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
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.