Adelges is a genus of insects which feed on conifers. Excepting galls formed by the spruce gall midge, galls are caused by aphid-like insects of the family Phylloxeridae (Adelgidae) commonly known as the spruce gall adelgids. They have complex life cycles, some species feeding exclusively on spruce, others feeding on spruce and an alternate conifer. However, galls characteristic of each species are formed only on spruce. Six generations are usually needed to complete the 2-year cycle, and in the case of species having an alternate host, winged adults about 2 mm long are formed only in the generations that move from one host to the other.