Introduction The Douglas-fir tussock moth (DFTM) is 

a native defoliator that reaches outbreak levels every 7 to 14 years in the western United States and Canada. The larval (caterpillar) stage of DFTM feeds on both new and old needles and can completely defoliate trees in one season. Douglas-fir tussock moth defoliates Douglas-fir, true firs, and spruce in rural forested and urban environments. Defoliation from DFTM can result in top and branch kill, reduced vigor, growth loss, increased susceptibility to attack by otherinsects and diseases, increased short-term fire risk, impacts to other resources such as water and visuals, and tree death. Fortunately, DFTM outbreaks typically last only 3-5 years before natural enemies or starvation cause populations to collapse. Several management options including thinning and insecticide treatments may reduce damage and potential mortality from DFTM. 

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Description A young larva is about 1/4” long, light 

tan to dark gray, with long body hairs. The 1” mature larva is gray to brown, with a shiny black head. Two long, horn-like dark tufts project forward from its head and a similar but longer tuft projects from its posterior end. Four dense, buff-colored “tussocks” with red tips are located on its back. The rest of the body is covered with short white hairs that protrude from red tubercles (knoblike bumps), and an orange stripe on each of its sides. 

Female and male adults differ greatly in appearance. Females are gray, wingless, have small threadlike antennae and a large abdomen, and are about 3/4” long. Males have gray-brown forewings with dark bar markings and whitish colored spots, and hind wings that are reddish-brown . They are 1/2” to 3/4” long with a wingspan of 1-1/4”. Male antennae are feathery. 

Young larva Mature larva 

Adult female and male DFTM 

Life Histo

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Cocoon with egg m

Evidence 

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• May-Augu

bing on treupper bran

• July-Nove

coons on founderstorydefoliation adult moth

• July-May: 

ened egg m
Management Options Microbial and chemical insecticides, 

and mating disruption pheromones can be effective at reducing DFTM populations and subsequent damage. State or Federal Forest Health Specialists should be consulted for treatment options and the most current information on registered insecticides. In addition, State and Federal Forest Health Specialists can provide information on silvicultural management practices to help minimize the impacts of DFTM. 

Microbial Insecticides: 

•Bacillus thuringiensis (Bt), an environmentally safe bacterium specific to 

Lepidoptera larvae. It is used in sensitive areas such as campgrounds or along riparian areas where chemical use is restricted or prohibited. 

•TM Biocontrol-1, a virus specific to 

DFTM larvae. The virus is currently not available for public use.

Chemical insecticides:** 

•Carbaryl, a broad spectrum, general 

purpose carbamate. 

•Dimilin®, a growth regulator that af

fects insect larvae mainly in the Lepidoptera and Diptera orders.

Mating disruption: 

•Disrupt® DFTM, a pheromone that 

interferes with male-female mating communication.

**Pesticides used improperly can be injurious to humans, animals, and plants. Follow directions and read all precautions on the label. 

Consult your local county agriculture agent or State extension agent about restrictions and registered used of particular pesticides. 

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Silviculture: 

•Thin Douglas-fir and true fir overstory 

and understory to help reduce susceptibility to DFTM and favor non-host leave trees such as pine, larch, or spruce. 

•In post-fire or post-management 

restoration planning, consider planting non-host species. 

•Prescribed fire can be used to reduce 

DFTM-susceptible fir understory and reduce competition and improve stand vigor. 

Natural Controls Populations of DFTM are usually kept 

in check by a combination of predators, parasites, 

pathogenic microbes, adverse weather conditions, and food that is either scarce or of poor quality. Major Parasitic wasp factors in end­ ovipositing on DFTM eggs ing outbreaks 

in forested settings appear to be starvation or viral infection. In urban settings, cultural practices such as thinning, watering, and fertilizing will help promote tree vigor, which may help trees survive repeated DFTM attacks. Maintaining a diverse habitat for insectivorous birds, mammals, and predaceous insects can also help keep DFTM populations at lower levels. This may be achieved through proper snag management and leaving adequate woody residues on managed site. 

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Photo credits: Phwere obtained froService, BugwoodColumbia, and C