Mountain beetle threatens Minnesota's pine forests

Pine beetle on a ponderosa pine
Pine beetle on the bark of a ponderosa pine.
Courtesy Derek Rosenberger / University of Minn.

A tiny beetle that has wiped out tens of millions of acres of forest in the western United States and Canada could be close to invading Minnesota's majestic pines.

Although mountain pine beetles are about the size of a grain of sand, they have devoured 45 million acres of pine trees in western North America over the past couple decades — the world's largest forest insect outbreak in recorded history.

The state Department of Agriculture is proposing a quarantine in hopes of keeping the beetles at bay and protecting the state's nearly 200 million pine trees large enough for them to attack — at least for the time being.

That likely will be difficult. Mountain pine beetles have marched east to the Black Hills of South Dakota. On at least two occasions, they have been transported all the way to Minnesota — once in a load of firewood, and once in timber for log cabins and furniture.

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But Minnesota was lucky because the bugs already were dead, said Mark Abrahamson, an entomologist for the Minnesota Department of Agriculture.

"In both cases it seemed like we were fortunate in that the material just happened to be aged long enough that nothing was alive in it," Abrahamson said. "But it's demonstrated to us that there is a real pathway across the plains and we need to take that seriously."

The proposed quarantine would ban freshly cut logs from states infested with the mountain pine beetle that have the bark still on them. Abrahamson said that should be effective.

"The main thing in any regulatory effort is that people understand what the issue is and how to address it," he said. "This is a big problem in the West. People realize that. No one wants to see this same thing happen here in Minnesota."

Abrahamson adds that the quarantine likely will do little harm to Minnesota's economy.

A mountain pine beetle attacks a tree.
A mountain pine beetle attacks a tree and excavates a tunnel. The tree then tries to defend itself by exuding resin. The combination of the resin and boring dust from the beetle is called a pitch tube, and a tree under attack may have hundreds to thousands of pitch tubes.
Courtesy Derek Rosenberger / University of Minn.

The Minnesota Forest Resources Council, which advises Gov. Mark Dayton on forest policy, voted unanimously to support the quarantine.

"In terms of the forest products industry, as far as we can determine, none of the forest products companies here in the state move western wood into Minnesota with the bark on," said Dave Zumeta, the council's executive director.

"So the industry representatives on our council voted in support of this exterior quarantine to help protect the interests of the industry," he said. "They do not want to see this insect in Minnesota."

But even if the quarantine proves effective, the mountain pine beetle could still make it to Minnesota, without human help.

In 2003, the beetle jumped from lodgepole pines west of the Rocky Mountains, over the continental divide, and into the jack pine forest in Alberta, Canada, said Brian Aukema, an entomologist at the University of Minnesota.

"Now the big concern is that it will come through the Canadian boreal forest, through jack pine, and reach the lake states region where we have a number of different pines that may be suitable for mountain pine beetle," he said.

Aukema said temperatures of 40 below zero knock back the mountain pine beetle. But he notes winters are warming and Minnesota is not reaching that temperature as often as 50 years ago.

"It looks like we do have a slowly ameliorating climate, and the climate appears to be suitable for the mountain pine beetle," he said.

Trees under attack
A farm in the Black Hills of South Dakota has trees behind it that were attacked last year by pine beetles. The green trees surrounding the dead ones likely were attacked by the emerging beetles this year and will be red next summer.
Courtesy Derek Rosenberger / University of Minn.

Aukema said it's still possible the beetle may have trouble reproducing in the particular strains of pine found in Minnesota. But, so far, tests he's conducting show there's no reason to believe the insects would not do quite well here.

In the first year of a $250,000 state funded study, Aukema took red, white and jack pine from Minnesota to the Black Hills to offer "a smorgasbord of pines" to the insects. So far they've concluded the beetles will bore into Minnesota pines, attract mates to them, and lay eggs. Next summer they'll see how well the newly hatched beetles do when they emerge from the trees.

As part of that same study, for the past two years the Department of Agriculture has placed traps throughout northern Minnesota, but so far has not captured any live mountain pine beetles.

"The results so far are encouraging," said Abrahamson, the department entomologist. "We seem to be ahead of the problem at this point."

But that advantage could quickly disappear if the beetle makes it to Minnesota, Aukema said.

"We know from outbreaks out west, [that] once insects move into live, green standing trees, and you have thousands and thousands of insects coming out of trees — mass attacking new trees every year — basically the insects will keep attacking those trees until they either run out of hosts, or you get a really cold winter that knocks populations down," he said.

"It's a very, very big concern."