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VII. Control of Insect Pests of Wheat
6. C. SALMON, 0. R. MATHEWS, AND R. W. LEUKEL
fly, jointworm, and sawfly attack wheat only or principally. Some are
native to the United States and have found in cultivated crops ideal
conditions for their development and spread. Others, including some
of our most destructive pests, have been introduced from foreign countries. Build-up of populations and damage by all of them are affected
greatly by weather and other environmental conditions. Often they are
quiescent for a number of years only to become agents of disaster when
conditions become favorable. In practically all cases, areas of infestation and losses have increased more or less continuously during the last
Control is often difficult or impractical even when effective methods
are known. For example, an insect that causes a consistent but small
percentage loss may account for a very material decrease in production
for the country BS a whole and yet mean very little to the individual
farmers. This is especially so if control measures involve inconvenient
or costly changes in management or cultural practices. Sometimes such
changes invite losses from other causes that are more important. It is
for these reasons that known control measures sometimes are used very
sparingly or not a t all. Another difficulty stems from the fact that in
many cases concerted community action is necessary in order to achieve
effective control. It is only when losses become heavy, as they often do
in particular localities, that serious attention is given to control measures. This means that research must and does aim to develop methods
of control that may be incorporated as a part of the general cultural
pattern insofar as is feasible, and to develop those that are simple and
inexpensive when special measures are necessary.
Such research has included especially investigations of insecticides,
cultural practices, life history studies including egg-laying and feeding
habits, and breeding resistant varieties. Methods of applying insecticides have had much attention. Correlating insect epidemics with
weather and other environmental conditions has provided information
that is very useful for predicting or forecasting outbreaks and thereby
preparing for them. Breeding resistant varieties has had a prominent
place in research to control insects only in relatively recent years.
1. Hessian F l y
The Hessian fly is without doubt the most destructive insect pest of
wheat. The estimated loss in a single year has amounted to as much as
$100,000,000. Haeussler (1952) estimated the annual loss in the United
States in 1945 at $37,000,000.
The Hessian fly occurs in California and in the Pacific Northwest and
generally from western Kansas and Nebraska the Atlantic seaboard
HALF CENTURY OF WHEAT IMPROVEMENT IN UNITED STATES
and from northern Oklahoma to Minnesota. It is most common in winter wheat but sporadically damages spring wheat. It was first discovered
on Long Island in 1779 in the vicinity of Lord Howe’s camp of three
years before. It is thought by many to have been brought in in bedding
used by the Hessian soldiers included in the British army; hence, the
name. It spread westward almost as rapidly as did wheat, reaching
Kansas in about 1871 (McColloch, 1923) and the West Coast by 1884.
Cultural practices, including destruction of volunteer wheat plants,
plowing under of stubble, and late seeding, which had developed largely
as a result of general observation were the commonly recommended control practices before the tu rn of the century. Late seeding, according to
Bidwell and Falconer (1941, p. 9 6 ) , was recommended as early as 1811.
These methods are still used. Other measures now known to be ineffective
or objectionable or both were also frequently recommended. These included pasturing, burning stubble, and the use of decoy o r trap crops.
Varieties of wheat believed to be less susceptible to the Hessian fly than
others were recommended in the nineteenth century but not until the
early 1940’s were varieties available in which fly resistance actually had
been bred as a n important character.
Date-of-seeding tests with wheat were conducted systematically and
for several years in Indiana and Ohio and perhaps other states beginning as early as 1887. Based on these tests and observations on time of
emergence of Hessicn fly in the fall, a map of Ohio showing approximate
dates for safe p1an;ing in various parts of the state was published by
Webster (1899) of the Ohio Station in 1899. I n the following year,
A. D. Hopkins (19Ci)), using these data and his own observations in
West Virginia as starting points and making use of the relation between
altitude and latitude on the one hand and certain phenological data on
the other, constructed a similar map for West Virginia. These probably were the first maps to be published showing “safe” or “fly-free”
dates of seeding. The West Virginia map was probably the first practical application of the principles that later became the well-known
Hopkins bioclimatic law.
