Welcome to the Oregon Department of Forestry! I'm Christine Buhl, forest
entomologist, with the forest health program. In this video we'll be
discussing insects, specifically bark beetles. Our forest health program
consists of me the entomologist, our forest pathologist who looks at tree
diseases, our invasive species specialists who looks at non-native
plants and insects, and our aerial survey specialists. The best way to prevent
insect outbreaks is to encourage tree health. Several different ways of doing
this include planting the right species in the right place, thinning and reducing
competition, removing stressed and damaged trees, and disposing of slash and
blowdown in a timely manner. Bark beetles are some of our smallest but most
damaging forest insect pests. Trees can defend themselves against small numbers
of beetles. But, large numbers of beetles can overcome a tree's defenses. Bark
beetles are about the size of a grain of rice are smaller. They attack trees by
burrowing under the bark and creating galleries, which girdle or cut off
vascular tissues. They also carry fungus, known as blue stain or sap stain, which
clogs vascular tissues, and hastens tree death. For bark beetles these features
can include: frass, which is sawdust kicked out by the beetle as it enters
the tree; fungus carried in by the beetle that causes wood staining; galleries
created underneath the bark; streaming pitch or pitch tubes created by the tree
to push the beetles out; or when a tree is partly or completely dead. Discolored
crowns indicating tree death may occur one year after bark beetle attack.
Although, during stressful periods such as during drought, it may occur within
the same year of attack. Trees have natural defenses. One of these is pitch.
They use pitch to push bark beetles out of the tree. A tree that is stressed does
not produce enough pitch and can be overcome by bark beetles. Bark beetles
are attracted to their preferred host via volatiles.
Volatiles are chemicals that either attract or repel insects. Stressed trees
emit additional volatiles. These volatiles are highly attractive to bark
beetles. And, they can be caused by damage such as fire, drought, and other
types of damage. Bark beetles also emit chemicals. These are called pheromones,
and they can attract or repel. Bark beetles will use them to attract mates
or more beetles of their species to the tree to overcome the trees defenses. Once
there are enough beetles that have overcome the trees defenses, they then
switch to repel. When there are many stressed trees in a stand it can create
a breeding ground for bark beetle population outbreaks.These are examples
of pitch tubes. Here's a pitch tube that has successfully pushed out a bark
beetle. And, you can see exit holes where bark beetles that have entered actually
created a brood gallery, and then the first generation exited the tree. They're
small and round, remember bark beetles are the size of a grain of rice, relative
to wood-boring beetles that come in after the tree is already on its way to
dying or already dead. And, those exit holes are significantly larger and they
can be oval or round. Woodpeckers sometimes flake off the bark of
different trees to get out bark beetles that are close to the surface. Woodpecker
damage can indicate that a beetle has infested. If you see flaking off the bark
this is typically seen in pine specifically for Western pine beetle, but
it does happen with other beetles as well. That indicates that the woodpecker
is trying to get at a beetle right underneath the bark. If they burrow
deeper that, means they're typically going after a wood borer.
Thank you and hope you enjoy Oregon's forests!