Douglas-fir tussock moth

Distribution

British Columbia

Micro-habitat(s)

Needle

Damage, symptoms and biology

The Douglas-fir tussock moth is a common and periodically destructive solitary defoliator.

Occasionally, localized outbreaks occur on individual or small groups of Douglas-fir or spruce in urban settings both on the coast and in the interior. Severe defoliation by the tussock moth may result in tree mortality, top-kill or weakened trees, making them susceptible to bark beetle attack.

Mature larva to 30 mm long. Head, unmarked black. Body covered with white hairs radiating out from red tubercles; middorsal tufts of rust-tipped white hairs on abdominal segments 1-4. Two long black pencil tufts project forward from the first thoracic segment and a similar one back from the rear of the body.

This species overwinters in the egg stage; larvae emerge in late May or early June and feed until late July or August. Larvae initially feed on the current year's foliage causing it to turn brown; later in the summer they may feed on both current and older foliage. Defoliation occurs first in the upper crown, then in the outermost portion of the branches and finally in the lower crown and farther back on the branches. The mature larva pupates within a cocoon on the foliage or on the trunk in August, adults emerge 10 to 14 days later and after mating, the wingless female lays up to 200 eggs on the empty cocoon.

Life cycle (West of the Rockies)

Other information

Repeated outbreaks (1918-22, 1928-31, 1946-49, 1961-64, 1970-76, 1981-85, 1991-93) have been recorded at various locations throughout the range of this insect in interior British Columbia.

Main host(s)

Grand fir, ponderosa pine, Rocky Mountain Douglas-fir, subalpine fir, western larch, white fir