Cooley Spruce Gall Adelgid

Every fall from mid-September through total freeze up a variety of aphids and Adelgids fly in swarms. Swarming of these insects is in the evening and can drive people crazy. They are locally called “little blue gnats”.

The most common this year was the Cooley Spruce Gall Adelgid (Adelges coolyi (Gillette) Homoptera:Adelgidae)). This Adelgid is a serious pest of spruce trees (Picea) and can damage Douglas Fir trees as well. The flyingadults actually resemble little cicadas and do not feed.

They swarm as mating behavior and lay eggs, after mating,on the needles of host trees. In the spring when the new needle bunches emerge the crawler nymphs form galls at the tips of branches. The galls look like little cones and many people think they are part of the tree.

The tip of the branch with Adelgid galls cease to grow and eventually the tree will be killed or deformed if no action is taken.Treatment with an insecticide as the beginning of tree bud break in the early spring will control the crawlers.