THE M0NTI1LY BULLETIN. 



391 



Maine (2). Our species is quite probably identical with the European pear woolly 

 aphis (Eriosoma lanugiitoxa, Hartig), but not sufficient European material has 

 been obtainable to make this point a certainty. 



Injurious Aspects. 



The injury occasioned by the root aphids consists in stunting and, infrequently, 

 outright destruction of young trees naturally weak. Naturally vigorous trees rarely 

 suffer beyond the extent of an early yellowing and dropping of the leaves. Older 

 trees sometimes show a stunting in the branches and early defoliation, but the 

 amount of injury suffered by trees with a well-established root system is obscured 

 by reason of the weak indications. Long and persistent study might show some 

 effect on the quality of fruit, but our present knowledge on such possible effects of 

 aphis work does not lead beyond theorizing. 



Woolly aphis injury is closely connected with soil conditions, the greatest amount 

 of damage occurring on heavy soils which become hard and dry after midsummer. 

 Trees on such soil presumably lack adequate moisture in the early fall when the 

 aphis is most abundant and they succumb to the combination of drought and aphis, 

 although normally the pear is capable of standing considerable dryness and 

 uninfected trees under normal orchard conditions pass through this period of 

 drought. On the lighter soils of sandy and gravelly types sufficient moisture is 

 conserved to enable infested trees to pull through. A like result obtains in irrigated 

 orchards, but the irrigation itself checks the aphis but little, rather serving to 

 invigorate the tree. 



Fig. 130. Eriosoma pyricola; mature gall on cork elm 

 leaf. (Original.) 



The insects confine their attention almost wholly to the fibers and smaller roots, 

 rarely infesting roots over half an inch in diameter. In this respect their feeding 

 habits differ from those of the apple woolly aphis, which abundantly colonizes large 

 as well as small roots. On pears the fibers are often heavily infested. Weldon (3) 

 found fiber infestations to a depth of three feet. Serious infestations occur in late 

 summer and fall at the bases of the current year's root growth and it is at this 

 point that the fall-winged migrants are chiefly produced, often in great quantities. 

 The aphids form their colonies in rings around the root, greatly weakening if not 

 being instrumental in killing it. The two-year-old wood is likewise attacked, but 

 much less often. It would appear that the nymphs of the migrants do more 

 collective damage than do those of the wingless form. Roots on which large num- 

 bers of migrants have developed are very susceptible to decay through the rains of 

 the winter following their infestation. This is presumably due to the impairment 



