Mountain pine beetle : biology overview

Lee Safranyik

This item was written and prepared by U.S. Government employees on official time, and is therefore in the public domain


The general biology and ecology of the mountain pine beetle in lodgepole pine forests was reviewed with emphasis on insect-host interaction and causes of outbreaks. During endemic periods the beetles normally infest trees of low vigor such as injured, diseased or otherwise weakened trees and windfalls, usually in association with secondary bark beetles. Attack success in such trees stands to be high even at low attack densities but brood production is usually low. When the beetle populations switch from endemic to epidemic, the beetles infest proportionately more of the larger diameter trees in the stand. Many of these trees have thick phloem. Normally, such stands are more than 60 years old and the average diameter for trees 10 cm and larger is about 20 cm. Precisely which factors are responsible for triggering outbreaks is uncertain; however, all factors that would significantly reduce host resistance or increase the size of the beetle populations above a threshold necessary for colonizing at least some of the large diameter trees with thick phloem could trigger outbreaks.