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.