Extensive date-of-seeding tests since conducted by the Bureau of
Entomology and Plant Quarantine and by the state agricultural experiment stations have provided the information for similar maps for all
Hessian fly-infested areas of the United States. Although the general
principles have not been changed, the application has been improved
and refined. One improvement in particular stems from recognition of
the fact that the best dates for seeding fluctuate considerably from year
to year, depending on weather conditions and the prevalence of Hessian
fly. Timely information regarding these factors supplied by entomolo-
8. 0. SALYON, 0. R. MATHEWS, AND R. W. LEUIcEzl
gists and county agents for each infested area has aided materially in
preventing serious losses.
Seeding on or after the fly-safe dates has been used extensively in
all Hessian fly-infested areas. It has not been fully effective, partly
because unexpected delays in seeding caused by unfavorable weather
invite losses from other causes and hence farmers tend to seed earlier
than the fly-safe dates, especially when infestation is light. Concerted
community action, sometimes difficult to achieve, is also necessary for
fully effective control. Other measures of control have therefore been
The most recent and theoretically, at least, the most satisfactory of
any control measure is the use of resistant varieties. Obviously, of
course, success here depends on the availability of varieties that not only
are resistant to Hessian fly but also satisfactory in other respects and
adapted to the areas where they are to be grown. Producing such varieties has, as would be expected, proved to be a difficult and time-consuming process.
The best examples of resistant varieties now in use by farmers are
the hard winter varieties PAWNEE and PONCA and the California varieties
BIG CLUB 43, POSO 44, and POSO 48, described in Section IV. 4b. The latter are credited with practically eliminating the Hessian fly in the
Montezuma Hills section of California, and PAWNEE is believed to be responsible for a very material reduction of Hessian fly in eastern Kansas
and contiguous areas. PONCA wheat, released by the Kansas and Oklahoma Agricultural Experiment Stations in 1951, is the most resistant
variety of hard red winter wheat available commercially.
Especially significant in relation to breeding other resistant varieties
is the discovery at the Indiana Station of an unusually high degree of
resistance in a durum wheat introduced from Portugal by the United
States Department of Agriculture. This resistance, unlike that found
in PAWNEE and other commercial varieties, appears t o be effective in all
areas of the United States and at high temperatures. Much progress
has been made in transferring this resistance t o commercial varieties of
common wheat, but the work is slow because of sterility and linkage such
as is invariably encountered in crosses of common and durum wheat.
Perhaps the most spectacular and useful research relating to the control of wheat insects is that concerned with the control of grasshoppers,
including Mormon crickets. These insects, of course, attack all crops,
including wheat, and are of particular concern here since they are most
destructive in areas where wheat is an important crop. According to
HALF CENTURY OF WHEAT IMPROVEMENT
IN UNITED STATES
Hyslop (1938), severe outbreaks occur in the United States a t least once
in every ten years and each may last from one to six years. On the
basis of reports by entomologists from twenty-three of the most heavily
infested states, Hyslop has estimated the annual loss from all crops a t
about $25,000,000 per year for the ten-year period 1925-1934. Haeussler (1952) recorded the estimated loss in eighteen states in 1950 a t
nineteen million dollars. Infestation and damage are greatest in those
areas where the annual rainfall is about 25 inches or less, partly because
dry climates favor the build-up of large populations and partly because
there is less vegetation other than cultivated crops on which grasshoppers
The most notorious outbreaks were those of the Rocky Mountain
grasshoppers, or locusts, as they were then called, during the developmental stages of agriculture in the Great Plains. This particular species disappeared about 1880 or were replaced by similar or identical
species with a different name. Three of the most important species in
the west today are the lesser migratory grasshopper, the differential
grasshopper, and the two-striped grasshopper. Depopulation of large
sections of the southern Plains in the 1880’s and 1890’s was in part due
to these and other species. Recurring ohtbreaks, aa indicated above,
continued to be a feature of Great Plains agriculture until new methods
of control were developed in recent years.
Various methods to control grasshoppers have been used. The first
ones were mechanical, such as hopperdozers, and for the nonflying Mormon crickets, trench, wood, or sheet iron barriers with pits at frequent
intervals in which the insects were collected and killed. Poison bait,
first used in the San Joaquin Valley of California in 1885, was a n important forward step. This device worked surprisingly well but was not
consistently effective because the grasshoppers would not always take
the bait. An important improvement was almost immediately made by
substituting wheat bran for middlings, and numerous subsequent attempts were made to make the bait more attractive by adding fruit
juices, molasses, banana oil, or flavoring of various kinds. In general,
however, according to Packard (1942) , the increase in effectiveness obtained with such attractants was not enough to offset the additional costs.
