Environment

Urban Forestry

Douglas fir Tussock Moth - Biology

Young larvae emerge from egg masses in late May to early June. They are 0.3 cm in length, light to dark brown, and covered with fine hairs. Mature larvae reach 3.0 cm in length and have four yellow to tan, rust-tipped tussocks on their backs and red spots located on the upper surface of each of the next three segments. There is one dark-coloured, pencil-like tuft behind each side of the head and one on the posterior. The head is glossy black.

The entire body is covered with hairs growing from small red nodes. A broken orange-yellow stripe runs along each side of the body. The larvae pupate in July to August, in greyish-brown, spindle-shaped, silken cocoons, which incorporate larval hairs. Pupae are found on foliage, branches, and boles of host trees.

Young larvae prefer current foliage, but mature larvae will consume older foliage. Silk threads will be evident, especially in tree tops. The upper third of the crown is defoliated first. Defoliation is most evident in late July to September when attacked trees initially turn reddish-brown, then greyish-purple.

Early in the outbreak cycle, defoliation is often first detected on large, open-grown Douglas-fir on rock outcrops or at the edge of open range.

For More Information: www.for.gov.bc.ca/hfp/publications/00198/dftm.htm

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