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US Forest Service Research & Development
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Western Bark Beetles

Mountain Pine Beetle
Mountain Pine Beetle

Western bark beetles are tiny insects with hard, cylindrical bodies that reproduce under the bark of a tree. There are 600 different species of bark beetles in the United States. Several species such as the mountain pine beetle (Dendroctonus ponderosae) attack and kill live trees. Most species of bark beetles, live in dead, weakened, or dying hosts.

Bark beetles are important disturbance agents in western coniferous forests. Population levels of a number of species oscillate periodically, often reaching high densities and causing extensive tree mortality when favorable forest and climatic conditions coincide. These events are part of the ecology of western forests and positively influence many ecological processes, but the economic and social implications can also be significant.

During the last decade, tree mortality caused by bark beetles has increased in western spruce, lodgepole, pinyon-juniper, and ponderosa forests. This increase has been correlated with shifts in temperature and increased water stress, creating conditions within the trees that are favorable to beetle survival and growth.

Climate change has also affected bark beetle population dynamics in significant ways. A synthesis of climate change effects on native bark beetles, important mortality agents of conifers in western North America, is available at Climate Change and Bark Beetles of the Western United States and Canada.

For many years, USDA Forest Service research scientists studied the biology, ecology and management of tree killing bark beetles. Historically, research reflected an emphasis placed on protection of timber resources. Today, changes in societal values, global trading practices, and an increased awareness of the importance of disturbances in the functioning of forest ecosystems present previously unexplored questions.

Because of the high regional significance of these bark beetle impacts on all values derived from forest ecosystems, the three western Forest Service research stations – Pacific Northwest Research Station, Pacific Southwest Research Station, and Rocky Mountain Research Station – formed the Western Bark Beetle Research Group (WBBRG) to strengthen cooperative working relationships among researchers and their many partners.

Recently, WBBRG met with US Forest Service, State and Private Forestry, and Forest Health Protection entomologists, our primary stakeholders, to identify bark beetle future research priorities. These include vegetation management; ecological, economic, and social consequences of outbreaks; fire and bark beetle interactions; effects of climate change on bark beetle populations, and chemical ecology. More on these priorities can be found at US Forest Service Bark Beetle Research in the Western United States: Looking Toward the Future.