Two-year cycle budworm

Last updated on January 30, 2025

Choristoneura biennis

The two-year cycle budworm is found in subalpine and boreal forests of B.C.'s Interior.

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Description

Two-year cycle budworm is found primarily in central and northeast British Columbia. This budworm presence is distinguished by noticeable defoliation every second year, corresponding to the two-year life cycle.

Two-year cycle budworm larvae initially mine the needles, buds and new cones, and feed on current foliage after the buds open. The heaviest feeding occurs during the second year of larval feeding which occurs from late April through June. 

Host tree species

The primary hosts are subalpine firwhite spruce and Englemann spruce. All ages of trees are susceptible.

Damage symptoms 

The crowns of damaged trees appear reddish-brown from June to September. Several successive years of severe defoliation can cause mortality, particularly on immature or suppressed trees. Other damage includes top-kill, reduced seed production due to damaged cones, and height and volume loss. 

Damage can be confused with other defoliators such as early feeding by the tussock moth or several species of cone worms. The different host species and provincial distribution distinguish species of budworm.

Identification images

Twigs from a tree that has been damaged

Feeding damage with brown tufts

Two year cycle pupae on a branch

close up of a pupae

Pupae

A budworm moth caught in a trap

Moth

Further reading

Read more about the two-year cycle budworm in the Field Guide to Forest Damage in B.C. (PDF, 6.6MB)

Fast facts

Type: defoliator

Targets: subalpine fir and hybrid white spruce