The spruce budworm, Choristoneura fumiferana (Clemens), is the most widely distributed and destructive defoliator of spruce-fir forests in North America. The insect feeds on a number of conifers, such as balsam fir (Abies balsamea [L.] Mill), white spruce (Picea glauca [Moench] Voss), red spruce (Picea rubens Sarg.), black spruce (Picea mariana [Mill] B.S.P.), eastern hemlock (Tsuga canadensis [L.] Carr.) and white pine (Pinus strobus L.).

The spruce budworm has a one-year life cycle. The female moths lay eggs in July. The eggs hatch into first-instar larvae in about 10 days to two weeks. The first-instar larvae react to light and temperature and move toward the branch tips, where they rarely feed, but they do spin hibernacula within which they soon molt to the second instar. The second instar larvae go through winter in diapause. In April or May of the next year, second-instar larvae emerge from their hibernacula and grow and feed again. In late May or early June, the third instar larvae feed on newly opened vegetative buds of the host trees. Fourth to sixth instar larvae cause the most damage, particularly the sixth instar larvae. Pupation occurs in late June. The pupal phase lasts about 10 days, and occurs from late June to mid-August. Adults live about two weeks and mate, completing a life cycle.

The budworm is naturally infected by a variety of microorganisms, including viruses, bacteria, protozoa, and fungi. Four types of viruses (nucleopolyhedrovirus, granulovirus, cytoplasmic virus, and entomopoxvirus) have been isolated from the native budworm population. (Cited from Spruce Budworms Handbook, Managing the Spruce Budworm in Eastern North America by USDA. Also see Managing the spruce budworm in eastern North America).