374 ECONOMIC ENTOMOLOGY 



2. Food Supply. — An important regulator of insect life (see Part I). 



3. Parasites. — Protozoa, bacteria, fungi and insects. 



4. Predatory Animals. — Birds, insects, snakes, toads, annelids, etc. 



5. Cultural or Preventive Methods (see below). 



6. Artificial or Remedial Methods (see below). 



The first four factors are, however, almost wholly beyond man's 

 control. 



Methods of Control 



The main practical methods of control of injurious insects may, 

 therefore, be grouped into two general classes : (a) Cultural or Preventive 

 Methods — those practices of culture or of handling the crop that 

 prevent, or interfere with, the development of injurious insects; and 

 (b) Artificial or Remedial Methods — those which deal with injurious 

 insects when they appear by the us^ of poisonous or contact substances, 

 or other artificial means. 



A. CULTURAL OR PREVENTIVE METHODS 



For most farm crops Cultural Methods are the only practicable 

 methods. They are essentially Preventives. The most important 

 cultural methods are the following: 



I. Rotation of Crops. — The growing of crops year after year on 

 the same land permits many insects which feed on the roots to develop 

 and multiply. On the other hand, a good crop rotation makes it 

 impossible, or very difficult, for an insect to pass through its life stages 

 without being seriously disturbed and its food supply destroyed. 



(a) Some rotations are preferable to others when wireworms and 

 white grubs are abundant. For example, where corn is the chief ' 

 crop a rotation of clover, corn, oats is better than forage grasses, 

 corn, oats. Professor Forbes, of Illinois, advises plowing the grass 

 in early fall, and sowing clover either with barley, wheat, or rye. 

 The clover is allowed to stand 2 years and is followed by corn or 

 roots. As certain crops such as clover, barley, wheat and rye are not so 

 liable to attack as corn, potatoes, mangels and oats they are better 

 adapted to follow sod. 



(b) Moreover, if sod infested with white grubs is broken up early, 

 sown to turnips or rape, and pastured with hogs in late summer and 



