148 INSECTS AFFECTING SHADE TREES. 



American species of the genus are known. The 

 Willow-grove Aphis (M. salicti) is probably the com- 

 monest in the eastern and middle states. It is very 

 similar in appearance and habits to the nearly re- 

 lated Spotted Willow-twig Aphis, represented at Figs. 

 74 to 76. This insect lives over in the egg state on 

 the bark of willow twigs. Early in spring the eggs 

 hatch into young plant-lice which insert their tiny 

 beaks into the tender bark and suck out the sap. 

 They grow rapidly, and each one soon becomes the 



Fig. 75. Spotted Aphis: winged male. Magnified. 



mother of several young aphides. The generation 

 from the egg are all wingless, but those of the second 

 generation probably develop into botli winged and 

 wingless forms, which are also viviparous. Succes- 

 sive broods continue to appear throughout the entire 

 summer, all being viviparous, and some having 

 wings while others lane none. By midsummer they 

 have often increased so enormously as to cover all 

 the twigs of infested trees, making them appear 



