Mountain pine beetle Mountain pine beetle is the most serious insect pest of ponderosa and lodgepole pine forests in Colorado.
Outbreaks periodically kill large numbers of pines.
Recent evidence indicates that mountain pine beetle populations are on the rise statewide. Mountain pine beetles only attack pines greater than seven to eight inches in diameter. The one-year life cycle of the beetle begins in August when adults exit dead trees and fly to attack nearby green trees. In early summer, about nine to ten months after being attacked, the needles of infested pines will turn reddish-brown. Mountain pine beetles overwinter in the tunnel system as small white grubs with brown heads.