Whitemarked tussock moth

Distribution

Manitoba, Alberta, From Saskatchewan east

From Alberta to the provinces of the maritime. Eastern United States.

Damage, symptoms and biology

This native insect occurs periodically in large numbers. Primarily it is a pest of broad-leaved trees but, when numbers are high, it also attacks coniferous species such as fir, spruce, and larch, and may cause severe damage to Christmas trees.

Moderate to severe infestations of this defoliator have occurred in the past over extensive areas exceeding 500,000 hectares. In New Brunswick it has been found mainly in Westmorland and Albert counties, while in Nova Scotia the infested counties have been Cumberland, Colchester, Lunenburg, Hants, and Halifax. In both provinces, defoliation is most evident on balsam fir, tamarack, and hardwoods, but field crops can also be affected.

Its food preferences may vary from time to time and in different places. Sometimes when trees are severely defoliated the caterpillars migrate to gardens or fruit trees and feed on almost every green crop, often invading summer residences in the process of migrating.

The caterpillar is characterized by a red head, two long black tufts of hair on each side of the head and one near its hind end, and four greyish brush-like tufts and two bright red spots on its back.

The eggs hatch in late June or early July. The caterpillars feed for about 6 weeks growing to about 38 mm long. They spin loose grey cocoons within which they transform to pupae. Greyish moths emerge about 2 weeks later. The males are winged and the females are wingless. The female lays its eggs on or near the cocoon. The insect overwinters as an egg on branches, crevices of buildings, or wherever the fully grown caterpillar crawled to spin its cocoon.

Other information

Tussock moth outbreaks normally last from 2 to 4 years and are usually brought under control by natural factors, mainly by a virus-induced disease in the caterpillars.