The evolution of mountain pine beetles to produce two generations of beetle per year instead of one has probably been a factor in the unparalleled damage that insects have caused in pine forests in the western United States and Canada over the last decade, according to a new study.
The findings, published online in The American Naturalist, may explain in part how the scale of beetle-killed forest in the West became so vast. The number of acres killed in the last decade or so is 10 times that of any previous epidemic recorded, and it’s not over. The damage stretches from California across the prairies to the east, and from New Mexico to northern Canada.
Jeffry B. Mitton, a professor of ecology at the University of Colorado at Boulder and the lead author of the study, and a graduate student, Scott Ferrenberg, watched the bugs attack 15 pine trees in the southern Rockies in Colorado in the first week of June, about six weeks earlier than normal. Then the bugs laid eggs that hatched, and the new beetles flew to other trees in early August, the time of year when the species would normally attack a tree.
Two generations of beetles in one summer greatly increases the army that attacks trees. “It’s not twice as many beetles, it’s an exponential increase,” Dr. Mitton said. Each beetle lays 60 eggs and, since nearly all survive, each of those beetles goes on to lay 60 eggs in the same summer, which means 3,600 more beetles.
From The New York Times: https://green.blogs.nytimes.com/2012/03/19/double-trouble-from-mountain-pine-beetles/