Long thought to produce only one generation of tree-killing offspring annually, some populations of mountain pine beetles now produce two generations per year, dramatically increasing the potential for the bugs to kill lodgepole and ponderosa pine trees, University of Colorado Boulder researchers have found.
Because of the extra annual generation of beetles, there could be up to 60 times as many beetles attacking trees in any given year, their study found. And in response to warmer temperatures at high elevations, pine beetles also are better able to survive and attack trees that haven't previously developed defenses.
These are among the key findings of Jeffry Mitton, a CU-Boulder professor of ecology and evolutionary biology, and Scott Ferrenberg, a graduate student in that department. The study is being published this month in The American Naturalist.
This exponential increase in the beetle population might help to explain the scope of the current beetle epidemic, which is the largest in history and extends from the Sangre de Cristo Mountains in New Mexico to the Yukon Territory near Alaska.
"This thing is immense," Mitton said. The duo's research, conducted in 2009 and 2010 at CU's Mountain Research Station, located about 25 miles west of Boulder, helps explain why.
"We followed them through the summer, and we saw something that had never been seen before," Mitton said. "Adults that were newly laid eggs two months before were going out and attacking trees" -- in the same year. Normally, mountain pine beetles spend a winter as larvae in trees before emerging as adults the following summer.
These effects may be particularly pronounced at higher elevations, where warmer temperatures have facilitated beetle attacks. In the last two decades at the Mountain Research Station, mean annual temperatures were 2.7 degrees Fahrenheit warmer than they were in the previous two decades.
|Contact: Jeffry Mitton|
University of Colorado at Boulder