Evaluation of ARS Program on Alternative Methods of
Insect Control: Host Plant Resistance to Insects
By
M. SCHALK AND ROGER H. RATCLIFFE
Plant Genetics and Germplasm Institute,
Agricultural Research Service, U.s.D.A.) Beltsville, MD 20705
JAMES
fort appears warranted based on the results obtained to
date. For instance, little work has been done on selection
for resistance in ornamental and forest crops; and, even
in crops that have received considerable attention, the
studies have often been limited to resistance to 1 or a few
of the most important insect pests. Actually, in some
crops, for example, forage grasses and legumes, a complex of insect species feed on the crop and contribute to
losses in yield and quality, but the individual species do
not in themselves do enough damage to warrant control.
Nevertheless, controls might be economical if the complex was viewed as a group. Moreover, these species may
vary considerably in such aspects as feeding habits and
time of development on the crop, so it may be impractical
to attempt to control them with insecticides, and utilization of multipest resistant cultivars may be the only feasible means of reducing losses.
Host plant resistance (HPR)
to insects was reported
in the 18th century, but concentrated efforts to search for
and develop resistant crop varieties did not begin until
the 19OOs,and widespread recognition of the potential of
HPR as a means of reducing populations of pest insects
was even slower. Indeed, strong support for such research
did not develop until the 1950s despite many significant
examples of resistance reported prior to this period. Then
as greater emphasis was placed on the development of
nonchemical means of insect control, attention was drawn
to the important role that insect resistant cultivars have
in insect management programs, either as a means of control in themselves or as part of an integrated control
scheme.
Host plant resistance is a method of suppressing insect
populations that is completely compatible with both chemical and nonchemical control measures. In addition, the
cost of resistant cultivars to the user is less than the cost
of chemical applications, which means that the method
can be applied to crops with low value per acre, such as
grains and forages, whereas chemical application may be
uneconomical. Plant resistance also affords built-in protection against insect attack without further action by the
grower that can extend through much or all of the growing season.
Yield Levels
Losses of field and vegetable crops due to insect attack
are estimated at over $1 billion yearly (Metcalf et al.
1962, Stoner 1970), and this figure does not include the
cost of applying insecticides. Much of this loss, and the
cost of direct control as with insecticides, could be reduced by developing and growing insect resistant cultivars.
Some examples of the value of plant resistance in reducing losses would include the following.
Presently, insect resistant cultivars are being continually developed for a wide range of crop species including
forage grasses and legumes, corn and small grains, many
vegetable crops, sugarcane and sugarbeets, oil crops, tobacco, and fruits, nuts, and ornamentals.
For many of
these crops, cultivars are available that are resistant to 1
or more insect species. According to estimates based on
a review of USDA research in 1974-75, studies of host
plant resistance are being conducted on 34 crops over a
wide range of commodities. This research is concentrated
in three major areas: (1) screening, isolating, and identifying sources of resistance; (2) development and release of germplasm as breeding material or cultivars for
use by growers or the seed industry; and (3) determination of the genetic basis of resistance and the morphological and biochemical factors and mechanisms (tolerance,
antibiosis and nonpreference) that contribute to resistance.
Research is also being conducted to a lesser degree on the
interaction of plant resistance with (1) development of
insect biotypes, (2) chemical, cultural, and biological control methods, and (3) external factors such as use of fertilizer and transmission of insect-borne agents. In many
instances, USDA research involves cooperative programs
with state or private research organizations, and it is
often undertaken by interdisciplinary groups of scientists,
for example, entomologists, plant breeders, agronomists,
plant pathologists, aml biochemists. It is, therefore, difficult to identify the contribution of USDA researchers or
the specific contribution of anyone scientific discipline.
R. L. Gallun, Entomologist, USDA, reported on the
economic importance of wheats resistant to the Hessian
fly, M ayetio/a destrltctor (Say).
Surveys conducted in
cooperation with plant scientists in the various wheatgrowing states indicated that 8.5 million acres of resistant
wheat were grown during 1964 (Luginbill 1969). It was
estimated that these cultivars prevented losses of 1-3
bushels/acre annually and that the net worth of these
savings amounted to 10-20 million dollars. In fact, W. B.
