BOULDER, Colo. (AP) — University of Colorado researchers say mountain pine beetles that are devastating forests across the West are now breeding twice in some years.

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.

According to the Boulder Daily Camera ( ), researchers saw the insects taking flight at odd times and determined they were breeding twice after emerging at the end of summer.

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.