Douglas-fir tussock moth, Orgyia pseudotsugata

Fig. 14    Distinctive mature larva of Douglas-fir tussock moth.	Fig. 15,  Douglas-fir tussock moth often defoliates upper third of crown first.	Fig. 16   Silk webbing produced in Douglas-fir tussock moth infestation.	Fig. 17   Douglas-fir tussock moth egg mass with young larvae emerging.

Distribution:  Warm, dry areas of the southern interior and occasionally on the south coast, 350 to 1250 m elevation.

Tree Species Attacked: Principally Douglas-fir, but other species such as ponderosa pine and western larch are occasionally attacked if adjacent to infested Douglas-fir. All ages are susceptible.

Insect Description & Damage Symptoms:  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.

Damage: The Douglas-fir tussock moth has the potential to cause significant mortality due to defoliation. In addition, top-kill, growth reduction, and secondary attacks by insects and fungi may follow severe defoliation.

Similar Damage: Early damage and webbing in trees may be similar to that caused by the western spruce budworm. The larvae are very different, however, and the tussock moth voraciously consumes both new and old foliage as opposed to the primarily new foliage consumption by the budworm. Tussock moth infestations tend to be relatively small and localized near the edge of open range, whereas western spruce budworm infestations are more widespread.

Back to the Pest Field Guide Index

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