ORCHARD INSECTS OF THE PACIFIC NORTHWEST 



25 



swellings and deformities (fig. 28) 

 that may result in severely hinder- 

 ing the growth of the tree. The 

 colonies of aphids appear as bluish- 

 white, woolly patches, which are 

 composed of the reddish insects 

 covered with woolly masses of 

 wax. When the aphids are nu- 

 merous this waxy material, which 

 contains some honeydew excreted 

 by the insects, hangs in festoons, 

 smears the fruit, and makes pick- 

 ing a disagreeable job. The aerial 

 form also apparently prevents 

 healing of cankers caused by the 

 perennial canker, in districts where 

 that disease occurs. The woolly 

 aphid is found in practically all 

 apple-growing districts. 



LIFE HISTORY 



The life history of the woolly 

 apple aphid in the Pacific North- 

 west appears to be somewhat di- 

 ferent from that in the East, 

 where wintering eggs are laid on 

 the elm trees. In the West this 



Figure 27. — Aerial colony of the woolly 

 apple aphid. 



habit has not been observed, but wingless forms hibernate on the 

 roots of the apple trees, and many f those on the upper portions of 



the trees survive mild winters. 

 Infestations above ground may 

 thus come from wintering forms 

 already present there or from 

 migrants from the roots. Heavy 

 infestations are likely to follow 

 mild winters. The aphids mul- 

 tiply rapidly, and winged forms 

 occur at times, which may fly to 

 other apple trees and establish 

 new colonies; and this may also 

 be accomplished by young aphids 

 which are carried from tree to 

 tree by the wind or by other 

 means. 



PREVENTION AND CONTROL 



The successful establishment of 

 the woolly aphid parasite Apheli- 

 nus maliiiald.in the Pacific North- 

 west now makes it unnecessary to 

 use sprays for its control in many 

 orchards. The presence of many 



Figure 28. — Nodular roots resulting from 

 attack by the woolly apple aphid. 



swollen and blackened aphids (fig. 81) is evidence that the parasite 

 is gaining control over the aphid. However, if the aphids become 



291255°— 41 4 



