Eastern spruce gall adelgid (Adelges abietis)
U.S. Department of Agriculture, Forest Service. 1979. A guide to common insects and diseases of forest trees in the northeastern United States. Northeast. Area State and Private Forestry, Forest Insect and Disease Management., Broomall, PA. p. 123, illus.(USDA Forest Service, Northeast Area State and Private Forestry Publication. NA-FR-4)
The eastern spruce gall adelgid, an introduced species, forms pineapple-shaped galls on the new shoots of Norway, white, red, black, and blue spruces. The galls are green at first but later turn pink and finally brown after they break open. Galls prevent twig growth and, if they are abundant, may affect entire trees. Individual trees vary in susceptibility to attack; some appear immune, others suffer growth reduction, and some are eventually killed. Trees growing on good sites are generally less susceptible to attack than those on poor sites.
Partially grown females hibernate in twigs near the terminal buds. Pear-shaped, soft-bodied green insects with long antennae, they lack the two tube-like projections that characterize other adelgids. They mature in spring and deposit eggs at the bases of the buds. Upon hatching, the nymphs crawl to the expanding buds and begin to feed. The injection of their saliva into the plant tissues causes the cells to enlarge to form bulb-like hollows. Thousands of cells within these hollows join together to form a gall, which may contain as many as a dozen nymphs. When these galls open in midsummer, winged females emerge and fly to new needles on the same or other spruce trees to lay eggs. They die shortly afterward, leaving the eggs protected beneath their bodies, which resemble a white, cottony twigs to overwinter. Only females are produced.
Unlike some adelgids, the eastern spruce gall adelgid requires no alternate host to complete its life cycle. It should not be confused with the Cooley spruce gall adelgis, which forms galls near the terminal portion of twigs.