Mountain pine beetles love a mild winter, and the past few years have been balmy. Now British Columbia is facing the biggest beetle infestation in its history. Short of praying for a deep freeze, all experts can do is "sanitation harvesting" — cutting down infested trees. As entomologist Steffan Lindgren tells As It Happens, the infestation is now like a raging forest fire: it has reached a size where it cannot be stopped without help from Mother Nature.

• The mountain pine beetle (Dendroctonus ponderosae) attacks lodgepole pine trees as well as western white, limber, Scots and other pines. It's a black beetle about the size of a grain of rice. Females dig egg "galleries" in the tree's inner bark, from which larvae tunnel out laterally. These effects cut off nutrient flow throughout the tree and kill it.

• Older trees are more resistant to the beetle and produce copious amounts of resin which can literally "pitch" the beetles out of the bark as it attempts to burrow through.
• The beetles also carry a symbiotic blue stain fungus which spreads throughout the sapwood, plugging resin vessels and circumventing the tree's defences.
• Outbreaks occur after a series of mild winters, or when stands of pines all reach a susceptible size and age.

• The pine beetle is very cold-resistant. The adult beetles develop antifreeze in their blood as temperatures decline, and their late larvae can withstand temperatures of –40 degrees for extended periods. However, if prolonged periods of very cold weather catch the beetle at any other stage in its life cycle, most of them will die.
• The winters since 2000 remained mild, and as of 2004 the infestation continued to spread rapidly.

• By 2002, millions of trees in an area the size of Vancouver Island had been infested. By some accounts, the area of infestation triples every year.
• The response by forest managers was to double the amount of logging, in an effort to head off the spread. Opponents argued that like a forest fire, the infestation is a natural part of the forest's life cycle, and should be left alone.

Medium: Radio
Program: As It Happens
Episode: B.C. Beetles
Broadcast Date: Nov. 13, 2000
Hosts: Mary Lou Finlay, Raffi Vigod
Guest(s): Staffan Lindgren
Duration: 8:00