on host plant resistance (HPR)
and its application (Painter 1951, Maxwell & Jennings 1980, Hedin 1983). Thus, the
principles of insect nutritional ecology provide a logical basis for choosing particular
plant attributes in the development and use of resistant crop varieties (Gould 1983,
Hare 1983, Slansky & Rodriguez 1987).
In order to effectively manipulate the biochemistry, physiology and behavior of pest
insects through use of HPR tactics, we must understand the links between the various
attributes of the insects' food, their food consumption and utilization, and subsequent
performance (Figure 1). In this paper I first describe some of the main plant attributes
that affect insect performance. Many of these plant characteristics can be altered
through selective breeding and cultural practices (Maxwell & Jennings 1980, Hare 1983,
Borlaug 1983, Osborn et al. 1988), and some are now (and others undoubtedly will soon
be) modifiable through bioengineering (Barton & Brill 1983, Gasser & Fraley 1989).
Thus, these plant attributes comprise key components of existing and future HPR
tactics. I then outline the consumption and processing of food by insects, suggesting
potential "weak links" in the chain of events leading from host plant to insect that might
be exploited through HPR tactics, toward achieving the goal of improved crop pest

September, 1990


Slansky: Symposium-Plant Resistance to Insects 361



understand manipulate


Fig. 1. Diagramatic representation of the interrelationship between insect nutri-
tional ecology and host plant resistance research and application. A major goal of nutri-
tional ecology is to understand the impact of food attributes, acting via effects on food
consumption and utilization, on the performance and fitness of insects, whereas host
plant resistance attempts to manipulate these relationships to better manage insect

management. I next indicate the importance of understanding the mode of action of the
various plant attributes used as HPR tactics, and delineate the impact of HPR tactics
on insect performance. I continue by discussing some possible biochemical, physiological
and behavioral responses by insects that may act to counter certain HPR tactics, and
indicate how these responses might be used as additional HPR tactics. Finally, I discuss
the development of resistance by insect pests to our HPR efforts, and suggest how this
phenomenon might be slowed or prevented. Throughout this paper I concentrate on
immature insects, although the ideas expressed also pertain to adults (e.g. Orthoptera,
Hemiptera, Homoptera and Coleoptera) that require nutrient intake. These concepts
fall primarily within the "antibiosis" component of Painter's (1951, p. 25) "threefold
basis of resistance". The ability of insects to locate and choose their host plants is also
an important link in the chain and is susceptible to modification through HPR [Painter's
"preference" component; more recently termed "antixenosis" (Kogan & Ortman 1978)],
but this topic is generally beyond the scope of the present paper, as is the third compo-
nent of the HPR triad, "plant tolerance".


Two main categories of plant attributes relevant to plant-feeding insects are nutri-
tional and non-nutritional factors, the latter being comprised of at least two sub-
categories: allelochemicals and morphological features. Nutrients can be defined gener-
ally as substances that are necessary or useful for the metabolic functioning of an
organism (i.e., proteins, amino acids, carbohydrates, lipids, vitamins, minerals, water,
etc.); the basic nutritional requirements of insects and vertebrates overlap substantially,

362 Florida Entomologist 73(3) September, 1990

with a few key differences, and there are various differences among insect species as
well (Hagen et al. 1984, Dadd 1985, Reinecke 1985).
Allelochemicals are defined as non-nutritional compounds "by which organisms of
one species affect the growth, health, behavior, or population biology of organisms of
another species" (Whittaker & Feeny 1971, p. 757; see also Reese 1979). Allelochemicals
comprise a diverse group of substances (i.e., alkaloids, phenolics, glucosinolates, ter-
penoids, etc.) and may be beneficial to either the organism producing them (e.g., by
repelling enemies) or the organism receiving them (e.g., a foodplant attractant); the
former are termed allomones, and the latter, kairomones (Whittaker & Feeny 1971,
Rosenthal & Janzen 1979). Morphological plant attributes form a broad group including
texture, "toughness", color, size, shape, growth form, etc. While morphological attri-
butes typically affect insects at the "preference" level (especially adult oviposition),
some of them (e.g., "toughness" and pubescence) also may function through "antibiosis"
(Norris & Kogan 1980).
This classification of plant attributes is based primarily on functional considerations
relative to the insects consuming the plants; thus a particular component may occur in
more than one category depending on the situation. For example, an allelochemical
toxic to one insect species may serve as an attractant or nutrient to another, and some
of the chemicals contributing to a leafs toughness may also have allelochemical activity
(see next section). In developing insect-resistant plant varieties, it is important to know
the functional mode of action of the different plant attributes relative to the target
insects, for several reasons as described below (see Importance of Understanding HPR


Food consumption. The initial interaction between insect and crop plant of concern to
the present discussion is feeding. Certain nutrients and allelochemicals (as defined pre-
viously) serve as feeding stimulants for insects, whereas others (especially allelochem-
icals) function as antifeedants (Hanson 1983, Stadler 1984, Miller & Strickler 1984,
Hsiao 1985). Thus, we could select for reduced amounts or the absence of the stimulating
chemicals to decrease the propensity of the target insect to initiate feeding, and/or for
the presence or increased amounts of antifeedant chemicals to repel or deter pest insects
from feeding (Bernays 1983, Frazier 1986, Smith 1986). For several different crops
grown in the southeastern United States, there are varieties exhibiting antibiosis-based
resistance, apparently due at least in part to antifeedant effects (e.g., Kleyla et al. 1978,
Lynch et al. 1981, Jackson et al. 1985, Peterson & Schalk 1985, Smith 1985, Wiseman
& Widstrom 1986, Wiseman et al. 1986, Chang et al. 1987, Isenhour & Wiseman 1987,
Jones et al. 1987, Beach & Todd 1988, Jackson et al. 1988, Niemeyer 1988, Parrott et
al. 1989).
In many cases, the factors presumably responsible for the observed resistance have
been delineated only recently. Most remain unknown, and often it has not been deter-
mined if the resistance results from a direct antifeedant effect or from a less direct,
toxic effect on growth which subsequently reduces feeding. Indeed, it can be difficult
to distinguish antifeedant versus toxic effects; time-intensive quantification and manip-
ulation of feeding rate are often required (Blau et al. 1978, Dimock et al. 1986, Puttick
& Bowers 1988). In addition to chemical compounds, physical factors such as greater
toughness of plant tissues associated with increased fiber may interfere with feeding.
For example, tough leaves wear down the cutting surface of the mandibles of adult
Plagioderma more so than tender leaves, reducing the beetles' feeding rate, which in
turn would cause fecundity to decline (Raupp 1985).
Along with sensory information from taste receptors, feeding by insects is regulated
through several mechanisms, including feedback from stretch receptors and from nutri-

Slansky: Symposium-Plant Resistance to Insects

ent levels in the hemolymph, with obvious involvement of the neurohormonal system
(Bernays 1985, Simpson & Simpson 1990). Thus, HPR tactics may be designed to influ-
ence neurotransmitters, etc., in the target insect to alter feeding behavior in the desired
manner. For example, consumption of an inhibitor of the neurotransmitter serotonin
altered feeding behavior in Heliothis zea (Boddie) caterpillars (Cohen et al. 1988a; see
Menn & Borkovec 1989, for a review of insect neuropeptides from an insect control
perspective). In some cases, it might be appropriate to stimulate feeding by a pest
insect, at least initially, if this results in an overall reduction in feeding damage (see
Insect Responses to HPR Tactics below).
Digestion and absorption. After food has been ingested, it must be digested and
absorbed by the insect. Certain allelochemicals, such as protease inhibitors, can hinder
these processes (Reese 1979, Ryan 1983, Shukle & Murdock 1983, Applebaum 1985,
Turunen 1985, Broadway & Duffey 1986, Osborn et al. 1988). These compounds occur
in certain crop plants, especially those in the Gramineae (e.g., corn), Leguminosae (e.g.,
soybean and alfalfa) and Solanaceae (e.g., potato and tomato), and their production by
the plant often seems to be increased (i.e., induced) in response to plant damage (Ryan
1983, Broadway et al. 1986). Thus, there seems to be good potential for their use in
The activity of some of these inhibitory compounds, of certain insect pathogens and
of the digestive enzymes themselves, is pH dependent, and gut pH can vary among
insect species as well as with the food eaten (Berenbaum 1980, Applebaum 1985). For
example, the virulence of nuclear polyhedrosis virus (NPV) tends to be highest at
neutral to acidic pH, whereas that of Bacillus thuringiensis (Bt) occurs in the basic
range; the effectiveness of these pathogens against various insect species therefore may
depend in part on an insect's gut pH, and the use of microbial chitinase (which is active
at acidic pH) to facilitate the penetration of pathogens through the peritrophic mem-
brane/gut wall of caterpillars may be more effective for NPV (e.g., Shapiro et al. 1987)
than for Bt (Schultz 1983). Thus, if some factor acting at the digestion/absorption level
is considered for use as an HPR tactic, it is important to confirm that it functions
adequately within the gut pH range of the target insect, or alternatively, plant quality
would need to be modified to create the appropriate pH level.
The fibrous component of plant cell walls (a chemically diverse mixture of cellulose,
hemicellulose, lignin and other substances occurring in various proportions depending
on plant species and variety, age and growing conditions) can interfere with food diges-
tibility in vitro and in vivo in cattle (Van Soest 1982), but our knowledge of the impact
of fiber on the digestion of food by insects is limited (Mattson & Scriber 1987). Few
insects can digest cellulose (Martin 1983); thus the dry weight digestibility of food
generally declines as this substance increases in the diet (Peterson et al. 1988, Timmins
et al. 1988, Slansky & Wheeler 1990). However, there seems to be no unequivocal
evidence for insects indicating that digestion/absorption of the nutrient component of
the food is reduced by the presence of fiber. For example, although the digestive effi-
ciency of dry weight declined with an increase in the cellulose content of an artificial
diet for the velvetbean caterpillar (Anticarsia gemmatalis Hiibner) (Slansky &
Wheeler, 1990), fall armyworm [Spodoptera frugiperda (J. E. Smith)] (Wheeler &
Slansky, unpublished data) and southern armyworm [Spodoptera eridania (Cramer)]
(Peterson et al. 1988), the efficiency of digestion/absorption of the nutrient portion of
the diet either did not decline or increased. Of course, adding powdered cellulose to an
artificial diet is a radically different situation from increasing the cell wall fiber in a
plant leaf; thus the relevance of these data to caterpillars consuming plant leaves is
questionable. We are not aware of any studies determining the impact of increased fiber
in plant leaves on nutrient utilization by insects, but the dry weight digestibility of
bermudagrass varieties for S. frugiperda did not appear to show a negative relationship
to the fibrous components of the foliage (Jamjanya & Quisenberry 1988). Thus, at pres-


Florida Entomologist 73(3)

ent we cannot conclude that increased fiber can be used to interfere with nutrient
digestion in insects; however, because an increase in plant fiber would most likely result
in a dilution of the nutrient portion of the food, which in turn would probably affect
insect feeding behavior, and for other reasons [see Food consumption above, and Norris
& Kogan (1980)], fiber may nonetheless be useful in HPR.
Decreased dietary water may reduce nutrient digestion/absorption because the
lower water level interferes with these processes (see Turunen 1985). In addition, the
increased concentration of nutrients associated with low dietary water may force the
insect to excrete excess nutrients that have been absorbed (see next section). Because
quantitative food utilization studies of insects often measure only the dry mass of the
food ingested and feces egested (rather than also measuring uric acid, etc., in the feces),
the separate contributions of decreased digestion/absorption and increased excretion of
metabolic wastes to a decline in the calculated value of the "digestion/absorption" effi-
ciency are seldom distinguished. Data compiled for the caterpillars of 25 species of
Lepidoptera indicate that the maximum values exhibited for dry mass digestion/absorp-
tion efficiency decline with a reduction in both leaf water (% fresh weight) and nitrogen
(% dry weight) (Slansky & Scriber 1985).
Conversion to biomass, metabolism, detoxication and excretion. After the nutri-
tional precursors have been absorbed from the gut, the insect allocates a portion of
them to growth and nutrient accumulation; much of the remaining portion is used to
supply energy and nutrients for metabolic processes. Interconversions and metabolism
of nutrients, often associated with nutrient imbalances, result in the production of
metabolic waste products requiring excretion. Potentially deleterious allelochemicals
may also be absorbed, which the insect may detoxify and excrete, whereas some insects
sequester allelochemicals from their food for use in defense from their enemies or as
pheromones. Many of these physiological events are regulated through the neurohor-
monal system. Thus, there is considerable potential to use HPR tactics to manipulate
these metabolic processes to affect deleteriously insect performance, as briefly discussed
in the remainder of this section.
One obvious possibility is to alter the nutritional composition of crop plants to reduce
or eliminate nutrients, or otherwise create nutritional imbalances. It would seem espe-
cially important to reduce the level of essential nutrients that are required but cannot
be synthesized by the target insect. For example, linolenic (C18:3) acid, which may be
synthesized rarely by insects, if at all (Downer 1978; see also Stanley-Samuelson et al.
1988), seems to be especially important for certain Lepidoptera; poor adult emergence
and wing deformities occur if the level of this fatty acid is too low in the diet, and thus
artificial diets are often supplemented with it (Bracken 1982, Turunen 1983). Soybean
lines low in linolenic acid in the seeds have been selected to improve seed oil quality
(Hammond & Fehr 1984), but levels of this fatty acid in the foliage are not closely
correlated with those in the seeds (Martin & Rinne 1985). Whether the performance of
soybean seed-feeding insects is affected on these lines, and whether a level of linolenic
acid in the foliage low enough to deleteriously affect leaf-feeding insects can be achieved,
has apparently not been investigated.
In addition to fatty acids, variation in sterols (Thompson et al. 1980, Al-Izzi &
Hopkins 1982; but see Grunwald & Kogan 1981), amino acids (Prestidge & McNeill 1983,
Brodbeck & Strong 1987, Febvay et al. 1988) and probably other nutrients may contrib-
ute to HPR. Unless a certain level of non-essential ("dispensible") amino acids is present
in insect diets, the essential amino acids may be depleted and growth slowed (Dadd
1985); thus, altering both essentials and non-essentials in a crop plant may be appropri-
ate in some situations. Amino acids are a typical source of nitrogen for plant-feeding
insects, but nitrogen fixation by rhizobial bacteria occurring in legume root nodules
(e.g., soybean plants) produces nitrogen-containing ureides (i.e., allantoin and allantoic

September, 1990


Slansky: Symposium-Plant Resistance to Insects 365

acid) which are transported in the plant. Wilson & Stinner (1984) found that these
compounds seem to be a poor source of nitrogen for certain crop pests; ureide production
can be manipulated by altering the amount of nitrogen fertilizer given to the plant. In
addition to direct reduction in growth due to nutrient limitation, the additional metabolic
interconversions and excretory demands of nutrient imbalances and excesses (e.g.,
Van't Hof & Martin 1989) could divert nutrients and energy from growth to greater
enzyme activity associated with the increased metabolic demands, further contributing
to a deleterious impact on insect performance.
Nutrient analogs, such as non-protein amino acids, are substances generally similar
enough in chemical structure to nutrients that they enter the metabolic pathways, but
they are different enough to not function properly and thus interfere with metabolism
(Reese 1979). Various non-protein amino acids have deleterious impacts on several
insects (Rosenthal & Bell 1979), although some insects are not affected (Srivastava et
al. 1988) and at least one beetle species is able to utilize a non-protein amino acid (i.e.,
canavanine) as a source of nitrogen (Rosenthal et al. 1982).
Anti-nutrients bind with certain vitamins or minerals (Reese 1979), possibly in the
gut or after absorption, reducing the availability of these nutrients. For example, phytic
acid, which occurs in several plant species (e.g., grains and legumes, especially in the
seeds), may bind with vitamin D, proteins and certain minerals (Reese 1979, Jaffe 1981).
In apparently the only study examining the impact of phytic acid on an insect, Bowen
& Slansky (unpublished data) found that this chemical prevented egg hatch when added
to an artificial diet at 2% dry weight (dw) and prevented egg production at 5% dw,
when fed to adult southern green stinkbugs (Nezara viridula L.).
A low level of water in the food may divert absorbed nutrients away from the
synthesis of biomass and to the production of metabolic water or to energy costs as-
sociated with excreting excess nutrients; in addition, low water may slow growth by
more directly limiting the rate at which hydrated tissue can be synthesized (Scriber
1977, Martin & Van't Hof 1988, Van't Hof & Martin 1989). High water content in the
food may increase an insect's energy costs if the insect increases its feeding rate suffi-
ciently in response to the dilution of the nutrients; it also may interfere with growth in
other ways, possibly by overdiluting the insect's hemolymph and by requiring extra
metabolic activity to maintain an appropriate water balance (Slansky & Wheeler 1989).
Many allelochemicals are toxins, affecting various components of metabolism, nerve
impulse transmisison, etc. (Reese & Holyoke 1987, Holyoke & Reese 1987). Insects
possess detoxication enzymes with which they metabolize certain allelochemicals to
generally less toxic metabolites (Ahmad et al. 1986), and the activity of these enzymes
is often induced by allelochemicals and pesticides (Yu 1986). Relevant HPR tactics could
involve the use of naturally occurring chemicals that inhibit detoxication enzymes (e.g.,
certain lignans and other compounds found in many economically important plants,
including black pepper, blueberry, nutmeg, sesame, soybean, tomato and various um-
bellifers), and substances that, rather than being detoxified, are activated to more
potent forms (Ahmad et al. 1986, Berenbaum & Neal 1987).
Many insects rely on sex pheromones as an essential component of the mating pro-
cess, and these are commonly synthesized de novo by the insects; in such cases
pheromone quality or quantity does not seem to be greatly influenced by larval food
quality, although associated processes (e.g., age at which pheromone release occurs)
may be altered significantly (McNeil & Delisle 1989). In species in which allelochemicals
are sequestered from the larval food, either to be used directly or as precursors for sex
pheromones or defensive agents against the insects' natural enemies, food quality can
have a substantial impact on these aspects of insect performance (Schneider et al. 1982,
Smiley et al. 1985, Brattsten 1986, McNeil & Delisle 1989). In such interactions involv-
ing insect pests of crops, manipulation of these compounds could be used in an HPR

366 Florida Entomologist 73(3) September, 1990

Regulation of the various metabolic processes involves neurotransmitters and
neurohormones (Steele 1985), and thus HPR tactics may be used to interfere with this
regulation (see Menn & Borkovec 1989). Naturally occurring chemicals with juvenile
hormone or ecdysteroid activity can have deleterious impacts on insects (e.g., Kubo et
al. 1983, El-Ibrashy 1987). Knowledge of the hormonal regulation of diuresis (Spring et
al. 1988) and uric acid excretion (Buckner 1982) may lead to manipulation of these
processes through HPR.


Although resistant plant varieties can be (and have been) developed without knowing
the specific mechanisms involved in conferring resistance, a more directed approach to
HPR, involving crop plant design and implementation within an integrated pest man-
agement scheme, necessitates an understanding of the mode of action of the plant
attributes, for several reasons. First, as mentioned previously, the effects of plant
attributes depend on the insect species involved. Thus, unless we know the mode of
action of a particular attribute relative to the key pests, we may be making a crop
variety more susceptible to one pest species while attempting to make it more resistant
to another.
Second, there may be interactions among the various plant traits, and between them
and other pest management tactics, which either enhance or diminish the success of an
HPR effort. For example, in the previous section possible interactions between insect
gut pH and the functioning of certain allelochemicals and insect pathogens were de-
scribed. Some plants, through their effect on insect detoxication enzymes, may make
an insect either more or less susceptible to synthetic insecticides (Yu 1986). Other
examples of interactions involve natural enemies, which may be a key part of an integ-
rated pest management scheme involving HPR (see next section). For example, an
alteration in a plant attribute that slows growth of the target insect may be advantage-
ously coupled with augmentation of a predator species, if the slower growth increases
the pest's exposure to the predator. However, there probably would be little need for
predator augmentation if a toxic allelochemical either killed off the early stages of the
target pest or if the compound were accumulated in the target insect, rendering it
unsuitable to the predator [see Bergman & Tingey (1979), Boethel & Eikenbary (1986)
and Barbosa & Letourneau (1988) for detailed discussions of such interactions]. Thus,
we need to know the effects of the plant attributes to promote or avoid such interactions,
as appropriate.
Third, in practical terms, it is obviously necessary to identify a particular resistance
factor before it can be introduced into a crop variety via gene-transfer. In regard to
traditional breeding programs, these may be simplified and streamlined through knowl-
edge of the underlying mechanisms of resistance. For example, if a crop variety is being
bred to increase an allelochemical in the foliage to a particular level previously deter-
mined in laboratory and limited field experiments to reduce feeding of the target pest
by 50%, then plants in each generation of the breeding program can be analyzed more
rapidly and possibly less expensively through chemical techniques to assess their al-
lelochemical concentration. If, however, the plants were being bred to increase their
resistance to the insect pest without knowing the role of the allelochemical, then each
generation of plants would have to be field tested to determine which individuals to
choose for the next cycle of breeding. Such field work, involving the arrangement,
planting and maintenance of field plots, and monitoring of insect numbers and damage
levels, would undoubtedly be more time-consuming and expensive. Of course, even in
the former situation, once the desired level of allelochemical was achieved, field work
would have to be carried out to confirm the previous experimental results, to assess
natural enemy interactions, etc., before full scale production and release of the variety.

Slansky: Symposium-Plant Resistance to Insects

Finally, an important consideration in the creation and implementation of insect-re-
sistant crop varieties is their long-term effectiveness; that is, whether and how rapidly
the target pest will develop resistance of its own to the HPR tactics (see Insect Re-
sponses to HPR Tactics below). If we are to understand the situations in which insects
evolve such resistance so that we can devise ways to avoid or slow this process, we
need to know which mechanisms and combinations thereof the insects have and have
not been able to overcome.


The ultimate goal of using HPR tactics to impact the consumption and utilization of
food by a target pest as described previously usually is to maintain crop damage below
economic injury levels. This can be done by killing the target pest outright, such as
through use of a potent toxin or antifeedant (the latter causing death through starva-
tion). Prevention of feeding may be necessary in a situation in which the target insect
is a vector of a disease agent or in other cases with a very low economic injury threshold.
However, heavy mortality caused by a single plant attribute, especially if a genetically
simple mechanism in the pest insect is involved, should probably be avoided because
the strong selective pressure imposed may lead to relatively rapid development of
resistance in the target insect population (see next section).
As discussed previously, there are many potential HPR tactics, and these can be
used to alter the performance of crop pests to exert deleterious effects on their fitness,
even if mortality caused directly by the plant attributes is low and food consumption is
not directly or immediately reduced. Many of the tactics described previously can result
in slowed development and reduced weight gain by the immature target insects, which
in turn may reduce overall feeding damage and help prevent a subsequent increase in
the pest population.
Slowed development will prolong an insect's exposure to the environment, including
rain, pathogens, parasitoids, predators and other potentially harmful agents, and thus
increase its probability of mortality prior to reaching the adult (reproductive) stage.
For example, an insect may be forced to remain longer in early instars, which might
be the only stages attacked by certain arthropod predators or arasitoids. Similarly, a
requirement for additional feeding (e.g., because digestion/absorption of the food is
partially inhibited by a protease inhibitor in the crop foliage) might result in greater
mortality if movement to a feeding site and during feeding increases the insect's expo-
sure to natural enemies, or if the increased consumption leads to ingestion of an infective
dose of a pathogen or lethal dose of a toxic allelochemical. Increased mortality of pest
insects feeding on resistant versus susceptible crop varieties caused by natural enemies
has been documented (Hare 1983, Price 1986, Isenhour et al. 1989); however, each crop
variety/insect pest/ natural enemy interaction of concern will probably need to be
evaluated prior to drawing any conclusions, because certain plant attributes may either
enhance or interfere with particular natural enemies (Bergman & Tingey 1979, Boethel
& Eikenbary 1986, Barbosa & Letourneau 1988).
If the target insect survives to the adult stage, slowed development may alter its
synchrony with important temporal features of the environment, including both abiotic
(e.g., the need to diapause or migrate prior to a killing frost) and biotic (e.g., foodplant
phenology) components, thereby reducing its fitness (Taylor 1980, 1981). Reduced
weight gain resulting in a sub-normal sized adult can decrease fitness by interfering
with mating success, by reducing fecundity and by making the adult less able to cope
with stresses (Slansky & Scriber 1985); in some cases, however, flight activity or mig-
ratory ability may increase in smaller individuals (Angelo & Slansky 1984). In addition,
stress during the immature stage (e.g., the presence of a particular non-lethal al-
lelochemical in their food) may affect the ability of the next generation immatures to


Florida Entomologist 73(3)

cope with stress (Gould, 1988). Thus, there is considerable potential to impose signifi-
cant deleterious effects on target pest performance associated with manipulation of crop
plant attributes, whether or not the HPR factor directly causes mortality of the target
insect pest.


