464 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



European varieties of grapes, and probably does not occur at 

 all in California. Most of the young which hatch from the 

 winter eggs crawl down to the roots, where their feeding causes 

 small cancerous swellings or galls. Generation after genera- 

 tion of wingless individuals may be produced on the roots with- 

 out any winged or sexual forms appearing, so that the whole 

 root system may soon become badly infested. As the at- 



FIG. 2 20. The grape phylloxera, Phylloxera vastatrix. In the upper 

 left-hand corner an egg from which a male has issued, next an egg from 

 which a female has issued; in upper right-hand corner, winter egg; at left- 

 hand of middle row, a just-hatched young, next a male (note absence of 

 mouth-parts); at right end of middle row, female; lower figure, winged 

 form. (Much enlarged; after Ritter and Riibsaamen.) 



tacked roots soon decay, the vitality of the vine is seriously 

 affected and it usually dies within a short time. Sometimes, 

 during the summer, a winged generation of females may appear. 

 These make their way to the surface, fly to other plants and lay 

 eggs there of two sizes. The smaller of these eggs produce the 

 males and the larger the females of the sexual generation that 

 lays the winter eggs. 



