Fir (Abies)-Spruce budworm (Western)

Choristoneura occidentalis

Pest description and damage Adult moths are mottled orange-brown and have a wingspan up to 1 inch. The larvae are typically green to brown with a darker head and white tubercles in later stages. They grow to approximately 1 inch in length. These larvae feed on the buds and foliage and may tie shoot tips together with webbing to make a nest. Spruce budworms are mainly pests of balsam and subalpine firs. They also attack spruce and Douglas-fir adjacent to infested fir trees. Although a significant problem in forestry situations, this insect is an infrequent pest in the landscape.

Biology and life history The larvae overwinter in small silken cocoons which are hard to locate. The following spring, larvae emerge and spin long silken threads that aid in their dispersal. Eggs are light green and laid in shingle-like masses on the underside of needles in mid-July. A needle with a layer of green eggs looks thicker than others.

Management-cultural control

Hand-pick and destroy larvae when found.

Management-biological control

Budworm populations are usually regulated by combinations of several natural factors such as insect parasites, vertebrate and invertebrate predators, and adverse weather conditions.

Management-chemical control

See Table 2 in:

For more information

See "Caterpillar" in:

Fellin, D.G. and J.E. Dewey. 1992. Western spruce budworm. USFS Forest Insect and Disease Leaflet 53 (http://na.fs.fed.us/spfo/pubs/fidls/westbw/fidl-wbw.htm)