Painter (1951, p. 85) recognized two important concerns regarding the use of resis-
tant crop plants: "Research in insect resistance in plants requires a knowledge of the
possible plasticity of insect behavior and of the possible rate of change of insect biotypes
and species." Indeed, insects are not passive creatures totally at the mercy of their
environment; their biochemical, physiological and behavioral activities are regulated
through neuroendocrine and other feedbacks, allowing adaptive responses to the chang-
ing environments in which they exist (Slansky 1982, Slansky & Rodriguez 1987). Thus,
individual insects may have the capacity to respond to certain of our HPR tactics,
possibly counteracting or mitigating them. Assessing these types of responses experi-
mentally is a major task of research in nutritional ecology; without such knowledge,
altering a food attribute as an HPR tactic might not have the intended effect of reducing
performance of the target insect, and could even increase feeding damage. In addition,
the genetic variability of insect populations, coupled with the differential impact on the
fitness of the target pests exerted by a resistant crop variety, may lead to the evolution
of resistance in the target species to an HPR tactic. These two issues are discussed in
this section.
Biochemical, physiological and behavioral responses. As mentioned previously, one
biochemical/physiological response exhibited by insects is the induction of detoxication
enzyme activity by allelochemicals, which may allow the insect to tolerate higher doses
of these potentially toxic compounds, as well as of certain insecticides. Habituation and
aversive learning in response to feeding deterrents have also been demonstrated in
insects (Jermy et al. 1982). A response by some insects to nutritionally variable food is
the phenomenon of "self-selection", in which individuals consume the most nutritionally
suitable tissue or a combination of tissues or foods to obtain an adequate balance of
nutrients (Waldbauer & Friedman 1988). For example, last instar Heliothis zea caterpil-
lers feed preferentially on the germ of maize kernals (Cohen et al., 1988b).
Several insect species alter food consumption in response to changes in food quality,
for example by increasing the feeding rate if their level of nutrients in the food declines
(Table 1). Such responses may eliminate or limit the impact of variation in food attri-
butes on insect performance. For example, dilution of an artificial diet with water,
which reduced the nutrient level from 35% to 21% fw (fresh weight), caused little
reduction in weight gain or relative growth rate (RGR) by A. gemmatalis caterpillars,
associated with their increase in food consumption (Slansky & Wheeler 1989). Although
both weight gain and RGR declined significantly with further dilution to 11% fw nutri-
ents, the continued increase in feeding mitigated the deleterious impact of diet dilution;
for example, on the latter diet, RGR would have been reduced about 40% more without
the increased-feeding response.
These physiological and behavioral responses do not necessarily have to be liabilities
to our HPR tactics; indeed, we might use them to further manipulate insect perform-
ance. For example, if a pest caterpillar is more susceptible to natural enemies while
feeding, then decreased foliage nutrient level could be used to increase feeding and the
insect's exposure to natural enemies. The increased-feeding response could also be used
to cause insects to consume sufficient doses of pathogens (Richter & Fuxa 1984) or
allelochemicals. For example, A. gemmatalis caterpillars were made to ingest a lethal
dose of a toxic allelochemical (i.e., the methylxanthine alkaloid caffeine) by diluting the


September, 1990

Slansky: Symposium-Plant Resistance to Insects


X-fold range in
Species Food consumpMio Reference

Cabbage Crucifier 2.2 Slansky & Feeny (1977)
butterfly var & spp
Fall Peanut 1.8 Lynch et al. (1981)
armyworm var & spp
Bermuda- 1.4 Quisenberry & Wilson
grass clones (1985)
Dilated art diet 2.5 Wheeler & Slansky
(unpubl data)
Green Soybean: grnhs 2.2 Hammond et al. (1979)
cloverworm vs field grown
Southern Alfalfa var 3.4 Scriber (1979)
Tobacco Diluted 2.6 Timmins et al. (1988)
hornworm art diet
Velvetbean Legume spp 2.0 Waters & Barfield (1989)
caterpillar Diluted art diet 2.8 Slansky & Wheeler (1989)

Mexican Soybean var 2.3 Barney & Rock (1975)
bean beetle

Locusta Diluted diet 1.7 Dadd (1960)
Melanoplus Diluted diet 6.9 McGinnis & Kasting (1967)
Schistocerca Diluted diet 3.1 Dadd (1960)

nutrients in an artificial diet with water, even though the concentration of caffeine (as
a % of diet fresh weight) was the same in all the diets (Slansky and Wheeler, unpublished
data). Because feeding rate increased with dilution of nutrients in the diet, the ingested
dose of the allelochemical increased, eventually to a toxic level. If the increased-feeding
response is a short-term phenomenon, resulting in reduced growth or death such that
the total damage done by a pest insect is reduced, then it has potential for use as an
HPR tactic.
Evolution of resistance. Several hundred cases are known of insects having evolved
resistance to insecticides acting as direct agents of mortality (Roush & McKenzie 1987);
common mechanisms of resistance are enhanced detoxication activity and target site
alterations that prevent insecticide binding, although behavioral avoidance also occurs
(Lockwood et al. 1984, Brattsten et al. 1986). Thus, use of a single plant attribute
intended to cause heavy mortality of an insect pest (e.g., an allelochemical toxin in the
plant acting analogous to a synthetic insecticide applied to the crop) may create strong
selection pressure leading to relatively rapid evolution of resistance in the target pest
population to the HPR tactic, especially if the tactic can be overcome by a genetically
relatively simple change in biochemistry, physiology or behavior. A better strategy for
maintaining long-term effectiveness of resistant crop varieties should probably involve
multiple HPR tactics, especially if deployed within a genetically diverse crop variety
or by changing the resistance factors in varieties planted in succession. In addition, it


370 Florida Entomologist 73(3) September, 1990

would probably be desirable if genetically complex alterations in physiology and be-
havior were necessary for an insect to evolve resistance (see below).
Painter (1951) recognized the interrelationships among the HPR triad, indicating
that various combinations of antibiosis, non-preference and plant tolerance within a crop
variety could achieve the desired level of plant resistance. He also suggested ways of
dealing with the development of resistance in pest insects to HPR tactics, stating (p.
105) that "A change in genetic factors for resistance [in a crop] or a combination of
several genetic factors constitutes a valid defense against biological strains [of an insect
pest]." Whether combining antibiosis (which traditionally has been considered to entail
primarily biochemical/physiological modes of action) and non-preference (i.e., primarily
behavioral modes of action) is more effective at limiting the development of insect
resist-ance than use of a single factor has apparently received little research attention,
although there is some evidence, based on a genetic model, that this dual approach may
slow the development of resistance in the target pest to the HPR tactics (Gould 1984).
Empirical research is clearly needed to confirm this.
Lockwood et al. (1984), in a discussion of insect resistance to insecticides, make the
valid point that behavior is "observable physiology" and thus there is really no funda-
mental difference between "behavioral" and "physiological" resistance in terms of in-
sects having the capacity to evolve either or both of these in response to selective
pressure from a toxicant (from an HPR perspective, these would be equivalent generally
to resistance to "non-preference" and "antibiosis" tactics, respectively). However, re-
sistance mechanisms in insects that require modification of more complex behaviors
than mere avoidance of a toxicant [the primary behavioral response discussed by
Lockwood et al. 1984)] would nonetheless seem to provide a means of slowing the
development of resistance (see below). Thus, it is important to broaden the traditional
view of HPR mechanisms: not only does behavioral "non-preference" have an underlying
physiological component, but biochemical/physiological "antibiosis" has a behavioral
component. This latter fact has become especially evident as research in insect nutri-
tional ecology uncovers the interactions between feeding behavior (i.e., alterations in
the rate and duration of food consumption, movement to and from feeding and resting
sites, searching for suitable food, etc.) and food utilization/allocation, as impacted by
food attributes (Slansky & Rodriguez 1987). From this perspective, there is substantial
potential to diverge from the traditional "antibiosis" tactics which attempt to use plant
attributes in a manner analogous to synthetic insecticides (e.g., allelochemical toxins as
"natural insecticides"), to instead manipulate a variety of biochemical, physiological and
behavioral components of pest insect performance in an effort to employ effective HPR
tactics that slow development of insect resistance to the tactics.
As an example of manipulating the performance of an insect pest in a way that may
slow the development of resistance, I present the following scenario. A crop variety is
bred with a reduced level of nutrients in the foliage (e.g., by increasing the water or
fiber contents), which forces the target caterpillars to spend twice as much time feeding
to obtain adequate nutrient intake for growth. During feeding, the cryptically colored
caterpillars are exposed to a certain arthropod predator, and this predator species is
augmented in the crop field to bring about a level of mortality adequate to maintain the
target pest below the economic injury threshold.
Several possibilities exist for the insect species to develop resistance to this HPR
tactic, including evolution of:

(1) reduced requirements for many different nutrients such that the caterpillars
would not need to increase their feeding in response to nutrient dilution (and thus not
increase their exposure to the predator);
(2) insensitivity to nutrient dilution such that the caterpillars would not respond via

Slansky: Symposium-Plant Resistance to Insects 371

increased feeding, which would reduce nutrient intake, requiring in addition the evolu-
tion of increased food utilization efficiencies and/or a smaller body size;
(3) and altered temporal activity pattern, such that the caterpillars feed when the
predator is inactive; and/or
(4) defensive mechanisms against the predator.

To the extent that these evolutionary alterations require a complex of biochemical,
physiological and/or behavioral changes, each is probably more-or-less unlikely to occur.
A more likely occurrence might be the evolution of a shift to a related host plant species
(see Diehl & Bush 1984), such that the insect would no longer be a pest of the target
crop. Indeed, generalized predators may be very important selective agents leading to
food plant specialization (Bernays 1988).
Simultaneous use of various plant attributes that differ substantially in mode of
action (e.g., an inhibitor or stimulant of the synthesis of a neuropeptide involved in
regulation of feeding, a digestion blocker acting in the lumen of the gut, and an inhibitor
of detoxication enzymes), may also slow the evolution of resistance in the target pest
population, because there would probably be few individuals in the population resistant
to all of the diverse modes of action even though there may be greater frequencies of
individuals resistant to any one factor. A somewhat analogous suggestion has been
made for use of a mixture of insecticides to help manage the development of insecticide
resistance in insects (Brattsten et al. 1986). Maintaining genetic diversity in a crop
variety, such that different plants in a field express differing degrees of the various
attributes serving as resistance factors, and/or alternating crop varieties manifesting
different resistance factors in subsequent plantings, may also slow or even prevent the
development of resistance in the target pest (see Denno & McClure 1983, Whitham
1989), because the selective pressures for resistance in the target pest will be inconsis-
tent (i.e., a particular insect genotype exhibiting a certain resistance mechanism may
be selected for on one plant or in one generation but not on a neighboring plant or in
the next generation).
The development of resistance in pests and its management are complex issues, as
yet poorly understood [for discussions, see Tabashnik & Croft (1983), Gould (1983,
1984), Lockwood et al. (1984), Pluthero & Singh (1984), Brattsten et al. (1986) and
Roush & McKenzie (1987)]. Much of this discussion of the development of resistance in
target insect pests to our HPR efforts has been speculative, in part because of a lack
of experimental data. Clearly, there appears to be a variety of strategies to discourage
the development of insect resistance, but much additional research is required before
we will understand this phenomenon sufficiently to be able to limit or prevent it.


Research in insect nutritional ecology has uncovered many links between food attri-
butes, food consumption and utilization, and subsequent insect performance. These
interactions can be manipulated in diverse ways through HPR tactics, especially as part
of an integrated pest management strategy, toward the goal of managing insect crop
pests to maintain crop damage below economic injury thresholds. In addition to attain-
ing effective short-term control, it is important to utilize HPR tactics in a manner which
impedes the evolution of resistance in the target pest population to the tactics. Tradi-
tional plant breeding programs, as well as more recent biotechnological advances (e.g.,
gene-transfer between plant species), allow crop plants to be "designed" with specific
resistance mechanisms directed at particular insect pests. Future research should con-
centrate on determining the mode of action and impact of plant attributes on key crop
pests, the interactions among multiple HPR tactics and between HPR and other man-

Florida Entomologist 73(3)

agement tactics (in particular, natural enemy augmentation), the implementation of
laboratory results to manipulating insect performance in the field, and the most effective
ways to restrict the development of resistance in insect pests to our HPR efforts.


I thank D. J. Schuster and B. R. Wiseman for organizing this symposium and for
inviting me to present this paper. This is Florida Agricultural Experiment Station
Journal Series No. R-00420.


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Slansky: Symposium-Plant Resistance to Insects

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United States Department of Agriculture
Agricultural Research Service
Crops Research Laboratory
Oxford, N. C.


A thorough understanding of the behavioral repertoire of an insect pest species is a
key element in the establishment of a successful program for the development of plant
cultivars resistant to insect attack. Behavioral components are especially important
during the host finding and host acceptance phases of a pest's biology. The behavior of
an insect pest is affected by the physical and chemical characteristics of its potential
host plant. Breeders may modify plant characteristics that affect the behavior of pest
species so they are less damaging. Avoidance or rejection of an unsuitable plant as food
or as an oviposition substrate represents one of the primary modalities, nonpreference
or antixenosis, of plant resistance to insects. The behavioral adaptations of insects in
relation to their host plants and the impact this has on host plant resistance are reviewed
here. In particular, the behaviors of the polyphagous Heliothis spp. (Lepidoptera: Noc-

September, 1990

Jackson: Symposium-Plant Resistance to Insects 379

tuidae) and the oligophagous Manduca spp. (Lepidoptera: Sphingidae) are emphasized,
as these are two important pest complexes in the southeastern United States for which
insect-resistant germplasm has been developed.


Un entendimiento complete del repertorio del comportamiento de una especie de
plaga de insecto es un element clave en el establecimiento de un program exitoso para
el desarrollo de variedades de plants resistentes a ataques de plagas de insects. Los
components de comportamiento son especialmente important durante la fase de la
bisqueda del hospedero y la aceptaci6n de la biologia de la plaga. El comportamiento
de una plaga de insects es afectada por las caracteristicas fisicas y quimicas de la
potential plant hospedera. Fitomejoradores pudieran modificar las caracteristicas de
la plant que afectan el comportamiento de una especie de plaga para que sean menos
dafiinas. El evitar o rechazar una plant no adecuada como alimento o como un substrato
de oviposici6n reprsenta una de las modalidades primaries, no-preferencia o antixenosis,
de resistencia de plants a insects. Se revisan aqui las adaptaciones de comportaminto
de insects en relaci6n a sus plants hospederas y su impact en las plants hospederas.
En particular se le da 6nfasis al comportamiento de las species polifagas Heliothis
(Lepid6ptera: Noctuida) y a las species olifagas Manduca (Lepid6ptera: Sphingida),
puesto que 6stas son dos complejos de species muy importantes en el sudeste de los
Estados Unidos para las cuales se ha desarrollado germoplasma resistente a insects.

An intimate understanding of the behavior of a pest species is a basic component of
a breeding program for the development of insect-resistant crop cultivars (Painter
1951). Behaviors associated with host finding, host recognition, and host acceptance are
especially important, as they determine whether a plant is initially attacked by an insect
pest. There are also behavioral components associated with an insect determining the
host's suitability as an oviposition substrate or as a food source. The physical and
chemical interactions between an insect and its host plant help determine the behavior
of that pest. Thus, we are often concerned with modifying various physical or chemical
characteristics of the plant in order to alter an insect's behavior to less destructive ends.
Also our experimental procedures for evaluating insect-resistant germplasm are almost
always dictated by some portion of the behavioral repertoires of insects. Also included
in their behavioral repertoires are activities that do not directly affect host finding or
host acceptance, such as mating activities, dispersal flights, avoidance of adverse wea-
ther conditions or predators, and construction of pupal cells. However, these activities
may interrupt host finding or host recognition processes, or they may be necessary to
put the insect in the proper physiological state before orientation behaviors can occur.
Thus, we should not lose sight of the fact that we must deal with the insect as a whole,
and not become excessively concerned over one portion of its behavior.
This paper reviews some examples of insect-host plant interactions that affect insect
behavior, and relates how these interactions may impact programs for breeding plants
resistant to insect pests. This discussion will primarily be concerned with examples
from the polyphagous Heliothis spp. and the oligophagous Manduca spp. because: (1)
these insects are major pests of field crops in the southeastern United States; (2) insect-
resistance germplasm has been developed against these species; and (3) they provide
convenient examples that easily illustrate certain principles.


Worldwide, Heliothis armigera (Hubner), H. virescens (F.) and H. zea (Boddie) are
the most damaging Heliothis species (Reed & Pawar 1982, Fitt 1989). Other Heliothis

380 Florida Entomologist 73(3) September, 1990

species are of lesser importance due to restricted host ranges, limited geographic distri-
butions, or inconsistent damaging populations (Fitt, 1989). The two economically impor-
tant Heliothis species in the United States (H. zea and H. virescens) are polyphagous,
and they attack several families of plants including many cultivated crops. In the south-
eastern United States, crops damaged by these two pests include corn, cotton, tobacco,
soybeans, peanuts, tomatoes, and edible peas and beans (Neunzig 1969, Schneider et
al. 1986, Fitt 1989).
There are two economically important Manduca species in North America. Manduca
sexta (L.), the tobacco hornworm, is more southern in distribution than the tomato
hornworm, Manduca quinquemaculata (Haworth) (Madden & Chamberlin 1945). How-
ever, their geographic ranges overlap widely, and in the middle Atlantic States both
species commonly occur. Hornworms are economically important only on tobacco and
tomato in the United States.


Host plant location and acceptance by an insect involves a sequence of encounters
that elicit either positive or negative responses. The term "encounter" is used here as
the initial reception of sensory information (Miller & Strickler 1984, Singer 1986). Accep-
tance or rejection of a host plant depends on the interactions of both the external host
stimuli and the internal state of the insect (Dethier 1982). Olfactory, gustatory, mechan-
ical, or visual receptors transmit sensory inputs to the central nervous system (CNS).
These contain both positive and negative information about a plant, and its acceptability
is in part a function of the ratio of positive to negative factors. The insect's response is
further modulated by the summation of positive and negative internal inputs (Dethier
Although plant discrimination by specialist insects may be mediated by specific key
stimuli (Stadler 1986, Visser 1986), it has been shown that for both specialist and
generalist herbivores of cabbage, the decision to reject or accept a plant is not uniquely
based on a few key stimuli, but rather on a chemical image of a large variety of stimulat-
ory and inhibitory plant chemicals acting together (Schoni et al. 1986). This concept of
a chemical "Gestalt" of a plant that constitutes the signal that is perceived by insect
herbivores is now widely accepted (Dethier 1982, Stadler 1983). However, specific repel-
lant or deterrent compounds from avoided plants may be important for host discrimina-
tion by generalist herbivores (highly polyphagous species) (Jermy & Szentesi 1978).
Insect-host plant relationships are affected by both abiotic factors, and by biotic
characteristics of the plant (Kogan 1975). Abiotic factors include the time of day, light
intensity, photoperiod, soil conditions, and weather phenomena such as temperature,
wind speed, relative humidity, and barometric pressure (Tingey and Singh 1980). All
of these factors must be considered when designing bioassays for measuring insect
behaviors. Just as important are the general characteristics of the plants to be
evaluated. Besides the genetic considerations of a breeding program (Gallun and Khush
1980), the plant must be in the proper phenological stage, and growing conditions should
be regulated to produce healthy plants. The visual, mechanical, and chemical cues pro-
vided by such leaf characteristics as size, color, shape, trichome density, and cuticular
chemistry may affect the behavior of the insect.
Insects are affected throughout their lives by chemicals in the environment. Chem-
ical diversity among plants is the principal factor underlying host specificity in
phytophaous insects (Schoonhoven 1981, Visser 1983). Chemical cues mediate many
aspects of insect behavior including host finding, host acceptance, avoidance of danger,
and mate location. Chemical nutrients and secondary plant components also determine

Jackson: Symposium-Plant Resistance to Insects 381

the suitability of a particular host plant for development and survival. Besides chemi-
cals, other environmental stimuli such as temperature, humidity, visual cues, and tactile
stimuli also contribute to the total sensory input to the insect's central nervous system.
Behaviors such as host finding and host selection consist of sequences of simpler
behavioral responses (Kogan 1975, Beck & Schoonhoven 1980). The sequential nature
of these behaviors is significant since each activity in the sequence conditions the insect
for the next behavioral state, which is achieved when the appropriate stimuli are re-
ceived. When the sequence is broken because the releasing stimulus for the next be-
havior is not received, the insect often reverts to earlier behaviors in the sequence
(Miller & Stickler 1984, Ramaswamy 1988).


Of Painter's (1951) three general modalities of resistance, nonpreference (or anti-
xenosis [Kogan and Ortman 1978]) is most closely associated with the behavior of insects
(Smith 1989). Such insect behaviors as non-recognition, avoidance, or rejection of a
plant may all be viewed as nonpreference responses. Several examples of behavioral
variations that encompass nonpreference are cited here. First, a plant may not be
attacked simply because pests are unable to find it. Although certain pseudoresistance
phenomena (as defined by Painter 1951) may sometimes cause a plant to remain pest-
free, insects may also fail to locate plants because they lack certain attractant qualities
found in susceptible plants. For example, a resistant cultivar may have a slightly differ-
ent shape, color, or odor than a susceptible one, and thus it may not be as attractive.
Plants which are not recognized by ovipositing moths, may or may not support larval
growth; and they have been termed acceptable non-hosts or unacceptable non-hosts,
respectively (de Boer & Hanson 1984).
Secondly, a resistant plant may be just as attractive over a distance as a susceptible
cultivar but it lacks specific stimuli that cause it to be recognized or accepted for ovipos-
ition or feeding. These characteristics are often determined upon contact. For example,
moths of H. virescens are stimulated to lay eggs on commercial tobacco cultivars due
to the proper physical texture of the leaf and due to contact ovipositional stimulants
(Jackson et al. 1983, 1984, 1986, Ramaswamy 1988). Thus, the near absence of cuticular
constituents normally found on commercial tobacco cultivars causes the tobacco intro-
duction (TI) 1112 to be resistant to oviposition by H. virescens due to nonpreference
(Jackson et al. 1983, 1984). Female moths of H. virescens may land on TI 1112, but they
apparently do not recognize it as a suitable host, and they do not lay as many eggs on
it as they do on a typical flue-cured tobacco cultivar such as NC 2326 (Jackson et al.
A third example of nonpreference has to do with insects rejecting a host due to
specific deterrent or repellant plant characteristics. Many non-host plant species have
chemical repellents or deterrents that prevent oviposition or feeding by lepidopterans
(Schoonhoven 1972, 1982, Jermy & Szentesi 1978, Renwick & Radke 1981, Tingle &
Mitchell 1984). The host ranges of larvae of Heliothis spp. and Manduca spp. are
broader than the actual host ranges determined by ovipositing moths. This phenomenon
is not unusual for lepidopterans, and it is likely that ecological pressures other than
merely feeding suitability restrict their host ranges (Schneider et al. 1986).
The remainder of this paper will consider the behavioral processes of insect herbi-
vores as they occur in sequence from hatching or eclosion through host utilization.
Included in this discussion will be the host finding, host recognition and acceptance, and
host suitability phases of an insect's behavior.