Noble, retired USDA entomologist, reported in 1950 that,
as the acreage of the resistant wheats 'Big Club 43' and
P05042 increased in California, the populations of Hessian flies decreased so much that the insect forms were
difficult to find, and infestations were reduced to less than
1% (Luginbill 1969). Thus, this fly is no longer a problem in California. Similar success was reported in central
Kansas after the release of 'Pawnee,' but newer wheats
that are susceptible have now been used, and infestations
are increasing. Populations of the Hessian fly could,
therefore, probably be reduced to minimum levels throughout all infested areas of the U.S. if the entire wheat acreage were seeded exclusively to resistant cultivars and if
breeding for resistance to biotypes of the Hessian fly continued to be done.
Seven wheat varieties with resistance to the wheat stem
sawfly, Cephlts cinctllS Norton, were being grown on 1.5
million acres in 1969. Savings to farmers that grew these
varieties were ca. $3-5 million/year.
In spite of the noted increase in recent years in research
on host plant resistance by the USDA, much greater ef-
The damage done by the European corn borer, Ostrinia
7
volved. About 40% of the entomology research in host
plant resistance is conducted on grain crops (field corn,
grain sorghum, and small grains); 13% each on vegetables, forage crops, and cotton; 870 on oil crops (peanuts
and soybeans) ; 670 on fruit and nut crops; 570 on sugar
crops; and the remaining 270 on tobacco and ornamentals.
nubilalis (Hiibner),
to corn has been reduced by $600
million annually because of resistant inbreds developed
and released by the USDA and state agricultural experiment stations. The inbreds reduce losses by at least $20/
acre when insect infestations are heavy. (Thus, breeding
for resistance has been greatly facilitated by rearing the
corn borer on meridic diet; 1%-2 million egg masses are
produced in the laboratory at Ankeny, lA, each summer
for field infestations.) F. F. Dicke indicated that growing
resistant corn reduced the borer population by as much as
50-6070 (Luginbill 1969). The cumulative effect of an
annual reduction in population of this magnitude would
be suppression of this insect to a low level, and such reduction has already taken place in some areas of Iowa.
For some crops, breeding programs to develop resistant
varieties are just starting. For example, the Department
has begWl an all-out effort to develop agronomically acceptable cotton varieties with built-in resistance to insects
based on observations that plants without nectar are less
attractive for oviposition than those with nectar to the
bollworm, H. zea, and tobacco budworm, H eliothis virescens (F.).
About 25 races of the world collection of corn lines
(sweet and field) have been screened in the field and
laboratory for resistance to the corn ear worm, Heliothis
zea (Boddie). The resistance mechanisms (nonpreference,
antibiosis, tolerance) have been identified in 75 of these
2000 corn lines, and mechanical and chemical factors were
found that contributed to resistance. W. A. Douglass,
USDA, estimated that in Mississippi alone the development of resistant dent corn hybrids-Dixie
18, Coker 811
and others-had
reduced losses due to the corn earworm
and rice weevil, Sitophilus or)'zae (L.), by $10 million
during 1958-68 (Luginbill 1969). Damage done to corn
by this pest has been estimated at $182 million/yr for the
entire U.S., and it appears that much of this loss could
be prevented by developing and growing resistant hybrids.
For instance, the experimental hybrid developed by crossing 471-U6 inbred with 81-1 inbred produced a plant almost immune to earworm damage. Moreover, when the
population of this insect was large, this hybrid only required one application of insecticide to achieve the same
high level of control produced by 7 applications of insecticide to a susceptible hybrid at twice the rate of active
material per acre.
Resistant Germplasm
Today
Field Corn.-Lines
with resistance to corn ear worm are
used in over 1 million acres in the Georgia coastal plain
area.
Tomatoes.-Germplasm
has been released that is resistant to potato aphid, Maerosiphum euphorbiae (Thomas);
twospotted spider mite, Tetranyehus urlieae Koch; Drosophila spp. ; and fiea beetles, Epitrix cucumeris (Harris)
and E. hirtipennis (Melshelmer).
Potatoes.- Two varieties have been released with resistance to potato leafhopper, Empoasea tabae (Harris),
and potato fiea beetle, E. cucumeris.
Onions.-Resistance
to onion thrips, Thrips tabaci
Lindeman, has been developed with germplasm release.
Altalta.-Fifteen
cultivars or lines have been released
with resistance to pea aphid, Acyrthosiphon pisum (Harris); spotted alfalfa aphid; potato leafhopper; alfalfa
weevil, Hypera postiea (Gyllenhal);
alfalfa seed chalcid,
BmehophagllS roddi (Gussakovsky);
or meadow spittlebug, PhilaenltS spumarius (L.).