A more important achievement was the reduction in costs by diluting
the bran with relatively inert materials such as sawdust and cotton seed
An interesting and significant discovery was the fact that Mormon
crickets, in contrast with other grasshoppers, would not eat bait containing axsenic compounds but readily took those containing the equally
poisonous sodium fluosilicates. Since grasshoppers readily took to either,
S. C. SALMON, 0. R. MATHEWS, AND R. W. LEUKEL
the cost of baiting was greatly reduced and the general effectiveness of
baits was greatly increased. The use of the motorized truck to transport
and spread poison bait, power mixing machines and spreaders, and the
adaptation of the airplane for distributing poison baits greatly extended
their use. The reduction in costs made control by poison baits practical
on a large scale, and they were used extensively for many years.
Without doubt, the most significant and far-reaching research achievements of all time relating to insect control methods were the discovery
and use of the new insecticides aldrin, chlordane, toxaphene, and others.
Incredible though it may seem, as little as 2 ounces of aldrin per acre,
applied as a spray or dust by airplane or ground equipment, will, under
favorable conditions, result in almost complete destruction of grasshoppers on the treated areas, and the residual effects are often sufficient to
protect the crop from later invasions. Sprays in general are less expensive and more effective than dusts, and they have many advantages
over baits. As a result of this development, sprays and dusts have practically replaced baits for the control of grasshoppers. Most useful also
in rela,tion to airplane spraying is the fact that good distribution may
be achieved with as little as a gallon or less of spray liquid per acre.
This means that a plane may spray a hundred acres or more with one
loading. It is not unusual to treat 1,000 acres per day per plane, and
large planes capable of treating 10,000 acres per day have been equipped
for the purpose. This, of course, is many times as rapid as treating with
Airplane spraying with the new methods is sufficiently inexpensive
that range and wastelands on which the large migratory swarms of grasshoppers once originated may now be treated. Some 12,000,000 acres of
range and cultivated land have been so treated during the past few
years with the result that migrations have been all but stopped, and
control is now largely on a preventive basis. As an example of control
a t the source of infestation, the area infested with Mormon crickets was
reduced from some 19,000,000 acres in 1938 to about 116,000 acres in
1949. Incidentally, the new insecticides and methods are used also for
the control of other insects.
3. Wheat-Stern Sawfly
Research designed to develop methods of controlling wheat-stem sawBy is a n excellent illustration of the interdependence of different countries and of the value of co-operation in developing control methods.
The most promising method for controlling this insect is by the use of
resistant varieties. The only resistant variety so far grown by the farm-
HALF CENTURY OF WHEAT IMPROVEMENT IN UNITED STATES
ers in the United States is the spring variety RESCUE, produced by Canadian research workers and introduced into the United States in 1947.
The wheat-stem sawfly is indigenous to the Great Plains, where it
has lived for untold centuries on wild grasses. It was collected in wheat
in Canada as early as 1895, in Montana in 1900, and in North Dakota in
1906. Infestation in Montana and Saskatchewan in 1908 was sufficient
to cause some alarm and likewise in North Dakota i n 1916. It has been
and sporadic outbreaks
a serious pest in Canada since the early 1930’~~
have continued in Montana and North Dakota. The insect appears to
have become firmly established in both states in about 1941 or soon thereafter and the infested area has increased nearly every year. Platt and
Farstad (1946) regard the wheat-stem sawfly as a major limiting factor
in the production of wheat in many areas of the Prairie Provinces of
Canada and have estimated the annual losses a t 20,000,000 bushels. The
estimated loss in the United States in 1951 was almost 5,000,000 bushels.
I n the United States it has been most destructive in spring wheat but in
recent years has caused severe losses in winter wheat in central Montana.
It has not as yet been a serious pest in the main winter wheat belt of
the United States. The use of strip cropping in Montana and Canada,
in which a narrow strip of wheat alternates with a strip of fallow, provides ideal conditions for the sawfly to migrate from stubble to the growing crop and is believed to have been a factor in establishing this insect
as a major wheat pest in recent years.
