Choristoneura occidentalis (Tortricidae)

the western spruce budworm


Choristoneura occidentalis, the western spruce budworm, adult moth. Wings folded flat over body - giving insect a bell-shaped outline, front wings almost rectangular; colour mottled, orange and brown.


Choristoneura occidentalis, the western spruce budworm, larva. Light green with brownish heads when newly hatched; brownish head and body with prominent ivory-coloured spots when fully grown. Large white oblong shape behind head is an ectoparasite.


Feeding damage caused by Choristoneura occidentalis. Damage by feeding of larvae. New foliage of the host tree is preferred, and trees of all ages are defoliated. In the spring, small larvae mine in needles and later enter the swelling buds. As shoot growth starts, larval feeding may cause malformation, webbed branch tips appear in July, indicating the presence of full grown larvae. After discoloured foliage has fallen, bare tips indicate that budworm feeding has occurred. Trees usually recover unless repeated severe defoliations occur for a period of 3 to 5 years, or longer. Life cycle takes 1 year. Extended periods of defoliation also increase susceptibility to the Douglas-fir bark beetle.

Principal Hosts:

Principally on Douglas-fir, true firs, occasionally found on western larch and Picea spp.

Economic Importance:

The western spruce budworm is the most destructive forest defoliator in western North America.

References and Links:

EAG: 481-483; FC: 168.

See HForest, Diseases and Insects, or JP17.

Western spruce budworm

Additional Images:

male adult on foliage prepupae wasteful feeding by L6 larvae on Grand Fir
heavily infested leader
close growth rings indicate period of defoliation pinned adult with orange and brown mottling wings

Additional Information About the Eastern Spruce Budworm, Choristoneura fumiferana, and the Two-Year-Cycle Budworm, Choristoneura biennis:

The Eastern spruce budworm, Choristoneura fumiferana, and the Two-Year-Cycle budworm, C. biennis, are also important defoliators.

Eastern spruce budworm, C. fumiferana: please see HForest and JP17.

Two-Year-Cycle budworm, C. biennis: please see HForest and JP17.