Cooperative Federal and State research has produced
lines with tolerance to the northern corn rootworm, Diabrotiea longieornis (Say).
However, the Department
does not have an accurate estimate of the amount of acreage that is planted to hybrids involving the tolerant lines.
So.\'bcal1s.-A variety was developed and released in
Maryland and Virginia with resistance to the Mexican
bean beetle, Epilaehna varivestis Mulsant.
Savings to farmers who plant barley have amounted to
15 bushels/acre when they have grown the cultivar released jointly by Oklahoma State University and the
USDA that is resistant to greenbugs, Sehizaphis graminum (Rodani).
The potential savings in grain to the
farmer from 1 such resistant barley would be tremendous
in years of heavy greenbug populations.
Sorghllllls.-Greenbug
resistant lines have been developed and will be released in the Midwest.
Wheat.- Thirteen varieties of wheat have been released
in the last 10 yr with resistance to Hessian fiy. Four
varieties have been released with resistance to wheat stem
sawfly in the last 10 years. Two lines resistant to cereal
leaf beetle, Ol/lema me!anoPlls (L.). were released for
development by breeders.
Annual savings to farmers who used cultivars of alfalfa
resistant to the spotted alfalfa aphid, Therioaphis maw/ala
(Buckton), were estimated to be a conservative $35 million in 1963 (Luginbill 1969). In Arizona, scientists
found that damage due to the spotted alfalfa aphid was
more than 20 times higher on susceptible than on resistant
alfalfas. Also, large-scale tests at Bakersfield, CA, indicated that resistant cultivars out-yielded susceptible cultival'S by as much as 5070. In 1970, an estimated 2 million
acres of alfalfa were planted to cultivars resistant to the
spotted alfalfa aphid.
Existing Programs
Available
Sweet Corn.-Six
inbred lines with resistance to corn
ear worm have been released and are used commercially.
A large amount of additional germplasm is being developed by commercial growers.
Impact of Program
Specific examples of the impact of insect resistant cui tival'S on crop yield and use of insecticides are given in
Table 1. The information on acreages planted to resistant
cultivars and on the increased yields resulting from their
use was taken from replies to a questionnaire recently
submitted by R. L. Gallun to ARS research entomologists.
The amounts of insecticides used were calculated on the
basis of the mean pounds of total active insecticide per
acre that would be applied annually for control of specific
insects based on present recommendations if 1 application
per year was made (except that 2 per year were assumed
for the European corn borer). The amount of insecticide
saved by use of resistant cultivars was then estimated by
in Host Plant Resistance
Presently, in the USDA, ca. 30 scientific years in entomology are involved in studying host plant resistance to
insects. This compares with an estimated 37 working in
this field in the 1965-74 period. Perhaps an equal number
from the plant sciences or related disciplines are also in-
8
Table I.-Use
Insect
of resistant cultivars in reducing the use of broad-spectrum
Crop
Total
acreage
(millions)
Acreage
planted to
resistant
cultivars
(millions)
Yield
increase/
acre by
resistant
cultivar
%-lh Ton
.9
NA
.5
25,000
.3
600,000
Alfalfa weevil
Alfalfa
62
Naa
Pea aphid
Alfalfa
62
.05
Spotted alfalfa
aphid
Alfalfa
62
2
Barley, oats,
wheat
Corn
95
64
NA
European corn
borer
Corn
Corn leaf aphid
Barley
Greenbug
Barley
Greenbug
Hessian fly
Sawfly
Cereal leaf
beetle
Chinch bug
insecticides.
Insecticide
applied to
control pest
(lb. AI/acre)
10-12 Tonb
Reduction in
insecticide
by resistant
cultivar
1.0
10
23%
1 Ton
1.5
15,000,000
64
21.5
30 Bu.
1.1
47,300,000
10
1 Bu .
Grain sorghum
12
.5
1 Bu .
lh Ton
.3
.3
125,000
10
.5
.5
.3
125,000
Wheat
62
8.5
1-3 Bu.
Wheat
62
1.5
• No information
availabl~.
b Yield has doub]~d to trip]~d sinc~ 1957.
e Where resistant cu1tivars are not used, field losses can range from
produc~rs is al1ticirat~d to b~ ca. $40 million over a 10·yr p~riod.
d Insecticides
seldom used or not recommended.
75-85%.
The
estimated
value
of sawfly
125,000
resistance
to wheat
beetle resistance in soybeans, and alfalfa weevil resistance
in alfalfa.
