Two-year cycle budworm

Choristoneura biennis

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

On this page

• Description
• Host tree species
• Life cycle
• Damage symptoms
• Identification images

---

Description

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

Host tree species

The primary hosts are subalpine fir, white spruce and Englemann spruce. All ages of trees are susceptible.

Life cycle

Two-year cycle budworm larvae initially mine the needles, buds and new cones, and feed on current foliage after the buds open. This budworm has two-year life cycle, and the heaviest feeding occurs during the second year of larval feeding.

Feeding takes place from late April through June. 

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