18 Farmers’ Bulletin 1128. 
The spring forms feed upon the underside of the leaves or on the 
tender twigs of the plums, but they do not curl the leaves to any ex- 
tent. The summer feeding habits of the species vn water plants are 
very interesting, as colonies often are partially submerged for some 
time without apparent injury. 
SEASONAL HISTORY. 
The stem-mothers of this species hatch early in the spring upon 
the plum, and soon the young produced cover the lower side of the 
leaves and the twigs. Winged forms are found during June and 
these fly to various water plants, on which they reproduce and live 
during the summer months. In the fall the migrants return to the 
plum and produce the egg-laying females, which, when adult, are 
fertilized by the winged males. The flight of the fall migrants and 
males extends over a long period, the males having been found on the 
plum trees from early until late fall. 
THE HOP APHIS.' 
A large green aphid, the hop aphis, is in some regions very common 
upon plums in the spring. The wingless forms are light green and 
the winged forms are light green with black head and body and a 
patch of the same color on the abdomen. 
The stem-mothers of this species feed upon both the flower buds 
and the leaf buds of the plum. After the leaves have expanded, the 
insects attack the underside of the leaves and often may be found 
thickly crowded thereon. 
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 occuring late in October or in November. 
These fertilize the egg-laying females, which then lay their eggs 
upon the twigs. 
In some cases the species 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. 
1Phorodon humuli (Schrank). 