Florida Entomologist 73(3)


In most insect pest species the host finding process is not entirely random. Also,
the immature stages of most insect pests are incapable of long-range movement, so they
seldom move from a host plant until fully developed. Thus, it is crucial that adult
females place their eggs (or nymphs) on or near a suitable host plant. For example,
neonate larvae of Heliothis and Manduca spp. do not wander far from their egg shells
before they begin to feed. If young larvae try to leave a plant, their chances of finding
another suitable host are slim. Larvae of Manduca spp. only leave plants under condi-
tions of severe crowding, and then usually as fifth instars (McFadden 1968).
An insect must be in the proper developmental, physiological and behavioral state,
and environmental conditions must be suitable, before that insect will initiate searching
for a host plant. Theoretically, cross wind flight is an efficient appetitive searching
strategy for flying insects, since it increases the probability of encountering a wind-
borne host odor (Card6 1984). However, this may apply more to male orientation to
female-produced pheromones than to host plant finding. Downwind flight is a more
efficient way of searching for plants because insects travel for longer distances, and
thus they have a higher probability of encountering suitable hosts. This might account
for the daily short-range, downwind flights of Heliothis adults before they feed (Lingren
& Wolf 1982). Unfortunately, appetitive searching behavior of insects has not been
extensively studied (Card6 1984).
Relatively little is known about how insects locate field crops over a long distance.
Some pests, such as aphids, are passively carried to fields by the wind. Landing by
aphids is fairly nonspecific with orientation only to color and light reflections (Van
Emden et al. 1969). Host discrimination takes place after alate aphids have probed a
plant, and they will leave unacceptable hosts. Many other insect species, such as
lepidopteran moths, use air-borne chemicals and visual cues to orient to plants (Miller
and Strickler 1984).
Olfactory, visual, and contact stimuli may all be utilized by ovipositing female moths
during the orientation process. Olfactory and visual cues are used for orientation to the
plant surface, but contact chemoreception and mechanoreception are typically necessary
before eggs are deposited (Ramaswamy 1988). Thus, behavioral experiments must be
carefully designed in order to determine the exact role plant-produced chemicals have
on ovipositional behavior. A particular chemical may act as an attractant, repellant,
arrestant, excitant, stimulant, deterrent, or have some other function (Singer 1986).
Orientation of flying insects to volatiles has been studied most extensively with
regard to the response of moths to pheromones (Card6 1984), but many of the same
principles apply to orientation by insect herbivores to plant-produced chemicals (Finch
1986). Volatiles travel downwind from point sources in filamentous plumes whose con-
centrations and shapes are determined by such factors as the amount of chemical re-
leased, wind speed, height of the odor source above the ground, turbulent diffusion,
and interference caused by objects in the pathway. The concentration gradient of chem-
icals in an odor plume varies comparatively little along the windward axis, but has
rather sharp variation laterally (Elkinton & Card6 1984). Within a few meters from an
odor source the filament becomes a chaotic tangle, and insects usually encounter pulses
of the volatiles in various dilutions (Murlis & Jones 1981, Kramer 1986).
Insects probably do not orient toward point sources of odors using concentration
gradients (Kramer 1986). This is especially true for plant-produced volatiles in the field
that do not emanate from point-sources. Instead, moths orient upwind toward odor
sources using an optomotor anemotactic mechanism in conjunction with counterturning
movements which may be either self-steered (Kennedy 1986) or provoked by transverse
chemo-klinotaxis (Card6 & Carlton 1985). Other behavioral mechanisms for the chemical
orientation of insects to plants have been proposed, but the optomotor anemotactic


September, 1990

Jackson: Symposium-Plant Resistance to Insects

mechanism is supported by most data and is widely accepted (Card6 1984). Some insects
orient by visual rather than by chemical cues, and there are examples of plants becoming
resistant to pests after the color of their foliage was genetically altered (Smith 1989).
Prokopy (1986) also stressed the importance of the interactions between visual and
olfactory stimuli in insect orientation to resources.
Yamamoto et al. (1969) proposed a generalized scheme of oviposition by moths of
M. sexta. They divided the orientation to plants into a non-discriminatory approach in
which visual and olfactory cues are utilized, and a discriminatory landing utilizing olfac-
tory stimuli. They also suggested that separate kairomones were involved in the attrac-
tion and ovipositional phases. Contact chemoreception is then required to elicit egg
Chemoreception by insects may be divided into contact chemoreception (or gusta-
tion) and olfaction, based on the characteristics of the stimuli, the transport mechanism,
and the morphology of the sense organs (Stadler 1984). However, the distinction be-
tween olfaction and gustation may sometimes become unclear, especially when insects
enter the boundary layer of a leaf where concentrations of plant volatiles may be high.
For example, the "gustatory" receptor cells of larvae of M. sexta respond to olfactory
cues of their host plants at close range (StAdler & Hanson 1975). For the most part,
however, long-range olfaction and contact chemoreception are quite distinct.
It is likely that separate plant-produced kairomones mediate such adult behaviors
as orientation to food sources, orientation to oviposition substrata, initiation and con-
tinuation of feeding, and stimulation of oviposition. In general, oviposition stimulants
and deterrents are different from chemicals that elicit or inhibit feeding responses of
larvae (Renwick 1983). For example, contact ovipositional stimulants can be separated
from larval feeding stimulants for M. sexta from extracts of dried tomato leaves and
horsenettle (Yamamoto & Fraenkel 1960a, Bordner et al. 1983). Alcohol or water ex-
tracts and steam distillates from fresh or dried leaves of several solanaceous species
elicit strong ovipositional activity by moths of M. sexta (Yamamoto & Fraenkel 1960a,
Yamamoto et al. 1969). Electroantennogram (EAG) analyses showed that the steam
distillates stimulated antennal chemoreceptors of M. sexta. Further fractionation by
gas chromatography yielded several isolates with EAG activity, but ovipositional be-
havior with individual components was lost (Tichenor & Seigler 1980). These tests
indicate that moths are attracted by specific mixtures of components and not by indi-
vidual compounds.
Female moths of Heliothis spp. prefer to lay eggs on or near the flowering or fruiting
portions of many of their host plants, but in the absence of flowers, vegetative struc-
tures are chosen (Hardwick 1965). For example, eggs may be found on all portions of
nonflowering tobacco plants, but they are concentrated on the first few leaves below
the leaf bud (Jackson et al. 1983).
The upwind orientation of moths of H. virescens toward nectar sources and ovipos-
itional sites suggests the presence of air-borne feeding and oviposition attractants being
emitted by the plants (Lingren & Wolf 1982). Heliothis subflexa (Guene6) exhibits
positive flight responses to odors extracted from the leaves of its host, ground cherry,
Physalis spp. (Tingle et al. 1989). Mitchell et al. (1990) reported a positive anemotactic
response by female moths of H. virescens toward volatile materials extracted from the
leaves of tobacco, cotton, and Florida beggarweed, Desmodium tortuosum (Swartz) de
Candolle, a wild host plant of Heliothis spp. In contrast, Ramaswamy (1988) was unable
to find any odor-mediated, upwind orientation by female moths of H. virescens to either
cotton (a host) or ground cherry (a nonhost). He argues that highly polyphagous insects
such as H. virescens and H. zea do not depend on olfactory cues for host location.
Instead, he suggests that they orient more randomly by upwind anemotaxis to
nonspecific olfactory cues.


Florida Entomologist 73(3)


Once an insect locates a plant using visual and olfactory cues, contact with the plant
surface is usually essential before feeding or oviposition is initiated. Both contact
chemoreceptors and mechanoreceptors are used to evaluate the plant surface. Many
phytophagous insects choose their host plants without perception of the leaf interior.
This is certainly the case with many lepidopteran pests whose adult females lay eggs
on undamaged plants. It is unlikely that the leaf surface provides much information
about the nutritional quality of the plant. Lepidopteran pests more likely utilize physical
characteristics and secondary plant metabolites (stimulants or deterrents) to identify
potential hosts for oviposition.
The initiation of feeding (tasting) also is mediated by stimulatory cues from the leaf
surface, but the continuation of feeding depends more on a sensory analysis of the
consumed material. Both nutrients and secondary plant compounds are important in
host identification by chewing and by sucking insects (Schoonhoven 1981, 1987).
Plant compounds may have immediate effects on insect behavior or they may have
delayed actions and affect physiological processes. Plant chemicals may adversely affect
insects by being directly toxic without affecting feeding, or by altering behavior and
reducing food intake. However, the results may be the same with each of these mod-
alities, and that is reduced growth or death of the insect. It is not easy to determine
whether a plant compound is a feeding deterrent and/or a toxin, thus, deterrence and
toxicity must be measured separately to determine which caused an insect's demise
(Bernays 1982). Some compounds may have more than one effect on insects. For exam-
ple, Chinaberry extract was reported as both a feeding deterrent and growth inhibitor
for H. zea (McMillian et al. 1969). Pyrethroids have repellent, antifeedant, and toxic
properties (Ruscoe 1977). Azadirachtin from the Neem tree acts as a feeding deterrent
and an insect growth regulator that affects a wide range of insects including M. sexta
and Heliothis spp. (Schluter et al. 1985, Barnby & Klocke 1987).
Lepidopteran larvae normally first encounter an undamaged plant surface after
hatching, and they must recognize that surface as a host before feeding is initiated.
Hatching larvae may simply refuse to feed on plants selected by their mothers, due to
the lack of necessary sensory inputs needed to identify the plant, or due to the presence
of specific feeding deterrents. Larvae of M. sexta have olfactory and gustatory recep-
tors, which are both used to discriminate hosts (Hanson & Dethier 1973). The stimula-
tion of either receptor may result in normal discrimination among acceptable hosts, but
gustatory reception alone appears to play a role in rejecting unacceptable plants (Han-
son & de Boer 1986).
Lepidopteran larvae use their subtle sense of taste to select the best part of the
plant and to avoid high concentrations of deterrents. When a larva tastes a food source,
receptor cells are stimulated and coded by the CNS. Each cell possesses its own sensitiv-
ity spectrum, and each plant tasted evokes a unique overall response pattern in these
cells. These external stimuli are weighed by the CNS against internal satiety signals
(ie. stretch receptors in the alimentary canal) and also against the general physiological
state of the insect that includes feedback from nutritional factors, nutritional deficien-
cies, and toxins (Schoonhoven 1987). When both olfactory and gustatory chemoreceptors
are removed by amputation of the antennae and maxillae, tobacco hornworm larvae will
feed on plants normally rejected (Waldbauer & Fraenkel 1961).
Both polar and nonpolar compounds stimulate feeding by larvae ofM. sexta (Bordner
et al. 1983, de Boer and Hanson 1988). Extracts, from leaves of tomato, tobacco, and
jimson weed, when applied to nonhost plants or to paraffin sheets, elicit feeding re-
sponses by hornworm larvae (Morgan & Crumb 1928). An active glycosidic substance
isolated from a crude ethanol extract of tomato leaf powder, in combination with various
sugars, is necessary to elicit maximal feeding by hornworm larvae on agar diets

September, 1990

Jackson: Symposium-Plant Resistance to Insects

(Yamamoto & Fraenkel 1960b). This illustrates the importance of both feeding stimul-
ants and nutritional factors in mediating the feeding response of these insects.
Yamamoto & Fraenkel (1960a) first demonstrated the induction of a host preference
as the result of a prior feeding experience for hornworm larvae. As early as the second
instar, larvae prefer to feed on host plants on which they had previously fed. Host plant
induction for M. sexta is chemically based (Stadler & Hanson 1976).
Moths of Heliothis spp. prefer to oviposit on pubescent rather than smooth surfaces
(Callahan 1957). Even in no-choice situations, few eggs are laid on cotton, corn, tobacco,
or tomatoes, with smooth leaves (Robinson et al. 1980, Jackson et al. 1988). The surface
texture is probably determined by mechanoreceptors on the tarsi and especially on the
ovipositor. Proper leaf moisture is also required by moths of H. virescens for oviposition
(Navasero & Ramaswamy 1990).
Ramaswamy (1988) presented an ethographic representation of moth ovipositional
behavior using H. virescens as a model. Visual, tactile, olfactory, and contact chemosen-
sory cues are all involved in the host finding and host acceptance processes. Oviposition
occurs as a series of 3 6 "major bouts" each consisting of 8 20 "minor bouts" where
moths lay 5 10 eggs. Between bouts, moths fly from plant to plant and/or rest. Moths
rely primarily on contact chemosensory and mechanosensory information and not olfac-
tory or visual information for close-range discrimination of host plants (Ramaswamy
1988, 1990, Ramaswamy et al. 1987).
After landing on a plant surface, moths of tobacco budworms exhibit "wing fanning
while walking" followed by "abdomen bending", "dragging of the ovipositor", then egg
laying. Other behaviors observed include "antennal movement", "wing buzzing", and
periods of inactivity. Walking over the plant surface, antennal tapping, and ovipositor
dragging all bring sensilla in contact with the plant surface, and provide moths with
sensory information (Ramaswamy et al. 1987). On inanimate surfaces, moths do not
exhibit "ovipositor dragging" before laying eggs, and they have more "no egg" (non-
oviposition) bouts. Cage screens do not provide appropriate chemical ovipositional cues,
but because screens provide acceptable tactile cues and they lack ovipositional deter-
rents, some Heliothis eggs are typically laid on them, especially in the absence of more
suitable plant substrata (Ramaswamy 1988, 1990). The repetition of behaviors probably
influences the internal state of the insect and lessens the intensity of external cues
necessary to elicit oviposition. The ovipositor drag observed for females on plant sur-
faces is utilized by the female to get a final sensory reconfirmation of the suitability of
the leaf (Ramaswamy 1988, 1990).
In paired choice tests with a typical flue-cured tobacco, NC 2326, less than 25% of
the eggs from H. virescens are deposited on TI 1112 in small field cages (Jackson et al.
1983). Commercial tobacco cultivars have glandular trichomes that secrete exudates,
whereas TI 1112 has simple trichomes that lack glands and the trichome exudates.
Certain components of trichome exudates from commercial tobaccos, especially duvat-
rienediols, duvatrienols, and sucrose esters, are ovipositional stimulants (Jackson et al.
1986, 1988). TI 1112 is not oviposited on to the same degree as NC 2326 due to its near
absence of ovipositional stimulants found on the commercial tobacco cultivar. Thus,
resistance in TI 1112 to tobacco budworms is due, in part, to ovipositional nonpreference
related to the near absence of the ovipositional stimulants from trichome exudates.
Oviposition by H. virescens on TI 1112 is somewhat analogous to oviposition by them
on cage screen as described by Ramaswamy (1988, 1990). TI 1112 has simple trichomes,
and thus the proper tactile cues are present and there are no chemical deterrents, but
ovipositional stimulants are nearly absent. Whole leaf washes from 6-week-old flue-
cured tobacco stimulate oviposition by tobacco budworms when sprayed on TI 1112
(Jackson et al. 1984).
Evidence that duvatrienediols are perceived by adult females of H. virescens upon
contact was gathered from a series of experiments (Jackson et al. 1989) using 1-35, a


Florida Entomologist 73(3)

glandless breeding line developed from TI 1112 (Miles et al. 1980). In one experiment,
duvatrienediols were sprayed onto whole 1-35 plants, and two treated plants were
bioassayed against two unsprayed 1-35 plants in field cages. In another experiment,
duvatrienediols were applied to every other leaf of four plants, and these were bioas-
sayed in a no-choice test. Interestingly, the same percentage of eggs (ca. 65%) was laid
on the duvatrienediol-treated leaf surfaces regardless of the treatment, indicating that
the close proximity of a treated leaf does not increase oviposition onto an untreated leaf
(Jackson et al. 1989). Similarly, the infestation levels of Heliothis spp. and Manduca
spp. on NC 2326 and TI 1112 in 1000-plant blocks in the field were the same whether
the plants were in pure stands of each tobacco type, or whether every other plant type
was alternated within rows (Jackson et al. 1988).
Tingle & Mitchell (1984, 1986) found ovipositional deterrents for moths of H. vires-
cens from aqueous extracts of several nonhost plant species. Deterrent compounds may
prevent Heliothis spp. from ovipositing on these plants in the wild. In generalist species
such as Heliothis, the acceptance of a host plant for oviposition is governed to a large
extent by the absence of deterrents (Renwick 1983, Ramaswamy 1988).
Nonpreferred plant species may have deterrent chemicals that prevent moths from
ovipositing on them, but that cause no harm to larvae feeding on that species. In the
field, moths of M. sexta oviposit exclusively on solanaceous host plants (Yamamoto &
Fraenkel 1960c). In the laboratory, however, they oviposit on Petunia, which is toxic
to their larvae, and on Nicandra physalodes (L.) Persoon, which is repellent to their
larvae (Yamamoto & Fraenkel 1960c, Thurston 1970, Dethier & Yost 1979). In both
laboratory and field experiments, females preferred to oviposit on tomato over several
other solanaceous species, including tobacco (Yamamoto & Fraenkel 1960b,c). However,
ovipositional preferences by Manduca spp. for host plants appear to be regionalized
and dependent on the predominantly available host plant species. In areas where to-
bacco is widely grown, it may be the preferred host (Madden & Chamberlain 1945).


It is often difficult to determine whether a larva dies from starvation because it
rejects a plant as unsuitable (a behavioral response) or whether it accepts that plant
and dies due to some antibiotic factor (a physiological response). This difficulty is espe-
cially acute with first instar larvae that hatch directly on undamaged plants. This is
further complicated by the fact that larvae will sometimes initiate feeding, but consume
very little before moving on. Do such larvae die of starvation or do they receive a lethal
dose of a plant allelochemical? Antibiotic factors also include physical plant characteris-
tics that entrap or injure insects as well as allelochemicals that poison insects, offset
their development, or reduce digestibility of their food. For example, some tobaccos,
such as TI 163 and TI 165, have high levels of cuticular duvane diterpenes and sucrose
esters, and they are very susceptible to oviposition by H. virescens (Jackson et al.
1988). However, poor survival of larvae results in little damage to these tobaccos in the
field (Johnson & Severson 1984). This resistance is due to both feeding nonpreference
and antibiotic factors. Feeding preference tests showed that newly hatched, 4-, 7-, and
10-day old larvae preferred NC 2326 over TI 165. Neonate larvae will initiate feeding
on TI 165, but they do not feed normally and they often move to other portions of the
leaf. Methanol-water soluble fractions from leaf extracts from both NC 2326 and TI 165
pipetted onto artificial diet were also toxic to first instars of H. virescens (Severson et
al. 1985).
Sticky trichome exudates may be a physical deterrent or an antibiotic factor that
prevents small larvae or nymphs from becoming established by entangling them on the
leaf surface or by gluing their mouthparts shut (Duffey 1986). Extremely villous sur-
faces may also limit establishment by small insects.


September, 1990

Jackson: Symposium-Plant Resistance to Insects 387

Although some toxic allelochemicals may be perceived before food is ingested and
cause it to be rejected (feeding deterrents), others apparently are not detected; or if
they are detected they do not deter feeding. Their deterrence may not be apparent until
feeding is initiated or it may be hidden by counteracting feeding stimulants. Insects
may therefore ingest lethal or sublethal doses of secondary plant compounds.
Waldbauer et al. (1984) proposed that insects can, to varying degrees, select a
favorable nutrient balance from their natural foods by consuming different plant struc-
tures that vary in their nutritive values. Larvae of H. zea can select an optimal nutrient
balance from two nutritionally deficient diets, one lacking only casein and one lacking
only sucrose. Larvae regulate their nutrient balance by switching back and forth be-
tween diets and by varying the length of feeding bouts on each one. In this fashion,
larvae consume both diets until they reach a 80:20 ratio of casein:sucrose, which is the
optimal ratio of these nutrients for larval growth (Waldbauer et al. 1984, Cohen et al.
Many insects optimize their intakes of protein. Given the opportunity, larvae of
Heliothis spp. will feed on the protein-rich fruiting structures or seeds of several crops,
and they selectively feed on different plant parts of tomato, cotton, corn, and tobacco
(Neunzig 1969). However, this may be due to the influence of environmental factors,
escape from predators, or the avoidance of secondary plant compounds, rather than to
nutrient self-selection. But, at least for fifth instar H. zea feeding on corn, larvae are
able to increase their intake of protein-rich germ over carbohydrate-rich endosperm
(Cohen et al. 1988). Larvae also regulate the amount of food eaten to provide adequate
nutritional requirements. Insects may also compensate for a deterioration in food quality
(such as leaf senescence) by increasing their consumption (Slansky 1981).


Breeding programs for the development of insect-resistant crop cultivars typically
involve the efforts of scientists from several disciplines, including plant breeders,
geneticists, chemists, ecologists, and entomologists. The primary roles of entomologists
in these programs are to identify sources of resistant germplasm and to determine the
modalities and mechanisms of resistance to insect pests. These tasks are achieved only
after the biologies of the pest species are thoroughly studied. To completely understand
the mechanism of resistance, an entomologist must understand the behavior of the pest
and the interactions between the plant and the insect.
Understanding insect behavior is an important element in a program for breeding
pest-resistant cultivars, because genetic alterations in the physical or chemical charac-
teristics of a plant may so alter the behavior of a pest that the plant becomes resistant.
Plant characteristics affect the behavior of insects in many ways, and thus there are
many ways in which plants may be altered to make them less susceptible to insect
attack. This paper has reviewed insect-plant interactions that affect the host finding,
host recognition, host acceptance, and host utilization behaviors of certain lepidopteran
pests. Breeders can alter plant characteristics to make a cultivar less attractive over a
distance or to make it less recognizable or acceptable as an oviposition substrate or food
source once insects have found it.


I thank Fred L. Gould, George G. Kennedy, and James F. Walgenbach for reviewing
earlier versions of this manuscript. This paper is a cooperative effort of the USDA-ARS
and the Department of Entomology, North Carolina State University, and it is paper
no. 12561 of the journal series of the North Carolina Agricultural Research Service,
Raleigh, N. C. 27695-7601.

388 Florida Entomologist 73(3) September, 1990


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Jackson: Symposium-Plant Resistance to Insects 389

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Am. Chem. Soc. Symp. Ser. 208.
RENWICK, J. A. A., AND C. D. RADKE. 1981. Host plant constitutes an oviposition
deterrents for the cabbage looper, Trichoplusia ni. Entomol. Exp. Appl. 30:
ROBINSON, S. H., D. A. WOLFENBARGER, AND R. H. DILDAY. 1980. Antixenosis
on smooth leaf cotton to the ovipositional response of tobacco budworm. Crop
Sci. 20: 646-649.
RUSCOE, C. N. E. 1977. The new NRDC pyrethroids as agricultural insecticides.
Pesticide Sci. 8: 236-242.
SCHLUTER, U., H. J. BIDMON AND S. GREWE. 1985. Azadirachtin affects growth
and endocrine events in larvae of the tobacco hornworm, Manduca sexta. J.
Insect. Physiol. 31: 773-777.
TER, AND G. R. ZUMMO. 1986. Interaction of Heliothis with its host plants,
pp. 3-21 in S. J. Johnson, E. G. King, and J. R. Bradley, Jr. [eds.], Theory and
Tactics of Heloithis Population Management: I. Cultural and Biological Control.
Southern Coop. Ser. Bull. No. 316.
SCHONI, R., E. STADLER, J. A. A. RENWICK, AND C. D. RADKE. 1986. Host and
non-host plant chemicals influencing the oviposition behavior of several herbivor-
ous insects. Ser. Entomol. 41: 31-36.
SCHOONHOVEN, L. M. 1972. Secondary plant substances and insects, pp. 197-224 in
V. C. Runeckes and T. C. Tso [eds.], Structural and Functional Aspects of
Phytochemistry. Recent Adv. Phytochem. 5.
SCHOONHOVEN, L. M. 1982. Biological aspects of antifeedants. Entomol. Exp. Appl.
31: 57-69.
SCHOONHOVEN, L. M. 1987. What makes a caterpillar eat? The sensory code under-
lying feeding behavior, pp. 69-97 in R. F. Chapman, E. A. Bernays, and J. G.
Stoffolano, Jr. [eds.], Perspectives in Chemoreception and Behavior. Springer-
Verlag, New York.
SEVERSON, R. F., A. J. JOHNSON, AND D. M. JACKSON. 1985. Cuticular constitutes
of tobacco: Factors affecting their production and their role in insect and disease
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Jackson: Symposium-Plant Resistance to Insects 391

SLANSKY, F., JR. 1981. Insect nutrition: An adaptationist's perspective. Florida En-
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SMITH, C. M. 1989. Plant Resistance to Insects: A Fundamental Approach. Wiley,
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TINGLE, F. C., AND E. R. MITCHELL. 1984. Aqueous extracts from indigenous
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Florida Entomologist 73(3)

September, 1990


United States Department of Agriculture
Agricultural Research Service
Crops Science Research Laboratory
Mississippi State, Mississippi 39762-5367


Entomologists and plant breeders have noted that glandless lines of cotton generally
are susceptible to phytophagous insects. Gossypol, the yellow pigment present in the
glands, has been shown to be the most important allelochemical that provides resistance.
In field tests, high gossypol lines have repeatedly been correlated with lessened insect
damage, probably due to toxicity of gossypol to Heliothis sp. and other cotton insects.
Recent behavioral-histochemical studies of newly hatched larvae of tobacco bud-
worm, Heliothis virescens (F), feeding on cotton showed that first-stage larvae avoided
consuming the glands. However, when these molt between 48 and 72 h of age, they
nonselectively consume the glands, suggesting a metabolic adaptation.
Young tobacco budworm larvae prefer to feed along the margin area of the calyx
crown of the square, an area devoid of gossypol glands. On resistant lines having glands
in the calyx crown, the larvae feed sporadically on the tissue thus avoiding the glands.
The numbers of gossypol glands on bracts of small squares, calyx crown, bract mid-rib,
and the entire calyx differed significantly between the susceptible and resistant lines.
First instar larvae placed on squares of cotton genotypes with high gland density in the
small square bract and in the calyx crown, were significantly smaller than larvae placed
on line with fewer glands. These and related studies suggest that breeding strategies
should concentrate on placing gossypol glands in the calyx crown, the primary site of
insect attack.


