CHAPTER XVII 

 INSECTS 



The relation of farm practice to insect control. It is a 

 well recognized principle of field-crop pest control that there 

 is a definite relation between farm practice and insect control, 

 and that in many cases good farm practices alone are sufficient 

 to overcome insect troubles. A recognition of the importance 

 of insects, and a knowledge of their habits and life history 

 and of certain relations existing between insects and their 

 plant hosts will enable the farmer to plan intelligently his 

 farm practices so as to reduce his insect problems to a 

 minimum. 



Insects both useful and harmful. Not all insects are 

 harmful. For instance, the bumble bee is essential to the 

 profitable production, of red clover seed and other insects 

 are similarly useful in pollenizing certain plants. Other 

 insects, such as the honey bee and the silkworm, are useful 

 because of some product they make. Others are beneficial 

 because of their destruction of insects that are harmful. The 

 lady beetle, syrphus fly, lace wing fly, and many kinds of 

 parasitic insects are examples of this group of insects. But 

 there are many kinds of insects which are injurious because 

 they interfere with crop production. 



Extent of harmful insects. A little observation during 

 the growing season will lead to the conclusion that there 

 are more kinds of harmful insects than useful ones. Each 

 kind of plant will be found to be subject to injury by some 

 kind of an insect, and many plants by many kinds. Among 

 the plants, for example, which have special insect pests are 



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