INSECTS 



259 



live on other crops. Therefore, it may be easily controlled 

 by rotating crops. 



Few insects cause so much loss in America as the chinch 

 bug. It is most harmful in wheat fields, but often migrates 

 from the wheat to corn and other crops and there continues 

 its ravages. There are no satisfactory remedies except 

 rotation of crops. 



We can never hope to exterminate any insect. The 

 best we can hope for is to limit the numbers so that 

 serious damage will be prevented. 



235. Chewing and Sucking Insects. 

 Orchards, potatoes and many vege- 

 tables are now commonly sprayed for 

 the control of insects. There are two 

 general classes of insects so far as 

 spraying is concerned: those that 

 chew their food and those that suck 

 the juices of the plant. Potato beetles 

 and cabbage worms eat the foliage. 

 All that is necessary in order to kill 

 them is to put some poison, such as 

 Paris green, on the leaves. The San 

 Jos6 scale, chinch bug, and plant lice 

 suck the juices of the plant. They 

 cannot eat poison. To try to poison 

 them would be like trying to poison a 

 mosquito by placing poison on the hand. A mosquito 

 would merely insert his bill and eat to his satisfaction 

 without getting any of the poison. In order to kill these, 

 it is necessary to spray with a contact insecticide one 

 that kills when it gets on their bodies. 



Fie. 140. 



Almost too late to spray 

 for codling moth 



