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MOUNTAIN PINE BEETLE (Dendroctonus ponderosae Hopkins)
Hosts in Southwest Oregon: Lodgepole, ponderosa, knobcone, white, sugar, and whitebark pines (Note: Jeffrey pine is infested by Jeffrey pine beetle (D. jeffreyi); Jeffrey pine beetles are very similar to mountain pine beetles in virtually all respects except for host range). Effects: Trees attacked by mountain pine beetles are generally killed. Attacks may occur on individual pines or involve variable-sized groups of hosts. Normally, mountain pine beetles attack trees that are under stress due to competition with other trees, are weakened by pathogens, or are otherwise debilitated. Periodically on some hosts, large-scale outbreaks can occur and infestations can extend into stands of healthy trees. Ecological Role: The ecological effects of mountain pine beetles differ depending on the pine host being considered. In the case of lodgepole pine, mountain pine beetles are the key agents responsible for recycling older stands. When a lodgepole stand reaches an age of about 80 to 100 years, mountain pine beetles frequently begin to infest the largest trees and within a 3 to 4-year period, may kill up to 80% of the trees in the stand. The advanced regeneration and smaller trees are all that remain after a typical mountain pine beetle event in this host type. In ponderosa pine stands or stand components, mountain pine beetles generally attack fairly young trees (75-100 years old) and act as thinning agents in dense stands. This thinning is often fairly irregular and may involve sizable groups of trees all dying at once or over a few years. In the case of five-needle pines where host trees are usually scattered among other tree species, mountain pine beetles will create small holes in stands as they attack individual trees or small clumps of hosts stressed by competition, white pine blister rust, or other factors. Life History:
Conducive Habitats: Mountain pine beetles generally prefer or are most successful on trees that are under stress from such factors as competition with other trees, wounding, fire damage, or infection by dwarf mistletoe, root disease organisms, or other pathogens. During drought periods, all of these factors become more important, and mountain pine beetle activity is at its greatest. In the case of lodgepole pine, stands are highly susceptible to mountain pine beetle attack when they have 90-100 trees per acre that are greater than 9 in (22 cm.) in diameter. Second-growth ponderosa pine stands are likely to be infested when growth rates of codominant trees are less than ¾-in (19 mm.) in diameter for the last decade. Other species of pine are likely to be killed by mountain pine beetles when growing under particularly dense stand conditions. Management: Mountain pine beetles are most effectively managed by providing vigorous growing conditions for host trees. The impacts of mountain pine beetles can be minimized at the stand level by regulating stocking levels in accordance with the "Upper Management Zone" described by Cochran (1992) and Cochran et al (1994). As a rule of thumb for Southwest Oregon, basal areas around pine trees should be kept under 100 square feet per acre on poor sites, 150 square feet per acre on moderate sites, and under180 square feet per acre on good sites if limiting the risk of infestation by mountain pine beetles is a desired objective. It may be beneficial to analyze stand densities across the landscape in order to determine the relative stability of stands in an area and hence the relative urgency for action from the perspective of the larger scale. Photos:
Reports and related publications: Wolfpine Thinning Evaluation Pine Monitoring in Galice Ranger District I & D Conditions Highway 62 References: Amman, G.D., McGregor, M.D., and Dolph, R.E., Jr. 1985. Amman, G. D., McGregor, M.D., Schmitz, R.F., and Oakes, R.D. 1988. Anhold, J. A. and Long, J.N. 1996. Cochran, P. H. 1992. Cochran , P. H., Geist, J.M., Clemens, D.L., Clausnitzer, R.R., and Powell, D.C. 1994. McGregor, M.D., and Cole, D.M. 1985. Mitchell, R. G., and Preisler, H.K. 1991. Sartwell, C., and Stevens, R.E. 1975. | |||||||||||
Identification: The adult is a black, cylindrical, medium-sized beetle (5 to 7.5 mm or 1/5 to 1/3 in long). The egg gallery in the phloem and inner bark is long and straight, oriented vertically, and has a slight J-shape at the base. The gallery is packed with frass. Larval galleries extend at right angles from both sides of the parent gallery. Sapwood of infested trees often contains a bluish stain from the associated fungi that are inoculated into the host tree by the bark beetles. Pitch tubes are generally visible on the boles of infested trees.
