n8 



THE STUDY OF INSECTS 



Family Phylloxerid^ 

 The Adelgids and the Phylloxerids 



In this family both the sexually perfect females and the partheno- 

 genetic forms lay eggs. Moreover, the cornicles are wanting and the 

 venation of the wings differs from that of the true aphids. 



Some members of this family live on conifers and cause galls on them. 

 One species, Adelges abietis, lives on the Norway spruce and causes 

 pineapple-shaped galls sometimes all over the tree (Fig. 196). 



Fig. 



abietis. 



196. — Gall of Adelges 



Fig. 197. — Phylloxera, root-inhabiting form: a, roots of 

 Clinton vine showing the swellings; b, nymph as it appears 

 when hibernating; c, d, antenna and leg of same; e,f, g, forms 

 of more mature lice. (From Riley.) 



The most notorious and serious pest of this family is the grape 

 phylloxera, Phylloxera vitifolice, which is a native insect on the American 

 wild grape. Some of these aphids live on the foliage of the vines and 

 cause small hollow galls on the leaves. Others live underground on the 

 roots and cause swellings or nodules to form on the roots (Fig. 197). 

 The infested roots may decay and the vines may die. In France where 

 the aphid has been such a serious pest on the European type of grape it is 

 the custom to use rootstocks of the native American wild grape on which 

 to grow the European vines. The American rootstocks are resistant to 

 the attacks of the phylloxera. 



Family Aleyrodid^e 

 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 § of an inch. In the adult 

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

 dae, 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 common name white flies. 



