The spruce
beetle is a highly destructive pest of mature spruce trees
and is found throughout the range of spruce in the Kamloops
Region. Sporadic outbreaks have killed extensive stands of
spruce in the province and usually last 5 or more years.
Outbreaks often occur when beetle populations build up to
high levels in downed material and move on to attack live,
mature, large diameter standing spruce. The beetle prefers
stands composed of more than 65% spruce occurring in well-drained
creek bottoms.
Host trees:
Hosts of the spruce bark beetle include Engelmann (interior),
white, sitka and occasionally black spruce. Preferred host
materials consist of weakened or windthrown trees, stumps
and large slash. Blowdown occurs naturally, but increases
along the edges of roads, utility right-of-ways, and logged
areas.
Description
and life cycle: The spruce beetle usually has a 2 year life
cycle, but can vary from 1-3 years depending on geographic
location, elevation and climatic conditions. Adults are hard,
stout-bodied, cylindrical, black-reddish black insects ranging
in length from 4.0-7.0mm.
In late
May to early July, females initiate attack by boring into
a host tree and releasing a pheromone that attracts both
sexes and ensures mass attack. Eggs are laid in galleries
that extend upwards from the entrance hole parallel to the
grain of the wood. At first the larvae bore out horizontally
in groups. When they are one third grown they then form individual
mines which often intersect to form fan-shaped galleries.
The brood overwinters as late instar larvae. The following
spring to early summer they pupate and become adults. In
late August many of these new adults bore out of the tree
and crawl or drop to the base of the tree where they again
bore under the bark to overwinter. Spruce beetles must overwinter
once as adults prior to attacking new host trees. The overwintered
adults emerge and attack fresh host material from late May
to early July.
Infested
trees have red brown boring dust present in bark crevices
and around the base. Small pitch tubes may form where beetles
attack. Woodpeckers may remove bark in search of larvae,
exposing red patches on the tree. Spruce may fade a yellow-red
but this is not always evident.
