/ 



642 NEW YORK STATE MUSEUM 



plete their growth within 16 to 20 days. They emerge from the galls and 

 migrate to birches toward the end of May or early in June. The various 

 forms of this generation are shown at figure 173. These plant lice live on 

 the underside of birch leaves, sometimes covering them. Their young are 

 met with in the vicinity of Washington early in June, attaining maturity in 

 about 14 days. This generation has a characteristic appearance in its 

 fourth stage, as shown in figure 174. It is remarkable because of its almost 

 perfect mimicry of certain Aleurodids. The insects are first pale brownish, 

 changing gradually to a dusky or black color. The fourth and fifth gen- 

 erations are essentially identical with the third, the last named attaining 



Fig. 175 Hormaphis hamamelidis, 6th generation, second stage : *i=dorsal view ; 

 £=dorsal view denuded, showing arrangement of pores, much enlarged. (After Per- 

 gande, U. S. Dep't Agric. Div. Ent. Tech. Ser. 9, 1901) 



maturity about the middle of August. It gives birth to a sixth generation 

 which presents an entirely different form, as shown at figure 175. 



The young are yellowish brown at first, naked, but soon become covered 

 with a pruinose or bluish white secretion, giving them a moldy appearance. 

 Later the bristly white iridescent waxy threads develop. This generation 

 acquires wings, feeds for a time and then forsakes the birch, migrating back 

 to the witch-hazel, where the sexual generation is developed. This latter 

 sometimes becomes exceedingly abundant. The general characters of this 

 generation are well illustrated at figure 176. Each female produces from 



