Unit 5 - Forest Protection

Lesson 4: Insect Pests

Native insects and diseases play an important role in the health of the forest ecosystem in Canada; they are usually classified
into 3 categories.


Indigenous species that have existed for thousands of years where outbreaks of the insects will occur periodically.
Examples are the spruce budworm, tent caterpiller and the mountain pine beetle.
These are species that have been introduced into the forests in recent history. Similar terms for alien species include: foreign, exotic and non-native.
Examples include the emerald ash borer, the brown spruce longhorn beetle, and Dutch elm disease.
These are species that spread beyond their known usual range.
The spread of mountain pine beetle from British Columbia’s lodgepole pine forests to Alberta’s jack pine forests is an example of a native forest insect behaving invasively.


Forest insects contribute to healthy change and regeneration in forest ecosystems; they help to renew the forests by:

  • removing old or susceptible trees
  • recycling nutrients
  • providing food and new habitats for wildlife


When insects severely infest an area, destroying large areas of forest or forest products, they are then known as pests.
A healthy tree can usually withstand an insect outbreak with minimal effect, but if the tree is weakened or stressed, the consequences of an insect infestation may be more serious.


If the insect pest is alien, the tree may have little or no natural resistance to it. This allows non-native species to do a lot of damage and spread quickly.

The major forest insect pests in Alberta's forests are the defoliators and the bark beetles; they significantly disturb forest ecosystems.

Defoliators feed on the tree's leaves. The spruce budworm and the forest tent caterpillar are two such pests. These defoliators consume part or all of the leaves of the tree that they are infesting.



Spruce Budworm






The bark beetles are the other major insect pest. These native insect pests attack old or weakened trees, which is ordinarily beneficial to the forest. However, unusually hot summers and mild winters, due to climate change, have led to an epidemic of mountain pine beetles in recent years.

The mountain pine beetle, the most damaging insect pest of pine trees in western North America, has devastated British Columbia forests and is now posing a serious threat to Alberta's forests.

From 1998 to 2008, the mountain pine beetle killed approximately 620 million cubic meters of pine in British Columbia, almost half of the province's commercial pine.

Click here to read about the devastation the mountain pine beetle has caused in Alberta.


If you have an interest in learning more about these tree killers, click here.