Feeding by the aphids produces a characteristic cone-like gall. The gall's shape, size and position on the twig aid in identifying the species involved. Heavy infestations give the trees a ragged appearance, destroying their beauty. Some trees have a natural resistance or immunity to these aphids, and in spite of the presence of the insects, the galls never completely develop or may not form at all. In early summer, new galls are green with purple or reddish curved markings.
Old galls are reddish-brown and have open cavities.
Terminal buds are not destroyed until the entire twig dies. Terminal buds are injured quickly. These aphids frequently migrate to Douglas-fir as an alternate host, but do not produce galls on this tree. Severe aphid feeding on Douglas- fir may cause yellowing and crooking of needles and partial needle fall, but normally little disfiguration of the tree results. Immature females winter on twigs, usually near the terminal buds.