Entom6logos y fitomejoradorea han notado que variedades de algod6n sin glAndulas
son generalmente susceptibles a insects fit6fagos. Se ha demostrado que gosypol, el
pigmento amarillo present en las glAndulas, es el mAs important aleloquimico que
provee resistencia. En pruebas de campo, variedades con alto contenido de gosypol,
repetidamente han estado correlacionadas con menor dafo por insects, probablemente
debido a la toxicidad del gosypol a Heliothis es. y a otros insects del algod6n.
Studios recientes sobre el comportamiento histoquimico de larvas recien nacidas
del gusano de la yema del tabaco, Heliothis virescens (F.), alimentAndose del tabaco,
demostr6 que larvas en la primera etapa evitaban consumer las glandulas. Sin embargo,
cuando estas mudan entire 48 y 72 horas de edad, ellas consume las glAndulas sin
seleccionar, lo que sugiere una adaptaci6n metab6lica.
Larvas jovenes de la yema del tabaco prefieren comer a lo largo del Area del margen
de la corona del cAliz del cuadrado, que es un Area que no tiene glAndulas de gosypol.
En variedades resistentes que tienen glandulas en la corona del cAliz, las larvas se
alimentan esporAdicamente del tejido y asi evitan las glandulas. El ntmero de glAndulas
de gosypol en la bractea de pequefios cuadrados, en la corona del cAliz, en la nervadura
central de la bractea, y en el cAliz entero, fueron significativamente distintos entire las
variedades susceptibles y resistentes. Larvas en el primer estadio puestas en cuadrados
de genotipos de algod6n con una alta densidad de glAndulas en la brActea de pequefios
cuadrados y en la corona del caliz, fueron significativamente mas pequeAs que larvas
puestas en variedades con menos glandulas. Este y otros studios similares sugieren
que estrategias de fitomejoramiento deben de concentrarse en poner glandulas de
gosypol en la corona del caliz, que es el lugar principal que los insects atacan.

Parrott: Symposium-Plant Resistance to Insects 393

Gossypol, the yellow pigment present in enclosed glands of the genus Gossypium,
was first reported to confer resistance to the cotton bollworm Heliothis zea Boddie by
Bottger et al. (1964). Since then, cotton breeders and entomologists have searched for
methods to select and develop plants with high gossypol content for resistance to this
insect and others. Most commercial cotton cultivars have a gossypol content of about
0.5% in squares. Lukefahr & Houghtaling (1969) concluded from laboratory tests that
the gossypol level in squares must be increased to approximately 1.2% to inhibit growth
and development of the cotton bollworm and the closely related species, the tobacco
budworm, H. virescens (F). Growth studies show an increase in growth of tobacco
budworm larvae on glandless cotton strains when compared with larval growth on their
glanded isoline (Lukefahr et al. 1966). Shaver & Lukefahr (1969) incorporated gossypol
into diets and demonstrated a reduction in larval growth rate. Bell & Stipanovic (1977)
isolated gossypol and related compounds from glanded cotton plants and found that
these compounds are toxic to tobacco budworm larvae. In fact, in some parts of the
plant, the related compound may occur in higher concentrations than gossypol itself. In
this paper the term "gossypol" is used in a general sense to indicate all the related
compounds that affect feeding of the tobacco budworm larvae on cotton plants.


Although researchers have tested gossypol for antibiosis (retarted growth and devel-
opment) to larvae, they have paid little attention to the deterrent effect of gossypol on
feeding behavior of young larvae.
Although newly hatched tobacco budworm larvae feed on cotton leaves, they seldom
feed on gossypol glands. Waiss et al. (1981) showed that first-stage larvae of the cotton
bollworm, generally avoided consuming gossypol glands. Lee (1976) observed that both
H. zea and H. virescens selected anthers of high-glandulosity cottons for feeding, but
avoid contact with the gossypol-rich ovary. If these Heliothis spp. larvae, at their most
susceptible age, avoid gossypol-containing plant parts or tissue, then one could question
whether antibiosis is the sole manifestation of the resistance of cotton to Heliothis spp.
via gossypol.
We placed laboratory-reared, first-stage larvae on terminal leaves (5 to 6 cm in
diameter) of 'Stoneville 213' (ST 213) cotton grown in the greenhouse and allowed to
feed for 24, 48, and 72 h. For the 72-h feeding period, newly hatched larvae were
allowed to feed on leaves for 48 h and were then transferred to fresh leaves of the same
size and allowed to feed for an additional 24 h. This procedure assured that larval
feeding damage occurred on the third day (or between 48 and 72 h). At the end of each
designated time period, leaves damaged by feeding were removed from the plants and
fixed in a Formalin-Acetic Acid-Alcohol solution for 4 h.
A stereomicroscope with 10 X power equipped with a 1-cm2 eye piece micrometer
grid divided into 1-mm squares was used to observe feeding damage on the leaves. The
number of glands present in 1 mm2 of leaf area was determined for both the feeding
and nonfeeding sites on the same leaves. Twenty sites per leaf were chosen randomly.
Ten replications were counted for each of the three feeding periods (24, 48 and 72 h).
Due to leaf expansion, gland density per 20 cm2 was greater in smaller (24 h) than
in older ones (48 h). There were no differences in the number of gossypol glands on the
nonfeeding area of the leaf as compared with the feeding area for the 24- and 48-h time
intervals. First-stage larvae frequently bit into the glands, but failed to consume them,
however, between 48 and 72 h, a difference between the number of glands was apparent.
During this time period, larvae consumed entire portions of the leaf, including the
glands. Apparently the older larvae were able tb metabolize the contents of the glands.
This finding is in agreement with previous work by Shaver & Parrott (1970), who found
young larvae to be more sensitive to gossypol than older larvae.

Florida Entomologist 73(3)


Newly hatched tobacco budworm larvae were placed on the terminal leaves of three
cotton types, 'ST-213' (normal gossypol glands), 'Stoneville 7AG' (glandless), and 'BW-
76-31-DH' (high gossypol) and allowed to feed for 24 h.
Histological comparisons of leaves with and without feeding damage were made by
selecting 20 leaves from each of the three cotton types and subjecting them to identical
histological procedures. Comparisons between fed and unfed leaves were made qualita-
tively on the basis of examination of similarly treated materials and similar sampling
procedures: no quantification was attempted. The extent to which young larvae dam-
aged or consumed glands was determined from the prepared slides. First stage larvae
fed on the perimeter of some glands but generally avoided the glands. These larvae fed
readily on the lower epidermal, spongy, and palisade cells, leaving the upper epidermis
intact. Larvae avoided the gossypol glands in the mesophyll tissue.
The association of anthocyanin with the gossypol glands was demonstrated by drop-
ping weak acid (HC1, ca 5%) on the tissue, producing a bright red halo around the
gossypol gland (Hedin et al 1967). The halo tissue turned green with the addition of
10% KOH, whereas gossypol, in the central area of the gland, remained red.
Beck (1965) proposed that resistance mechanisms which have a direct effect on
insect feeding be classified as nonpreference. Hedin et al (1980) reported anthocyanins
and anthocyanidins to be toxic to larvae of tobacco budworm. These data suggest that
the anthocyanin present in the envelope which surrounds the gossypol glands may serve
as a feeding deterrent, resulting in nonpreference of the young larvae.
The most critical life stage of the tobacco budworm is immediately after egg hatch
when the young larvae search for feeding sites. The influence of gossypol, anthocyanins
and other plant allelochemics at this early developmental stage should be greater than
that of these compounds during later developmental stages of the insect, since more
mature larvae may be better adapted to tolerate previously effective resistance


During the early 1970's, an extensive breeding program was begun to develop cotton
resistant to the Heliothis spp. complex. This breeding effort was primarily the result
of widespread insecticide resistance that was developing in H. zea and H. virescens
throughout the cotton belt.
Sappenfield et al. (1974) initially used XG-15, a cotton line developed by Lukefahr
& Houghtaling (1969) as a primary gossypol source. In the early stages of their work,
they were compelled to rely on expensive analytical chemistry to isolate plants with
high gossypol content. Little was known about phenotype expression and gossypol
content. Then, Sappenfield et al. (1974) showed a relationship between calyx gland size
and density and square gossypol content. This finding provided breeders with the first
phenotypic marker to identify cotton plants high in gossypol.
Preliminary observations noted that neonate larvae feed on the margin of the calyx
(calyx crown) of cotton cultivars which generally have no gossypol glands in this feeding
site. Previous studies by Parrott et al. (1983) showed that first instar tobacco budworm
larvae avoid feeding on gossypol glands. The feeding sites and behavior of early instars
were observed to determine the effect of gland density and distribution as potential
mechanisms of resistance, and to measure the growth of tobacco budworm larvae fed
squares from lines with high and low gland densities in the calyx crown.

September, 1990

Parrott: Symposium-Plant Resistance to Insects


In 1984, five lines of cotton were planted on the Plant Science Research Farm,
Mississippi State, MS. Four of these lines, BW-76-31, DH-126, 83 MHR-1, and 84-MHR-
3 had resistance to the tobacco budworm. The susceptible '(ST-213)', was used as a
control. Squares (8 mm diameter) were harvested throughout the summer, and placed
individually into 30-ml plastic cups with 2% agar in the botton (6.4 mm) to prevent
square desiccation. A neonate tobacco budworm larva was placed on the square and
allowed to feed. Fresh squares were introduced every 2 d. Larvae were weighed at 7
or 12 d. Counts were made on the number of gossypol glands present on bracts of small
squares, calyx crown, bract mid-rib, and the total glands present on the calyx.
DH-118, 121, and 126 each were crossed with 'ST-213' and 'Stoneville 825' (ST-825)
and lines developed with either high or low densities of glands in the calyx crown from
each cross. Lines were selected for gland density in the F2 generation and advanced to
F5. In 1986, 12 F5 lines plus the five parents were investigated for resistance to tobacco
budworm. Fresh squares were offered to larvae and gland counts made as described
Neonate larvae preferred to feed on the calyx crown of the square, the same mor-
phological area used by Sappenfield et al. (1974) to select for high gossypol content.
While Sappenfield et al. (1974) were selecting for lines with high gossypol gland density
on the calyx crown, they were selecting also plants that were resistant to the tobacco
More glands were present on the bract mid-rib and the entire calyx of DH-126,
BW-76-31, and 83-MHR-1 than on 'ST-213', and more were present on the calyx crown
of DH-126 and BW-76-31 than 'ST-213' (P s 0.05). Gland density on the calyx crown
was correlated with that on the small square bract (r = 0.58). bract mid-rib (r = 0.65),
and total calyx (r = 0.68) gossypol. Each high gossypol line produced larvae smaller
than larvae on 'ST-213'.
As with most cultivars, 'ST-213' has few glands on the calyx crown, whereas line
DH-126 has glands distributed throughout the calyx. When young larvae feed on buds
of 'ST-213', a susceptible line, the margin area of the calyx crown, which is devoid of
glands, is perferred; however, on lines with glands in the calyx crown, the young larvae
avoid those glands.
In the F5 progeny from DH lines X 'ST-213' and 'ST-825', larvae that fed on high
gland density lines were similar in size to those fed on the DH parent, whereas larvae
fed on the low-density lines were similar to those fed on the cultivars. Thus, the calyx
crown gland density is a measure of resistance, and crosses of high gland density lines
with commercial cultivars produced progeny resistant to tobacco budworm larvae.
Gossypol glands are controlled genetically: cotton breeders can manipulate gland
size and density through appropriate crosses followed by selecting lines with high gland
density in the calyx crown, a preferred feeding site for young larvae.


BECK, S. D. 1965. Resistance of plants to insects. Annu. Rev. Entomol. 10: 207-232.
BELL, A. A., AND R. D. STIPANOVIC. 1977. The chemical composition, biological
activity, and genetics of pigment glands in cotton. Proc. Beltwide Cotton Prod.
Res. Conf. 1977: 244-258.
BOTTGER, G. T., E. T. SHEEHAN, AND M. J. LUKEFAHR. 1964. Relation of gossypol
content of cotton plants to insect resistance. J. Econ. Entomol. 57: 285-288.
N. JENKINS. 1980. Proc. Int. Conf. Reg. Insect Dev. Behav., Wroclaw Tech.
Univ. Press. Wroclaw, Poland, p. 1071.


396 Florida Entomologist 73(3) September, 1990

1967. Constituents of the cottonbud. VII. Identification of the anthocyanin as
chrysanthemin. Phytochemistry 6: 1165.
LEE, J. A. 1976. Reaction of Heliothis larvae to high-glandulosity cottons of an im-
proved type. Proc. Beltwide Cotton. Prod. Res. Conf. 1076: 90.
LUKEFAHR, M. J., AND J. E. HOUGHTALING. 1969. Resistance of cotton strains with
high gossypol content to Heliothis spp. J. Econ. Entomo. 62: 588-591.
LUKEFAHR, M. J., L. W. NOBLE, AND J. E. HOUGHTALING. 1966. Growth and
infestation of bollworms and other insects in glanded and glandless strains of
cotton. J. Econ. Entomol. 59: 817-820.
PARROTT, W. L., J. N. JENKINS, AND J. C. MCCARTY, JR. 1983. Feeding behavior
of first-stage tobacco budworm (Lepidoptera: Noctuidae) on three cotton cul-
tivars. Ann. Entomol. Soc. Am. 76: 167-170.
SAPPENFIELD, W. P., L. G. STOKES, AND K. HARRENDORF. 1974. Selecting cotton
plants with high square gossypol. Proc. Beltwide Cotton Prod. Res. Conf. 1974:
SHAVER, T. N., AND M. J. LUKEFAHR. 1969. Effect of flavonoid pigments and
gossypol on growth and development of the bollworm, tobacco budworm, and
pink bollowrm. J. Econ. Entomol. 62: 643-646.
SHAVER, T. N. AND W. L. PARROTT. 1970. Relationship of larval age to toxicity of
gossypol to bollworms, tobacco budworms and pink bollworm. J. Econ. Entomo.
63: 1802-1804.
WAISS, A. C., Jr. B. G. CHAN, C. A. ELLIGE, AND R. G. BINDER. 1981. Biologically
active cotton constituents and their significance in HPR. Proc. Beltwide Cotton
Prod. Res. Conf., 1981: 61.


US Vegetable Laboratory
2875 Savannah Highway
Charleston, SC 29414


Insecticides are the first line of defence in reducing damage to vegetable crops. The
removal of persistent insecticides, the development of insect resistance to insecticides,
EPA reregistration requirements and the concern of farm chemicals in ground water,
have increased interest in other control strategies including biological control, cultural
practices and breeding for insect resistant crops. This presentation is to report on the
evaluation, mechanism, chemistry and cultivar/clone development in vegetables with
resistance to insects for the southeastern United States.


Insecticidas son la primera linea de defense en reducir dafio a cultivos de vegetables.
La eliminaci6n de insecticides persistentes, el desarrollo de resistencia a los insecticides
por los insects, los requisitos de re-registrar los insecticides por el EPA (la Agencia
de Protecci6n del Medio Ambiente), y la preocupaci6n por los products quimicos ag-
ricolas en el manto de agua, han aumentado el interns en otras estrategias de control

Schalk: Symposium-Plant Resistance to Insects

incluyendo el control biol6gico, prActicas culturales y el fitomejoramiento de cultivos
con resistencia a insects. Esta presentaci6n es para reporter sobre la evaluaci6n,
mecanismos, quimica, y el desarrollo de variedades/clones de vegetables con resistencia
a insects en el sudete de los Estados Unidos.

Insecticides are the first line of defence in reducing damage to vegetable crops. The
removal of persistent insecticides, the development of insect resistance to insecticides,
EPA reregistration requirements and the concern of farm chemicals in ground water,
have increased interest in other control strategies including biological control, cultural
practices and breeding for insect resistant crops. This presentation is to report on the
evaluation, mechanism, chemistry and cultivar/clone development in vegetables with
resistance to insects for the southeastern United States.


Cabbage looper and imported cabbage worm: Chalfant & Brett (1967) studied feeding
damage and populations of the cabbage looper (Tricoplusia ni Hubner), and the cabbage
worm (Pieris rapae L.) on numerous commercial varieties of cabbage. The most resis-
tant varieties, based on feeding damage, were Mammoth Red Rock and Savoy Perfec-
tion Drumhead, while the most susceptible were Copenhagen Market 86 and Stein's
Flat Dutch. In detailed feeding tests antibiosis to the cabbage looper was observed in
Mammoth Rock. More eggs and small larvae were found on Mammoth Red Rock than
on the other three varieties, however, the cultivar had fewer large larvae and relatively
light feeding damage. Almost all eggs were deposited on the outer leaves. As larvae of
both insect species matured they migrated to the plant heads. Resistant varieties re-
sponded more favorably to insecticidal treatment than susceptible varieties. However,
this difference tended to disappear under the heavier infestations of late season.
Creighton et al. (1975) found that populations of both cabbage loopers and imported
cabbage worms were about the same on 4 cabbage cultivars treated weekly with Bacil-
lus thuringiensis and chlordimeform. However, Stein's Early Flat Dutch and Ferry's
Round Dutch had more plants with uninjured heads and wrapper leaves than did
Copenhagen Market No. 86 and Resistant Golden Acre. Data suggested complementary
effects of host plant's natural resistance and the microbial-chemical spray. On the basis
of the amount of feeding injury Stein's Early Flat Dutch was most resistant and Resis-
tant Golden Acre was most susceptible.


Cucumber beetles: Chambliss & Cuthbert (1968) evaluated a number of cultivars (251)
and germplasm (2339) of squash (Cucurbita pepo L., C. maxima Duch, C. mixta Pang),
muskmelon (Cucumis melo L.), and watermelon (Citrillus lanatus Thunb) for resist-
ance to the banded cucumber beetle (Diabrotica balteata LeConte). Emergent seedlings
were evaluated for resistance in the greenhouse by exposing them to high populations
of the adult beetles. The total number of lines and cultivars identified with resistance
to D. balteata were 36 and 20 respectively.
Thirteen cultivars of cucumber (Cucumis sativus L.) were evaluated by Lower et
al. (1974) in the greenhouse and field for resistance to cucumber beetles (Diabrotica
undecimpunctata howardi Barber, Acalymma vittata Fabricius). A positive correlation
was observed between field and greenhouse tests for cotyledon feeding. Two non-bitter
cultivars were most resistant to hypocotyl feeding in the greenhouse but not in the field
test. The absence of the bitter principle was of little significance in cotyledon feeding
(Lower et al. 1974).
Nugent et al. (1984 a and b) identified multiple insect resistance to D. balteata, D.
undecimpunctata howardi and A. vittata in muskmelon lines (C. melo) C922-B1, C922-
B2, and C922-B3.


Florida Entomologist 73(3)

Pickleworm and melonworm: Research on cucurbit resistance to pickleworm
(Diaphania nitidalis Stroll) in cucurbits has been conducted by several researchers in
South and North Carolina. Wehner et al. (1985) evaluated 1160 lines of cucumbers (C.
sativus L.) for resistance to this destructive pest. The authors developed a laboratory
screening procedure by applying neonate pickleworms to excised cucumber leaves, and
enclosing leaves and larvae in plastic petri plates for 4-6 days. Larval counts and leaf
feeding damage scores on a scale of 1 (little damage) to 9 (heavy damage) were taken.
Of the 1160 lines tested in the initial screening test, 8 were selected for further evalu-
ation (5 resistant and 3 susceptible). Parent-progeny regression analysis run on a pop-
ulation developed from resistant lines indicated that the trait is not heritable (Wehner
et al. 1983).
Elsey (1981, conducted another series of antibiosis tests on cucurbits and observed
a significant degree of antibiosis resistance to the pickleworm in an inedible wild gourd
(Lagenaria sicerania Mol.).
Elsey & Wann (1982), used artificial infestations of moths on cucumbers and followed
natural populations in the field, found that both pickleworm and melonworm (D.
hyalinata L.) preferred to oviposit on the pubescent rather than glaborous types of leaf
foliage. However, the glaborous cucumber is less vigorous than the pubescent type,
which limits its value in breeding programs.
Elsey (1985) compared eggs and larval infestations of the pickleworm on two Cucur-
bita moschata Poir cultivars, Butternut and Calabaza, and a susceptible control (C.
pepo, Tablequeen). During the peak oviposition period about 10 times as many
Diaphania sp. eggs and correspondingly higher numbers of both pickleworm and melon-
worm larvae were found on the control cultivar. Laboratory tests failed to detect any
larval antibiosis or preference factors among the cultivars. Therefore, Elsey (1985)
suggest that the mechanism of resistance is ovipositional non-preference in the C. mos-
chata cultivars and that chemical differences among them are responsible for the non-
preference (Elsey et al. 1984). Then Elsey investigated chemical influences on
pickleworm oviposition using yellow squash (C. pepo). He found that ethanol extracts
from the volatile components of squash foliage contained chemicals that stimulate
oviposition when sprayed on a medium such as fiberglass insulation. He has further
found that pumping air containing squash volatiles into pads sprayed with extract in-
creased oviposition over pads treated with extract only (Elsey et al. 1984).
Squash vine borer: Borchers & Taylor (1977) used Cushaw and Butternut squash as
sources of vine borer resistance (Melittia cucurbitae Harris). Attempts to cross Butter-
nut (C. moschata) with summer squash (C. pepo) were unsuccessful. However, progeny
from crosses with Cushaw (C. mixta) and summer squash were highly resistant to the
vine borer. Backcrossing the Fi to summer squash yielded some highly resistant non-
bitter segregates.
Leafminer: Kennedy et al.(1978a) evaluated over 50 muskmelon accessions for resist-
ance to leafminer (Liriomyza sativae Blanchard). Potentially useful levels of resistance
to the leafminer were identified in C. melo in greenhouse and field studies. Resistant
lines were identified as having the fewest mines per leaf per test. Two distinct sources
of resistance were found in Plant Introduction (PI) 282448 from Africa and PI 313970
from India. The resistance of PI 282448 appeared to be controlled by recessive genes,
while those of PI 313970 appeared to be controlled by partially dominant genes.
Melon aphid: Kennedy & Kishaba (1977) reported the response of alate melon aphids
(Aphis gossypi Glover) to resistant and susceptible muskmelon (C. melo L.) lines. The
insects were exposed in cages on the test plants in the greenhouse in choice no-choice
situations. Transfer tests were also conducted to determine if a period of feeding on
resistant plants had any residual effects. There was no effect on survival and reproduc-
tion of melon aphids which were confined for 16h on resistant plants and transferred to

September, 1990

Schalk: Symposium-Plant Resistance to Insects

susceptible plants. When given a choice, melon aphids preferred the susceptible plants.
In the absence of a choice 51% of uncaged aphids remained on resistant plants as
compared to 83% on the susceptible plants, indicating the resistant plants exerted a
weaker arrestant resulting in greater interplant movement of aphids. Resistance was
retained by excised leaves, even after 4 days. Neither resistance nor susceptibility was
translocated across the graft union.
Microscopic examination of stylets and sheaths and electronic recording of the prob-
ing behavior of the melon aphid on resistant and susceptible muskmelon revealed pro-
nounced differences in probing on 2 lines (Kennedy et al. 1978c). There was significantly
more probing by the aphids on the resistant muskmelon line as shown by the many
branches in the phloem. Electronic recording of aphid probing revealed that on the
resistant plants a greater percentage of probes led to stylet contact with the phloem
sieve cells, but a smaller proportion of the sieve cell contacts resulted in ingestion than
on susceptile plants. Duration of ingestion from the sieve cells was 2 to 3 times greater
on susceptible than on resistant plants.
A. gossypii Glover was not as effective in transmitting watermelon mosaic virus 2
when feeding on an aphid resistant genotype of muskmelon. This genotype alters the
aphid probing behavior and may reduce the rate of inoculation of nonpersistently trans-
mitted viruses by interfering with ability of the aphid to deposit virus in sites appropri-
ate for initiation of virus infection. The ability to obtain more frequent infection of
aphid-resistant plants by increasing the number of viruliferous aphids probing each
resistant plant occurs because the likelihood of observing a rare event (infection) is
increased by increasing the number of attempted transmissions (Romanow et al. 1986).
Kennedy (1976) reports that cultivars resistant to insect vectors of plant viruses can
alter the population size, activity, and probing and feeding behavior of the vector, thus
influencing the pattern of spread. The effect of a vector resistant cultivar on virus
spread will depend on the type of resistance (nonpreference, antibiosis, or tolerance),
the level of resistance, the relative importance of primary and secondary virus spread,
the length of the acquisition, inoculation, retention, and latent periods of the virus, and
the effect of virus infection on vector resistance in the plant. Each combination of these
factors may result in a different pattern of virus spread.


