FAMILY APHIDIDAi 127 



most part being noted upon apple trees and is credited with 

 attacks both on the roots and trunks of some trees, limbs 

 or larger twigs near the ground. It is covered with a white 

 cottony substance and this tends to shed water. On the 



Fig. 84. — Woolly aphis (Schizoneura lanigera) : a, root of young tree 

 illustrating deformation; b, section of root with aphides clustered over 

 it; c, root louse, female — a and h, natural size; c, much enlarged. (From 

 Marlatt, Div. Ent., Circ. 20, 2d series, U. S. Dept. Ag.) 



roots it produces large knotty swellings and these injuries 

 cause serious effects upon the tree. Usually these insects 

 are observed in a wingless form but in the autumn some of 

 the individuals become winged and migrate to the elm, 



