Illustrated Guide to Pests


Douglas-fir beetle, Dendroctonus pseudotsugae


The Douglas-fir beetle is an important native pest in older Douglas-fir stands. Beetles frequently follow stand disturbances such as fire, wind or disease. Infestations are often associated with successive years of moderate to severe spruce budworm damage. Though commonly sporadic and short in duration, outbreaks are capable of killing large numbers of trees.

Host trees: Its primary host is Douglas-fir, however it will occasionally attack western larch. Trees attacked are most often felled, wind thrown, injured, diseased, or otherwise stressed.

Description and life cycle: Adult Douglas-fir beetles are robust, cylindrical insects that range in length from 4.4-7.0 mm. They are dark brown to black with black heads and reddish wing covers.

Typically, Douglas-fir beetles fly and attack susceptible trees in May and June. If conditions are favourable, some adults may re-emerge later in the summer to attack new trees and establish a second brood. Female beetles seek out Douglas-fir trees and burrow into the living tissue under the bark. They release pheromones that attracts male beetles and other females to the tree. After mating, the beetles excavate a vertical egg gallery, which runs parallel to the grain of the wood. Females lay about 50 eggs in small groups on alternate sides of the gallery. The eggs hatch into larvae which mine horizontally out from the main gallery. At the end of each mine larvae construct a chamber where they pupate and become adults. The brood overwinters as larvae or immature adults and in the spring mature adults emerge to attack new host trees.

Attack is noted by the presence of red-orange boring dust in the crevices of bark and at the base of attacked trees. Trees turn red in the spring following attack.


Last updated on January 28, 2008
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