28 BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 



/V 



Fig. 4. — Phylloxera ritifoliae: Genealogical graph of the grape phylloxera in the eastern 

 part of North America and in the Mediterranean regions. A, Hibernant radicicole ; 

 B-G, successive radicicole generations : H, winged sexuparous migrant ; I, sexes ; 

 ./, stem-mother gallieole ; K-P, successive gallicole generations, part of the young larva; 

 of which proceed below ground (0) to join the radicicole circle at various stages de- 

 pendent upon the gallicole generation of which they were members ; Z, emergence above 

 ground of the wandering radicicole larva 5 . In this figure, in order to avoid undue con- 

 fusion, no account has been taken of the development in the galls of winged sexuparous 

 migrants. Such development is unusual, but it indicates the possibility of a life cycle 

 entirely aerial. 



