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.
