transform to winged adults and fly to Douglas-fir, if present. 
Eventually, a winged generation is produced on this host, and it 
returns to spruce (179). Where spruce and Douglas-fir do not 
occur close enough together for the aphid to move back and forth 
from one to the other, generations may be produced continuously 
on either species. 
The Cooley spruce gall aphid is not usually considered an im- 
portant pest in the forest. However, it may be troublesome where 
spruce and Douglas-fir are growing close together. Ornamental 
spruce and young spruce trees in Christmas tree plantations are 
often seriously damaged by excessive numbers of unsightly galls. 
The balsam woolly aphid, Adelges piceae (Ratz.), an introduced 
species first recorded in North America from Brunswick, Maine, 
in 1908, now occurs throughout the Maritime Provinces, Canada, 
and the Northeastern States (except the northern parts of Maine 
and New Brunswick Province). Infestations also occur over much 
of Newfoundland, in the Gaspé Peninsula, in the southern Appala- 
chians, and in the Pacific Northwest. Its hosts are balsam and 
Fraser firs in eastern America. Full-grown aphids are roughly 
spherical in shape, less than a millimeter long, and almost in- 
visible to the naked eye. Because of a covering of white wax 
threads, however, they appear as dots of white “wool” (fig. 21). 
Eggs are deposited in late spring and early summer, each egg 
being attached to the bark behind the female’s body by a silken 
thread. Newly hatched larvae crawl rapidly over the bark until 
they find suitable feeding places. When these are found, they insert 
their feeding stylets, become stationary, and turn black except for 
fringes of white wax plates around the edges of the body and 
down the dorsum. After a short period of rest they develop into 
the second generation. Adults of this generation deposit eggs 
during midsummer. Hatching soon occurs and all stages are found 
until late fall. The winter is spent as a first-instar larva. In the 
spring these larvae resume activity and reach maturity by the 
time the buds begin to swell. New adults appear by mid-April in 
the southern Appalachians and in early May in the Northeast. 
There are two generations per year in the Northeast; in the 
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FIGURE 21.—Infestation of the 
balsam woolly aphid, Adel- 
ges piceae, on trunk of 
Fraser fir. 
