DENVER (AP) — Mountain pine beetles that are devastating forests across the West have been breeding twice a year the last three years, not just once, University of Colorado researchers say.
Researchers say the beetles usually lay their eggs in late July or August. The larvae then burrow deeper into the bark, where they spend the winter. In the spring, the beetles emerge and fly away, seeking other trees.
But now, an extra "summer generation" of beetles are growing into full adults in three months over the summer, the CU study found.
Adult beetles emerging around May and June are laying eggs that hatch soon after. Instead of spending the winter developing into an adult, those larvae are shown to grow into full adults by the end of the summer and lay their own eggs at that time for the next year.
"This would be like our parents being born in the fall and reaching maturity in the spring, giving birth to us in May (or) June," said Scott Ferrenberg, an author of the study with Jeffry Mitton. "We subsequently grow to maturity by August and have our own children that continue along a similar cycle."
This is all but doubling the mountain pine beetle population. The study links the accelerated growth in beetles to increases in air temperature over the last two decades.
The fact that climate change has been directly linked to biological reproduction is an important correlation to make, says ecology professor John Harte.
Harte, who teaches at University of California, Berkeley and follows Ferrenberg and Mitton's work, says the study "relates global warming, to a specific biological mechanism that results in damage." The topic of climate change, Harte says, is controversial to some.
Ferrenberg, a graduate student, said he and his adviser, Mitton, saw the insects taking flight at odd times and determined they were breeding twice a year.
Ferrenberg and Mitton, a CU-Boulder professor, began studying the beetles in June 2008, observing activity for the next three years.
Research was conducted on pine trees in the Niwot Ridge near Nederland in Boulder County.
A 2011 aerial survey showed about 4.6 million acres in Colorado, Wyoming and South Dakota have been affected since the first signs of the outbreak in 1996. That's up from about 4.3 million acres in 2010.
Ferrenberg and Mitton's study will be published this month in The American Naturalist.
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