MOUNTAIN PINE BEETLE

Mountain pine beetle is a natural pest of white pine forests. While beetle kill is a natural process that benefits forest ecosystems by opening the canopy and providing snags for cavity - nesting birds, when the beetle populations grow to epidemic levels and interact with climatic change, this pest can become more invasive and expand its range and impacts. The beetles usually hit larger trees and weakened trees first, yet during an epidemic all mature trees in a stand can become victims. In contrast to blister rust, mountain pine beetle does not infest and kill seedlings and young trees such that natural regeneration of an impacted forest can occur. However, the combination of blister rust with a mountain pine beetle epidemic can be particularly damaging since (1) both pests impact mature trees and therefore seed production, (2) the beetles can kill the few rust - resistant mature trees and (3) the rust will kill any seedlings that remain or become established. Forest recovery after this combination of impacts will likely require active management intervention.

Management tools to control impacts caused by mountain pine beetle include chemical sprays, tree removal, thinning and other approaches. As with all intervention frameworks, guidelines may be revised periodically and one should consult with a forest health specialist for the latest advice and methods.

1. Preserving high value trees
2. Restoring ecosystem integrity in impacted areas
3. Sustaining ecosystem integrity and preparing ecosystems not yet impacted

Preserving high value trees

A high value tree may be an individual that is integral to a campground, cultural site or residential or commercial landscape or otherwise has characteristics that are deemed valuable such as resistance to other pests or pathogens, historical/cultural significance, extreme age or morphology, etc. For a tree of this type, survival of the individual is paramount. A plus tree having heritable resistance to white pine blister rust would be a high value tree worthy of protection from mountain pine beetle.

Chemical sprays

Applied directly to the main stem of a high value tree, chemical sprays can reduce the success of beetles entering and infesting the tree. The chemical must be applied each year before the beetles fly. One should consult with a forest health specialist for the latest recommendations for chemical treatment.

Biochemical detractants (pheromones)

The beetles produce chemicals called pheromones which are used as communication. When a tree is initially hit, the successful beetles emit a pheromone that attracts other beetles to that tree; when the tree is fully occupied by beetles a different pheromone is released that repeals new beetles from boring into that tree. The pheromone that repeals beetles can be produced (synthesized) in a laboratory and packaged in envelops. Research is currently underway to assess if these envelops, when stapled to the high value tree, can prevent beetle attacks.

Removal of near - by beetle infested material

Beetles multiply in the tree and then fly to a new tree and the cycle repeats itself. Killing the larvae in the tree before they turn into winged beetles can be an effective way to control the population when the populations are small. Removal of the infested trees near the high value tree before the beetles have flown can reduce the likelihood of the high value tree being hit.

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Restoring ecosystem integrity in impacted areas

To prevent the growth of beetle population to epidemic levels there are two approaches: reduce the beetle population and reduce the susceptibility of the forest. The combination of white pine blister rust and mountain pine beetle is particularly threatening to the high elevation white pine ecosystems. Few trees have resistance to the rust and they can easily be lost due to mountain pine beetle.

Reducing the beetle population

Beetles multiply in the tree and then fly to a new tree and the cycle repeats itself. Killing the larvae in the tree before they turn into winged beetles can be an effect way to control the population when the populations are small. The infested trees can be cut and the bark peeled off to expose and kill the immature beetles. Alternatively, the infested tree can be cut into sections and exposed to the sun to heat and kill the larvae inside. Guidelines exist for these options and one should consult with a forest health specialist for the latest advice and methods.

Reducing the susceptibility of trees and the forest to impacts

Healthy trees have defenses to mountain pine beetle, therefore providing optimal conditions for tree health can reduce impacts. Mountain pine beetle also prefers large trees such that a younger stand may be less susceptible to attack when the beetle populations are small. To reduce impacts, forests can be thinned to produce a forest of varying tree ages. Thinning will often increase the health of the remaining trees and further increase their defenses to the beetles. This approach has been used in forests of other tree species but not yet for high elevation white pines. Since the high elevation white pine forests are often low density, it is unclear if thinning would produce the desired effect. When beetle populations are large, the beetles can attack both healthy and small trees.

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Sustaining ecosystem integrity and preparing ecosystems not yet impacted

Any intervention that might increase the health and therefore the defenses of a tree to bark beetles will reduce impacts when the beetles invade. Reducing competitors, whether they are herbaceous plants near the base of the trees or nearby trees, may increase the defenses of high elevation white pines to beetle attacks. More research is needed to determine the effectiveness of such a treatment.

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