APHIDS INJURIOUS TO ORCHARD FRUITS. 21 



of the leaves or on the very tender twigs. Practically all the injury 

 clone to the trees is by the spring forms, the fall migrants being 

 scattered. 



SEASONAL HISTORY. 



The eggs of this species are laid upon the plum, as are those of the 

 rusty plum aphis. In the early spring the stem-mother hatches and 

 gives birth to living j^oung. Winged forms begin to appear as early 

 as the second generationvand continue to be produced until midsummer. 

 These migrate to thistles, where they produce the first of the sum- 

 mer forms. After having produced numerous generations on the 

 thistle during the summer, fall migrants are produced which return 

 to the plum trees to deposit the young egg-laying females. These, 

 after being fertilized by the males, lay the winter eggs. 



THE WATER-LILY APHIS.^ 



Plum trees are sometimes thickly infested by an aphid with swol- 

 len honey tubes, the Avater-lily aphis. The insects are brownish, the 

 winged forms having a black head and body. 



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 on water plants are 

 \ ery 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 w^ater 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.2 



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. 



^ Siphocoryne nympliaeae (L.). - Phorodon humuli (Schrant. 



78569°— Bull. 804—17 4 



