INSECT ENEMIES — PACKAKD 325 



measures discovered by research, not only for one year but for many 

 years, the returns become continuous and enormous as compared 

 with the original cost of finding and perfecting them. 



MODES OF INSECT ATTACK 



Like human armies, insects attack in a variety of ways. There are 

 the aviators, the ground troops, the subs (though subterranean lather 

 than submarine), and the borers from within, all in most efficient 

 combination. What they lack in size is more than made up in num- 

 bers. They attack our cereal crop plants underground, bore within 

 them or eat the leaves or grain during part of their lives, and then 

 become aviators for purposes of infiltration and advance. White 

 grubs, wireworms, and rootworms gnaw the roots of grain crops, 

 change to actively flying beetles in their adult stages, efficiently select 

 favorable locations for the next attack by their underground progeny, 

 and plant time bombs in the form of eggs which hatch into most 

 effective sapper battalions. The adult moths of corn ear worms, corn 

 borers, and army worms; the adults of the hessian fly, jointworm, 

 and sawflies ; and the winged adults of chinch bugs, and grasshoppers, 

 fly from field to field — some of them for much longer distances — and 

 locate their ground troops of borers and scorched-earth specialists in 

 the most advantageous positions for crop destruction. 



In their ability to change from one form to another, and to live off 

 the country, the insect enemies of our cereal crops are in some ways 

 more efficient than we or our human enemies. This ability greatly 

 complicates the problem of fighting them, since only in certain 

 stages of their insidious, versatile, and persistent attack can they be 

 fought successfully. Furthermore, the methods of defense usable 

 against them are limited by the low value per acre of these crops. 

 Even though in the aggregate the cereal crops are by far the most 

 essential and valuable of our farm products the returns per acre to 

 the individual grower are in general comparativelj'' small and he 

 cannot afford expensive measures for control of the insects attacking 

 them. 



JVIETHODS OF REPELLING INSECT ATTACKS 



Painful experience and painstaking study have, however, shown 

 many ways of overcoming these pests. Fortunately for us, each 

 species always follows about the same tactics and usually there are one 

 or more vulnerable points in the course of their activities at which 

 they can be attacked successfully. In some instances no highly ef- 

 fective and practical means of overcoming them have yet been found, 

 and in others a combination of several control measures is necessary 

 in order to subdue them. Obviously, the first essential in the control 

 of an insect is a thorough knowledge of its life history and habits in 



