PLANTS AND ANIMAL PARASITES 



167 



in suspension in the water with which they are diluted, 

 and unless there is some means of keeping the water 

 in motion they settle to the bottom of the container, 

 making even distribution and efficient work im- 

 possible. Spray pumps should therefore be fitted 

 with an agitator to keep the spray materials in 

 suspension. 



305. The use of insecticides. — In treating any given 

 insect, the most important question to decide is the 



Fig. 74. — Disk nozzle (left) and Bordeaux nozzle (right) . 



manner in which it appropriates its food, as upon this 

 will depend the preventive measures to be used. 



306. Classes of insects. — Injurious insects are refer- 

 able to two classes, viz., eating insects, i.e., those feeding 

 directly upon the plant tissues, such as the potato bee- 

 tle, the apple-tree borers (the round-headed apple-tree 

 borer is Saperda Candida; the Hat-headed apple-tree 

 borer is Chrysohothris femorata), the plum curculio (Cono- 

 trachelus ne7iupJiar) and the sucking insects, i.e., those 

 feeding only upon the juices of the plant, such as plant- 



