Rapid Pine Beetle Breeding Destroying Forests in the American West
The mountain pine beetle epidemic is considered to be the largest forest insect blight in North American history. In the past, the pine beetles played a humble role, attacking old or weakened trees, making room for new healthy trees. The changing climate has turned their seemingly benign role into something much more insidious. An explosion in pine beetle size and numbers has forced them to turn their attention to healthy trees. Furthermore, they are reproducing twice as much as normal. Once thought to only produce one generation of tree-killing offspring per year, new research now shows that some populations are producing two generations per year, potentially increasing overall population by 60 times.
The mountain pine beetle affect the trees by laying their eggs under the bark. Their trees of choice include the ponderosa and lodgepole pine. A fungus is secreted by the beetle to protect the eggs from a counterattack by the tree through the use of tree pitch flow. The fungus also prevents water and nutrient transport within the tree.
The combination of fungal infection and the beetle larvae feeding from within can kill the tree in a few weeks. The tree may appear healthy at first, but eventually the pine needles turn red and bark turns gray. By the time the tree is fully deceased, the beetles have moved on to infest their next tree.
New research from a duo of scientists at the University of Colorado, Boulder has discovered the pine beetle's unique reproduction trait as key to the current epidemic. The extra annual generation could produce up to 60 times more beetles. Warmer temperatures have also expanded the beetle's range, helping it come into contact with trees that have not adapted proper defenses. The earlier arrival of spring also gives them a head start in reproduction.
The dramatic increase in pine beetle population helps explain the extent of the epidemic, ranging from the Sangre de Cristo Mountains in New Mexico to the Yukon Territory in Canada.
"This thing is immense," said Jeffry Mitton, CU-Boulder professor of ecology and evolutionary biology. Mitton explained that the pine beetles have expanded their range 240 miles farther north in Canada and 2,000 feet higher in elevation within the last 25 years.
The research was conducted by Mitton along with graduate student, Scott Ferrenberg. It has been published in the journal, The American Naturalist.
For more information: http://asnamnat.org/amnat
Image credit: Canadian Forest Service / 2005