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VANCOUVER (Reuters) - Winter and spring temperatures Western Canada were cold enough to help slow the spread of mountain pine beetles in Alberta's forests, according to the province's latest survey.
The cold weather destroyed a significant number of the tree-killing insects, but did not eliminate them, and Alberta remains threatened by beetles crossing the Rocky Mountains from British Columbia.
Beetle survival rates were low in most areas except in northwest Alberta, near Grande Prairie. Insects being carried by the wind from British Columbia remain a problem in southwest Alberta and the forests near Banff National Park.
Efforts to control the insects remains a high priority in the forests south of Grande Prairie because of the high concentration of susceptible pine, according to the survey released on Wednesday.
The tiny beetles, Dendroctonus ponderosae, lay eggs under the bark of mature lodge-pole pines, eventually killing them. Once beetles infest a tree, it cannot be saved.
The lumber remains usable, but loses its value the longer the dead tree remains in the forest before harvesting. The beetle also spreads a fungus that can give the wood fiber a blue stain.
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.
Western Canada's current outbreak began in British Columbia in the mid-1990s, and some experts have cited the longevity and severity of the infestation as a result of climate change, which has moderated winter temperatures.
In addition to threatening lumber supplies in Western Canada -- a major producer of construction timber -- the insects can also create indirect environmental problems such as an increased flooding threat by killing forests that control the rate of spring snow runoff.
Reporting Allan Dowd; editing by Rob Wilson