There are many other crops than those listed in Table
1 for which insect-resistant germplasm has been developed
and made available to industry but where information is
too limited on use to obtain reasonable estimates of present impact. This was noted earlier in regard to lines of
corn that are tolerant to corn rootworm damage and corn
cultivars resistant to European corn borer. Also there are
problems with the acceptance by growers of resistant cultivars of vegetable crops. Since they are high value crops
in terms of dollars per acre, growers can still afford to
apply insecticide to maintain good appearance and increased yield. In addition, vegetable crops are usually
susceptible to a complex of insect species so multiresistant
cultivars are needed. Finally, growers need a high level
of control to prevent insects from invading harvestable
areas of the plant since the presence of a dead insect is
as important as the presence of a live one in affecting
quality in crops such as broccoli.
multiplying the pounds of insecticide used annually by the
acreage planted to resistant cultivars. We also assumed
that no insecticides were applied to resistant cultivars for
control of the insect for which resistance was developed.
This may not always be the case, of course, since the
need for insecticides on resistant cultivars may vary depending on the level of resistance available, the insect infestation, and the extent to which insect injury can be
tolerated before significant losses in yield or quality occur.
In the U.S. in 1971, 170 million pounds of insecticides
were applied (Andrilenas 1974), and we have estimated
that almost 63,300,000 Ib of insecticide are saved annually
through the planting of corn, barley, grain sorghum, and
alfalfa cultivars resistant to the chinch bug, Blissus ICIIcofi/crus lcucop/crus
(Say);
corn leaf aphid, Rhopalosiph 11m maidis (Fitch) ; European corn borer; greenbug;
pea aphid; or spotted alfalfa aphid. We made no attempt
to attach a dollar value to these savings, but it would be
substantial in terms of the direct cost of insecticides and
their application and such indirect benefits as reduced loss
of beneficial organisms and damage to the crop during application. For example, according to the estimates we
received, the benefits to be derived from greenbug-resistant grain sorghums are just beginning to be felt, because
the % million acres presently planted to resistant cultivars should increase to 8 million acres by 1976. It is
estimated that the value of sawfly-resistant wheats has
been $40 million over a 10-yr period. Where resistant
cultivars are not used, field losses can range from 75--S5%.
Summary
The use of insect-resistant cultivars has been very successful in controlling insect pests and reducing the use of
insecticides. In fact, if all acreage planted to resistant
cultivars was eliminated and replaced with susceptible
cultivars, a 37% (over 63 million pounds) increase in the
use of insecticide would be required to maintain the present level of control. However, research should emphasize the discovery and development of cultivars with multiple resistance to insects. This work will involve finding
new sources of insect-resistant germplasm and combining
this germplasm into agronomically
acceptable plants,
learning more of the nature of plant resistance, and investigating biotypes associated with resistant cultivars, including the search for new sources of resistance when
such biotypes develop.
In some of the examples shown in Table 1, it is still
too early to measure the impact of research conducted on
host plant resistance, since resistant cultivars are not yet
available or have just recently been released and are
planted to limited acreage. The future impact should be
substantial, however, in instances such as cereal leaf beetle resistance in wheat, barley and oats, Mexican bean
9
Acknowledgment
P. A. Andrilenas, T. F. Branson, R. A. Byers, R. L.
Gallun, W. D. Guthrie, F. Holbrook, S. D. Kindler,
A. Kishaba G. R. Manglitz, M. W. Nielson, E. E. Ortman, K. J. Starks and B. Wiseman.
This paper was originally prepared as part of a broader
review on evaluation of the ARS program on alternative
methods of insect control at the request of the Office of
Planning and Evaluation. Coordination of this work was
under the direction of W. Klassen, National Program
Staff Scientist for Pest Management. We want to acknowledge Dr. Klassen's guidance and support in the
preparation of this report.
REFERENCES
CITED
Andrilenas, P. A. 1974. Farmer's use of pesticides in
1971. USDA Agric. Econ. Rep. No. 252. 56 pp.
Luginbill, P. 1%9. Developing resistant plants-The
ideal method of controlling insects. USDA Produ.
Res. Rep. No. 111. 14 pp.
Metcalf, E. 1., W. P. Flint, and R. 1. Metcalf. 1962.
Destructive and useful insects. McGraw Hill Book
Co., N. Y., San Francisco, Toronto and London.
1087 pp.
Stoner, A. K. 1970. Breeding for insect resistance in
vegetables. Hort. Sci. 5 (2): 76-9.
