The Douglas-fir tussock moth (Orgyia pseudotsugata) is a moth of the subfamily Lymantriinae found in western North America. Its population periodically irrupts in cyclical outbreaks. The caterpillars feed on the needles of Douglas fir, true fir, and spruce in summer, and moths are on the wing from July or August to November.
Adult males are grayish brown moths with mottled light and dark markings. The males' wingspread is 25–34 mm (0.98–1.34 in). When the wings are spread open, the brown hind wings can be seen. Individuals in the northern part of its range are darker in color and southern populations are lighter. Antennae are plumose (feathery). Females are flightless with only rudimentary wings. Larvae (caterpillars) are 20–26 mm (0.79–1.02 in) and colorful with red spots, white spines, conspicuous red-tipped white tufts or “tussocks“, and dense bunches of long, black hairs projecting to the front and behind.
Range and host plants
The Douglas-fir tussock moth is native to forests of western North America and outbreaks have been identified in British Columbia, Idaho, Washington, Oregon, Nevada, California, Arizona, and New Mexico. Outbreaks occur in cycles around eight to 12 years and usually last up to four years, sometimes longer. Reports from Idaho and Washington indicate 2011 had a major outbreak. The larvae feed on Pseudotsuga and Abies species, especially Douglas fir, grand fir, white fir, and subalpine fir.
Eggs hatch in spring (May to June) and the young larvae begin feeding on new foliage (the current season’s growth of needles). Later, they feed on both new and old foliage. The movement of the caterpillars is the main means of biological dispersal. They produce long, silky threads which can catch the wind when they drop from one branch to another. They produce loose webbing which forms a netting. In this cocoon, they pupate in July or August. Adults emerge and are active as late as November. The flightless females stay near the cocoons from which they emerged and mate straight away. Eggs are spherical and white and are laid in a mass which protects them through winter. Because the female is sedentary, population outbreaks always form in place.
One key to management of outbreaks is detection. Entomologists monitor forests using an “early warning system” of pheromone-baited traps. Outbreaks subside on their own, but silvicultural techniques for managing affected timber can be employed, or the chemical carbaryl can be sprayed aerially.
- O. p. pseudotsugata (British Columbia to Idaho, western Montana, eastern Washington, Oregon, Colorado, Nevada, California)
- O. p. morosa Ferguson, 1978 (British Columbia to California)
- O. p. benigna Ferguson, 1978 (Arizona)
- "Moth Photographers Group". Mississippi Entomological Museum at Mississippi State University. Retrieved 2 October 2011.
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- "Douglas-fir tussock moth (Orgyia pseudotsugata) defoliation in Kootenai and Benewah Counties" (PDF). Idaho Department of Lands. Retrieved 2 October 2011.
- Wickman, Boyd E.; Mason, Richard R.; Trostle, Galen C. (30 April 1998). "Douglas-Fir Tussock Moth". Forest Insect & Disease Leaflet 86. United States Forest Service. Retrieved 2 October 2011.
- Kramer, Becky (17 August 2011). "Tussock moths' impact on fir trees visible". The Spokesman-Review. Spokane, WA. Retrieved 2 October 2011.
Dekker-Robertson, Donna; Griessmann, Peter; Baumgartner, Dave; Hanley, Don. "DOUGLAS-FIR TUSSOCK MOTH (Orgyia pseudotsugata)". Forest Health Notes. Washington State University Cooperative Extension. Missing or empty
- "Douglas-fir Tussock Moth, Orgyia pseudotsugata". Decayed Wood Advisor. United States Forest Service. Retrieved 2 October 2011.
- "Douglas-fir tussock moth (Orgyia pseudotsugata): Outbreak status of a conifer defoliating caterpillar" (PDF). Washington Department of Natural Resources. 31 December 2010. Retrieved 2 October 2011.
- "Douglas-fir Tussock Moth Outbreak". National Park Service. 17 December 2008. Retrieved 2 October 2011.