22 FARMERS BULLETIN 804. 



SEASONAL HISTORY. 



The eggs hatch on the plum twigs considerably later as a rule 

 than those of the thistle aphis. The young stem-mothers soon de- 

 velop and begin the production of young. Winged forms soon 

 appear, the greater number of these occurring in the third generation. 

 These winged forms fly to hop vines, where they produce young that 

 feed upon the hop plant. Eight or more generations of these sum- 

 mer forms are produced upon the hop, and winged fall migrants are 

 then produced, which return to the plum trees to produce the sexual 

 females. Males appear during the fall for a period of several weeks, 

 the last ones usually occurring late in October or in November. 

 These fertilize the egg-laying females, which then lay their eggs 

 upon the twigs. 



In some cases the sj^ecies is able to complete its life cycle on the 

 hop and does not necessarily alternate with the plum, whereas in 

 other cases it remains all summer upon the plums. 



THE MEALY PLUM APHIS.' 



The mealy plum aphis is a common form on plum trees and it can 

 be distinguished from the other species attacking ])lum foliage by 

 its uniform green color and the fine, white, powdery covering of 

 the body. The honey tubes also differ in that they are very short. 



These insects feed upon the underside of the leaA'es, often being- 

 very closely packed together. (Fig. 16.) As a rule they do not 

 curl the leaves, even when present in great ninnbers. 



SEASONAL HISTORY. 



The stem-mothers of this species hatch from the winter eggs on 

 the plum early in the spring and in about 10 days they are mature. 

 They then give birth to young, and these when grown produce others 

 until the leaves are often thickly covered with the insects. "Winged 

 forms develop toward late spring and continue to appear until late 

 midsummer or later. These winged forms migrate to certain grasses 

 and produce numerous generations during tlie summer. In the fall 

 return migrants are produced, which give birth to the egg-laying 

 forms on the plums. These migrants first appear in early Septem- 

 ber, but continue to arrive until late October or early November. 



CHERRY APHIDS. 



THE BLACK CHERRY APHIS-^^ 



The black cherry aphis is an abundant species almost everywhere 

 upon cherry trees. The wingless insects have a rounded abdomen, 

 which gives them a more or less globular appearance. Both wing- 



^ Hyalopterus arundinis (Fab.). ^ Myzus cerasi (Fab.). 



