Douglas-fir tussock moth

The Douglas-fir tussock moth (Hemerocampa pseudotsugata) is a lepidopteran insect belonging to the Erebidae family. It is a significant forest defoliator that frequently causes widespread damage to coniferous stands, particularly in the western regions of North America.

The primary host trees for this species include Douglas-fir, grand fir, and subalpine fir. During outbreak years, larval feeding can be so intensive that it strips the trees of their needles, causing significant physiological stress and, in some cases, total tree mortality.

The life cycle consists of one generation per year. The species overwinters in the egg stage, with eggs laid in hair-covered masses on tree trunks and branches. Upon hatching in the spring, larvae begin feeding on the current year’s needles, eventually moving to older growth as they mature.

Feeding damage is characterized by a distinctive reddening of the needles, which later turn brown and drop. Severe defoliation over consecutive years often makes the host trees susceptible to secondary infestation by bark beetles and wood-boring insects, further increasing the potential for timber loss.

• Application of biological insecticides such as Bacillus thuringiensis (Bt).
• Use of pheromone monitoring traps to predict outbreaks and timing of interventions.
• Encouraging natural enemies including parasitic wasps and specialist viral pathogens.
• Silvicultural management to maintain healthy and diverse forest stands.