30 



BULLETIN 903, U. S. DEPARTMENT OF AGRICULTURE. 



The part of the life cycle from the sexes to the gallicoles through 

 the winter egg and fundatrix is either omitted or does not proceed 

 beyond the winter egg in California, notwithstanding the frequent 



Fig. 5. — Phylloxera vitifoUae: Genealogical graph of tho grape phylloxera in California. 

 A, hibernant radicicole ; B-G, successive radicicole generations ; H, winged sexuparous 

 migrant ; J, sexes ; Z, emergence above ground of the wandering radicicole larva. 



abundance of resistant types of vines, types many of which normally 

 bear galls in other localities. The result is that the California cycle 

 (fig. 5) is purely parthenogenetic and is therefore greatly modified 

 from the original cycle (fig. 1) occurring on wild vines, the natural 

 hosts of the insect. 



