programs but do not possess enough desirable characters to be acceptable 
for commercial production. 
Most of the progress with insect resistance in economic plants has been 
made in field crops, principally alfalfa, corn, wheat, barley, sorghum, and 
sugarcane. 
The control of the hessian fly by the use of resistant varieties has been 
especially successful. Seventeen hessian-fly resistant wheats are now being 
grown on 45 million acres in 26 States. Previous to the availability of these 
resistant varieties, the only method for controlling the fly in winter wheats 
was delayed seeding, a method that was effective only for control of the fall 
generation. Farmers can now plant fly-resistant wheat earlier, get fall and 
winter pasture for livestock, and avoid hessian fly damage the following 
spring. 
Five varieties of alfalfa resistant to the spotted alfalfa aphid have been 
released to farmers in the infested area and the total acreage of these 
varieties is increasing each year. Control of the aphid with insecticides is 
seldom, if ever, required in fields where resistant varieties are grown. In 
Arizona, over a 3-year period, damage to alfalfa foliage by the spotted 
alfalfa aphid was 15 to 22 times greater on susceptible than on resistant 
varieties. 
The development of corn-earworm-resistant cornhas been encouraging. 
In the South the percentage of kernels damaged by corn earworm in Dixie 18, 
a hybrid dent corn, has been only about 1/6 that of susceptible hybrids. Due 
to the development of corn-earworm resistance in sweet corn, some of 
today's hybrids have only 10 tol5injuredkernels per ear as contrasted with 
22to25for susceptible hybrids grown afew years ago. These corn-earworm 
resistant hybrids require less insecticide application to obtain 100 percent 
worm-free ears than susceptible hybrids. 
Potato varieties have been reported resistant to at least 14 species of 
insects, including leafhoppers, Colorado potato beetle, and the tuber flea 
beetle. 
Effect of Resistant Crop Varieties on Insect Populations 
Varieties on which insects feed may exert a profound influence on 
insect's fecundity. For example, the spotted alfalfa aphid produces about 
30 offspring per week on a susceptible variety, whereas on resistant plants 
the aphid produces only 4 or 5. 
The most striking examples of the effect of resistant varieties on insect 
populations over wide areas resulted from releases of hessian fly resistant 
wheats in California and Kansas. From 1942 to 1944 two soft white wheats, 
Big Club 43 and Poso 42, both resistant tc hessian fly, were released in 
areas in California where plant injury by the fly was serious. Asa result, 
infestation levels of 50 to 100 percent, which had occurred annually from 
1920 to 1944, were reduced by 1946 so that the insect was no longer a 
problem. A similar situation occurred in central Kansas where the variety 
Pawnee, moderately resistant to the hessian fly, was released in 1943, This 
variety soon became the predominant wheat grown in central and eastern 
Kansas, and from 1948to 1962 there was no serious infestation of the hessian 
fly in that area. 
The effect of resistant hybrids in reducing the number of surviving 
European corn borers has been reported frequently. Federal and State 
workers in Iowa found that resistant hybrids commonly have 50 to 60 percent 
less borer survival than susceptible ones. 
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