Gall adelgid

The gall adelgid (Adelges cooleyi) is an adelgid species that produces galls in spruce trees. They infect the new buds of native spruce trees in the[foothills of the Rocky Mountains in the spring. They also attack blue spruce to a lesser degree. The insects complete two generations within the year. They require two different trees for its life cycle, the second being the Rocky Mountain Douglas-fir. They may also attack Sitka, Engelmann, or white spruce. There are many different species of adelgids that produce different galls on different spruce species.

The Cooley spruce gall adelgid (Adelges cooleyi Gillette) is mainly a western species that usually alternate between white spruce and Douglas-fir. It is rare in eastern Canada. In Ontario, the galls are found mostly on Colorado spruce.

Identification

The infection is most noticeable on Cooley Spruce in the spring, May to June, when the galls appear. This infection may be mistakenly diagnosed to as caused by worms, grubs, or even as a sex organ of the spruce. Spruce pollen, however is released from a smaller structure that lacks needles. The galls are characterized by this pineapple-like form, with a length of 0.5 cm to 8 cm depending on the growth capacity of the tree. Most galls take on a pink, red or even deep purple colour while the needles usually remain green. The segments of the new bud that have this gall form will die after the aphids leave in the summer. Once on Douglas-fir, the adelgids consume the needles but do not form galls.