VANCOUVER (Reuters) - Alberta reported mixed results on Thursday in its battle with the mountain pine beetle, with six million hectares of forest in the western Canadian province susceptible to attack.
Milder winter temperatures allowed more beetles to survive in northwestern Alberta, which also remained at risk of continued migration of beetles from British Columbia, Alberta's Sustainable Resource Development Ministry said.
The situation remained stable in central Alberta.
Beetle survival rates were low in southwestern Alberta, marking the second-consecutive winter in which cold weather helped kill off insects in that region.
The tiny beetles, Dendroctonus ponderosae, lay eggs under the bark of mature lodge-pole pines, killing them within a year. Infested trees cannot be saved, although the lumber can be harvested for several years after the tree dies.
Nature has historically controlled the beetle population with early or late winter cold snaps that kill the insects when they are not ready for a deep freeze. Up to 97 percent of the insects have to be killed to stop their spread.
The beetles attack mature lodgepole pines. There has been scientific concern the beetles will evolve to attack other pine species in Alberta, which could allow the infestation to spread to eastern Canada.
The Canadian infestation began in British Columbia in the late 1990s. There are also mountain pine beetle outbreaks in several western U.S. states.
(Reporting Allan Dowd, Editing by Jeffrey Hodgson)