Leafhoppers: Twenty eight cultivars of bunch beans were evaluated for resistance to
the potato leafhopper, Empoascafabae Harris (Chalfant 1965). Differences were found
among cultivar damage scores and nymphal counts. Least damaged cultivars were Cor-
neli, C-14, Top Most, Green Cluster, Topcrop, Pearlgreen, and Tenderpod. Damage
scores correlated with insect counts. Insecticide treatment in combination with the
cultivars showed that a 50% damage reduction resulted regardless of the crop suscepti-
Cowpea curculio: Cuthbert & Davis (1972) described several factors contributing to
cowpea resistance to the cowpea curculio (Chalcodermus aeneus Boheman). Insect pref-
erence resulted from differences in the amount of feeding stimulants extracted from
pods, and adults showed a similar pattern of preference for seedlings of the lines.
Chalfant & Gaines (1973) found that chemical factors associated with plant resistance
to the insect and differing amours of nutrients affected insect feeding. Positive correla-
tions existed between percent concentration of total carbohydrate in the hull and feeding
punctures in the hull and pea, and between hull and seed N and feeding punctures.
Successful penetration of the pods was negatively correlated with pod wall thickness
which impeded oviposition (Cuthbert & Davis 1972, Chalfant et al. 1972).


400 Florida Entomologist 73(3) September, 1990

A collection of Plant Introductions (PI), acessions, varieties, and breeding lines of
southernpea were evaluated by Cuthbert & Chambliss (1972) for resistance to C.
aeneus. Resistance to this insect was found in 10 lines and one cultivar (Ala. 963.8, Fla.
68F-213, Fla. 68F-63, Fla. 421-07, Floricream, PI 123267, PI 180494, PI 205140, PI
250238 and PI 196301).
Cuthbert et al. (1974) reported that resistance in southern pea to C. aeneus was
dependent on various levels of nonpreference, a pod factor inhibiting penetration
through the pod wall by the adult beetle, and antibiosis. The resistance factors were
genetically controlled and capable of being transmitted to progeny (Cuthbert et al.
1974). Cuthbert & Fery (1975) released C. aeneus resistant germplasm cowpea lines
(CR 17-1-13, CR 18-13-1, CR 22-2-21). The gene action for insect resistance was mainly
additive. The number of genes differentiating the parents was one pair. The narrow-
and broad-sense heritability estimates were 45.47 and 49.02 percent, respectively (Fery
& Cuthbert 1975, 1978). Fery & Cuthbert (1979a) found that pod-wall resistance to C.
aeneus could be efficiently evaluated by means of pod:seed (weight of pods-weight of
seeds/weight of seeds) ratio measurements. In a 2 year study, by Cuthbert & Fery
(1979b), resistance found in 2 cowpea breeding lines was more effective in reducing C.
aeneus injury than insecticide treatments. No synergism between plant resistance and
insecticide treatment was found. Fery & Dukes (1984) released a cowpea cultivar,
Carolina Cream, with resistance to C. aeneus pod penetration and oviposition.
Southern green stink bug: A 4 year study was conducted by Schalk & Fery (1986) to
determine the range of available resistance in cowpea to the southern green stink bug
Nezara viridula L. A total of 24 cowpea cultivars, breeding lines, and Plant Introduc-
tions were evaluated. PI 293557 and PI 293570 produced appreciable seed yield under
conditions that reduced yields in the susceptible controls. Tolerance to N. viridula
appeared to be the mechanism of resistance in these lines.
Twenty cowpea cultivars were evaluated for resistance to 9 different insect pests
by Nilakhe & Chalfant (1982). Cultivars differed in degree of susceptibility to Aphis
sp., thrips, tarnish plant bug (Lygus lineolaris (Palisot de Beauvois)), velvetbean cater-
pillar (Anticarsia gemmatalis Hubner), southern green stink bug (N. viridula), and
cowpea cucurlio (C. aeneus). Nilakhe & Chalfant (1982) concluded that chances of finding
a cultivar resistant to several of these insects was poor.


Corn earworm: Chambliss & Wann (1971) report an antibiotic type of resistance in
sweet corn (Zea maize) inbred lines and hybrids to the corn earworm (Heliothis zea
Boddie). Resistant lines (81-1, 471U6 and M119B) were distinguished from susceptible
by significant increase in larval mortality of the resistant type. Resistant lines also
retarded larval growth, decreased depth to which larvae penetrate the ear and delayed
Chalfant (1974) evaluated 15 sweet corn cultivars for resistance to corn earworm (H.
zea) damage in the field. He found that percent ear damage was negatively correlated
with days from planting. The most susceptible cultivars tasseled before 40 days.
Wiseman et al. (1977, 1978, 1981) studied ear characteristics and mechanisms of
resistance of corn to H. zea. The authors found that tolerant lines, Dixie 18 and 471-U6
X 81-1, had long silk channels and large amounts of silk that maintained a high moisture
content over the period of larval infestation. The resistant factor in Zapalote Chico was
antibiosis or non-preference as the plant had a long tight silk channel with small amounts
of silk that decreased in moisture over the period of larval development. McMillian et
al. (1980) released 2 inbred sweet corn lines, GTS1 and GTS2, with resistance to H. zea
(Table 1). Wiseman et al. (1984) found that the resistance mechanism of GTS1 and GTS2
was tolerance and a possible low level of antibiosis.

Schalk: Symposium-Plant Resistance to Insects

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Sweetpotato weevil: In recent years small field plot tests were conducted comparing
numerous sweetpotato (Ipomoea batatas L.) breeding lines for resistance to the sweet-
potato weevil Cylasformicarius elegantulus (Summers). Significant differences among
the plant entries with respect to damage from C. formicarius elegantulus were found
(Waddil and Conover 1978, Rolston et al. 1979, Mullen et al. 1981, 1982, 1985). Similar
differences appear in multiple choice laboratory tests (Mullen et al. 1980, Barlow &
Rolston 1981). Barlow & Rolston (1981) concluded that most of the resistance exhibited
in small plot tests was nonpreference, although some cultivars escaped damage to some
degree because their roots were small or deep in the soil and relatively inaccessible to
this pest. Barlow & Rolston (1981) found no antibiosis resistance among the cultivars
in no-choice tests. However, recent findings indicate a moderate level of antibiosis in
some white fleshed cultivars (Rolston unpublished).
Mullen et al. (1985) reports that resistance to C. formicarius elegantulus was signif-
icantly higher in two cultivars under field conditions. The yields of these cultivars were
higher but insect damage was lower (Mullen et al. 1982). Jansson et al. (1987) found
that resistance was overcome in these same cultivars under very heavy population
Recent studies by Nottingham et al. (1987, 1988 a) showed that female C. for-
micarius elegantulus were attracted to extracts of sweetpotato roots identified as ses-
quiterpenes. Extracts from the root surface of a susceptible cultivar contained an
ovipositional stimulant, tentatively identified as a triterpenol acetate, while different
unidentified compounds were extracted from roots of the resistant cultivars. Wilson et
al. (1989) developed an improved bioassay to characterize an ovipositional stimulant
from the surface of sweetpotato roots. The nonpolar fractions produced significantly
higher oviposition of C. formicarious elegantulus (Wilson et al. 1989). In foliage prefer-
ence tests females differentiated between resistant and susceptible cultivars while no
differences were observed in no choice tests. Volatiles from foliage were attractive to
both sexes. Differences between leaf surface chemistry was not significant between
resistant and susceptible cultivars and probably are not importance in breeding for C.
formicarius elegantulus resistance (Nottingham 1988 b).
Other insect pests: Cuthbert & Davis (1970) found large differences among cultivars
for susceptibility to sweetpotato flea beetle the grub Plectris aliena Chapin and the
wireworm, Diabrotica, Systena complex (WDS). The level of resistance to the WDS
complex and also P. aliena, increased after 4 cycles of recurrent selection in randomly
crossed populations of plants (Cuthbert & Jones 1972). Further selection produced a
highly resistant cultivar that suffered less injury from the WDS complex than a suscep-
tible cultivar protected by an insecticide (Cuthbert & Jones 1978). Damage to roots in
the presence of moderately high populations of the grub Phyllophaga ephilida (Say)
was reduced by use of resistant cultivars, and excellent control resulted by using an
insecticide as an adjunct to resistance (Rolston et al. 1981).
Schalk & Jones (1982). developed a field technique to artificially infest sweetpotato
roots with a .125% agar-water egg suspension of D. balteata. Insect eggs were applied
to resistant and suscepltible sweetpotato roots. Larval damage was highest when roots
were infested at preroot enlargement with 1000 eggs per hill. The technique should be
useful for evaluating sweetpotato lines for resistance to D. balteata larvae.
An unidentified factor in the root periderm deterred injury by species in the WDS
complex (Cuthbert & Davis 1971). Schalk et al (1986a, b) found that, although positively
correlated with the level of resistance to the WDS complex, skin thickness was not the
only factor involved because some highly resistant and susceptible cultivars did not
differ in periderm thickness. Total soluble recoverable compounds were not correlated
with WDS resistance found in the field. However, feeding experiments with D. balteata

September, 1990

Schalk: Symposium-Plant Resistance to Insects

larvae using the same genotypes with intact or with periderm removed showed differ-
ential responses among cultivars. Resistance was highest in whole roots (periderm
intact). The cortex was intermediate in antibiosis while least antibiosis was recorded in
the stellar tissue. Antibiosis of peridermal and cortical tissues were more pronounced
earlier and later in the season than during mid-season.
In order to identify chemicals responsible for resistance against D. balteata, a bioas-
say involving second instar larvae was developed using a meridic diet. Weight gain by
second instar larvae after 7 days exposure to this diet relative to a control diet of
germinating wheat was 80%. Survival on the meridic diet was equivalent to that of
germinating wheat for larvae and adults. The diet consisted of 14 ingredients of which
beta-sitosterol and fresh wheat germ were the most critical components (Schalk &
Peterson 1990).
Breeding for insect resistance in sweetpotato is a relatively recent endeavor, yet
several breeding lines and named cultivars with multiple insect, disease and nematode
resistance have been released (Sumor, HiDry, Resisto, Regal, Southern Delite, Excel
and Beauregard) (Hamilton et al. 1985, Jones et al. 1975, 1980, 1983, 1985, 1987a, 1989,
Rolston et al. 1987). Sources of resistance to nearly all insect and disease pests of
sweetpotato in the United States have been identified, and as far as is known in no case
is resistance linked to any undesirable trait (Jones & Cuthbert 1973).
Development of commercial cultivars resistant to the complex of soil insects permits
production of quality sweetpotatoes without insecticides in some circumstances (Jones
et al. 1987b). However, in most cases resistant cultivars will be one part of an integrated
control program that will result in a product of better quality at reduced cost than has
been attainable in the past.


Insects-general: Fery et al. (1979 b) developed a method to artificially infest tomato
plants (Lycopersicon esculentum Mill) with H. zea eggs in .2% aqueous agar suspension.
There was a curvilinear relationship between number of eggs and degree of fruit dam-
age. H. zea damage increased with egg dosage but at a declining rate. Application of
eggs was most effective about 1 month before first harvest. Multiple or repeated appli-
cations were no more effective than a single application of an equivalent number of eggs
In evaluating tomatoes for resistance to H. zea under field conditions Fery &
Cuthbert (1973) showed that characteristics like vine size had a large pleiotropic effect
on insect resistance. Vine size was negatively correlated with insect damage and ac-
counted for 61.2% of the variation among accessions. When resistance in a resistant
entry was adjusted for vine size, by covariance analysis, it was no different from the
susceptible entries. Fery & Cuthbert (1974a) screened 1,030 accessions of tomato for
resistance to H. zea. No immunity was found but differences in susceptibility were
significant. Tiny Tim was, respectively, 83.1 and 57.6% less damaged than the suscep-
tible and resistant controls. Cultivar damage by H. zea was highly correlated with
planting density (Fery & Cuthbert 1974b). Increases in damage of 31.4 to 67.1% were
associated with increase in density from 1 to 16 plants per 3 m row. This relationship
will effect efficiency of selection for H. zea resistance in tomato breeding programs.
Leaves of Lycopersicon hirsutum Humb. and L. hirsutumf. glabratum C. H. Mull
were reported to contain a factor highly antibiotic to H. zea (Boddie) larvae. Ethanol
leaf extracts added to an artificial diet and fed to larvae resulted in high mortality. The
factor was inherited recessively. Since the larvae of H. zea will feed on the foliage when
they are young, this antibiotic factor will be a valuable source of resistance for commer-
cial cultivars (Fery & Cuthbert 1975a).


404 Florida Entomologist 73(3) September, 1990

Removal of glandular trichome exudate from leaflets of the wild tomato of L. hir-
sutum f. glabratum (PI 134417) with ethanol resulted in loss of resistance to larvae of
H. zea. An extract of the exudate was toxic to 1st instar larvae. The toxic component
was identified as 2-tridecanone. The toxin was only found on the leaflet surface. First
instar larvae of H. zea were killed by fumes from the leaf surface extract and 2-
tridecanone. However, many first instar larvae exposed to the fumes of the resistant
foliage became temporarily paralysed but recovered within 24h. Revived larvae were
tolerant to 2-tridecanone in subsequent exposures indicating 2-tridecanone is not the
sole defensive compound in PI134417 against this pest (Dimock & Kennedy 1983, Ken-
nedy 1984, Kennedy et al. 1987a).
A laboratory assay for evaluating tomatoes for resistance to tobacco hornworm
Manduca sexta L. was developed by Kennedy & Henderson (1978b). Results from their
test, which employed excised foliage from greenhouse grown plants and 1st instar M.
sexta larvae from a colony maintained in the laboratory on artificial diet, were similar
to those obtained with intact plants, with field collected larvae, and with fieldgrown
resistant plants. Selections of L. hirsutum f. glabratum (PI 134417, LA 407) were
highly resistant to M. sexta. Resistance was expressed as reduction in both larval
survival and weight gain by survivors over 72h period. The interplant variation in larval
weight gains within accessions was highly significant, suggesting that most of the acces-
sions tested were segregating for resistance to M. sexta.
Kennedy (1984) and Kennedy et al. (1987a) state that 2-tridecanone resistance in the
wild tomato (L. hirsutum f. glabratum) to M. sexta L. and the Colorado potato beetle
(Leptinotarsa decemlineate Say) enhances a level of tolerance to the carbamate insec-
ticide carbaryl for H. zea. This phenomenon is an important consideration when combin-
ing 2-tridecanone-mediated resistance in tomato with insecticides for the control of a
large spectrum of tomato insect pests.
Farrar & Kennedy (1987a) found that L. hirsutumf. glabratum (PI 134417) resistant
to H. zea contained factors in both trichomes and leaf lamellae which increased larval
mortality, and reduced larval weight, consumption rate, and efficiency of conversion of
ingested material (except in second instars). Susceptible foliage (L. esculentum) also
contained trichome-based factors which increased larval mortality and decreased
weight, consumption rate of second instars, and efficiency of conversion of ingested
material of 5th instars, but to a lesser extent then resistant foliage.
Farrar & Kennedy (1988) reported that 2-Undecanone, found in the tips of Type VI
glandular trichomes of L. hirsutum f. glabratum (PI 134417), when incorporated into
an artificial diet, caused pupal deformity and mortality among H. zea. 2-Undecanone
increased larval mortality of H. zea in the first 48h when combined with 2-tridecanone,
but not alone. 2-Undecanone had no effect on M. sexta larvae or pupae (Farrar &
Kennedy 1987b).
Kennedy et al. (1981) grew L. hirsutumf. glabratum (PI 134417) plants under long
and short-day regimes. First instar larvae of M. sexta reared on the foliage of the
long-day regime plants exhibited greater mortality and 2-tridecanone was significantly
more abundant in the foliage. Light intensity had no effect on 2-tridecanone production
or the expression of resistance. The density of gladular trichomes was influenced by an
interaction between day length and light intensity.
Genetic analysis by Fery & Kennedy (1987) suggest that M. sexta resistance in
tomato plants was conditioned by at least 3 recessive genes and high 2-tridecanone
concentration was found to be inherited in a similar manner. No associations were found
between type VI trichome morphology and 2-tridecanone, type VI trichome density, or
M. sexta resistance. Polynomial regression analysis showed that there was a
semilogarithmic relationship between 2-tridecanone concentration and resistance rat-
ings. Multiple linear regression analysis indicated that 2-tridecanone was principally
responsible for the high degree of resistance in PI 134417 to M. sexta.

Schalk: Symposium-Plant Resistance to Insects

Kennedy & Sorenson (1985) identified resistance in L. hirsutum f. glabratum (PI
134417) to the Colorado potato beetle. The beetle laid 3 times more eggs on this resistant
line than on the control cultivar in field tests, but extensive mortality of larvae resulted
on the resistant plants. In laboratory tests removal of glandular trichome tips from PI
134417 with ethanol resulted in reduced resistance, but did not render the plants as
susceptible to the beetle as the control.
A strain of insecticide-resistant and insecticide-susceptible Colorado potato beetle
were exposed to 2-tridecanone and foliage of the wild tomato L. hirsutumf. glabratum.
Exposure of both beetle strains to sublethal doses of 2-tridecanone did not increase
tolerance of either population to subsequent exposure to 2-tridecanone. The insecticide
resistant strain of the beetle suffered higher mortality than the other beetle strain when
fed both the resistant wild species (PI 134417) with the toxin 2-tridecanone removed
and susceptible tomato (L. esculentum) (Kennedy & Farrar 1987b).
Sorenson et al. (1989) determined that the component of resistance to L. decem-
lineata associated with the foliar glandular trichomes, in crosses between resistant and
susceptible tomatoes, segregated in a manner identical to M. sexta resistance. The
levels of resistance to both insect species were highly correlated in segregating Fi
backcross populations, indicating a common mechanism of resistance. The authors also
found that Fi plants from crosses between susceptible and resistant tomatoes lacked
the trichome-mediated component of resistance to L. decemlineata but substantial levels
of lamella-resistance components were found. The authors suggest that the lamella-
based and trichome-mediated resistance components are under separate genetic control.
Schuster (1977a) studied the effect of tomato cultivars on insect damage and chemical
control. Pennorange E 106A and Pearson tomatoes had less fruit damage by tomato
pinworm (Keiferia lycopersicella Wal.), and armyworms (Spodoptera eridania Cramer)
when compared with the cultivar Walter. When measured by the number of damaged
fruit, the degree of control of the tomato pinworm and southern armyworm with Dipel
WP (Bacillus thuringiensis) and chlordimeform was affected by tomato cultivar. When
insect populations were low, many cultivars sustained less damage, but when popula-
tions were high very few cultivars were free of damage. The number of leafminer L.
sativae per 10 trifoliates was less on UF-763292, Earliana, Pennorange E160A, Pearson
and Pritchard tomato cultivars. Pennorange E160A and Pearson have potential value
in breeding programs because of their resistance to tomato pinworm, armyworm and
In the greenhouse, seedlings of 235 PI's of Lycopersicon sp. were evaluated for K.
lycopersicella resistance. The highest level of resistance was found in L. hirsutum and
L. hirsutum f. glabratum with 25-50% less damage and 50-75% fewer larvae than the
cultivar Walter. In secondary screening, accessions of L. cheesmanif. minor, L. glan-
dulosum, L. hirsutum and L. hirsutumf. glabratum had less damage and fewer larvae
per plant than Walter. In a laboratory study using excised leaflets, larval survival and
weight were less on PI 126445 and PI 127826 (L. hirsutum) and PI 126447 (L. hirsutum
f. glabratum) than on Walter (Schuster 1977 b). Field trials were conducted to evaluate
tomato accessions, breeding lines and cultivars to K. lycopersicella and L. sativae. PI
126445 and PI 127826 (L. hirsutum) and PI 126449 (L. hirsuatumf. glabratum) demon-
strated the highest level of resistance to both insects as measured by number of leaf
mines and damage (L. sativae), and number of larvae of K. lycopersicella (Schuster et
al. 1979).


Turnip aphid: Barns & Cuthbert (1975) identified turnips resistant to the turnip aphid,
Hyadaphis erysimi (Kaltenbach). Robbins & Cuthbert 1980 released two cultivars
Charlestowne and Roots which were resistant to the turnip aphid (Table 1). The


Florida Entomologist 73(3)

September, 1990

mechanism of resistance appears to be antibiosis (Kennedy & Abou-Ghadir 1979). How-
ever, the resistant cultivars were susceptible to the green peach aphid (Myzus persicae
(Sulzer)) and cabbage aphid (Brevicoryne brassicae (L.)).


I have described the research on the development of vegetables with insect resist-
ance for the southeastern United States. The research deals with screening methodol-
ogy, germplasm identification, mechanism of resistance and cultivar and germplasm
However, the use and development of insect resistant vegetable crops as an alterna-
tive control has been limited because: 1) zero tolerance for insect damage or presence
by the industry and consumer encourages the use of insecticides; 2) reasonable cost of
insecticides, relative to other operating expenses and the high cash value of the crop,
makes them economical to apply; and 3) most vegetables have multiple insect problems
which makes the development of multiple pest resistant cultivars difficult.
Tremendous pressure on the vegetable industry in the near future is expected due
to EPA mandatory reregistration of all insecticides, and the withdrawal of insecticides
for environmental and human health reasons. This will create an economic crisis in the
chemical industry resulting in product withdrawal, reduced spending for research and
development for broad spectrum pesticides, and reduced availability of effective chem-
icals. Therefore, the registration of new insecticides for use on minor crops like veget-
ables will become critical. The most likely alternatives to fill the insecticide voids will
be the development of insect resistant cultivars, biological control, narrow spectrum
and safer insecticides, more effective use of broad spectrum insecticides, and sex
pheromones incorporated into an IPM program.


BARLOW, T., AND L. H. ROLSTON. 1981. Types of host plant resistance to the sweet-
potato weevil found in sweetpotato roots. J. Kansas Entomol. Soc. 54: 649-57.
BARNES, C. W., AND F. P. CUTHBERT, JR. 1975. Breeding turnips for resistance to
the turnip aphid. HortScience. 10: 59-60.
BROCHERS, E. A., AND R. T. TAYLOR. 1977. Breeding vine border resistant squash.
The Vegetable Growers News. 32(3).
CHALFANT, R. B. 1965. Resistance of bunch bean varieties to the potato leafhopper
and relationship between resistance and chemical control. J. Eco. Entomol. 58:
CHALFANT, R. B., AND C. H. BRETT. 1967. Interrelationship of cabbage varieties
and insecticide on control of the cabbage lopper and the imported cabbage worm.
J. Econ. Entomol. 60: 687-90.
CHALFANT, R. B., AND T. D. CANERDAY. 1972a. Feeding and oviposition of the
cowpea curculio and laboratory screening of southernpea varieties for insect re-
sistance. J. Georgia Entomol. Soc. 7: 272-77.
CHALFANT, R. B., E. F. SUBER, AND T. D. CANERDAY. 1972b. Resistance of south-
ern peas to the cowpea curculio in the field. J. Eco. Entomol. 65: 1680-82.
CHALFANT, R. B., AND T. P. GAINES. 1973. Cowpea curculio: correlations between
chemical composition of the southern pea and varietal resistance. J. Eco. En-
tomol. 66: 1012-13.
CHALFANT, R. B. 1974. Response of sweet corn varieties to the corn earworm. Geor-
gia Agric. Exp. Sta. Res. Bull. 161. 7p.
CHAMBLISS, O. L., AND F. P. CUTHBERT, JR. 1968. Vegetable Improvement News-
letter No. 10, Feb. 29 Cornell University Ithaca, NY.
CHAMBLISS, O. L., AND E. V. WANN. 1971. Antibiosis in earworm resistant sweet
corn. J. Amer. Soc. Hort. Sci. 96: 273-77.


