Check at more than one point around the tree's circumference. Mountain area infested by MPB, showing three years of mortality. Some trees may also be infested but do not turn color until nine months or so under attack. These are found under the bark in tunnels. Life History and Habits Mountain pine beetle has a one-year life cycle in Colorado.
Females seek out living, green trees that they attack by tunneling under the bark.
Coordinated mass attacks by many beetles are common. Note the beetle trapped in this large pitch tube. If the majority of tubes look like this, the tree may have survived the current year's attack. The underbark area looks like this in late spring. Bluestained wood is caused by fungi the beetles introduce.