274 



INSECTS INJURIOUS TO STAPLE CROPS. 



million before the period of blooming or burning; so that 

 the issue from a single stem-mother may, under favoring 

 circumstances, blight hundreds of acres in the course of 

 two or three months. " * 



Daring September a brood of winged females are pro- 

 duced which fly back to the plum-trees and in the course 



Fig. 157. — The Hop Plaut-louse, third generation on plum— the 

 generation which flies to the hop — enlarged; head below at right 

 — still more enlarged. (After Riley, U. S. Dept. Agr.) 



of a few days give birth to three or more young. These 

 never become winged, but are the true sexual females 

 which lay the winter eggs. The true winged males are 

 developed during the latter part of the season and may be 

 found pairing with the wingless females at that time, these 

 being the only males during the year. 



Remedies. — From a knowledge of the above-described 

 life-history several methods of treatment have been 

 secured. By spraying plum-trees neighboring the hop- 



* Rfley, "The Hop-louse," " Insect Life," Vol. I, p. 135. 