Schalk: Symposium-Plant Resistance to Insects 407

CREIGHTON C. S., T. L. MCFADDEN, AND M. L. ROBBINS. 1975. Complementary
influence of host plant resistance on microbial-chemistry control of cabbage cater-
pillars. HortScience 10: 487-88.
CUTHBERT, F. P. JR., AND B. W. DAVIS. 1979. Resistance in sweetpotatoes to
damage by soil insects. J. Econ. Entomol. 63: 360-63.
CUTHBERT, F. P. JR., AND B. W. DAVIS. 1971. Factors associated with insect resist-
ance in sweetpotato. J. Econ. Entomol. 64: 713-17.
CUTHBERT, F. P. JR., AND O. L. CHAMBLISS. 1972. Sources of resistance to cowpea
curculio in Vigna sinensis and related species. J. Econ. Entomol. 65: 542-45
CUTHBERT, F. P. JR., AND A. JONES. 1972. Resistance in sweetpotato to coleoptera
increased by recurrent selection. J. Econ. Entomol. 65: 1655-58.
CUTHBERT, F. P. JR., R. L. FERY, AND 0. L. CHAMBLISS. 1974. Breeding for
resistance to the cowpea curculio in southern peas. HortScience, 9: 69-70.
CUTHBERT, F. P. JR., AND R. L. FERY. 1975. CR 17-1-13, CR 18-13-1, CR 22-2-21.
Cowpea curculio resistant southernpea germplasm. HortScience, 10: 628.
CUTHBERT, F. P. JR., AND A. JONES. 1978. Insect resistance as an adjunct or alter-
native to insecticides for the control of sweetpotato soil insects. J. Amer. Soc.
Hort. Sci. 103: 443-45.
CUTHBERT, F. P. JR., AND R. L. FERY. 1979a. Measurement of pad-wall resistance
to the cowpea curculia in the southernpea (Vigna unguiculata (L). Walp.).
HortScience 14: 29-30.
CUTHBERT, F. P. JR., AND R. L. FERY. 1979b. Value of plant resistance for reducing
cowpea curculio damage to the southernpea (Vigna unguiculata (L.) Walp.). J.
Amer. Soc. Hort. Sci. 104: 199-201.
DIMOCK, M. B., AND G. G. KENNEDY. 1983. The role of glandular trichomes in the
resistance of Lycopersicon hirsutum F. glabratum to Heliothis zea. Ent. Exp.
Appl. 33: 263-68.
root knot resistant sweetpotato germplasm. HortScience 13: 201-2.
DUKES, P. D., M. G. HAMILTON, A. JONES, AND J. M. SCHALK. 1987. 'Sumor' A
multi-use sweetpotato. HortScience 22: 170-71.
DUKES, P. D., A. JONES, AND J. M. SCHALK. 1989. Notice of release to plant breed-
ers of DW-8, a semi-dwarf sweetpotato parental clone. USDA-ARS Washington,
ELSEY, K. D. 1981. Pickleworm: survival, development, and oviposition on selected
hosts. Ann. Entomol. Soc. Am. 74: 96-99.
ELSEY, K. D., AND E. V. WANN. 1982. Differences in infestation of pubescent and
glabrous forms of cucumber by pickleworms and melonworms. HortScience 17:
ELSEY, K. D., J. PENA, J. PETERSON, T. WEHNER. 1984. Recent advances in
research on control and biology of pickleworm and melonworm. W. Kuausen-
berger, R. Webb, and L. Yutema [eds.]. Proceedings of the 20th annual meeting,
Caribbean Food Crops Society. Oct. 21-26. 330p.
ELSEY, K. D. 1985. Resistance mechanisms in Cucurbita moschata to pickelworm
and melonworm (Lepidoptera:Pyralidae). J. Econ. Entomol. 78: 1048-51.
FARRAR, R. R. JR., AND G. G. KENNEDY. 1987a. Growth, food consumption and
mortality of Heloithis zea larvae on foliage of wild tomato Lycopersicon hirsutum
f. glabratum and the cultivated tomato, L. esculentum. Entomol. Exp. Appl. 44:
FARRAR, R. R. JR. AND G. G. KENNEDY. 1987b. 2-Undecanone, a constituent of the
glandular trichomes of Lycopersicon hirsutum f. glabratum: Effects on Heliothis
zea and Manduca sexta growth and survival. Entomol. Exp. Appl. 43: 17-23.
FARRAR, R. R. JR, AND G. G. KENNEDY. 1988. 2-Undecanone, a pupal mortality
factor in Heloithis zea: sensitive larval stage and in plant activity in Lycopersicon
hirsutum f. glabratum. Entomol. Exp. Appl. 47: 205-10.
FERY, R. L., AND F. P. CUTHBERT, JR. 1973. Factors affecting evaluation of fruit-
worm resistance in the tomato. J. Amer. Soc. Hort. Sci. 98: 457-59.
FERY, R. L., AND F. P. CUTHBERT, JR. 1974a. Resistance of tomato cultivars to the
fruitworm, Heloithis zea (Boddie). HortScience 9: 469-70.

408 Florida Entomologist 73(3) September, 1990

FERY, R. L., AND F. P. CUTHBERT, JR. 1974b. Effect of plant density on fruitworm
damage in the tomato. HortScience, 9: 140-41.
FERY, R. L. AND F. P. CUTHBERT, JR. 1975a. Antibiosis in Lycopersicon to the
tomato Fruitworm (Heliothis zea). J. Amer. Soc. Hort. Sci. 100: 276-78.
FERY, R. L., AND F. P. CUTHBERT, JR. 1975b. Inheritance of pod resistance to
cowpea curculio infestation in southern peas. Heredity 66: 43-44.
FERY, R. L., AND F. P. CUTHBERT, JR. 1978. Inheritance and selection ofnonprefer-
ence resistance to the cowpea cuculio in the southernpea (Vigna unguiculata (L.)
Walp.). J. Amer. Soc. Horti. Sci. 103: 370-72.
FERY, R. L., F. P. CUTHBERT, AND W. D. PERKINS. 1979. Artificial infestation of
the tomato with eggs of the tomato fruitworm. J. Econ. Entomol. 72: 392-94.
FERY, R. L., AND F. P. CUTHBERT, JR. 1979. Measurement of pod-wall resistance
to the cowpea curculio in the southern pea (Vigna unguiculata (L.) Walp.).
HortScience 14: 29-30.
FERY, R. L., AND P. D. DUKES. 1984. 'Carolina Cream' Southernpea. HortScience,
19: 456-57.
FERY, R. L., AND G. G. KENNEDY. 1987. Genetic analysis of 2-tridecanone concen-
tration, leaf trichome characteristics, and tobacco hornworm resistance in to-
mato. J. Amer. Soc. Hort. Sci. 112: 886-91.
sweetpotato. HortScience 20: 954-55.
JANSSON, R. K., H. H. BRYAN, AND K. A. SORENSON. 1987. Within-vine distribu-
tion and damage of sweetpotato weevil, Cylasformicarius elegantulus (Coleopt-
era: Curculionidae) on four cultivars of sweetpotato in southern Florida. Florida
Entomol. 70: 523-26.
JONES, A., AND F. P. CUTHBERT, JR. 1973. Associated effects of mass selection for
soil-insect resistance in sweetpotato. J. Amer. Soc. Hort. Sci. 98: 480-82.
JONES, A., P. D. DUKES, AND F. P. CUTHBERT, JR. 1975. W-13 and W-178 Sweet-
potato germplasm. HortScience 10: 533.
PATERSON, AND T. E. BOSWELL. 1980. W-71, W-115, W-119, W-125, W-149
and W-154 sweetpotato germplasm with multiple insect and disease resistance.
HortScience. 15: 835-36.
sweetpotato. HortScience 18: 2512-52.
sweetpotato. HortScience 20: 781-82.
1987a. 'Southern delite' sweetpotato. HortScience 22: 329-30.
JONES, A., J. M. SCHALK, AND P. D. DUKES. 1987b. Control of soil insect injury by
resistance in sweetpotato. J. Amer. Soc. Hort. Sci. 112: 195-97.
JONES, A., P. D. DUKES, J, M, SCHALK, AND M. G. HAMILTON. 1989. 'Excel'
sweetpotato. HortScience 24: 171-72.
KENNEDY, G. G. 1976. Host plant resistance and the spread of plant viruses. Environ.
Ent. 5: 827-32.
KENNEDY, G. G., AND A. N. KISHABA. 1977. Response of alate melon aphids to
resistant and susceptible muskmelon lines. J. Econ. Entomol. 70: 407-10.
KENNEDY G. G., W. BOHN, A. K. STONER, AND RALPH E. WEBB. 1978a. Leafminer
resistance in muskmelon. J. Amer. Soc. Hort. Sci. 103: 571-74.
KENNEDY, G. G., AND W. R. HENDERSON. 1978b. A Laboratory assay for resistance
to the tobacco hornworm in Lycopersicon and Solanum spp. J. Amer. Soc. Hort.
Sci. 103: 334-36.
KENNEDY, G. G., D. L. MCLEAN, AND M. G. KINSEY. 1978c. Probing behavior of
Aphis gossypii on resistant and susceptible muskmelon. J. Econ. Entomol. 71:
KENNEDY, G. G., AND M. F. ABOU-GHADIR. 1979. Bionomics of the turnip aphid on
two turnip cultivars. J. Econ. Entomol. 72: 754-57.

Schalk: Symposium-Plant Resistance to Insects

NER. 1981. Effect of day length and light intensity on 2-tridecanone levels and
resistance in Lycopersicon hirsutum f. glabratum to Manduca sexta. J. Chemical
Ecol. 7: 707-15.
KENNEDY, G. G. 1984. 2-tridecanone, tomatoes and Heliothis zea: potential incompati-
bility of plant antibiosis with insecticidal control. Entomol. Exp. Appl. 35: 305-
KENNEDY, G. G., AND C. F. SORENSON. 1985. Role of glandular trichomes in the
resistance of Lycopersicon hirsutum f. glabratum to Colorado potato beetle (Col-
eoptera: Chrysomelidae). J. Econ. Entomol. 78: 547-51.
KENNEDY, G. G., R. R. FARRAR, AND M. R. RISKALLAH. 1987a. Induced tolerance
of neonate Heliothis zea to host plant allelochemicals and carbaryl following incu-
bation of eggs on foliage of Lycopersicon hirsutum f. glabratum. Springer-Ver-
lag. 73: 615-20.
KENNEDY, G. G., AND R. R. FARRAR, JR. 1987b. Response of insecticide-resistant
and susceptible Colorado potato beetles, Leptinotarsa decemlineata to 2-
tridecanone and resistant tomato foliage: the absence of cross resistance. En-
tomol. Exp. Appl. 45: 187-92.
LOWER, R. L., A. R. QUISUMBING, AND F. P. CUTHBERT, JR. 1974. Screening of
cucumber for resistance to cucumber beetle. HortScience 9: 36.
Registration of GTS1 and GTS2 parental lines of maize. Crop. Sci. 20: 420.
E. BOSWELL, AND D. R. EARHART. 1980. Field selection of sweetpotato lines
and cultivars for resistance to the sweetpotato weevil. J. Econ. Entomol. 73:
ance in sweetpotato lines to infestations of sweetpotato weevil, Cylas for-
micarius elegantulus (Summers). HortScience 16: 539-40.
MULLEN, M. A., A. JONES, R. T. ARBOGAST, AND T. E. BOSWELL. 1982. Resistance
of sweetpotato lines to sweetpotato weevil. HortScience. 17: 931-32.
ance in sweetpotatoes to the sweetpotato weevil, Cylasformicarius elegantulus
(Summers). J. Entomol. Sci. 20: 345-50.
NILAKHE, S. S., AND R. B. CHALFANT. 1982. Cowpea cultivars screened for resist-
ance to insects pests. J. Econ. Entomol. 75: 223-27.
NUGENT, P. E. 1984a. Release of enhanced muskmelon germplasm C922-B1, C922-B2,
and C922-B3. USDA, ARS Washington, DC.
NUGENT, P. E., F. P. CUTHBERT, JR. AND J. C. HOFFMAN. 1984b. Two genes for
cucumber beetle resistance in muskmelon. J. Amer. Soc. Hort. Sci. 109: 756-59.
Feeding and oviposition preference of the sweetpotato weevil, Cylasformicarius
elegantulus, on the outer periderm and exposed inner core of storage roots of
sweetpotato cultivars. Entomol. Exp. Appl. 45: 271-75.
1988a. Feeding and oviposition preference of sweetpotato weevil, Cylas for-
micarius elegantulus (Summers), on storage roots of sweetpotato cultivars with
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KAYS. 1988b. Attraction of adult sweetpotato weevil, Cylas formicarious
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POPE, D. T., L. W. NIELSON, AND N. C. MILLER. 1971. 'Jewel' a new sweetpotato
variety for North Carolina. N. C. Agric. Exp. Stn. Bull. 442.
ROBBINS, L. M., AND F. P. CUTHBERT, JR. 1980. 'Charlestowne' and 'Roots' Tur-
nips. HortScience 15: 534.
1979. Field evaluation of breeding lines and cultivars of sweetpotato resistance
to the sweetpotato weevil. HortScience 14: 634-35.

Florida Entomologist 73(3)

of host plant resistance in sweetpotato for control of a white grub, Phyllophaga
ephilida say (Coleoptera: Scarabaeidae). J. Kansas Entomol. Soc. 54: 378-80.
W. WILSON, AND M. L. ROBBINS. 1987. 'Beauregard' sweetpotato. HortSci-
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ROMANOW, L. R., J. W. MOYER, AND G. G. KENNEDY. 1986. Alteration of efficien-
cies of acquisition and inoculation of watermelon mosaic virus 2 by plant resist-
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SCHALK, J. M., AND A. JONES. 1982. Methods to evaluate sweetpotatoes for resist-
ance to the banded cucumber beetle in the field. J. Econ. Entomol. 75: 76-79.
SCHALK, J. M., AND R. L. FERY. 1986. Resistance in cowpea to the Southern green
stink bug. Hort Science, 21: 1189-90.
JR. 1986a. The anatomy of sweetpotato periderm and its relationship to
wireworm, Diabrotica, Systena resistance. J Agric. Entomol. 3: 350-56.
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ance in recently developed sweetpotato cultivars and germplasm to the banded
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SCHALK, J. M., AND J. K. PETERSON. 1990. A meridic diet for banded cucumber
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SCHUSTER, D. J. 1977a. Effect of tomato cultivars on insect damage and chemical
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SCHUSTER, D. J. 1977b. Resistance in tomato accessions to the tomato pinworm. J.
Econ. Entomol. 70: 434-36.
comparisons of Lycopersicon accessions for resistance to the tomato pinworm
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SORENSON, C. E., R. L. FERY, AND G. G. KENNEDY. 1989. Relationship between
Colorado potato beetle (Coleoptera: Chrysomelidae) and tobacco hornworm
(Lepidoptera: Sphingidae) resistance in Lycopersicon hirsutum f. glabratum. J.
Econ. Entomol. 82: 1743-48.
WADDILL, V. H., AND R. A. CONOVER. 1978. Resistance of white-fleshed sweet-
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WEHNER, T. C., KENT D. ELSEY, G. G. KENNEDY. 1985. Screening for cucumber
antibiosis to pickelworm. HortScience. 20: 1117-19.
Characterization of an oviposition stimulant from the surface of sweetpotato
Ipomoea batatas storage roots for the sweetpotato weevil, Cylas formicarious
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WISEMAN, B. R., N. W. WIDSTROM, AND W. W. MCMILLAN. 1977. Ear characteris-
tics and mechanisms of resistance among selected corns to corn earworm. Florida
Entomol. 60: 97-103.
WISEMAN, B. R., N. W. WIDSTROM, AND W. W. MCMILLAN. 1978. Movement of
earworm larvae on ears of resistant and susceptible corns. Environ. Entomol. 7:
WISEMAN, B. R., N. W. WIDSTROM, AND W. W. MCMILLAN. 1981. Influence of corn
silks on corn earworm feeding response. Florida Entomol. 64: 395-99.
WISEMAN, B. R., N. W. WIDSTROM, AND W. W. MCMILLAN. 1984. Insect resistance
in two recently released sweet corn inbreds, GTS1 and GTS2. J. Entomol. Sci.
20: 16-19.

September, 1990


Quisenberry: Symposium-Plant Resistance to Insects


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


A review of research in the southeastern United States related to the evaluation of
forage and turf grass germplasm for resistance to insect and mite pests is presented.
Resistance to insect and mite pests has been found in genotypes of bermudagrass (Cyno-
don spp.), centipedegrass (Eremochloa ophiuroides [Munro] Hack.), St. Augustinegrass
(Stenotaphrum secundatum [Walt.] Kuntze), and zoysiagrass (Zoysia spp.). Factors
(i.e., fertilization, cultural condition, insect strain, dietary conditioning, assay methods)
that influence the screening of germplasm for resistance to insects are discussed.


Se present una revision de investigaciones en el sudeste de los Estados Unidos
relacionada a la evaluaci6n de resistencia a insects y a acaros en germoplasmas de
forrajes y de cespedes. Se ha encontrado resistencia a plagas de insects y acaros en
genotipos de hierbas de Cynodon esp., Eremochloa ophiuroides (Munro) Hack,
Stenotaphrum secundatum (Walt.) Kuntze, y Zoysia esp. Se discuten factors (tales
como fertilizaci6n, condiciones culturales, razas de insects, acondicionamiento dietdtico,
metodos de ensayo) que influyen la evaluaci6n de germoplasma resistente.

Forage yield and quality, and turfgrass adaptability and aesthetic traits have been
emphasized in the development of grass cultivars. The development of insect and mite
resistant cultivars was neglected until recent years. The need for insect resistant
turfgrass cultivars arose because of problems associated with pesticide use (i.e., resist-
ance and phytoxicity to pesticides, pest resurgence, outbreaks of secondary pests, and
potential for environmental contamination) (Reinert 1982, Tashiro 1982, 1987).
Reinert (1982) provided an excellent review of resistance in turfgrasses to insects
and mites. In this paper, a review of research in the southeastern United States relevant
to the evaluation of bahiaqrass (Paspalum notatum Flugge), bermudarass (Cynodon
spp.; i.e., C. dactylon [L.] Pers., C. magenissii [Hurcombe], and C. transvaalensis
Burtt-Davey), centipedegrass (Eremochloa ophiuroides [Munro] Hack.), rhodesgrass
(Chloris gayana Kunth), St. Augustinegrass (Stenotaphrum secundatum [Walt.]
Kuntze), and zoysiagrass (Zoysia spp.; i.e., Z. japonica Steud., Z. tenuifolia Willd. ex
Trin., and Z. matrella [L.] Merr.) germplasm for resistance to insect and mite pests
was presented (Table 1). Factors that influence germplasm screening for insect resist-
ance were discussed.


Mole Crickets- Reinert & Busey (1985) evaluated southern turfgrass species for
susceptibility to the southern mole cricket, Scapteriscus acletus Rehn and Hebard, and

Florida Entomologist 73(3)

September, 1990





















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September, 1990

Quisenberry: Symposium-Plant Resistance to Insects

tawny, S. vicinus Scudder, mole cricket. Bahiagrass was identified as a major host of
both insect species. Hudson (1986) reported damage by S. acletus was less severe to
'Pensacola', and 'Argentine' bahiagrass than for S. vicinus.


Bermudarass Mite- Johnson (1975) evaluated bermudagrass cultivars for resistance
to the bermudarass mite, Eriophyes cynodoniensis Sayed. Cultivars 'Tifgreen' and
'Tifway' were resistant. Reinert et al. (1978) screened accessions of bermudagrass and
Tifway for susceptibility to the mite. FB-119 was highly resistant to the mite, while
Tifway and FB-141 were moderate in resistance with only 44 and 50% of the plants
infested, respectively. FB-119 showed no mite infestations during the 8 month experi-
ment or in 6 years of field observations (Reinert 1982). Tashiro (1987) reported research
results that identified high mite resistance in the cultivars 'Midiron', 'Tifdwarf, 'Tifg-
reen' (328), and Tifway (419).
Fall Armyworm- Resistance of bermudagrass to the fall armyworm, Spodoptera
frugiperda (J. E. Smith), was first reported by Leuck et al. (1968). Of the genotypes
screened, 429 were susceptible, nine intermediate in resistance, and two Tifton 292
(PI-290884) and Tifton 296 (PI-290891) were resistant to fall armyworm. Lynch et al.
(1983) and Chang et al. (1985b) confirmed a high level of antibiosis and nonpreference
(Chang et al. 1985c) in Tifton 292 to fall armyworm; however, Jamjanya & Quisenberry
(1988) found Tifton 292 to be only intermediate in resistance to fall armyworm. Leuck
& Skinner (1970) showed antibiosis in Tifton 239 (PI-289931).
Combs & Valerio (1980) studied the development of fall armyworm on bermudagrass
cultivars ('Common', 'Callie', 'Coastal', and 'Alicia') at constant temperatures and found
Alicia to be the least suitable host. Quisenberry & Wilson (1985) evaluated seven bermu-
dagrass genotypes and found Alicia and OSU 71 X 6-7 were resistant to fall armyworm
and the least preferred. Of the genotypes evaluated by Jamjanya & Quisenberry (1988),
only OSU 71 X 6-7 was resistant, five were intermediate in resistance (#1 R12P5,
Coastal, Tifton 292, OSU 74 X 11-2, and Tifton 44), and three were susceptible (Tifton
78, OSU 74 X 12-1, and 'Grazer') to fall armyworm. Lynch et al. (1983) also showed
Tifton 44 was intermediate in resistance to fall armyworm. Quisenberry et al. (1988)
concluded that the resistance observed in bermudagrass to fall armyworm was antibiosis
rather than tolerance or nonpreference. Leaf extracts of Grazer, Coastal, Tifton 292,
and OSU 71 X 6-7 were incorporated into artificial diet. High fall armyworm mortality
occurred on diets supplemented with nonpolar leaf extracts (petroleum ether and
dichloromethane); however, less mortality occurred when fall armyworm were fed leaf
extracts of Grazer, a susceptible cultivar. Grazer had half as much extractable material
in the combined nonpolar extracts than the other bermudagrass.
Cell culture was evaluated as a screening technique by Croughan & Quisenberry
(1989a) to screen bermudagrass for resistance to fall armyworm. Fall armyworm were
fed callus tissue from Grazer, Coastal, Tifton 292, and OSU 71 X 6-7 but resistance
ratings from the callus screening were not comparable to excised leaf evaluations
(Quisenberry & Wilson 1985, Jamjanya & Quisenberry 1988).
Croughan & Quisenberry (1989b) used tissue culture methods to develop plants
regenerated from bermudagrass cultivars ('Brazos' and Grazer) and accession (OSU
LCB W26). Regenerated plant lines were evaluated for resistance to fall armyworm.
Of the regenerated lines evaluated, Brazos-R3 and OSU LCB W26-R2 showed increased
resistance to fall armyworm.
Mole Crickets- The susceptibility of bermudagrass, bahiagrass, St. Augustinegrass,
centipedegrass, and zoysiagrass to the southern and tawny mole crickets was reported
by Reinert & Busey (1984). Bermudagrass was identified as a major host of both insect


Florida Entomologist 73(3)

species. Of the bermudagrass genotypes evaluated, several (i.e., PI-290659, FL-2400,
and PI-291586) showed less reduction in root and shoot growth indicating some level of
mole cricket resistance. Busey (1986) reported good field performance from the same
three genotypes under heavy mole cricket infestation.
Rhodesgrass Mealybug- Schuster (1967) evaluated 56 species of native and intro-
duced grasses for susceptibility to the rhodesgrass mealybug, Antonina graminis (Mas-
kell). Rhodesgrass mealybug significantly damaged 38 grass species, including bermuda-
grass, C. dactylon (L.) Pers.
Tropical Sod Webworm- Bermudarass, C. dactylon and C. x magenissii, selections
and cultivars were compared for resistance to the tropical sod webworm, Herpetog-
ramma phaeopteralis Guenee (Reinert & Busey 1983). PI-289922 had significantly less
damage and lower larval counts than other bermudagrasses evaluated. Webworm toler-
ance was indicated in Common and FB-119.
Twolined Spittlebug- Genotypes of four Cynodon species were screened for resist-
ance to the twolined spittlebug, Prosapia bicinta (Say), by Taliaferro et al. (1969).
Among the genotypes evaluated, 190 were susceptible, 189 intermediate in tolerance,
and 19 were highly tolerant to spittlebug. Further investigations by Stimmann &
Taliaferro (1969) showed that PI-289931 (C. transvaalensis) exhibited tolerance to the
twolined spittlebug, while PI-224128 (C. dactylon) was the least damaged after a feeding
period of 72 h.


