While some resistant varieties cause a reduction in the rate of repro- 
duction of the insect, other varieties are resistant because they can withstand 
or tolerate a heavy insect infestation without serious permanent injury. The 
general vigor of the plant at the time of insect attack may affect the amount 
of injury. Strong healthy plants growing in fertile soil are frequently most 
subject to infestation by insects. The European corn borer, for example, 
usually chooses the most vigorous plants on which to deposit eggs. Some 
varieties are able to recover from injury more rapidly than others. For 
example, some corn hybrids are capable of producing new roots rapidly 
when the corn rootworm feeds on the older roots. 
Because of widespread development of insect resistance toinsecticides, 
entomologists and plant breeders have been concerned about the permanency 
of insect resistance in crop varieties. Scientists have found biological races 
of hessian fly which are able to develop on wheat varieties resistant to the 
predominant race found under field conditions. However, in spite of this 
situation, Pawnee, a variety resistant to the hessian fly, has maintained a 
satisfactory degree of resistance for more than 20 years. Atlas, a variety 
of sorghum resistant to the chinch bug, has remained resistant to this insect 
since release in 1928, Even though instances of biological races of insects 
capable of infesting formerly resistance crops have so far been rare, 
entomologists and plant breeders are attempting to develop crop varieties 
that are resistant to all races and to more than one species of insect. 
LOOKING AHEAD 
Until alternate methods of insect control are developed we must con- 
tinue to use insecticides to produce the quantity and quality of foods and 
fibers we enjoy today. However, research is taking new directions which 
may progressively open up alternative methods of insect pest control and 
reduce our dependence on such insecticides. 
The use of insect parasites and predators has in many instances been 
very much worthwhile. In most cases, however, the natural enemies of 
insect pests under natural conditions do not provide adequate control. 
Entomologists face these realities and attempt to create conditions more 
favorable for the parasites and predators or by mass producing and releas- 
ing them to prevent buildup of the host insect. 
The use of insect diseases offers another promising way to obtain 
insect control, Like parasites and predators, the disease organisms often 
fail to achieve the desired degree of control under natural conditions. 
ARS is currently constructing a laboratory at Columbia, Mo., that will 
be devoted to basic research on the use of insect parasites, predators, and 
diseases for the biological control of insects. The work will include genetic 
studies of parasites and predators, factors that affect host preferences, the 
nutritional requirements of parasites and predators, research on insect 
diseases, and ways to integrate biological and chemical insect control 
programs. 
The sterility approach to insect control holds great promise as a new 
way to control insects, either by the rearing and release of sterile insects 
or by the developing of ways to sterilize insects in the natural population. 
Research in these areas is progressing at an encouraging rate. 
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