By Sindya N. Bhanoo / The New York Times
Mountain pine beetles attack and kill weak pine trees, boring into bark to lay their eggs. They attack the trees in hordes, and their larvae feed off fungi in the trees.
Now, the beetles are reproducing twice a year instead of once, and millions of trees are dying as a result.
The beetle species is several million years old, and historically larvae grow to be adults in July or August every year. But it has been getting warmer earlier in the year, and larvae mature faster and emerge as early as May. These new beetles then immediately lay eggs, and a second generation of adult beetles emerges as early as July because summers are so warm, said Scott M. Ferrenberg, an evolutionary biologist at the University of Colorado at Boulder and an author of a study in the coming issue of The American Naturalist.
The researchers did their work at Niwot Ridge in Boulder County, at an elevation of 10,000 feet. Several decades ago, pine beetles were not found at that elevation, Mr. Ferrenberg said. “The invasion of that habitat above 9,000 feet has happened after several decades of significant warming,” he said.
He called the beetle phenomenon an epidemic, not limited to mountain pine beetles. Other trees are also under stress from other species of beetles.
“Spruce beetles and Douglas fir beetles are at epidemic levels,” he said. And southern pine beetles, typically found in the American South, are moving north.
“People are finding outbreaks in New Jersey,” Mr. Ferrenberg added.