Plant-Lice 



during each season a generation of winged females, thus provid- 

 ing for the dispersal of the species and not only for the dispersal 

 of the species but for the return to a perennial plant in the 



autumn from the weeds, 

 grasses and other annual 

 plants upon which the 

 summer generations may 

 have fed. 



Plant-lice are attacked 

 by a host of natural ene- 

 mies. The little Braconid 

 parasites of the subfamily 

 Aphidiinae are practically 

 exclusively parasites of 

 the plant-lice. Their eggs 



Fig. 160. Phylloxera vastatrix: root form. 

 (After Marlatt.) 



are laid in the body of the 

 louse, the young live 

 within the body until they reach full growth, and the little four- 

 winged parasite eventually emerges as an adult. Plant-lice 



Fig. 161. Phylloxera vastatiix : leaf-gall form. (After Marlatt.) 



parasitized in this way become swollen and dark in color and 

 can readily be distinguished. These parasites themselves breed 

 with extraordinary rapidity and are frequently responsible for the 



264 



