These insects are not a serious pest under forest conditions as they injure only a small portion of the foliage. At times, they disfigure ornamentals, and continued infestations may weaken trees and make them susceptible to attack by other insect pests and disease-producing organisms. Damage Feeding by the adelgids produces a characteristic conelike gall. The galls' shape, size and position on the twig aid in identifying the species involved. Galls interfere with the natural formation of twigs and cause curling, stunting and the eventual death of new growth.
Heavy infestations give the trees a ragged appearance and destroy their beauty.
Continuous infestations can seriously devitalize trees and render them more susceptible to attack by other organisms. Some trees have a natural resistance or immunity to these adelgids, and in spite of the presence of the insects, the galls never completely develop or may not form at all. When galls are first produced, they are green, soft and made up of many individual cells which are inhabited by the developing adelgids. The galls mature by midsummer when the cells open and the adelgids emerge. The empty galls soon dry, become brittle and turn a light to dark brown.