APHIDS INJURIOUS TO ORCHARD FRUITS. 



33 



THE GRAPEVINE APHIS. 



The grapevine aphis is very numerous in some localities, infesting 

 the tender shoots and leaves (fig. 24) and sometimes the fruit clusters, 

 causing the berries to drop. 

 It can be distinguished easily 

 from any other forms occur- 

 ring upon grape by its large 

 size and its dark-brown color. 



SEASONAL HISTORY. 



The eggs of this species are 

 laid upon the twigs of the black 

 haw {Viburnum 'prunif ol'mm) . 

 Very early in the spring they 

 begin hatching, but these first 

 stem-mothers may be killed by 

 frost. Six or eight weeks later 

 the aphids of the second genera- 

 tion mature, and these nearly 

 all become winged. These mi- 

 grants fly to the grape and pro- 

 duce 3^oung upon the tender 

 growing shoots, where in less 

 than 10 days they are mature 

 and producing young. Repro- 

 duction on the grape continues 

 throughout the summer, and 

 often more than a dozen gen- 

 erations may occur. In each 

 generation winged forms are 

 found, and these carry the in- 

 festation to new Amines. Dur- 

 ing October fall migrants are 

 produced, which return to the 

 haw trees and deposit the egg- 

 laying females. ^Mien mature 

 these are fertilized by the 

 winged males which follow the fall migrants, and egg laying follows 



Fig. 24. — The grapevine aphis (Macrosiphum 

 iUiiioiciisis) : Colony on grape shoot. (Orig- 

 inal.) 



NATURAL ENEMIES OF APHIDS. 



Aphids are attacked by various species of parasitic and predacious 

 insects and by fungous diseases, and these agencies exert a verv im- 



Macrosiphum ilUnoiensis (Shimer). 



