insect pests are fairly host-specific and are mostly associated with older
forests. Cycles of insect infestation are natural. Two insect pests that cause
the most damage to Alberta forests are the spruce budworm and forest tent
caterpillarboth insects cause damage to trees by eating the foliage
(defoliation). Different levels of defoliation, over various periods of time,
can reduce a tree's growth. If the defoliation is prolonged, the tree may die.
Infestations also weaken affected trees, making it easier for disease to take
The extent of
growth loss or mortality varies with damage intensity, site condition, tree age,
tree health, weather conditions, and the like. Damage from the spruce budworm
and tent caterpillar fluctuates from year to year. Between 1978 and 1996, these
two insects caused moderate to severe damage on an average of 11,700 square
kilometres of forest annually. Widespread insect damage may limit the economic
use of certain tree species and render areas of forest unsuitable for
recreation, wildlife habitat or other uses.
Department of the Environment. State of the Environment Report, Terrestrial Ecosystems. Edmonton: n.p., 2001. With permission from Alberta Environment.