The eastern spruce gall aphid is a serious pest in nurseries and 
Christmas tree plantations and on park and other ornamental trees. 
Its damage is limited primarily to a reduction in the esthetic value 
of the trees. 
The Cooley spruce gall aphid, Adelges cooleyi (Gill.), occurs 
from coast to coast in northern United States and throughout the 
range of white spruce in Canada. Its primary hosts are recorded 
as white, Colorado blue, Sitka, Engelmann, and big-cone spruce. 
It also has an alternate host, Douglas-fir. 
The Cooley spruce gall aphid winters as immature stem-mothers 
under bark scales near the terminals of twigs of spruce. The 
female becomes mature in early spring and deposits a large num- 
ber of eggs under a mass of white, cottony wax. The eggs hatch 
in about a week and the nymphs settle down to feed at the bases 
of young needles. Galls (fig. 20) begin to form immediately and 
develop rapidly, enclosing the nymphs. Young galls are green or 
purple in color; older ones are 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, allow- 
ing the nymphs to escape and crawl to the needles. Here they 
F 519584 
FIGURE 20.—Galls of Cooley 
spruce gall aphid, Adelges 
cooleyi, on blue spruce. 
