APPLE INSECTS 



157 



of the leaves and are soon surrounded by a numerous family 

 of young aphids. The presence of the lice cause the elm leaves 

 to swell and curl, as shown in Figure 166. The next generation 

 is also wingless, but with the third brood winged forms appear 

 and continue abundant throughout the summer. Some of these 

 fly back to the apple and there establish colonies on the branches, 



others probably , 



found colonies on the 

 tender elm branches, 

 and some of those ap- 

 pearing early in the 

 season may migrate 

 to other elm leaves. 

 When living on the 

 elm the woolly aphis 

 has been known as 

 the woolly elm leaf 

 aphid {Schizoneura 

 americana Riley) . 



Enemies. 



The woolly aphis 

 has its natural ene- 

 mies, which help to 

 keep it in check. 

 Spiders often spin their webs over a colony of the aphids 

 and then live at their ease. Many of the aphids are para- 

 sitized by the minute chalcis fly, Aphelinus malt, and the 

 larvae of lace-wing flies and a syrphus fly, Pipiza radicum, often 

 work destruction in the woolly clusters. The larvae and adults 

 of several ladybird beetles, particularly the small, brown Seym- 

 nus ceryicaulis, and the nine-spotted Coccinella 9-notata, are also 

 active enemies of the woolly aphis, but the combined efforts of 

 all these foes do not often sufficiently control it, so as to make 

 remedial treatments unnecessary, especially on young trees. 



Fig. 166. — Elm leaves curled by the woolly aphis. 



