Douglas-Fir Tussock Moth

Orgyia pseudotsugata (McDunnough)

From: Field Guide to Diseases and Insect Pests of Idaho and Montana Forests, USDA Forest Service Northern Region, Publication Number R1-89-54

Hosts. – Douglas-fir, all true firs, and spruce.

Distribution. – May be found throughout host ranges.

Damage. – Young larvae feed on underside of new foliage causing needles to shrivel and die. Later in season, older needles are fed upon. When populations are high, entire tree may be defoliated and killed.

Identification. – This is one of the easiest forest pests to identify because some obvious signs of its presence are apparent the entire year. Look on trees for hairy cocoons and eggs in a mass of frothy, gelatinous substance covered with hairs (fig. 99) from August until May. Look for hairy larvae from late May until August on foliage. First instars are gray with long hairs. Later instars develop four dense tussocks (brushes) of yellow-brown hairs on their backs. Mature larvae are up to 1-1/4 inches long, have two long, dark tufts or "pencils" (horns) of hair just back of the head, a similar but longer "pencil" on the posterior end, four tussocks on their backs, and the rest of the body is covered with short hairs radiating from red, button-like centers (fig. 100). Moths emerge in August and wingless females lay their eggs on top of their cocoons.

Figure 99 - Douglas-Fir Tussock Moth egg masses are laid on cocoons of the flightless female. Eggs are held in masses by a gelatinous substance containing hairs from the female's body.	Figure 100 - Mature Douglas-Fir Tussock Moth larva. Note "tussocks" of hair on larva's back from which the species gets its name.

Similar damages. – Early damage and webbing in trees may be similar to that caused by western spruce budworm. Larvae are very distinct, however.

Link to Images in Forestry Images

References.

Anonymous. 1982. For. Insect & disease identification and management. USDA For. Serv.,Northern Region; Idaho Dept. of Lands, Insect and Disease Control; Montana Dept. of State Lands, Division of Forestry. 192 p.

Furniss, R. L., and V. M. Carolin. 1977.  Western For. Insects. USDA Forest Serv., Misc. pub. 1339, 654 p., illus.

Wickman, B. E., R. R. Mason, and G. C. Trostle. 1981. Douglas-fir tussock moth. USDA For. Serv., For. Ins. & Dis. Leaflet 86, 10 p., illus.

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