Feeding results in flagged lateral shoot tips that begin to appear in mid-summer. Winged adult with reddish eggs under wings can be found on previous years needles. This shoot droop may persist on the tree into the following year.
Heavy populations occur on pine and spruce in alternate years.
The pine leaf adelgid has a complex life history which occurs over a two year period and involves two hosts and five distinct life stages. From the discolored shoots, a winged form of the adelgid is produced which flies to spruce and causes production of leafy, cone-like galls at the tip of the new growth in the spring. Heavy production of galls on spruce may indicate that there is a threat of high populations on pine the following year. The mortality of young shoots during infestations appears to become a limiting factor, contributing to population collapse. To date, insecticidal treatments have proven ineffective.