Adelges

Genus of minute gall lice or aphids in the family Adelgidae of the order Hemiptera, which infests conifers, especially Norway and sitka spruce. Generally two hosts are required to complete the life cycle, which extends over two years.

Adelges abietis is typical. The young insects feed at the base of the leaf needles in the spring, causing swellings or galls, like false cones, which contain 100 or more cavities, each harbouring several young aphids. The galls open in June and winged aphids are released, which fly to infest secondary hosts, such as larch, pine, or silver fir, for several generations without forming galls. In July of the second year a winged generation appears; these insects fly to the spruce again to lay eggs and repeat the life cycle.

A. cooleyi infests Douglas fir and sitka spruce, A. nusslini, silver fir. Infestation of the primary host can be detected by the presence of galls. Specks of sticky white down on leaf needles indicates secondary host infection. Damage is rarely severe on trees grown under good conditions.