By Julian Siddle
Discovery, BBC World Service
The Beetles dig tunnels under the bark of the tree
A plague of tree-killing beetles which swept across British Columbia is threatening to spread 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.
Mountain pine beetles occur naturally in British Columbia but in the last few years their numbers have reached plague proportions.
Staffan Lindgren, professor of entomology at the University of Northern British Columbia, says the beetles have now moved on from British Columbia to neighbouring Alberta.
Tree-killing beetles are moving east
"In places in Alberta there were stories of what they call beetle rain, where under a perfectly blue sky farmers would start hearing what sounded like rain on their tin roofs," said professor Lindgren.
"It turned out it was beetles coming out and falling on the roofs, literally billions and billions of beetles."
Without interference from man, mature lodge pole pine would be regularly destroyed by forest fires. But, Professor Lindgren explained, the species has evolved to use fire to aid regeneration.
"Lodge Pole pine has a cone that's adapted to fire," he said.
"As fire goes through, it kills off all the other species, but actually aids in opening up the cone, and re-establishes pine as the dominant species.
"We've kept fire out of the ecosystem and created huge areas of mature lodge pole pine, which are ideal for mountain pine beetle.
Although less valuable than spruce or cedar, lodge pole pine has become a cash crop species, as it grows quickly and is ideally suited for turning into the "sticks" widely used in the US house-building industry.
Jim Snetsinger, chief forester with British Columbia's Ministry of Forests and Range, said the beetle could be controlled when it was confined to small areas.
But the recent explosion in numbers has meant that the best the forest industry can do is to salvage the trees already killed by the beetle.
Clear cutting is British Columbia's most common method of harvesting timber
"The first phase is to detect and monitor the beetles. Second phase is to harvest affected areas as soon as possible so you can remove the beetles, and the last phase, which is what we're in at the moment, is to salvage as much timber as you can before it loses its economic value.
"We hit this perfect storm of warm winters, very warm summers and this large expanse of mature lodge pole pine." he said.
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.
Dezene Huber at the University of Northern British Columbia is investigating how the beetle larvae keep themselves alive during the sub-zero winters.
"The insect is generally able to survive at temperatures as low as minus 37C, minus 40C starts to push it," said Dr Huber.
"My lab is looking at some of the genes involved in making glycerol, a particular component of the antifreeze that these larvae use.
"We're looking at the larvae in the autumn and the spring to see which genes are turned on and off in relation to glycerol production."
The damage caused by the beetle, combined with the downturn in the demand for wood due to the global recession, has brought about a rethink on forest policy in British Columbia.
Mixed forests, rather than monocultures, are now seen as healthier both for the trees and other plant and animal life - even though a lack of uniformity makes them more difficult to harvest.
Jim Burrows, forest stewardship officer with British Columbia's ministry of forests and range said: "There's a balance to find in terms of what we do - whether we should rehabilitate them and just be concerned about that future crop of merchantable timber, or whether we look at some of the other values like wildlife habitat."
However the threat from the beetle is by no means over. Dr Huber believes it could spread across North America.
"In Alberta, the neighbouring province just to the east, you have lodge pole pine which they're attacking now, and then after that you have jack pine all the way across the continent, down through Ontario and even into places like New Jersey," he said.
"We know mountain pine beetles can survive and reproduce in jack pine, but we don't know how well they can do that. The question now is are they going to be able to exploit jack pine to the same degree that they exploited lodge pole pine?"
Discovery is broadcast on BBC World Service on Wednesday at 1232 GMT and repeated at 1632 GMT, 2032 GMT and on Thursday at 0032 GMT.
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