CHAPTER XIII 



Insecticides — General Principles 



The use of chemicals for the destruction of insect pests had its origin 

 with the advent of the Colorado potato beetle in our fields, about 1870. 



The beetle first came to notice as a pest of cultivated potatoes in the 

 region between the Mississippi River and the Rocky Mountains. It 

 spread steadily eastward, and in a few years reached the Atlantic 

 coast. It was feared at the time that the growing of potatoes was 

 doomed, and famine was freely predicted. 



Then came the suggestion that the potato tops be dusted or sprayed 

 with Paris green, so as to poison the pest. The remedy was found to 

 work. And thus was started the modern practice of using chemicals 

 for the control of injurious insects. 



To-day a large proportion of our insect pests, more especially those 

 infesting garden truck, fruits, and stored products, are controlled by 

 some form of spraying, or by fumigation. 



The primary rule governing the appHcation of chemicals for the con- 

 trol of an injurious insect is to determine the feeding habits. If the 

 pest is one that eats the foliage or tissues^ in other words, if it has bit- 

 ing mouth parts, it may usually be killed by applying to the plant some 

 form of stomach poison, such as Paris green or lead arsenate. If, on 

 the other hand, the pest sucks the plant juices instead of chewing or 

 eating the tissues, in other words, if it has sucking mouth parts, it is 

 utterly useless to apply any of the stomach poisons to the surface of 

 the plant, for they will not be taken up by the insect. The sucking 

 beak, thrust down through the surface of the leaf, misses the poison. 

 In this class of insects, therefore, the chemicals applied must be such 

 as will Idll the insect by contact with it, usually by entering its breath- 

 ing pores. 



