by Bethany Kyre, Plant Pathology major
Mountain Pine beetle, Dendroctonus ponderosae, is a species of bark beetle. They feed on the inner bark of ponderosa, lodgepole, limber, and scotch pines of the western United States. MPB prefer older, stressed trees because, as a defense, healthy trees produce resins that can physically push the beetle back out of the tunnel they have burrowed and encase them in a sticky tomb. The more stressed a tree is, the less resin it produces. MPB is responsible for the death of great swaths of forest throughout the Rockies.
Upon maturity, an adult beetle will emerge from a tree and fly to another, guided by the scent of terpenes. Older trees produce a different scent than younger trees, allowing the beetle to differentiate between the two. Once a female beetle has found an appropriate tree and a mate, she will dig out a gallery and lay her eggs. Once the eggs are laid, the adult beetles will die. MPB have a complete lifecycle, meaning they hatch from their eggs, grow into larva (the overwintering stage), pupate, and then emerge as adults to begin the cycle again.
One very interesting part of the story takes in the high elevation forests of above Nevada, outside of Great Basin National Park. In these 10,000+ ft tree stands, scientists from the Rocky Mountain Research Center in Utah have noticed that not a single bristlecone pine has been killed by the MPB, despite growing in mixed stands with limber pines. Bristlecone pines are among some of the oldest living organisms in the world – some have been aged at 5,000 years old! It could be that bristlecone pines encountered the beetle thousands of years ago and have since evolved MPB specific defenses.
Sources:
Colorado State Forest Service > Mountain Pine Beetle
Bentz BJ, Hood SM, Hansen EM, Vandygriff JC, Mock KE. 2017. Defense traits in the long-lived Great Basin bristlecone pine and resistance to the native herbivore mountain pine beetle. New Phytol. 213(2):611-624.
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This blog post was an assignment for Societal Issues: Pesticides, Alternatives and the Environment (PLNTPTH 4597). The views expressed are those of the author and do not necessarily reflect the views of the class, Department of Plant Pathology or the instructor.