Spruce pineapple galls develop on the swollen, needle-bearing branchlets of Engelmann spruce, white spruce and Colorado blue spruce (P. pungens) in Montana. The galls are caused by an aphid-like insect (Adelges cooleyi) of the order Homoptera that invades the needle-bearing branch tips. In California, this insect also attacks the sitka spruce (P. sitchensis), weeping spruce (P. breweriana) and several cultivated trees, including the oriental spruce (P. orientalis) and Norway spruce (P. excelsa). The tiny insects escape from the galls through lip-like slits above each needle. This insect has a complex life cycle that involves two genera of host trees, including several species spruce (Picea) and Douglas fir (Pseudotsuga meziesii).

Tiny adult females emerge from the pineapple galls in late summer. Each female has an aphid-like body with sucking mouthparts and two pairs of transparent wings. [Drawing by W.P. Armstrong © 2003]