Community Agriculture Alliance: Q&A: Mountain pine beetles

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Q. What is the mountain pine beetle?

A. The mountain pine beetle (Dendroctonus Ponderosae Hopkins) is a member of the bark beetle family and is the most damaging insect pest of pine trees in western North America. The adult beetles are black and small - just 5 to 7 mm long - while the larvae look like small maggots under the bark.

Q. What damage can they cause?

A. Mountain pine beetles mass attack and kill mature pine trees within a year. The adult beetles introduce blue-stain fungi into the tree when they attack. These fungi, along with insect feeding, kill the tree by cutting off paths for nutrients and water. Each female lays 60 to 80 eggs, enabling populations to grow very quickly. There often are enough insects emerging from one tree to attack 15 additional trees.

If the forests are not managed while the beetle populations are low, severe damage to pine stands can result. Outbreaks can destroy thousands of acres of mature pine forest in a single year.

Q. Where do they live?

A. The range of mountain pine beetle extends from Mexico to British Columbia. They breed in lodgepole, ponderosa, white bark, limber, and white pines. The beetles prefer mature (older than 80 years), large trees. Beetles may attack younger trees, but they are usually less successful.

Q. How far can they fly?

A. Most species of bark beetles are good flyers. Mountain pine beetles can potentially disperse over great distances if the winds are in their favor. The jury is out on the exact mileage these little creatures can fly. Some say as far as six miles : some say farther.

Q. What is their role in the environment?

A. In their normal habitats, beetles are stand-replacing factors. Beetle outbreaks remove the over-mature pine from the stand and allow other tree species to take over. However, with the current bark beetle epidemic, the mountain pine beetle has been very destructive in our forests. It may have detrimental impacts on the native fauna and flora, as well as the watersheds, soils, water quality and natural ecosystem succession.

Q. Do they have any natural enemies?

A. Yes - birds, especially woodpeckers, eat a large number of insects. In addition, while the birds feed, they remove bark and expose the remaining insects to the elements. Insect parasites, predators and fungal diseases also attack bark beetle larvae. During outbreaks, these organisms probably have little effect on the pine beetle population.

Q. What is Blue Stain?

A. As the beetles attack lodgepole pine trees, they introduce fungal spores into the wood that quickly germinate and infect the sapwood. As the fungus grows, the sap flow within the tree becomes hindered. This combination of beetle infestation and fungal growth can lead to massive tree fatalities.

The introduction of fungus into the tree and its continued spread from mountain pine beetle attacks results in a bluish discoloration in the timber, principally in the sapwood (Byrne et al. 2005: 6). This staining poses a significant problem for the wood products industry. Discoloration leads to a loss in the economic value of the tree due to a loss of marketability as consumers equate this bluish discoloration with some sort of defect.

Q. Will cold temperatures kill the mountain pine beetles?

A. As the fall temperatures drop, the larvae, under the bark, expel the water content within their bodies, becoming, in essence, a sack of antifreeze. For winter mortality to be a factor of significance, a severe early freeze is necessary while the insects are still getting rid of the water. An early spring with warming temps and the insects taking on water again, followed by a hard freeze also will result in higher levels of mortality. Research indicates cold weather in the middle of winter is not going to increase the mortality level.

Q. What products can be produced from trees killed by pine beetles?

A. Bluestain fungi are not mold and do not cause decay or rot problems. They are considered harmless with respect to both wood products and people, and usually are dead by the time they have left the manufacturer (Forintek 2003: 1). With this in mind, wood that contains the blue stain fungus can be used in all of the same markets as non-stained wood with some qualifiers. Beetle-killed lodgepole pine can also be used in the fuel wood and biomass markets.

Hagenbuch is an employee of the Colorado State Forest Service

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