About half of the marketable pine trees in West Coast Canadian province of British Columbia have been ravaged by a nearly decade-long beetle infestation, according to new government statistics.

The outbreak of mountain pine beetles has affected trees over an area of 13.5 million hectares (33.4 million acres) in the Western Canadian province, which is a major source of softwood lumber exports to the United States.

The insects have infested and killed about 710 million cubic meters of timber as of this month, up from 582 million cubic meters at the same time last year, according to a news release posted on the province's Web site.

The tiny black beetles lay their eggs in the lodgepole and ponderosa pines with the hungry larvae killing the trees by destroying their ability to take in water and nutrients. They also carry a fungus that stains the wood blue.

British Columbia has about 1.35 billion cubic meters (4.8 billion cubic feet) of saleable pine lumber in its public and private forests, and the province estimates about 76 percent of it will have been killed by 2015.

A provincial report last fall predicted the infestation rate will return to pre-outbreak levels after 2015 because most of susceptible trees will be dead by then, although there are fears the insects will spread into the neighbouring province of Alberta.

The insects have lived in Western Canada for thousands of years, but nature has controlled major outbreaks by killing the beetles through extreme winter cold and forest fires.

Much of the infected area has not had the required cold snap in recent years and British Columbia Premier Gordon Campbell has cited the outbreak as evidence Canada needs to take aggressive steps to address global warming.

The outbreak is contributing to the lumber industry's woes.

Sawmills have rushed to process the dead trees before the wood deteriorates, but are selling the lumber into a market hit hard by reduced demand because of the collapse of the US housing market.