Between 1996 and 2010, some 6.6 million acres of forests in Colorado were affected by bark beetle attacks. Like other states in the Southwest, bark beetles of the Ips spp. played a role in the widespread mortality of conifer trees in Colorado. Additionally, mountain pine beetle (Dendroctonus ponderosae) outbreaks were particularly severe in Colorado, affecting some 4 million acres by 2010. The mountain pine beetle attacks and reproduces in at least 12 different species of pine, including lodgepole pine (Pinus contorta), ponderosa pine (Pinus ponderosa), and whitebark pine (Pinus albicaulis). In addition to the impacts of the beetles themselves, mountain pine beetles carry a pathogen (blue stain fungi) that is often responsible for tree mortality.
Bark beetles are a natural part of forest ecosystems, having been associated with forests in the western United States for the past 12,000 years. For reasons that are not entirely understood, recent bark beetle attacks have been more severe in their intensity and extent than outbreaks documented in the previous century. Although the role of climate change and drought are not well understood in this process, they are thought to influence both the insects and the host trees. For example, because temperature is an important population regulating factor for beetles, the mountain pine beetle is expected to experience increased population success as the result of projected warming, although there is considerable temporal and spatial variability. Additionally, warmer temperatures and drought conditions can stress trees and makes them less able to resist insect attacks.