CHAPTER II 



PREVENTION BY FARMING METHODS 



Having shown in a general manner what is desirable for the 

 best understanding of the subject under consideration, it is next 

 in order to point out how this knowledge may be utilized in the 

 prevention or mitigation of injury. 



A knowledge of the origin and distribution of insects enables 

 us to judge of the probable and ultimate spread of introductions 

 from abroad and from one portion of our country to another. 

 Thus we can predict, with a considerable degree of certainty, 

 that certain species will not be injurious beyond certain bound- 

 aries, and that others will widen their range beyond known 

 limits. Knowing the effects of atmospheric conditions, of heat 

 and cold, dryness and humidity upon insect reproduction, we can 

 be forewarned of injury and can plan accordingly. Experience 

 having taught that the clearing of uncultivated or neglected land 

 is almost certain to be followed by depredations of insects which 

 had inhabited the wild plants and weeds, we are enabled to 

 plant such crops as will be least affected by these insects. 

 Knowing what insects are controlled by predaceous, parasitic and 

 other enemies, such as beneficial insects, contagious diseases, 

 wild and domestic animals, we can in many cases, untilize these 

 natural agencies in our warfare against them. 



Most of the different farming methods which Aill be con- 

 sidered are of use in combatting insect enemies of cereals; in 

 short, without their employment it is impossible to avoid losses 

 from these insects, as it is seldom practicable to use insecticides 

 on growing grain. The usefulness of many of these methods 

 is due to the slow spread of many species except at more or 

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