TREE INSECTS AND THEIR CONTROL 187 



The sap-sucking type, however, cannot be reached by 

 poisons, so they must be killed by contact insecticides; 

 therefore, they have to be destroyed by materials applied 

 after they have begun operations, and every insect must 

 be touched by the appropriate insecticide for it to be 

 effectual. 



For the leaf-chewers and sap-suckers wholesale de- 

 struction is possible, because their destructive work is in 

 the open, on the outside of bark or foliage. 



For borers and others, which conduct their operations 

 within the wood or underground, the measures of elimi- 

 nation are aimed at the individual insect, by means of 

 digging it out or by killing by the use of a wire probe 

 or injection of carbon bisulphide. 



A point to be remembered in applying remedies by 

 spraying is that the application must be thorough. 

 Thoroughness means completely covering the leaves, in 

 order to make certain that all the insects will be reached 

 by the poison placed on their food, or killing the body of 

 each insect by smothering with a contact insecticide. 



Effectual remedial measures require knowledge of the 

 habits of the type of insect to be controlled. This knowl- 

 edge should at least include the ability to distinguish 

 between the leaf-chewers, the sap-suckers and the borers, 

 in order to determine the steps that must be taken. In 

 compiling the suggestions for treatment, which appear in 

 subsequent pages of this chapter, an effort has been made 

 to give data which will enable the layman to identify and 

 classify the insects that may appear on his trees. 



Spraying materials may be bought at seed stores and 

 other places. For small operations it is best, with most of 

 them, to use the commercial preparations rather than to 

 undertake to prepare them at home. In buying them, the 

 highest quality should always be insisted upon. The 



