INSECTS INJURIOUS TO THE GRAPE 



495 



frequently completely studding the leaves with galls." In 

 California the young hatching from the winter eggs go directly 

 to the roots where they give rise tp new colonies, there being no 

 gall forms, according to Quayle. Where the leaf-gall females 

 occur many of them probably migrate to the roots during the 

 summer, and all do so with the approach of cold weather. In the 

 spring the roots are attacked and a series of generations of wingless 

 females multiply on them. As there are five to seven generations 

 in a season and each female lays from 30 (Quayle) to 100 (Marlatt) 

 eggs, i f is evident that they will soon be numerous enough to 

 destroy the vine. The root-inhabiting females are very similar 





Fiu. 356, Grapevine phylloxera: a, root galls; b, enlargement of same 

 showing disposition of lice; c, root-gall louse much enlarged. (After 

 Marlatt, U. S. Dept. Agr.) 



to those in the leaf -galls, and are about .one-twenty-fifth inch long 

 when mature and half as long when young and active. They are 

 light greenish-yellow in summer and darker in winter, and when 

 numerous the infested roots look as if dusted in spots with pow- 

 dered mustard, according to Quayle. He states that " the newly 

 hatched insect is fairly active, and at first moves from place to 

 place on the roots, but finally, when it reaches the egg-laying 

 stage, inserts its sucking-tube into the root and remains fixed." 

 During the late summer and early fall some of the root-lice develop 

 into winged females which escape through cracks in the soil and 



