INSECTS INJURIOUS TO PEACH, PLUM AND CHERRY 593 



are to be found on the plum throughout the summer. In the 

 fall they return to the plum, where the winter eggs are laid. This 

 species is known to occur in Germany, England, Australia, and 



FIG. 521. Mealy plum aphides clustered on leaf. (After Lowe.) 



New Zealand, and seems to be widely distributed over the United 

 States. It occurs here on plum and prune and in Europe is said 

 to infest grape, peach, apricot, and nectarine, according to Lowe. 



The Hop Plant-louse * 



This species is best known as a pest of hops during the summer 

 and rarely does very serious damage to the plum, though often 

 quite abundant on it. The wingless aphids are light green or 

 yellowish green without any noticeable markings. The winged 

 forms have the same body color, with the head, thoracic lobes, 

 and a few dashes on the abdomen, black. The species may be 

 readily distinguished by the prominent tubercle which projects 

 from the head on the inside of the base of each antenna, and a 

 less prominent tubercle on the basal segment of each antenna. 

 According to the studies of Dr. C. V. Riley and his assistants, 

 the third generation in the spring migrates from the plum to 

 hops in late spring and in fall winged viviparous females give 

 birth to a few young which develop into egg-laying females which 



* Phorodon humuli Schrank. Family Aphididce. See C. V. Riley, Report 

 U. S. Dept. Agr., 1888, p. 93; W. T. Clarke, Bulletin 160, Cal. Agr.Exp. Sta. 



