h\SECTS INJURIOUS TO FRUITS. 77 



on their food. The great problem in dealing with this class is 

 to find something which will hold the poison on th-e leaves for 

 a reasonable length of time and will at the same time prevent 

 the arsenical poisons from burning the leaves. This is particu- 

 larly true of plants belonging to the plum family, including 

 plums, peaches and apricots, which are easily injured by ar- 

 senious acid even when present in such small quantities that it 

 would not be injurious to the foliage of apple, pear, currant or 

 gooseberry. This burning is especially bad when its application 

 is followed by several days of bright, dry weather. Another 

 Important problem which we have not solved Is how to apply 

 these poisons so that they will not wash off from the leaves. 

 Among the insecticides commonly used for this class of insects 

 are Paris Green, arsenate of lead and hellebore. Some of the 

 chewing insects may be destroyed by the acrid or oily applica- 

 tions which are commonly used for the destruction of sucking 

 insects, such as tobacco water and kerosene emulsion. 



Insects that work in the wood of the tree belong to the class 

 of chewing insects. These vary in their habits and nearly as 

 various are the remedies used against them; each must be con- 

 sidered in the light of its life history. When borers are in 

 their holes and can be reached easily by gas fumes, perhaps as 

 satisfactory a remedy as any is to squirt a small amount of 

 carbon bisulfide into their holes with a common oil dropper 

 and stop up the holes with a little putty. In the cas-e of borers 

 that tunnel just under the bark, the location of which can be 

 seen by the discoloration of the surface bark (as with the borer 

 of the peach), the best remedy is probably to look over the 

 trees in the early spring and again in the late summer and dig 

 them out with a sharp knife. 



Sucking Insects. — Examples of this class of insects are plant 

 lice, scale insects and chinch bugs. These do not chew, but 

 their food is the juice of plants. They obtain it by sucking. 

 As they do not bite they cannot be destroyed by internal poisons, 

 such as arsenic and hellebore, but they must be r-eached by 

 something that will affect their respiratory organs. All such in- 

 sects breathe through small pores in their sides and may be de- 

 stroyed by a covering of a film of oil or soap (whale-oil soap 



