14 MAINE AGRICULTURAL EXPERIMENT STATION. 



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 indi- 

 cation 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, 

 of a reddish-brown color, and abundantly covered, especially in 

 those above ground with a flocculent waxy secretion. Fig. 56. 



In August and later, among the wingless ones, winged females 

 appear in abundance. They are little, clear-winged aphids 

 which look nearly black unless carefully examined when the 

 abdomen is found to be dark yellowish red or rusty brown. 

 These are the fall migrants that leave the apple and seek the 

 elm before giving birth to the generation of true sexes, — minute, 

 wingless, beakless creatures, the female of which deposits a 

 single "winter egg" within a crevice of the elm bark. 



On the elm the stem mother, which hatches from the over- 

 wintering eggs sheltered probably in rough crevices of the bark, 

 appears early in the spring and may be found in Maine before 

 the middle of May stationed on the partly opened leaf buds. 



The beak punctures on the rapidly expanding new leaves 

 cause an unevenness of growth which forms a protection for the 

 aphid. By the last of May the earliest of these wingless stem 

 mothers are mature and found in the deformed elm leaves 

 (Fig- 57) producing the next generation. 



These nymphs, like the stem mother, are a wingless form and 

 they become fully developed about the tenth of June. Their 



