Two-year-cycle budworm, Choristoneura biennis
 

Fig. 3   2-year-cycle budworm pupa	Fig. 4  2-year-cycle budworm egg mass after hatching.

Distribution:  The 2-year-cycle budworm is found in the subalpine and boreal forest types of the interior.

Tree Species Attacked: The primary hosts are sub-alpine fir and the white spruce/Engelmann spruce complex. All ages of trees are susceptible.

Insect Description & Damage Symptoms: Young larvae are very small and light yellow-green. As they grow, larvae become brown with a dark brown head capsule. In the last instar, some larvae turn olive-brown. Larvae are 1.6 to 3.2 cm long. Larvae pass through six instars before they pupate. 

The larvae pupate within webbed foliage from late June to mid-July. Pupae are dark reddish-brown and 1.2 to 1.6 cm long. The 2-year-cycle budworm moth is darker and slightly larger than the western spruce budworm. The female moths lay eggs in masses on the underside of needles in a shingle-like pattern in August. The egg masses are bright green when laid, and translucent white when empty. This budworm, as its name suggests, takes two years to complete its life cycle, with eggs laid primarily in even-numbered years.

Initially, larvae mine the needles, buds, and new cones, and feed on current foliage after bud flush. Older larvae prefer current foliage but will feed on older foliage if current foliage is depleted. Feeding on old foliage does not take place until the second spring. This is the year that damage is the heaviest. Feeding takes place from late April through June. The crowns of damaged trees appear reddish-brown from June to September. The initial symptoms of defoliation may be seen in tree tops and branch tips, where chewed needles accumulate in webbing.

Damage:  Tree mortality can occur after several successive years of severe defoliation, particularly on immature or suppressed trees. Other damage includes top-kill (resulting in stem defects), reduced seed production due to damaged cones, and height and volume loss.

Similar Damage:  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 the various species of budworm from each other.

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Contact Tim Ebata if you have comments on the presentation of this information.

BC Ministry of Forests
Forest Practices Branch
P.O. Box 9513 Stn. Prov. Gov.
Victoria, BC
V8W 9C2

Section phone: (250) 387-8739
Section fax: (250) 387-2136

Last updated March 04, 2002