Fall Armyworm- Wiseman et al. (1982) compared Common centipedegrass, Coastal
bermudagrass, and carpetgrass, Axonopus affinis Chase, for susceptibility to the fall
armyworm. Common centipedegrass was highly resistant to the fall armyworm and
caused high larval mortality. Nonpreference for centipedegrass was also observed.
Chang et al. (1985b, 1985c) evaluated fall armyworm orientation, preference, and anti-
biosis for bermudagrass, centipedegrass, and zoysiagrass. Centipedegrass was not
found to express the same level of resistance to fall armyworm as reported in the
previous study.


Rhodesgrass Mealybug- According to Reinert (1982) and Tashiro (1987), the rhodes-
grass mealybug is a serious pest of St. Augustinegrass.
Tropical Sod Webworm- Reinert (1982) reported unpublished data which evaluated
St. Augustinegrass accessions and cultivars for susceptibility to the tropical sod web-
worm. 'Roselawn' St. Augustinegrass was less preferred than the other genotypes
Southern Chinch Bug- Reinert (1982) provided an in-depth review of host resistance
in St. Augustinegrass to the southern chinch bug, Blissus insularis Barber. Resistance
to the chinch bug was identified in FA-223 (Kerr 1962); Zaleski-1 (Stringfellow 1969);
FA-108 (= 'Floralawn') and FA-110 (= 'Floratam') (Reinert 1972); Floralawn,
Floratam, and FA-118 (Reinert & Dudeck 1974); and FA-46, FA-73, FA-87, Floratam,
FA-121, and FA-131 (Reinert 1978). Of these genotypes, Floratam (FA-110) was re-
leased by the University of Florida and Texas A&M University as a southern chinch
bug resistant cultivar (Horn et al. 1973). Carter & Duble (1976) confirmed Floratam as
resistant to the southern chinch bug in Texas. Reinert et al. (1986) evaluated genotypes
of S. secundatum and S. dimidiatum (L.) Brongn. St. Augustinegrass from the Repub-
lic of South Africa, Tanzania, Zimbabwe, and Malagasy Republic, and reported several
genotypes with high levels of resistance to chinch bug. Genotypes resistant to chinch


September, 1990

Quisenberry: Symposium-Plant Resistance to Insects 417

bug were polyploid, but not all of the polyploid genotypes were resistant. Floratam,
Floralawn, St. Augustinegrass mutants, and TX-33 were the only New World polyploid
genotypes reported resistant to chinch bug.
Evaluations were subsequently made on the same St. Augustinegrass genotypes for
resistance to the St. Augustine decline strain of Panicum mosaic virus (Bruton et al.
1979). They reported Floratam, Floralawn, FA-46, FA-64, FA-118, FA-121, and FA-
243 were resistance to the virus, while Reinert et al. (1980) reported FA-2002, TX-33,
Floralawn, Floratam, 'Raleigh', and 'Seville' resistant to the virus. Floratam, Floralawn
and TX-33 also expressed resistance to the chinch bug. Of the genotypes of St. Augus-
tinegrass evaluated by Crocker et al. (1982) for resistance to the chinch bug and St.
Augustine decline virus, TX 100, TX 102, PI-410357 (from Africa), and Floratam were
resistant to the chinch bug and virus, while TX 101, TX 102, TX 105, and TX 106 and
PI-410356, PI-410360, and PI-410364 (from Africa) were resistant only to the virus.
Bruton et al. (1983) screened southern chinch bug resistant St. Augustinegrass
genotypes for resistance to the virus. Symptomless carriers of the virus were FA-38,
FA-82, FA-217, and FA-236. Floralawn, FA-46, FA-64, FA-118, FA-121, and FA-243
showed combined resistance to chinch bugs and virus. Floralawn and FA-118 had dis-
ease and insect resistance equal to that of Floratam.
Reinert et al. (1981) evaluated mutants of Floratam for resistance to the chinch bug
and the decline virus. All mutants retained resistance to the virus and all but one
mutant showed higher antibiosis to the chinch bug.


Rhodesgrass Mealybug- Shuster & Dean (1973) evaluated rhodesgrass genotypes for
susceptibility to the rhodesgrass mealybug. 'Bell' (Syn3), G-77, and 'Australian Common'
showed tolerance to the mealybug. Bell and G-77 had equal levels of tolerance and,
subsequently, Bell rhodegrass was released as a rhodesgrass mealybug resistant cul-


Banks Grass Mite- Zoysiagrass genotypes and cultivars were evaluated by Busey
et al. (1982) for susceptibility to the Banks grass mite, Oligonychus pratensis (Banks).
A highly resistant genotype, Z. tenuifolia, to the mite was identified.
Fall Armyworm- Bermudagrass, centipedegrass, and zoysiagrass were compared
for orientation and preference (Chang et al. 1985c) and expression of antibiosis (Chang
et al. 1985b) to fall armyworm. Zoysiagrass showed high levels of nonpreference and
antibiosis to the fall armyworm.


Soil Fertility- A significant interrelationship exists between soil fertility and plant
resistance to insects (Tingey & Singh 1980). Heavily fertilized Coastal bermudagrass
pastures were reported by Martin et al. (1980) to be more susceptible to fall armyworm.
Lynch (1984) showed that high nitrogen fertilization levels on Coastal were more suita-
ble for fall armyworm growth and development, and thus speculated that highly fer-
tilized pastures would support higher populations of fall armyworm than pastures that
were poorly managed. Chang et al. (1985a) found nitrogen fertilization influenced the
expression of resistance to Common centipedegrass and Coastal bermudagrass. At low
levels of nitrogen fertilization, Coastal, normally preferred by fall armyworm, became

Florida Entomologist 73(3)

Cultural Condition- The influence of growing bermudagrass in different cultural
(greenhouse and field) conditions on evaluation of germplasm for resistance to fall ar-
myworm was reported by Jamjanya et al. (1990). Tifton 292 was intermediate in resist-
ance when grown under greenhouse conditions but did not differ from a susceptible
cultivar (Grazer) when grown in the field.
Host Strain- The host strain of the insect used in the screening of germplasm for
resistance can influence the evaluation process. Pashley (1986, 1988b) reported two
genetically differentiated host-associated fall armyworm strains. One strain feeds on
corn, Zea mays (L.), and the other on rice, Oryza sativa (L.), forages (i.e., bermuda-
grass), and native grasses. Physioloical (Pashley et al. 1987a, 1988a) and behavoral
(Whitford et al. 1988) differences found between the corn and rice strains influence the
selection of bermudagrass resistant to the fall armyworm (Lynch et al. 1983, Pashley
et al. 1987b, Quisenberry & Whitford 1988).
Artifical Diets- Quisenberry & Whitford (1988) reported differences in response of
the corn and rice fall armyworm strains to different artificial diets. Consequently, the
acceptance of Coastal and Tifton 292 bermudagrass were influenced by dietary condi-
tioning. When the rice strain was conditioned on one diet, Tifton 292 was preferred over
Coastal; however, in contrast, when conditioned on another diet, Coastal was preferred
over Tifton 292.
Free-Choice and No-Choice Assays- Tingey (1986) reported insect responses may
differ between free-choice and no-choice assays. Wiseman et al. (1961) and Overman &
MacCarter (1972) found free-choice bias; i.e., genotypes identified as resistant using
free-choice assays were not resistant when isolated. Free-choice assays are commonly
used in mass screening forage and turf germplasm for resistance. Since the opportunity
for an insect to exercise choice is limited in a commercial situation, free-choice assays
may influence resistance results and reflect free-choice bias.


Turfgrass research programs in Florida and Texas have identified insect and mite
resistant germplasm, and insect resistant cultivars have been released. Resistant cul-
tivars include Midiron, Tifdwarf, Tifgreen, and Tifway bermudagrasses resistant to the
bermudagrass mite; Bell rhodesgrass resistant to the rhodesgrass mealybugs; and
Floratam and Floralawn St. Augustinegrass resistance to the southern chinch bug.
Resistance to other insect pests has also been reported in bermudagrass, centipedeg-
rass, St. Augustinegrass, and bahiagrass genotypes and Z. tenuifolia. Significant prog-
ress has been made over the last decade in understanding the mechanisms of resistance
in bermudagrass to the fall armyworm.
Germplasm evaluation for resistance to insect pests may be influenced by soil fertil-
ity, cultural conditions in which the grass is grown, physiological and behavioral differ-
ences between insect strains, the preconditioning effects of artificial diets, and assays
used for evaluating turf and forage germplasm for resistance. Thus, researchers should
consider these factors when screening germplasm for resistance to insect pests.
Biotechnological methods such as cell and tissue culture, genetically engineered
plants, and electrophoretic techniques may offer new possibilities for developing forage
and turf grasses resistant to insect and mites. Plants generated from callus tissue of
bermudagrass cultivars were more resistant to fall armyworm (Croughan & Quisen-
berry 1989a). Ratcliff (1985) reported the potential value of endophyte (Acremonium)-
induced resistance in turf grasses for management of foliar and crown feeding insects.
Endophyte-enhanced resistance has been reported in tall fescue (Festuca arundinacea
Schreb.), perennial ryegrass (Lolium perenne L.), and fine leaf fescues (Festuca spp.)
(Funk et al. 1985, Saha et al. 1985, Siegel et al. 1985). Improved inoculation or tissue

September, 1990

Quisenberry: Symposium-Plant Resistance to Insects

culture techniques would enable the interspecific transfer of endophytes for the devel-
opment of resistant grass cultivars. If animal toxicosis could be prevented through
selective breeding or biotechnological methods, forage grass cultivars that contain en-
dophytes resistant to insects also could be developed for grazing and thus, provide
effective and economical management of insect and mite pests (Pottinger et al. 1985).


The author would like to thank T. J. Riley, R. N. Story, and S. S. Croughan for
their critical review of the manuscript. Approved for publication by the Director of the
Louisiana Agricultural Experiment Station as manuscript number 89-17-3427.

BRUTON, B. D., J. A. REINERT, AND R. W. TOLER. 1979. Effects of the southern
chinch bug (Blissus insularis) and the St. Austine decline strain of Panicum
mosaic virus (PMV-SAD) on seventeen accessions and two cultivars of St. Augus-
tinegrass. Phytopathology 69: 525-526. (Abstr.).
BRUTON, B. D., D. W. TOLER, AND J. A. REINERT. 1983. Combined resistance in
St. Augustinegrass to the southern chinch bug and the St. Augustine decline
strain of Panicum mosaic virus. Plant Disease 67: 171-172.
BUSEY, P. 1986. Bermudagrass germplasm adaptation to natural pest infestation and
suboptimal nitrogen fertilization. J. Am. Soc. Hort. Sci. 111: 630-634.
BUSEY, P., J. A. REINERT, AND R. A. ATILANO. 1982. Genetic and environmental
determinants of zoysiagrass adaptation in a subtropical region. J. Am. Soc. Short.
Sci. 107: 79-82.
CARTER, R. P., AND R. L. DUBLE. 1976. Variety evaluations in St. Augustinegrass
for resistance to the southern lawn chinch bug. Texas Agric. Exp. Stn. Prog.
Rep. pr-3374C.
CHANG, N. T., B. R. WISEMAN, R. E. LYNCH, AND D. H. HABECK. 1985a. Influence
of N fertilizer on the resistance of selected grasses to the fall armyworm larvae.
J. Agric. Entomol. 2: 137-146.
CHANG, N. T., B. R. WISEMAN, R. E. LYNCH, AND D. H. HABECK. 1985b. Fall
armyworm: expressions of antibiosis in selected grasses. J. Entomol. Sci. 20:
CHANG, N. T., B. R. WISEMAN, R. E. LYNCH, AND D. H. HABECK. 1985c. Fall
armyworm (Lepidoptera: Noctuidae) orientation and preference for selected
grasses. Florida Entomol. 68: 296-303.
COMBS, R. L., JR., AND J. R. VALERIO. 1980. Biology of the fall armyworm on four
varieties of bermudagrass when held at constant temperatures. Environ. En-
tomol. 9: 393-396.
CROCKER, R. L., R. W. TOLER, AND C. L. SIMPSON. 1982. Bioassay of St. Augus-
tinegrass lines for resistance to southern chinch bug (Hemiptera: Lygaeidae) and
to St. Augustine decline virus. J. Econ. Entomol. 75: 515-516.
CROUGHAN, S. S., AND S. S. QUISENBERRY. 1989a. Evaluation of cell culture as a
screening technique for determining fall armyworm (Lepidoptera: Noctuidae)
resistance in bermudagrass. J. Econ. Entomol. 82: 232-235.
CROUGHAN, S. S., AND S. S. QUISENBERRY. 1989b. Enhancement of fall armyworm
(Lepidoptera: Noctuidae) resistance in bermudagrass through cell culture. J.
Econ. Entomol. 82: 236-238.
FUNK, C. R., P. M. HALISKY, S. AHMAD, AND R. H. HURLEY. 1985. How en-
dophytes modify turfgrass performance and response to insect pests in turfgrass
breeding and evaluation trials, pp. 137-145, in F. Lamaire [ed.]. Proc. Fifth Int.
Turfgrass Conf., Avignon, France.
HORN, G. C., A. E. DUDECK, ANDR. W. TOLER. 1973. Floratam St. Augustinegrass
a fast growing new variety for ornamental turf resistant to St. Augustine decline
and chinch bugs. Florida Agric. Exp. Stn. Cir. S-224.

Florida Entomologist 73(3)

HUDSON, W. G. 1986. Mole cricket (Orthoptera: Gryllotalpidae) damage to Hemar-
thria altissima: resistance or nonpreference? J. Econ. Entomol. 79: 961-963.
JAMJANYA, T., AND S. S. QUISENBERRY. 1988. Fall armyworm (Lepidoptera: Noc-
tuidae) consumption and utilization of nine bermudagrasses. J. Econ. Entomol.
81: 697-704.
Comparison of bermudagrass lines grown in different cultural conditions and the
effect on screening for fall armyworm (Lepidoptera: Noctuidae) resistance. J.
Econ. Entomol. 83: 585-590.
JOHNSON, F. A. 1975. Bermudagrass mite, Eriophyes cynodoniensis Sayed (Acarina:
Eriophydae) in Florida with reference to its injury symptomology, ecology, and
integrated control. PhD. Dissertation, University Florida, Gainesville.
KERR, S. H. 1962. Lawn insect studies. University Florida Turf-Grass Management
Conference Proceedings 10: 201-208.
BOWMAN. 1968. Resistance in bermudagrass to the fall armyworm. J. Econ.
Entomol. 61: 1321-1322.
LEUCK, D. B., AND J. L. SKINNER. 1970. Resistance in bermudagrass affecting
control of the fall armyworm. J. Econ. Entomol. 63: 1981-1982.
LYNCH, R. E. 1984. Effects on Coastal bermudagrass fertilization level and age of
regrowth on fall armyworm (Lepidoptera: Noctuidae): larval development and
adult fecundity. J. Econ. Entomol. 77: 948-953.
LYNCH, R. E., W. G. MONSON, R. B. WISEMAN, AND G. W. BURTON. 1983. Bermu-
dagrass resistance to the fall armyworm (Lepidoptera:Noctuidae). Environ. En-
tomol. 12: 1837-1840.
MARTIN, P. B., B. R. WISEMAN, AND R. E. LYNCH. 1980. Action thresholds for fall
armyworms on grain sorghum and Coastal bermudagrass. Florida Entomol. 63:
OVERMAN, J. L., AND L. E. MACCARTER. 1972. Evaluating seedlings of cantaloupe
for varietal nonpreference-type resistance to Diabrotica spp. J. Econ. Entomol.
65: 1140-1144.
PASHLEY, D. P. 1986. Host-associated genetic differentiation in fall armyworm
(Lepidoptera:Noctuidae): a sibling species complex. Ann. Entomol. Soc. Am. 79:
PASHLEY, D. P. 1988a. Quantitative genetics, development, and physiological adapta-
tion in host strains of fall armyworm. Evolution 42: 93-102.
PASHLEY, D. P. 1988b. Current status of fall armyworm host strains. Florida En-
tomol. 71: 227-234.
DOWD. 1987a. Two fall armyworm strains feed on corn, rice, and bermudagrass.
Louisiana Agric. 30: 8-9.
PASHLEY, D. P., S. S. QUISENBERRY, AND T. JAMJANYA. 1987b. Impact of fall
armyworm (Lepidoptera:Noctuidae) host strains on the evaluation of Bermuda-
grass resistance. J. Econ. Entomol. 80: 1127-1130.
QUISENBERRY, S. S., AND H. K. WILSON. 1985. Consumption and utilization of
Bermudagrass by fall armyworm (Lepidoptera:Noctuidae) larvae. J. Econ. En-
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QUISENBERRY, S. S., AND F. WHITFORD. 1988. Evaluation of bermudagrass resist-
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dietary conditioning. J. Econ. Entomol. 81: 1463-1468.
QUISENBERRY, S. S., P. CABALLERO, AND C. M. SMITH. 1988. Influence of bermu-
dagrass leaf extracts on development and mortality of fall armyworm (Lepidopt-
era:Noctuidae). J. Econ. Entomol. 81: 910-913.
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accessions. J. Econ. Entomol. 71: 21-24.


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Quisenberry: Symposium-Plant Resistance to Insects

REINERT, J. A. 1982. A review of host resistance in turfgrasses to insects and
Acarines with emphasis on the southern chinch bug, pp. 3-12, in H. D. Niemczyk
and B. G. Joyner (eds.). Advances in turfgrass entomology. Hammer Graphics,
Inc., Piqua, Ohio.
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tinegrass to southern chinch bug and St. Augustine decline strain of Panicum
mosaic virus. J. Econ. Entomol. 73: 602-604.
REINERT, J. A., AND P. BUSEY. 1983. Resistance of bermudagrass selections to the
tropical sod webworm (Lepidoptera:Pyralidae. Environ. Entomol. 12: 1844-1845.
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tomol. 79: 1073-1075.
REINERT, J. A., AND A. E. DUDECK. 1974. Southern chinch bug resistance in St.
Augustinegrass. J. Econ. Entomol. 67: 275-277.
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AND C. R. FUNK. 1987. Occurrence and significance of endophytic fungi in the
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422 Florida Entomologist 73(3) September, 1990


Insect Biology and Population Management Research Laboratory
U. S. Department of Agriculture, Agricultural Research Service
Tifton, GA 31793-0748


Resistance of peanut, Arachis hypogaea L., and wild species of Arachis, to many
major arthropod pests has been identified in the United States. Plant resistance has
been confirmed to the following species: thrips Frankliniella schultzei (Trybom) and
F. fusca (Hinds); the groundnut aphid, Aphis craccivora Koch; leafhoppers Empoasca
kerri Pruthi and E. fabae (Harris); lepidopterous defoliators Heliothis zea (Boddie),
Spodoptera frugiperda (J. E. Smith), and S. litura (F.); groundnut leaf miner, Ap-
roaerema modicella (Deventer); southern corn rootworm, Diabrotica undecimpunctata
howardi Barber; lesser cornstalk borer, Elasmopalpus lignosellus (Zeller); the twospot-
ted spider mite, Tetranychus urticae Koch; and podborers such as termites of the genus
Odontotermes, millipedes of the genus Peridontopyge and white grubs, Eulepida
mashona Arrow. Several peanut cultivars are resistant to multiple pests. Many of the
resistant genotypes of A. hypogaea are readily available for breeding and development
into commercial cultivars. Related diploid species of the section Arachis are cross-com-
patible with the tetraploid A. hypogaea and offer the greatest potential for increasing
cultivated peanut resistance to pests. Cooperative research among institutes, research
organizations, and countries is needed to evaluate the known sources of resistance for
cross-resistance to related species of insects.


Se ha identificado resistencia en el mani, Arachis hipogaea L., y en species salvajes
de Arachis, a plagas importantes de artr6podos en los Estados Unidos. Se ha confirmado
resistancia a las siguientes species: tris-Frankliniella schultzei (Trybom) y F. fusca
(Hinds); afidos-Aphis craccivora Koch; saltahojas-Empoasca kerri Pruthi y E. fabae
(Harria); defoliadores lepid6pteros-Heliothis zea (Boddie), Spodoptera frugiperda (J.
E. Smith), y S. litura (F.); minador-Aproaerema modicella (Deventer); Diabrotica
undecimpunctata howardi Barber; Elasmopalpus lignosellus (Zeller); Tetranychus ur-
ticae Koch; Odontotermes; Peridontopyge y Eulepida mashona Arrow. Varias vari-
edades de mani son resistentes a varias plagas. Muchos de los genotipos resistentes de
A. hypogaea estan disponibles para fitomejoramiento y para desarrollar como vari-
edades comerciales. Especies de diploides relacionadas con la secci6n de Arachis son
compatibles en cruces con el tetraploide A. hypogaea y ofrecen el mayor potential para
aumentar la resistencia a plagas del mani cultivado. Se necesita cooperar en inves-
tigaciones entire institutes, organizaciones de investigaci6n, y entire naciones, para
evaluar las fuentes conocidas de resistencia para ver si hay resistencia a otras species
afines de insects.

The cultivated peanut, Arachis hypogaea L., originated in South America along the
eastern Andes (Hammons 1982). The genus Arachis is composed of 32 identified species
(Smartt and Stalker 1982) in six sections with an estimated 40 species yet to be identified
(Gibbons 1987). Early explorers disseminated the peanut to Europe, Africa, Asia, and
the Pacific Islands, and eventually to the southeastern United States.
Currently, commercial production of peanut is limited to A. hypogaea and its botan-
ical types, A. hypogaea subspecies hypogaea variety hypogaea (runner and virginia

Lynch: Symposium-Plant Resistance to Insects 423

market types), A. hypogaea subspecies fastigiata variety fastigiata (valencia market
type) and variety vulgaris (spanish market type) (Norden et al. 1982). The U.S. ranks
third behind China and India in world peanut production. Production in the U.S. is
confined to three major areas, the Virginia-Carolina area, the southeast (Alabama,
Florida, Georgia), and the southwest (Oklahoma, New Mexico, Texas). The Virginia-
Carolina area primarily produces the virginia market type, the southwest area produces
spanish, valencia, and runner market types, and the southeast area produces the runner
market type. Over 70% of the total U.S. production is the runner market type, ca. 19%
is virginia market type, and ca. 9% is the spanish market type. One variety, 'Florunner',
accounts for 53.6% of the total U.S. peanut production and 74.3% of the production in
the southeast (Holbrook & Kvien 1989). Annually, ca. 635,850 ha (1,570,000 acres) in
the U.S. are planted to peanut, with an average yield and value of ca. 2688 kg/ha (2,400
lbs/acre) and over $1 billion, respectively (USDA 1988). Approximately 62.3% of the
peanut crop is produced in the southeast, while ca. 19.2% is produced in the southwest
and 17.5% is produced in the Virginia-Carolina area. Georgia is the leading state in
peanut production, accounting for 40-45% of the annual U.S. production.
Peanut is unusual in that the plant flowers above ground while the fertilized ovule
elongates, penetrates the soil, and produces fruit below the surface of the soil. Insects
and related arthropods have exploited every niche on this unusual plant. Over 400
species of arthropods have been reported as pests of preharvest peanut (Smith & Bar-
field 1982) and an additional 80+ species as pests of postharvest peanut (Redlinger &
Davis 1982). Insects that feed on peanut are intracellular feeders (e.g., aphids and
leafhoppers), intercellular feeders (thrips); defoliators (e.g., lepidopterous larvae); root,
peg, or pod feeders (e.g., termites, millipedes, earwigs, ants, coleopterous and lepidop-
terous larvae); and transmitters of viruses (e.g., aphids groundnut rosette and peanut
stripe virus; thrips tomato spotted wilt virus and peanut yellow spot virus).
Recent reviews by Amin & Mohammad (1980), Womack et al. (1981), Wightman
(1985), Lynch et al. (1986), Wightman et al. (1987), and Wightman & Amin (1988) have
identified the major peanut pests in the U.S., Asia, and Africa (Table 1). In all three
areas, similar groups of insects have exploited peanut as a host and, under certain
conditions, produce economic losses. In Africa and Asia, the importance of insects may
be ranked as follows: 1) termites, 2) white grubs, 3) thrips as a vector of bud necrosis
virus (tomato spotted wilt virus), 4) leafhoppers, 5) A. craccivora as a vector of
groundnut rosette, 6) lepidopterous defoliators. In addition, the groundnut hopper,
Hilda patruelis Stal., millipedes, Peridontopyge spp., a subterranean ant, Dorylus
orientalis Westwood, would be ranked among the top pests in Southern Africa, West
Africa, and Southeast Asia, respectively.
In the U.S., major insect pests vary considerably among years and locations. Soil
pests, especially the wireworm, Conoderus scissus Schaffer, in the southeast, are be-
coming an increasing problem. In most years tobacco thrips (Frankliniella fusca
Hinds), potato leafhopper (Empoascafabae [Harris]) corn earworm (Heliothis zea [Bod-
die]), southern corn rootworm (Diabrotica undecimpunctata howardi Barber), lesser
cornstalk borer (Elasmopalpus lignosellus [Zeller]), and the twospotted spider mite
(Tetranychus urticae Koch) are among the major pests. The tobacco thrips and the
western flower thrips (F. occidentalis [Pergande]), as vectors of tomato spotted wilt
virus, may take on additional importance since the incidence of the disease increased
dramatically in Georgia in 1989 (personal communication, J. W. Todd, Dept. of Entomol-
ogy, Georgia Coastal Plain Experiment Station, Tifton, GA).
Plant resistance in peanut to insect pests offers a tremendous potential to alleviate
production losses, especially in the developing countries and for insects that transmit
virus diseases. Over the past 10 years, research on peanut resistance to insects has
increased substantially. Major programs have been initiated by the International Crops
Research Institute for the Semi-arid Tropics (ICRISAT) in India by North Carolina

424 Florida Entomologist 73(3)


September, 1990

Insect species
site U.S. Asia Africa

Foliage Frankliniellafusca
Heloithis zea
(J. E. Smith)
Feltia subterranea (F.)