The RESCUE variety was produced from a cross of the Canadian variety APEX with another known as s-615, which was originally from Portugal but was secured by Canadian workers from New Zealand. I n the
United States RESCUE has yielded somewhat less than other varieties in
the absence of sawfly and f o r other reasons is not regarded as completely
satisfactory. It has reduced losses in the sawfly-infested areas, however,
and is grown extensively by Montana farmers for that reason. Additional sources of resistance have been discovered in recent years, and
breeding is under way to incorporate these into commercial varieties.
4 . Other Insect Pests of Wheat
Control of some insect pests of wheat has not been conspicuously successful. In some cases, losses suffered by individual farmers have been
small or they have been infrequent, which means that it has been difficult or quite impossible to get the continuing support that is often necessary for successful research, Nevertheless, much has been learned in
the past fifty years that will be most useful if serious outbreaks do occur
and for most insect pests methods of control now recommended and
6. C. SALMON, 0. R. MATHEWS, AND R. W. LEugEL
sometimes used are, without doubt, f a r superior to those used in the
As a result of recent research, for example, about 1,000,000 acres of
wheat was sprayed, mostly with parathion, to control greenbugs in Oklahoma in 1950 and 1,800,000 acres in the state were treated in 1951. This
is the first successful method developed for the control of this pest, credited with the destruction of 50,000,000 bushels of grain or more in the
southern Great Plains in 1907 and again in 1942, and with that of 25,000,000 bushels in Oklahoma in 1950 (Haeussler, 1952), with several
serious outbreaks in other years.
New insecticides have also been found useful in the control of the
armyworm, fall armyworm, wireworm, stored-grain insects, and others.
Chemical dust barriers of which the active ingredients are DDT or dinitro compounds have been found useful supplements to other methods in
preventing the migration of chinch bugs from small grains to corn and
Studies of the taxonomy, life histories, and egg-laying and feeding
habits, have been most useful in suggesting control methods. Knowledge
of these for many insects was completely lacking or was very incomplete
fifty years ago. Wade and St. George (1923), for example, state that
false wireworms have often been confused with other species, and hence
not recognized ag the destructive pests they really are. The reliability
of forecasts and warnings of destructive epidemics so necessary for organized large-scale control campaigns has been greatly improved in recent
years as a result of more complete information regarding the relation of
insect populations to weather and other environmental factors.
Among the more significant discoveries of recent years in relation to
future control is the resistance or tolerance of varieties of wheat to most
insects that attack it. Jones (1943), for example, points out that varieties of wheat have been reported as resistant or tolerant to a t least fifteen
insects besides Hessian fly. Painter (1951) has published an excellent
review of the attempts to breed varieties of wheat resistant to various
insects. Briefly, the principal achievements are the varieties mentioned
above that are resistant to Hessian fly and to the wheat-stem sawfly, and
the discovery more or less incidentally of several sources of resistance,
as mentioned by Jones. Efforts to transfer newly discovered genes for
resistance to commercial varieties will be made a t the first opportunity.
HALF CENTURY OF WHEAT IMPROVEMENT IN UNITED STATES
The experimental data on which most of this paper is based were obtained by
various agencies, principally the various state agricultural experiment stations in
those states in which wheat is an important crop; by the Bureau of Plant Industry,
Soils, and Agricultural Engineering, usually i n cooperation with the state agricultural
experiment stations; by the Bureau of Entomology and Plant Quarantine; and by the
Grain Branch, Production and Marketing Administration, of the United State8 Department of Agriculture. Much of these data have been published and are referred
to in the text. The use of unpublished data is, in general, referred to i n footnotes to
tables or in text. Permission for the use of these data is gratefully acknowledged.
The authors are indebted to various individuals for providing data, and for assistance
in assembling data and in reviewing the manuscript. Among these are E. R. Ausemus, B. B. Bayles, C. C. Fifield, K. F. Finney, J. H. Martin, L. P. Reitz, C. A.
Suneson, and 0. A. Vogel, of the Bureau of Plant Industry, Soils, and Agricultural
Engineering; and numerous staff members of the various state agricultural experiment stations. The authors are also indebted to the Division of Cereal and Forage
Insect Investigations of the Bureau of Entomology and Plant Quarantine for suggestions and criticisms of the section on the Control of Insects of Wheat. Limitations
of space and time have prevented the use of many suggested additions to this paper,
including important contributions relating to soil chemistry and soil physics, genetics
and cytology, plant pathology, plant physiology, and cereal chemistry.
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