CHAPTER NIII 
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 application 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 kill the insect by contact with it, usually by entering its breath- 
ing pores. 
63 
