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Mountain Pine Beetles (MPB) are one of the most damaging insect pests of Wyoming's pine forests. The MPB has caused extensive damage to trees on mountains, and in urban or urban-interface areas. They have resulted in the loss of millions of trees annually. The problem exists Statewide in any forested area. MPB develop in all mature pine species, especially in ponderosa, lodgepole and limber pine. All pines are susceptible.

Outbreaks of MPB develop regardless of property lines, being equally evident in wilderness areas, mountain subdivisions and urban back yards. Even windbreak or landscape pines many miles from the mountains can succumb to beetles imported in infested firewood.

During epidemics, widespread tree mortality alters the forest ecosystem. Beetles have almost totally depleted some commercial pine forests and, in some cases, have converted valuable forests to less desirable timber species such as subalpine fir. Sometimes, forested areas are reduced to grass and shrubs.

The profusion of beetle-killed trees can change wildlife composition and distribution by altering their habitat, hiding and thermal cover, and by impeding their movement. Moreover, the dead trees left after epidemics are a source of fuel accumulation that will, in time, burn unless removed.

Mountain pine beetles and related bark beetles in the genus Dendroctonus can be distinguished from other large bark beetles in pines by the shape of the hind wing cover (Figure 1). In side view, it is gradually curved. The wing cover of Ips or Pine Engraver beetle, another common group of bark beetles attacking conifers, is sharply spined.

The most common hosts for adult MPB’s include large ponderosa, lodgepole and limber pines. During early stages of an outbreak, the trees most likely to be attacked are limited largely to trees not growing vigorously due to stress from injury, drought, poor site or growing conditions, fire or mechanical damage, overcrowding, root disease or old age. However, as beetle populations increase, MPB attacks may involve most large trees in the outbreak area, healthy or not.