other ornamental trees. It damages trees by reducing their vitality, detracting from 
their esthetic value, and weakening shoots at points of gall formation. 
The Cooley spruce gall adelgid, Ade/ges cooleyi (Gillette), is a native pest that 
occurs from coast to coast in the Northern United States and throughout the range 
of white spruce in Canada. Its primary hosts in North America are white, blue, 
Sitka, and Engelmann spruces. It also has an alternate host, Douglas-fir. 
The Cooley spruce gall adelgid overwinters as an immature female under bark 
scales near the terminal of twigs of spruce. In early spring the female develops into 
a stem-mother and deposits up to 350 eggs under a mass of white, cottony wax. The 
eggs hatch in | to 2 weeks. and the nymphs settle down to feed at the bases of young 
needles. Elongate, conelike galls (fig. 26) begin to form immediately and develop 
rapidly, enclosing the nymphs. Young galls are fleshy and green or purple; older 
ones are dry and reddish brown. They vary greatly in size, from about 25 to 75 mm 
in length and 12 to 18 mm in diameter. When the nymphs become mature, the galls 
open, allowing the nymphs to escape and crawl to the needles. Here they transform 
into winged adults and fly to Douglas-fir, if present. Eventually, a winged genera- 
tion is produced on this host, and it returns to spruce (27/). Where spruce and 
Douglas-fir do not occur close enough together for the aphid to move back and 
forth from one to the other, continous generations may be produced independently 
on either species. 
F-519584 
Figure 26.—Galls of Cooley spruce gall adelgid, 
Adelges cooleyi, on blue spruce. 
82 
