Looking for a silver lining to our extreme cold temperatures? They're likely to kill loads of emerald ash borers, the nasty invasive pest that threatens the state's ash trees.
The insect goes through winter as larvae under ash tree bark, and when the temperature falls to minus 30, nearly all the larvae die, according to Rob Venette, a research biologist with the U.S. Forest Service based in St. Paul.


That won't eliminate the problem, but it's likely to slow the spread.

"This isn't the cure-all," Venette said. "But it definitely is going to help get rid of these insects."
The emerald ash borer, which originated in Asia, was first detected in Minnesota in 2009. It is spread through transported infested firewood.

Four counties in the state -- Hennepin, Ramsey, Houston and Winona -- have confirmed emerald ash borer populations, and state officials want to keep the invaders confined.

So far, only a couple thousand infested trees have been removed throughout the Twin Cities area, said Mark Abrahamson, an entomologist with the state Department of Agriculture. But the risks from the ash borer are high.

Minnesota has about a billion ash trees, more than any other state, according to the forest service. They are thought to be completely defenseless against the ash borer, which can lay waste quickly once it gets a foothold.

"It's that out-of-control kind of a situation we're trying to avoid," Abrahamson said.

The emerald ash borer seems to be spreading in Minnesota more slowly than in other states, perhaps because of early detection and community remediation efforts, along with the cold weather, Venette said.
His research found that 5 percent of larvae will die at 0 degrees, 34 percent at 10 below, 79 percent at 20 below and 98 percent at minus 30.

Apparently, just hitting the temperature mark does the trick.

"It's almost instantaneous. So once it gets to those critical temperatures, that's enough to kill them. What we don't know is what prolonged exposure to slightly warmer temperatures will do. So for example, we've now had several days where we've been at minus 10 or colder. And we just don't know at this point what that does to emerald ash borers," Venette said.

In 2009, the ash borers' first year in the state, temperatures dropped to around 30 below zero, and roughly 90 percent of the larvae died, he said.

"The fluid inside their body literally turns to ice, and that ice just tears up their organs, and it kills them."

Doug Belden can be reached at 651-228-5136. Follow him at twitter.com/dbeldenpipress.