HOMOPTERA 



425 



beaks, they feed, and the oviparous female lays more than one egg. 

 In this subfamily great specialization of wax-producing organs occurs. 

 In many species some of the agamic generations become greatly modi- 

 fied in form so that they do not resemble the more typical aphids. 

 In some species these modified forms have the appearance of an 

 Aleyrodes; in other species, that of a coccid. 



Our best-known representatives of this subfamily are two species 

 of gall-makers, each of which infests alternately witch-hazel and 

 birch. The life-histories of these were ver\' carefullv worked out bv 



Fig. 495. — The witch-hazel cone-gall: a, natural size; b, section of gall, enlarged. 

 (From Pergande.) 



Pergande ('01); the followini:: accounts are greatly condensed from 

 that author. 



The witch-hazel cone-gall aphid, Hormaphis hamamelidis. — The 

 winter-egg is deposited on the branches and twigs of witch-hazel 

 and hatches early in the spring. The stem -mother, which hatches 

 from this egg, attacks the lower surface of the leaf, causing the growth 

 of a conical gall on the upper surface of the leaf with a mouth on 

 the lower surface (Fig. 495). The second generation, the offspring 

 of the stem-mother, consists of many individuals; these are pro- 

 duced within the gall, which becomes crowded with them. These 

 are agamic females, which become winged, leave the gall, and mi- 

 grate to birches, where they deposit their young on the lower side 

 of the leaves. The first instar of the third generation, the offspring 

 of the migrants, is broadly oval, with the entire margin of the body 



