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CSU-Extension states: “Mountain Pine Beetles (MPB), Dendroctonus ponderosae, are the most important insect pest to Colorado’s pine forests.” They can have devastating effects on whole systems. Unfortunately, there are currently millions of dead trees across western North America. Prior to signs of dying trees, indications of an MPB infestation include: pitch tubes on the tree’s trunk, boring dust on or near the tree, yellow to reddish foliage, and the presence of live beetles (eggs, adults, etc.) under the bark.
The term “Pine Beetle” is often used as an umbrella term to discuss these insects. There are actually several different types of these infectious insects. The true Mountain Pine beetle affects many different types of pines, including Ponderosa, Lodgepole, Scotch, and Limber. Bristlecone and Pinyon pine are less likely to be infested. The Douglas-Fir beetle attacks Douglas-Fir; usually accompanied by other stressors. The Spruce beetle infests Englemann and Colorado Blue spruce. The Red Turpentine beetle attacks injured pines. The Ips Beetles, a group of eleven species of bark beetles, also infest pine and spruce trees.
Prevention of MPB is critical. Most mature Colorado forests have about twice as many trees per acre as those forests which are more resistant to MPB. Beetles prefer old, dense forests. Beetle infestations can be prevented simply by managing the forest to create diversity in age and structure. Diversity results in a more resilient and less vulnerable forest.
Large scale control options are limited to extreme cold temperatures (-30° for five days or more) which may have a significant effect on larvae populations. For more information, contact CSU Extension or visit https://extension.colostate.edu/topic-areas/insects/mountain-pine-beetle-5-528/