Cooley Spruce Gall Adelgid On Douglas Fir

Day 274: Some forms of the Cooley Spruce Gall Adelgid (Adelges cooleyi) spend a portion of their life cycle solely on Douglas fir while others migrate from fir to spruce as the insects reach maturity. On spruce, an infestation of Adelges cooleyi may form unsightly galls on branch tips, but these galls do not form on Douglas fir. According to the Oregon Dept. of Forestry, "The conspicuous presence of woolly adelgids on Douglas-fir foliage and the galls produced by this same insect on branch tips of spruce generate more public inquiries than any other forest insect. In natural stands the presence of the Cooley spruce gall adelgid is of little consequence, but severe infestations on ornamental trees, nursery stock, or Christmas trees may justify control. The damage caused by this insect affects only aesthetics and does not threaten tree survival." Adelgids are more likely to occur on stressed trees than on healthy ones, as evidenced by this infestation on a young fir struggling for survival in rocky, dry fill. The white, cottony masses shown in this image are the waxy secretions produced by the insect which helps it adhere to the branch and affords it protection from other insect predators. A few unconcealed Adelgids can be seen here as tiny black spots.