Cooley spruce gall adelgid
Cosmetic
Cooley spruce gall adelgid (Adelges cooleyi) is a species of aphid that colonizes on spruce (white spruce, Colorado blue spruce) in the prairies. Closer to the rocky mountains, it also feeds on Douglas fir and Engleman spruce.
The nymphs and adults of the Cooley spruce gall adelgid are tiny, dark insects. The complete 2-year life cycle includes an alternation of generations between Douglas fir and spruce species. However, the insect is capable of surviving on either species when the other is not present.
The galls do not cause damage to the tree.
Symptom:
The damage to the spruce becomes evident in late May when new growth on the branch tips develops into cone-shaped swellings or galls as shown in the photo. The galls contain hundreds of adelgids feeding on sap. At first the galls are green, then red, maturing to brown as they age. The adelgids also feed on the needles which causes them to dry and fall off.
Control:
- The Cooley spruce gall adelgid has few predatory enemies.
- Removing galls as they form will improve the tree’s appearance and reduce populations.
- Avoid planting Douglas fir and spruce close together.
Sources:
Philip, H., Mengersen, E. (1993). Insect pests of the prairies. Edmonton, Alberta: University of Alberta Press.