33O MAINE AGRICULTURAL EXPERIMENT STATION. 1916. 



HABITS AND GENERAL DISCUSSION. 



The woolly aphid occurs upon the apple as a bark feeder 

 and is found upon branches, roots, and tender places on the 

 trunk. These insects are covered by a white flocculent waxy 

 secretion given off as fine filaments through pores in the skin 

 and their colonies are thus readily detected by the masses of 

 white "wool" which renders them conspicuous. Figs. 58 and 67. 



On the roots its attacks induce enlargements and in the 

 creases of these malformations the root form occurs in clus- 

 tered masses. The injury to the trees is due both to the suck- 

 ing up and exhaustion of the vital plant juices and to the 

 poisoning of the parts attacked, as indicated by the consequent 

 abnormal growths. Fig. 66. 



The damage is particularly serious in the case of nursery 

 stock and young trees and is less often important after the tree 

 has once become well established and of some size, though it 

 may be troublesome then, too. Where this insect is abundant 

 all the roots of a young tree to the depth of a foot or so become 

 clubbed and knotted by the growth of hard fibrous enlargements 

 with the results in a year or two of the death of the rootlets 

 and their ultimate decomposition with subsequent disappearance 

 of the galls and also of the aphids, so that after this stage is 

 reached the cause of the injury is often obscure. 



On the trunks the presence of the aphids results in the rough- 

 ening of the bark or a granulated condition which is particu- 

 larly noticeable about the collar and at the forks of branches or 

 on the fresh growth around the scars caused by pruning, which 

 latter is a favorite location. On the water shoots, they collect, 

 particularly in the axils of the leaves, often eventually causing 

 them to fall, and on the tender growth of the stems. The dam- 

 age above ground, even when insignificant, is useful as an 

 indication of the probable existence of the aphids on the roots. 

 A badly attacked tree assumes a sickly appearance and does not 

 make satisfactory growth, and the leaves become dull and yel- 

 lowish, and even if not killed outright it is so weakened that it 

 becomes especially subject to the attacks of borers and other 

 insect enemies. 



The common forms both on the roots and above ground are 

 wingless aphids, not exceeding one-tenth of an inch in length, 





