clipped from: news.bbc.co.uk   

A plague of tree-killing beetles which swept across British Columbia is threatening to spread east, to the US.

The mountain pine beetle has killed more than half of all lodge pole pine in the province and is now active in neighbouring Alberta.

Cold winters usually kill off the beetle larvae, but the region has been warmer than usual in recent years.

Scientists say the beetle could attack and kill jack pines, which are found throughout North America.

Beetles tunnel under the tree bark
Mountain pine beetles occur naturally in British Columbia but in the last few years their numbers have reached plague proportions.
As the beetle burrows under the bark of the tree, it secretes a fungus from its mouthparts which blocks the transport system of the tree. This, combined with the stress of the beetle attack, kills the tree.
In the past, cold snaps before or after winter killed off many of the beetle larvae, but these have not occurred for a number of years.