EDMONTON - Mountain pine beetles are still thriving in parts of Alberta and are spreading east despite $300 million and years of effort to thwart the tiny tree-killers.

A new generation of bugs took flight this summer, with some landing in mixed boreal forest close to the Saskatchewan boundary.

Experts have been reviewing the spread of the infestation as the Alberta government plans a new winter campaign to cut, remove and burn stricken trees. Last winter, 170,000 trees were destroyed in a bid to reduce the threat.

"The battle rages on," said Prof. Allan Carroll, a University of British Columbia forest insect ecologist. "We had them last year as far as Slave Lake, Alta., and they have got well past that now."

Last year, scientists noted the beetles were starting to jump from lodgepole pine, a species of tree common in Western Canada, to jack pine, which grows in the boreal forest right across Canada.

Carroll said more and more bugs are being found in jack pine. What isn't clear is whether the beetles can cause the same devastation to jack pine forests as they do to lodgepole stands.

The bugs kill by depositing a fungus in the tree's bark. Moderate winter temperatures allow the black beetles to survive and fully develop. They spread when newly born larvae develop wings in summer and fly in search of more trees or are blown eastward by prevailing westerly winds.

The beetles have already ruined billions of dollars worth of timber in British Columbia. Alberta has been actively battling the bugs since 2004. Saskatchewan could be next -- and the tiny insect has the potential to kill pine trees right across the country.

"I am still quite concerned with regards to eastward movement and invasion of the boreal forest," Carroll said. "I'm a bit on the edge of my seat."

Alberta has earmarked about $34 million to fight the beetle this year, including funding for the upcoming winter tree removal.

Frank Oberle, Alberta's minister of sustainable resource development, said he will be asking for at least that much money in the spring budget for similar work next year, despite tight government budgets and the economic downturn.

He will also be asking the federal government to pledge more cash to fight the beetle. There is a big outbreak in Jasper National Park. The offspring of those bugs could spread east into central and northern Alberta next summer.

Oberle is a professional forester who once worked in B.C.'s beetle-ravaged Cariboo-Chilcotin region. It's estimated the bugs have killed more than 675 million cubic metres of timber in the province.

"What happened in B.C. is going to have long-lasting impacts on communities and on the forest industry and on ecosystem health," Oberle said. "That would be a giant risk here."

Alberta is to release its latest detailed mountain pine beetle survey results later this month. The province estimates it has spent about $300 million fighting the pests since 2004, including $18 million in federal funding.

Carroll said provincial and federal governments concerned about the spread of the beetle have a choice to make when preparing their spring budgets. He said they can spend money on mitigation measures now, or they can pay much more in years to come.

"If suppressing the population, slowing the spread eastward, remains their primary objective, then they cannot slack off, because any break in effort will mean an increase in population, which will subsequently mean a more difficult situation to control."