Fir
engraver beetle,
Scolytus ventralis,
Tree Species Attacked: The
primary hosts are true firs, though occasionally Douglas-fir and
spruce are infected. Trees from pole-size to mature are susceptible.
Insect Description & Damage Symptoms: The adult beetles are
shiny, black to reddish-brown, and about 4 mm long. A side view shows
that the end of an adult's abdomen is incurved. The beetles bore into
the inner bark of trees from June through September, leaving
reddish-brown boring dust on the outer bark. The beetles introduce a
brown-stain fungus to the sapwood. The galleries the beetles form are
very distinctive, in that the egg gallery is constructed horizontally
across the grain of the wood for a distance of 5 to 15 cm on both
sides of a central entrance chamber. These galleries are deeply scored
into the wood. When they hatch, the larvae mine up and down the bole
for distances of 13 to 18 cm. The life cycle of the fir engraver
beetle is usually completed in one year, though in colder, upper
elevations it may take up to two years to complete.
Damage: Trees are often top-killed, can be killed outright if
attacked by enough beetles, or may survive repeated attacks for many
years. Trees that survive may only be attacked in patches on the bole.
Within a patch attack, the cambium is killed and a brown pitch pocket
is formed in the wood. These partial attacks are seen externally as
roughened patches of bark or scattered dead branches that have been
girdled by egg galleries. Trees that are weakened by drought or root
disease are particularly susceptible to attack. Populations can build
up in slash or windthrow before attacks are made on living trees.
Similar Damage: May be confused with other bark beetles
initially, but the distinct gallery pattern and the deep scoring of
the wood differentiates the fir engraver beetle.
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Contact Tim Ebata
if you have comments on the presentation of this information.
BC Ministry of Forests
Forest Practices Branch
P.O. Box 9513 Stn. Prov. Gov.
Victoria, BC
V8W 9C2
Section phone: (250) 387-8739
Section fax: (250) 387-2136
Last updated February 15, 2002 |
