INSECTS INJURIOUS TO ORCHARD TREES 441 



the winter on the roots of the tree. Early in the spring 

 some of these migrate to the trunks or branches, where they 

 feed during the summer. There are several generations 

 of apterous females during the summer. In the fall winged 

 females appear which, it is believed by some students, migrate 

 to elm trees, where the eggs are laid in crevices in the bark. 

 These hatch early in the spring and cause the curly leaves on 

 the elm. A little later a generation containing winged females 



FIG. 210. Woolly aphis, Schizoncura lanigcra, and the galls caused by 

 their attacks on apple tree roots. (Two-thirds natural size.) 



appears, and some of these migrate back to apple trees and start 

 new colonies there. Elm trees near an orchard may thus serve 

 as a source of infection. It would probably be much easier 

 to keep nursery trees free from woolly aphis if the nurseries 

 were not located near groves of elms. 



The aphids that occur on the trunk and branches may be 

 killed by spraying with kerosene emulsion, whale oil soap, 

 tobacco extract or other contact sprays. It is necessary that 



