XVIII 

 CONTROL MEASURES 



The thing most needed in the control of insect pests is 

 knowledge of their habits. Without this the means available 

 cannot be intelligently applied. We will discuss the control 

 measures as we have done the injuries. Under separate 

 classes, beginning with the most modern, and now the most 

 used, means: 



Insecticides. These are poisons. They take effect either 

 through the digestive system of the insect or through the 

 respiratory system or through the skin. If through the first, 

 they are food poisons. Otherwise, they are contact insecticides 

 and fumigants. Food poisons are cheapest and easiest to 

 apply and would be preferred, but for a limitation that will 

 be at once understood, if we recall the difference between 

 biting and sucking mouthparts. Biting mouthparts chew 

 the food and take in the poison with it. Sucking mouthparts 

 penetrate to the sap beneath, and so avoid the poison that is 

 sprayed or dusted upon the surface. It is, therefore, the suck- 

 ing insects and those others to whose food the poison cannot 

 be applied that have to be reached through their respiratory 

 system or through their skin. 



1. Food poisons. — These are chiefly arsenicals. Paris 

 green was the first to be used extensively. Nowadays lead 

 arsenate and calcium arsenate are preferred, for they are 

 less liable to "burn" tender foliage. These may be applied 

 either as a spray or as a dust. 



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