Because of the broad nature of the report we also felt
it important that there be opportunity for review and input, prior to its completion, by other scientists actively
working on or very familiar with research on host plant
resistance to insects. Following such review, additional
information and suggested revisions were incorporated
into the final report. The authors gratefully acknowledge
the contribution of the following persons in this respect:
BOOK REVIEW
URBAN ENTOMOLOGY
by Walter Ebeling, 1975. Publications, Division of Agricultural Sciences, University of
California, 1422 South 10th Street, Richmond, CA
94804. 695 pp., 391 figs., $27.50 including shipping
charges. Make checks payable to Regents of the University of California (California residents please add
6% for California State sales tax).
Stored Food Products, Pests of Fabrics and Paper, Pests
Attacking Man and His Pets, Pests in Excessively Damp
Locations, Pests of House Plants, Miscellaneous Pests,
and Vertebrate Pests: Rodents, Bats and Birds.
Chapter 14 discusses Delusory
Mite" Dermatitis.
Parasitosis
and "Cable
The book is well indexed with 25 pp. devoted to this
purpose. It is also an excellent source of up-to-date, as
well as older references to scientific papers and other publications related to urban entomology, with 51 pp. of
cited literature.
Dr. Ebeling, who for many years has been Professor
of Entomology and Entomologist in the Experiment Station, University of California at Los Angeles, has chosen
the title well for this book. The principle theme of the
volume centers around some old, but many new pest
problems that have arisen as a result of the unprecedented rate of urbanization in the United States and
other countries. Not only does it treat pest problems of
man and his buildings within the city, but those arising
from encroachment of cities upon agricultural lands and
the resulting proximity of large human populations to
cattle, poultry and other agricultural operations that provide places for flies to breed. It also deals with mosquito, midge and other pest problems resulting from impoundment of water in flood control projects, water
settling basins, recreational lakes and water storage facilities. Many of the problems treated have resulted from
people building homes in forested or brush covered suburban areas and from the weekend exodus of thousands
of urban dwellers to recreational areas outside the city.
Here picnic foods and people are attacked by wasps, bees
and ants and those strolling through the park are annoyed by mosquitoes, gnats, biting flies, chiggers and
ticks. The pests discussed are not limited to entomological species, but also include molluscs (slugs and snails),
crustaceans (pillbugs, sowbugs) and vertebrates such as
rodents, bats and birds. It even includes imagined pests
(delusory parasitosis)
which may' result from worry,
stress, emotional upsets and other conditions common to
human beings everywhere, but perhaps more concentrated
in urban areas.
"Urban Entomology" is well illustrated with 391 black
and white photographs, tables, charts, diagrams and drawings located with pertinent subject matter. In addition,
there are 8 pp. of plates, each containing 8 or more excellent colored photographs. A large proportion of these
photographs were taken by entomologists associated with
the author on the University of California campus at Los
Angeles. The pages are 7 X 10% inches and the reproduction by offset is excellent.
*
Dr. Ebeling has drawn upon his many years of experience in dealing with actual urban pest problems, his research and a thorough literature search for the contents
of his book. While he has been very meticulous in assuring scientific accuracy and detail, he has also recognized
the importance of practical application of information and
methods. He employs just the right amount of description, distribution, biology, habits and ecology of the various pest species to be most helpful in the field. He provides field keys to the species where they will be helpful.
Although scientific names and some scientific terminology
is used, the author writes in language that should be
understood by most at the senior high school or 1st year
college level.
As a county Extension worker and later an Extension
entomologist for many years, I find "Urban Entomology"
to be a book that should be a "must" for those involved
in urban pest control work. This would include pest control operators, regulatory personnel, Extension entomologists, county Extension agents and others. It would be
especially useful to students interested in pest problems
common to urban environments and to those preparing for
examinations for licensing as pest control operators.
The 1st 4 chapters deal with some historical facts, basic
principles and other information related to insect pest
control in general, but a great deal that is strictly pertinent to urban pest contro\. Chapter I covers Entomological Organization and Legislation. The next 3 chapters
include Pesticides and Their Uses, Equipment Used for
Applying Pesticides, and Classes of Arthropod Pests of
Urban Areas.
ANDREWS. DEAL
University of California
Agricultural Research and
Extension Center
Parlier, CA 93648
Chapters 5-13 deal with pests in relationship to specific
materials or locations. For example, Wood-Destroying
Insects and Fungi, Pests on or Near Food, Pests of
10