HOMOPTERA 



439 



from the caudal end of the body. The excrement is in the form of 

 honey-dew, of which much is excreted. 



Formerly all the members of this family were included in a single 

 genus, Aleyrodes; consequently, except in comparatively recent works, 

 the various species are described under this generic name. In later 

 days, very extended studies have been made of the family ; and the 



Fig. 511. — AsterocUton vaporariorum: a, egg; b, larva, first instar; c, puparium, 

 dorsal view; d, puparium, lateral view; e, adult. (After Morrill.) 



genus Aleyrodes has been divided into many genera, which are now 

 grouped into three subfamilies. The most complete systematic works 

 on the family are those of Quaintance and Baker ('13 and '17). The 

 following species are among our more common representatives of the 

 family. 



The greenhouse white fly, Asterochiton vaporariorum. — One of 

 the most important of the greenhouse pests is this insect, which infests 

 very many species of plants that are grown under glass ; and some- 

 times it is a serious pest in the open on tomato and other plants that 

 are set out after the weather is warm. 



The adult measures about 1.5 mm. in length, and like other 

 aleyrodids is covered with a white, waxy powder. The eggs are only 

 .2 mm. in length, and are suspended from the leaf by a short stalk 

 (Fig. 511, a). In the first instar the larva is flat, oval in outline, 

 and with each margin of the body furnished with eighteen spines 

 (Fig. 511, b), of which the last is much the longest. In the second 

 and third instars there are only three pairs of marginal spines, a very 

 small pair near the cephalic end of the body and two somewhat 

 larger ones near the caudal end. The marginal fringe of wax is 



