440 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



to the apple trees and give rise to the sexual generation which 

 produces the winter eggs. 



The Woolly Apple Aphis (Sckizoneura 'lanigera). -This is 

 the most destructive of the apple aphids, doing particular 

 damage in young orchards, and as its most injurious work 

 is on the roots of the trees its presence is often not suspected 

 until the trees have been badly damaged. These aphids 

 secrete a white, woolly, waxen substance that covers the body, 

 and when a number of them are feeding together the white 



FIG. 209. Apple leaves curled by rosy aphis, Aphis sorbi. (Reduced.) 



patches that they make are quite conspicuous. The forms that 

 feed above ground usually attack the new shoots or the tender 

 bark about wounds or scars on the trees. The greatest damage, 

 however, is done by the root-feeding forms. These gather in 

 small colonies over the smaller roots, where their feeding causes 

 knots or galls. If they are abundant many of the smaller 

 rootlets are killed and young trees, particularly, are thus seri- 

 ously injured. The larger roots may become very knotty and 

 much deformed, but the aphids are usually found on the 

 smaller tenderer roots. Many of the wingless aphids live over 



