Minn. research aims at beetles

Published 4:05 pm Saturday, November 22, 2014

MINNEAPOLIS — The mountain pine beetle has devastated huge swaths of forest in the Rockies, and scientists fear the insects could threaten the majestic pines of Minnesota and states farther east someday.

Initial results from a three-year, $250,000 research project by the University of Minnesota and the Minnesota Department of Agriculture back up some fears about the risk. There’s no evidence that the insects have gained a beachhead in the state yet, but the researchers caution that they can’t be sure that some pests aren’t already hiding someplace, waiting until conditions are ripe to launch an attack. They’re already established in the Black Hills of South Dakota.

“This is one problem that we have to take very, very seriously,” said Brian Aukema, a forest entomologist at the university.

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The scientists wanted to confirm in the first phase of the study whether the beetles would find the most common species of pines in Minnesota delicious and nutritious. Experiments this summer in the Black Hills show that they do, Aukema said.

Some dead mountain pine beetles were found in a shipment of logs to Minnesota two years ago. The initial screening of pheromone-baited traps placed across the state this year didn’t turn up any living specimens, but a more detailed analysis hasn’t been completed, said Mark Abrahamson, an entomologist with the state agriculture department.

Mountain pine beetles are the most devastating forest insect in North America. They’ve damaged almost 125 million acres of mature pine forests in the West, including 45 million acres in a current outbreak in Canada. Minnesota has around 191 million red, white and jack pines that are large enough for the insects to attack.

Cold winters historically have kept the beetles in check, but the trend toward warmer winters has fueled devastating outbreaks in the Rocky Mountains. So it’s feared they could eventually reach the Upper Midwest and Great Lakes region, with serious damage to the Northwoods ecosystem, outdoor recreation and the forest products industry.

The researchers said there are two likely ways the beetles could reach Minnesota: via logs shipped from areas where the pest is established or by migrating along jack pines that stretch across Canada into northern Minnesota. There’s little pine forest between Minnesota and the Black Hills, so the main threat from South Dakota would be imports of infested timber.

The insects kill by breeding in and tunneling through a tree’s water-conducting tissues just under the bark. They can only breed in trees larger than 5 inches in diameter, and they’re also unusual in that they actually need to kill a tree to reproduce. When the bugs are on the move in an outbreak they can travel 500 miles in a year if there’s enough pine along the way. Their swarms can even turn up on Doppler radar.

Aukema and graduate student Derek Rosenberger did their research in the Black Hills this summer because they didn’t want to risk bringing mountain pine beetles to Minnesota. So they sent freshly cut green logs from red, white, jack pine and Scotch pines from Minnesota to the Wheaton College Science Station near Rapid City, S.D., and exposed them to trap-caught live beetles. They found that the insects readily colonized the logs. They also confirmed that the male beetles were attracted to females that had tunneled into the logs.

The researchers will monitor the logs to see if the insects survive cold winters in Minnesota’s pine species and how well they reproduce in them. Some logs will be returned to Minnesota over the winter for more study under secure conditions. They will also set out more traps in Minnesota to look for evidence beetles have arrived.

The beetles have some similarities with emerald ash borers in the way they kill trees. The borers have already devastated ash populations in the East and are becoming established in Minnesota. The researchers hope their work can help devise rapid response strategies for stopping its advance.

“Unlike emerald ash borer, there is an effective trap and lure. Management of isolated, endemic populations may not be impossible — if we know they are there first,” the researchers wrote in their funding request.