Forest Pests and Pathogens

Pine Bark Beetle Larva Gallery, NPS photoBlister Rust Canker, NPS photoPine Beetle Kill, NPS Photo, R.H. Hendrickson

Forest insect pests make life challenging as the forests within the Crown of the Continent struggle to remain healthy. The larvae of the native western spruce budworm munch on new growth of conifer needles causing the tips of the branches to appear reddish-brown. Although they are destructive defoliators, they typically don’t cause enough damage to kill trees. However, multiple years of defoliation combined with drought and other stresses can eventually weaken trees enough to kill them. White pine blister rust is a non-native fungus that infects pines such as western white pine and whitebark pine. The first report of blister rust in Glacier National Park was in 1939 and since then it has infected over 75% of the park’s whitebark pine trees. The mountain pine beetle spends its entire life cycle underneath the bark of its host tree until it emerges as an adult and flies away in search of a new tree to lay its eggs. A single generation of mountain pine beetles can kill a tree.

Within national parks, natural ecological processes often determine management policies. In Glacier and Waterton Lakes National Parks, select Douglas fir and whitebark pine trees are treated with anti-aggregation pheromones to dissuade dispersing beetles.