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ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 47 



Cooley Spruce Gall Aphid, Chermes cooleyi Gill. — Gall aphids 

 of this species produce thick, elongate galls at the tips of twigs 

 of Colorado blue spruce, Sitka spruce, and Engelmann spruce. 

 The galls are so heavy that usually they cause the twigs to bend. 

 In midsummer, the galls open and the aphids emerge. Some of 

 the gall aphids develop wings. Gall aphids of the winged form 

 migrate to Douglas fir, where the females lay eggs. The eggs 

 and young gall aphids are covered with patches of cottony wax. 

 No galls develop on Douglas fir. 



Control Measure 3 or 8 (end of circular) in late September 

 or October or in early spring. 



Eastern Spruce Gall Aphid, Chermes abietis L. — Gall aphids 

 of this species produce somewhat pineapple-shaped galls near the 

 bases of spruce twigs. Sometimes these gall aphids cause severe 

 damage to Norway spruce. 



Control Measure 3 or 8 (end of circular) in late September 

 or October or in early spring. 



Spruce Bud Scale, Physokermes piceae (Schr.), fig. 45. — The 

 mahogany-brown, globular scales of this species cluster at the 



Fig. 45. — Spruce bud scale: infestation on spruce. The globular, ma- 

 hogany-brown scales resemble spruce buds and are difficult to detect. 



