HOMOP TERA 



437 



Certain varieties of American grapes are not seriously injured by the 

 root-form of the Phylloxera. By growing these varieties, or by using 

 the roots of them as stocks on which to graft the susceptible European 

 varieties, the danger of injur^^ by this pest is greatl}' reduced. 



Fig. 509. 

 besii. 



-Aleurochiton for- 



Family ALEYRODID^ 

 The Aleyrodids or White Flies 



The members of this family are small or minute insects ; our more 



common species have a wing-expanse of about 3 mm. In the adult 



state both sexes have four wings, differing in this respect from the 



Coccidag, with which they were classed by the early entomologists. 



The wings are transparent, white, clouded or mottled with spots or 



bands. The wings, 



and the body as well, 



are covered with a 



whitish powder. It is 



this character that 



suggested the name of 



the typical genus,* 



and the common name 



white flies. 



In the immature 



stages, these insects Fig- 508. — Analeyrodid 



are scale-like in form 



and often resemble somewhat certain species of the genus Lecanium 



of the family Coccidas. Except during the first stadium, the larvae 



remain quiescent upon the 

 leaves of the infested plant 

 and in most species are sur- 

 rounded or covered by a 

 waxy excretion. In Figure 

 508 there is represented one 

 of the many forms of this 

 excretion. Here it consists 

 of parallel fibers, which ra- 

 diate from the margin of the 

 body, and its white color 

 contrasts strongly with the 

 dark color of the insect. In 

 some species the fringe of 

 excretion is wanting; and 

 in others, the excretion from 

 the margin of the body, in- 

 stead of extending laterally 

 and forming a fringe, is di- 

 rected toward the leaf upon 

 which the insect rests, and 



Fig. 510. — Wings of Udamoselis. (After En- 

 derlein, with changed lettering.) 



*Aleyrodes (a\evpd)8r]s), like flour. 



