[ 



154 FBUIT INSECTS 



structurally and one can readily colonize the branch-inhabiting 

 aphids on the roots and vice versa; furthermore, the aphids 

 may often be seen during the growing season wandering from 

 roots to branches or going down the trunk on to the roots, and in 

 either case soon establishing themselves in their new location. 

 / This woolly aphis has ranked as a serious apple pest for more 

 than a hundred years both in Europe and America. In spite 

 of much discussion and controversy, it is not definitely known 

 which of these countries is its native home; it is found upon 

 native apple and thorn trees in both countries. In America 

 the insect is commonly known as the woolly aphis, but in 



Fig. 165. — The woolly aphis, a cluster of lice with the woolly covering removed. 



England it is the ''American blight" and in Germany it is 

 called the '' blood-louse " from the red color of the crushed 

 bodies of the aphids. 



The woolly aphis sucks its food from the tissues of the bark 

 and often causes an abnormal growth or swelling where it works. 

 Above ground colonies of the aphids often develop about the 

 leaf axils on sprouts or new growths and particularly at abra- 

 sions (Fig. 165) on the bark or where a branch has been cut off. 

 The aphids often prevent the injured bark from healing nor- 

 mally, and as considerable enlargements of the surrounding tis- 

 sues result, infested branches often present a swollen and scarred 

 appearance. A favorite location for their work is on the crown 

 of the tree just above the roots. Underground the aphids 

 cause conspicuous, rounded, nodular swellings or galls to de- 