Anticarsia gemmatalis

Tetranychus urticae

Diabrotica undecimpunctata
howardi Barber

Elasmopalpus lignosellus

Conoderus sissus

Frankliniella schultzei
Scirtothrips dorsalis
Caliothrips indicus
Spodoptera litura (F).

Empoasca kerri
Heliothis armigera
Aproaerema modicella
Aphis craccivora
Amsacta spp.
Odontotermes sp.

Microtermes sp.
Anisolabis stali
Dorylus orientalis

Aphis craccivora
Empoasca dolichi
trips (several species)

Heliothis armigera
Spodoptera littoralis

Microtermes thoracalis
Hilda patruelis Stal.
Caryedon serratus

Eulipida mashona
Peridontopyge sp.

Elasmolomus sordidus

'Modified after Amin and Mohammad (1980), Wightman (1985), Lynch et al. (1986), and Wightman et al. (1987).

State University and by the USDA Insect Biology and Population Management Re-
search Laboratory and Department of Entomology, Coastal Plain Experiment Station,
Tifton, GA. Germplasm for evaluation is readily available through the Genetic Re-
sources Unit, ICRISAT, where a collection of over 11,500 peanut lines is maintained,
and at the USDA Southern Regional Plant Introduction Station, Griffin, GA, where a
collection of ca. 8,000 peanut lines is maintained.
Techniques for evaluating peanut germplasm for insect resistance have been de-
scribed by Amin (1985a). Most evaluations have been conducted in the field with natural
insect populations or in a greenhouse using laboratory-reared insects. Several tech-
niques have been employed to enhance or augment field infestations. Populations of
Empoasca kerri Pruthi were increased by planting one row of cowpea, Vigna un-
guiculata (L.) Walt., a preferred host of the leafhopper, alternately with every four
rows of groundnut and the cowpeas infested with laboratory-reared E. kerri; cowpea
plants were later uprooted and the plants distributed evenly in the field to facilitate
transfer of leafhoppers to peanut (Amin et al. 1985). Termite populations were increased
in a field by spreading sawdust over the field during the dry season and uniformly
releasing winged adults captured from light traps (Amin et al. 1985). Peanut plants have

or pod

Lynch: Symposium-Plant Resistance to Insects 425

been artificially infested in the field with corn earworm eggs, neonate fall armyworm
larvae, or neonate lesser cornstalk borer larvae mixed with corncob grits or vermiculite
and applied with a mechanical infestation device (Wiseman et al. 1980). Twospotted
spider mites have been maintained in the greenhouse on lima bean plants from which
infested leaves were used to artificially infest peanut (Campbell & Wynne 1980). Screen-
ing for thrips and groundnut leafminer has been conducted with natural field infesta-
tions, and screening for aphid resistance has been conducted in greenhouses.
Thrips on peanut feed primarily in developing terminals by rasping the developing
tissue, which causes scarring and distortion of the leaflets as they emerge (Bass &
Arant 1973). Extensive feeding by thrips can result in necrosis and death of individual
terminals. Extensive research has been conducted on peanut resistance to thrips,
primarily F. fusca in the U.S. and F. schultzei in India. In the U.S., thrips are early
season pests of questionable economic impact (Tappan & Gorbet 1979, 1981, Lynch et
al. 1984). In India, thrips have been shown to produce economic yield loss (Senapathi
& Patnaik 1973). However, their ability to transmit viral diseases, especially the tomato
spotted wilt virus, drastically increases their importance to peanut production (Amin &
Mohammad 1980). Peanut resistance to thrips has been identified in numerous plant
introductions, wild species, and breeding lines (Table 2). Both antibiosis and nonprefer-
ence have been reported as resistance mechanisms in peanut (Kinzer et al. 1972, Amin
& Mohammad 1980, 1982). Antibiosis results in both reduced larval survival and reduced
fecundity of adults when reared as larvae on peanut (Amin & Mohammad 1980, 1982,
Amin 1985b). Resistance approaching immunity has been identified among wild species
of Arachis; no thrips damage was found among 17 accessions of the wild species during
3 yrs of evaluation (Stalker & Campbell 1983). Resistance to tomato spotted wilt virus
has not been found in A. hypogaea. However, several A. hypogaea genotypes consis-
tently show a low field incidence of tomato spotted wilt virus due to nonpreference of
thrips for these cultivars (Amin 1985c, 1987). Conversely, A. chacoense has shown
resistance to both the virus and its vector (Wightman 1985).
Leafhopper adults and nymphs feed on the lower surface of peanut leaves by insert-
ing their stylets into the midrib or vein to inject saliva and withdraw plant fluids (Bass
& Arant 1973, Womack et al. 1981). Their feeding causes leaflets to turn yellow from
the point of feeding to the apical end. These symptoms are commonly referred to as
"hopperburn" in peanut. Research to identify sources of resistance to E. fabae in the
U.S. and E. kerri in India has been extensive (Table 3). Excellent sources of resistance
to both species of leafhoppers have been found in A. hypogaea from the North Carolina
accessions (Campbell & Wynne 1980, Campbell et al. 1971, 1975, 1976, Amin & Moham-
mad 1980, Amin et al. 1985). Stalker & Campbell (1983) reported immunity to damage
by leafhoppers among 21 accessions of wild species of Arachis.
Campbell et al. (1976) reported that the resistance to leafhoppers in the North
Carolina peanut lines was associated with their thick epidermis, long trichomes on the
lower epidermis, and a higher percentage of straight trichomes; more susceptible lines
had either trichomes that curved inward or an appressed surface texture on their leaves.
Nonadditive genetic variance has been reported for peanut trichome characters in gen-
eral, while additive variance has been found for long trichomes on the midrib and
petioles (feeding sites of the leafhopper), and for leafhopper damage (Dwivedi et al.
1986). Antibiosis expressed as reduced fecundity for leafhoppers feeding on the resistant
genotypes may also be present in both cultivated and wild peanut genotypes (Campbell
& Wynne 1980, Amin & Mohammad 1982, Amin & Singh 1983, Amin 1985b). Resistance
to "yellowing," i.e., the damage symptoms, has been reported for several peanut lines
with moderate resistance to leafhoppers (Amin et al. 1985). These lines supported inter-
mediate populations of leafhoppers but did not show damage symptoms that other lines
with similar populations of leafhoppers showed.

426 Florida Entomologist 73(3) September, 1990

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430 Florida Entomologist 73(3) September, 1990

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Lynch: Symposium-Plant Resistance to Insects

The groundnut aphid, A. craccivora, is an important vector of viral diseases to
peanut. Seven viral diseases are known to be transmitted to peanut by aphids, but A.
craccivora is the only aphid that is known to transmit all seven viruses (Wightman
1985). A. craccivora and the rosette virus were the major causes of the epidemic that
reduced peanut yield in West Africa by almost 75% in 1975 (Gibbons 1977). Research
with cultivars of A. hypogaea to identify resistance to groundnut aphid has not been
very successful (Table 4). Only two genotypes, ICG 5240 and EC 36892, have been
identified as highly resistant to A. craccivora in the field (Bock, Amin, Wightman,
unpublished) and are being used in breeding programs for Africa. However, a high level
of resistance to the groundnut aphid that approaches immunity has been identified in
A. chacoense, A. glabrata, A. marginata amd the interspecific hybrid A. chaconese x
A. villosa (Amin & Mohammad 1982, Amin 1985b). Germplasm with resistance to infec-
tion by the rosette virus has been identified (Table 4) and is being used extensively in
breeding programs for Africa. Resistance to rosette in peanut is recessive and governed
by two genes (Nigam 1987).
The most common defoliators of peanut, worldwide, are Heliothis and Spodoptera
species (Smith & Barfield 1982). Neonates of these defoliators initially feed in terminals
or, in the case of Heliothis, flowers. Later stage larvae feed openly on the plant but
still show a decided preference for terminals and newly expanded leaflets (Garner &
Lynch 1981). Moderate levels of resistance to H. zea have been identified in the culti-
vated species of A. hypogaea (Table 5). Hammons (1970a) noted resistance to damage
by leaf-chewing insects, presumably H. zea and/or S. frugiperda, in 'Spancross'.
Campbell et al. (1982) reported that peanut introductions from South America are sus-
ceptible to defoliation by Heliothis; PI 269062 from China is resistant, and the sister
lines NC-GP 343 and NC Ac 342, and NC-6, a progeny of NC 343 x Va-61 R, are
moderately resistant to defoliation by Heliothis. Resistance to H. zea approaching im-
munity was reported among the wild species of Arachis; 20 accessions had less than 2%
damage compared with 38% for 'Florigiant', the susceptible check.
The mechanisms of resistance to H. zea include nonpreference and antibiosis
(Campbell & Wynne 1980, Campbell et al. 1982, Stalker & Campbell 1983, Holley et al.
1984). Holley et al. (1984) reported that a flavone glucoside in peanut leaves is probably
responsible for antibiosis against H. zea larvae. They also reported that results from
laboratory assays in which H. zea larvae were fed foliage of NC-6 x 'Florigiant' are
inconsistent and could not be used in lieu of results from field evaluations. However,
laboratory assays with wild species resulted in 100% mortality of Heliothis larvae fed
Arachis sp. (Coll. No. 10596C) and A. batizocoi (Stalker & Campbell 1983). Further-
more, progeny of interspecific hybrids A. hyogaea x A. cardenasii, A. hyogaea x A.
duranensis, and A. hypogaea x (A. batizocoi x A. spegazzinii) showed potential as
sources of resistance to the corn earworm and the potato leafhopper.
Much less research has been conducted to identify peanut resistance to Spodoptera
in peanut (Table 5). Hammons (1970b) noted resistance to damage by the fall armyworm,
S. frugiperda, in 'Southeastern Runner 56-15' (SER 56-15). Leuck & Skinner (1971)
found reduced survival and increased generation time for S. frugiperda larvae reared
on SER 56-15 compared with larvae reared on 'Starr'. Similarly, reduced survival and
weight gain for S. litura larvae fed foliage of C-501 were observed (Tiwari et al. 1980).
Lynch et al. (1981) evaluated 14 species of Arachis for resistance to the fall armyworm
and reported reduced survival and leaf consumption, increased time for development,
and differences in accession preference by larvae. Using a host suitability index, A.
hypogaea cv. 'Florunner', A. monticola, A. stenosperma, and A. batizogaea were the
most suitable hosts for larvae of the fall armyworm, while A. repens, A. glabrata cv.
'Florigraze', A. chacoense, A. villosulicarpa, A. correntina, A. lignosa, A. cardenasii,
A. burkartii, and A. villosa were the least suitable hosts; no larvae survived on A.


Florida Entomologist 73(3)

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438 Florida Entomologist 73(3) September, 1990

burkartii or A. villosa. Both nonpreference and antibiosis resistance mechanisms among
the Arachis species were found to be operative against larvae of the fall armyworm
(Lynch et al. 1981).
In the southeast, especially in North Carolina and Virginia, the twospotted spider
mite, T. urticae, is often a major pest of cultivated peanut (Campbell et al. 1974, Smith
& Barfield 1982) The application of fungicides on a 10-14 day schedule for control of
leafspots, Cercospora arachidicola Hori and Cercosporidium personatum (Berk. &
Curt.) Deigh., plus the application of insecticides for insect control synergize spider
mite outbreaks (Campbell 1978). Peanut lines with resistance to spider mites are listed
in Table 6. Johnson et al. (1980) reported nonpreference to spider mite feeding in PI
262286 and PI 262840. However, only moderate levels of resistance to the spider mite
were reported among advanced breeding lines NC Ac 302, 343, 469, 17347, and 17367
(Johnson et al. 1982). Higher levels of resistance to the spider mite have been reported
among the wild species of Arachis. Leuck & Hammons (1968) found resistance to T.
tumidellus in Arachis sp. (PI 268241), A. villosulicarpa (PI 263396), and A. repens.
Johnson et al. (1977) also found resistance to the twospotted spider mite, especially
among the Rhizomatosae; PI 338296, PI 338317, PI 262840, and PI 262827 remained
almost mite-free throughout their evaluation. PI 331194 from section Arachis, PI276203
from section Extranervosae, and PI 262142 from section Erectoides also had lower
damage ratings than susceptible standards, but only members of section Arachis readily
hybridize with A. hypogaea. Tolerance, nonpreference, and antibiosis mechanisms of
resistance to spider mites have been identified in peanut (Johnson et al. 1977, 1980,
Larvae of the southern corn rootworm (SCRW) feed on developing peanut pods
below the soil surface, most often in heavier, poorly drained soils (Bass & Arant 1973).
Fronk (1950) and Alexander & Boush (1964) reported that damage by SCRW was
greater on spanish peanut lines than on virginia lines. Smith (1970) and Smith & Porter
(1971) noted differences in percentage of damaged pods among cultivated peanut lines
when they were artificially infested with second-instar larvae of the SCRW, but not a
high level of resistance. Even lines with moderate levels of resistance to pod injury at
low levels of infestation were susceptible at higher levels. Similar results were reported
by Chalfant & Mitchell (1970), who reported only a moderate level of resistance to pod
injury by the SCRW in the field. However, Campbell et al. (1977) reported a high level
of resistance, 85% less damage in NC6 than in 'Florigiant' (Table 7). NC-6 also had
moderate resistance to the potato leafhopper and the corn earworm and a low level of
resistance to the tobacco thrips (Campbell et al. 1977, Campbell & Wynne 1980, 1985).
The resistance in NC-6 resulted in the use of 60 to 80% less insecticides for SCRW,
leafhopper, and thrips control than was required for control of these insects on
'Florigiant' (Campbell & Wynne 1985).
The lesser cornstalk borer (LCB) larvae are primarily subterranean, feeding on the
main stem of seedling peanut, tunneling in the lateral branches of more mature plants,
or feeding on the developing pegs and pods (Tippins 1982). Larvae prefer immature
pods before the mesocarp develops structural rigidity (Lynch 1984). LCB is most often
an economic pest on well drained, sandy soils, especially during periods of inadequate
soil moisture (Tippins 1982). Peanut resistance to both plant and pod damage by LCB
has been reported (Table 7). Schuster et al. (1975) reported that runner cultivars
'Florunner', 'Florigiant', 'Early Runner', all appeared to possess a moderate level of
antibiosis to LCB and were less susceptible than spanish cultivars. Females emerging
from the spanish cultivar 'Spanhoma' produced significantly more eggs than females
emerging from the runner cultivar 'Florunner' (Berberet et al. 1982). Greenhouse evalu-
ation of 490 peanut lines for resistance in the seedling stage to LCB damage showed a
moderate level of resistance to plant damage in 'Early Runner', Virginia Bunch 67',
'Florunner', Florigiant', and 'Dixie Spanish' (Smith et al. 1980a, b). Stalker et al. (1984)

Lynch: Symposium-Plant Resistance to Insects

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Florida Entomologist 73(3)

reported peg and pod resistance to LCB damage; PI 269116, PI 275744, PI 262000, PI
269006, PI 261955, and PI 269005 had significantly less LCB damae than 'Florigiant'.
They also reported high levels of resistance in several of the wild species of Arachis.
In India, and especially in Africa, termites are among the most important pests of
cultivated peanut (Amin & Mohammad 1982, Wightman 1985, Lynch et al. 1986). Ter-
mites damage plants by either tunneling in the main stem, which causes the plant to
wilt and die, or by feeding on pods, which results in pod scarification or penetration
(Johnson et al. 1981, Johnson & Gumel 1981). Resistance to pod scarification by termites
has been reported by Amin & Mohammad (1980 and Amin et al. (1985) (Table 8). NC
Ac 2243T, NC Ac 2243DP, NC Ac 2240T, NC Ac 2240DP, and NC Ac 2242 are highly
resistant to pod scarification by termites.
Research to identify resistance to the groundnut leafminer and 'pod-borers', i.e.,
millipedes, wireworms, and earwigs is under way (Wightman et al. 1987). ICG 2271
(NC Ac 343) is reported to have resistance to several species of insects including A.
modicella, thrips, leafhoppers, and "pod-borers" (Amin 1987). In addition, NC Ac 2240
is resistant to pod-boring insects (Wightman et al. 1987).
In conclusion, resistance in peanut to most of the major insect pests has been iden-
tified. However, cross-resistance to congeneric insects has not been investigated or
confirmed in most instances and warrants further investigation. Also, resistance to
multiple insects has been identified in both cultivated peanut (Campbell & Wynne 1980,
Amin et al. 1985, Amin 1987) and in a number of wild species of Arachis (Stalker &
Campbell 1983). In addition, high levels of resistance to some major disease pathogens
of peanut have been identified in the wild species of Arachis (Gibbons 1987). These
accessions, especially diploid species of the section Arachis, which are cross-compatible
with the tetraploid A. hypogaea, offer tremendous potential for the development of
cultivars with increased levels of resistance to both insects and plant pathogens.
Cooperative research among research institutes, organizations, and countries is needed
for evaluation of peanut germplasm for cross-resistance and resistance to multiple pests.


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HAMMONS, R. O. 1970b. Registration of Southeastern Runner 56-15 peanuts. Crop
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444 Florida Entomologist 73(3) September, 1990

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446 Florida Entomologist 73(3) September, 1990


Insect Biology and Population Management Research Laboratory
Agric. Res. Serv., USDA, Tifton, GA 31793
Crop Science Research Laboratory, Agric. Res. Serv., USDA
Mississippi State, MS 39762


North Carolina and Tennessee ranked as the number one and two states in the
Southeast in 1986 in corn (Zea mays L.) production with 1.6 and 0.9 million acres and
value of the crop at 167.0 and 94.0 million dollars, respectively. Arkansas and Louisiana
were the top two sorghum [Sorghum bicolor (L.) Moench] producers in 1986 with 675
and 370 thousand acres and the value of the crop at 56.0 and 35.2 million dollars,
respectively. There are three major efforts to develop plant resistance in corn to insects
in the southeast: USDA's Insect Biology and Population Management Research Labora-
tory at Tifton, GA; USDA's Crop Science Research Laboratory at Mississippi State,
MS; and the program of Dekalb/Pfizer Genetics at Union City, TN. Only the Tifton,
GA, program has resistance of sorghum as one of its goals. Mass rearing [except for
Contarinia sorghicola (Coq.)], infestation technology, and evaluation systems for iden-
tification of resistant germplasms have been perfected for several growth stages of both
crops. A total of 12, 10, 9 (corn), and 54 (grain sorghum) resistant cultivars have been
released and registered from the southeastern United States over the last 15 years for
public use with resistance to corn earworm, fall armyworm, southwestern corn borer,
and the sorghum midge, respectively. Some releases of corn germplasm possess resist-
ance to as many as six leaf-feeding insect species.


Carolina del Norte y Tennessee fueron los estados uno y dos en el sudeste en 1986
en la producci6n de maiz (Zea mays L.) con 1.6 y 0.9 millones de acres con valores del
cultivo de 167.0 y 94.0 millones de d6lares respectivamente. En 1986 Arkansas y
Louisiana fueron los principles productores de sorgo [Sorghum bicolor (L.) Moench]
con 675 y 370 mil acres con valores del cultivo de 56.0 y 35.2 millones de d6lares
respectivamente. En el sudeste hay tres esfurzos principals para desarrollar resistencia
en el maiz hacia plagas: en el Laboratorio, del USDA de Administraci6n de Poblaciones
y de Biologia de Inscto en Tifton, Georgia; en el USDA Laboratorio de Investigaci6n
de Ciencias de Cultivos en la Univeridad de Mississippi State, Mississippi; y en el
program Genetico de Dekalb/Pfizer en Union City, Tennessee. 561o el program de
Tifton, Georgia, tiene como meta la resistencia del sorgo. La cria en masa excepto
Contarainia sorghicola (Coq.)], la thcnica de infestaci6n, y los sistemas de evaluaci6n
para identificar germoplasmas resistentes se han perfeccionado para varias etapas de
crcimiento de ambos cultivos. Un total de 12, 10, 9 (maiz), y 54 sorgoss de grano)
variedades resistentes se han liberado y registrado en el sudeste de los Estados Unidos
durante los tiltimos 15 afios para el uso del piblico, con resistencia al gusano del maiz,
al gusano cogollero, al taladrador del maiz y a la mosca del sorgo respectivamente.
Algunas liberaciones de germoplasmas de mafz poseen resistencia hasta tanto como seis
species de insects comedoras de hojas.

Field corn is the most valuable cereal crop grown in the United States (United
States Department of Agriculture, 1988). Although the amount of corn planted and the

Wiseman & Davis: Symposium-Plant Resistance to Insects 447

value of the crop has fluctuated over the past few years, 76.7 million acres were planted
in 1986 in the United States with a value of 12.5 billion dollars.
Sorghum is the third most important cereal crop in the United States, ranking
behind corn and wheat. Sorghum was planted on 15.3 million acres in 1986 in the United
States, with a value of 1.3 billion dollars (United States Department of Agriculture,
United States Department of Agriculture (1988) lists the number of acres planted
to corn and sorghum in the southeastern United States, number of bushels harvested,
and the value of the crop in 1986 (Tables 1 and 2). In the southeastern United States,
acres planted to corn, yield, and the value of the crop decreased by 5, 25, and 47
percent, respectively, from 1985 to 1986. Acres planted to sorghum, yield, and the value
of the production decreased 38, 49, and 63 percent, respectively, from 1985 to 1986.
Estimates for both crops in 1987 show more reductions.


Many species of insects attack corn and grain sorghum in the southeastern U.S.
However, only five of the more important species will be discussed herein: corn ear-
worm, Heliothis zea (Boddie); fall armyworm, Spodoptera frugiperda (J. E. Smith);
southwestern corn borer, Diatraea grandiosella Dyar; European corn borer, Ost:rnia
nubilalis (Hfibner); and the sorghum midge, Contarinia sorghicola (Coquillett).


The corn earworm (CEW) is distributed over the entire corn growing area of the
United States and can be particularly devastating to corn in some years. Of more
importance is the contribution of susceptible and/or tolerant corn in the production of
massive corn earworm populations that complete their development on corn and move
during the season to more vulnerable crops such as cotton, soybean, peanut, and sor-
ghum, producing extensive damage and causing tremendous economic losses (Wiseman
& Morrison 1981). Corn earworms may feed on the whorl leaves and on the emerging
tassel, but most frequently feed on the tips of the ears (Dicke 1988). Losses caused by
corn earworms in the United States have been estimated at 2.5% annually. However,


Acres planted Yield/bushels Value of
State (1000) (1000) production ($1000)

Alabama 340 15,390 29,241
Arkansas 90 8,480 14,586
Florida 200 9,920 19,344
Georgia 900 42,340 81,716
Louisiana 400 44,660 78,155
Mississippi 210 13,500 27,000
North Carolina 1,600 93,840 167,035
South Carolina 550 21,160 38,088
Tennessee 910 56,980 94,017
Total 5,200 306,270 549,182

'Source: U. S. Department of Agriculture 1988.

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