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A warm winter's effect on the emerald ash borer

Stripped ash tree bark reveals tunnels created by emerald ash borers.
University of Minnesota
Stripped ash tree bark reveals tunnels created by emerald ash borers.

The director of Minnesota Invasive Terrestrial Plants and Pest Center has been working in Cass County to study the effects of this warmer winter on the emerald ash borer.

CASS COUNTY — Everyone keeps saying it: "It's been a weird winter!"

What could that mean for invasive pests like the emerald ash borer? Research biologist Rob Venette and his co-workers want to find out. Venette joined John Latimer and Jennifer Barr on the KAXE Morning Show to talk about this nasty little bug and what can be done about it.

What is an emerald ash borer?

Minnesota first saw emerald ash borers in 2009. Since then, the invasive insect has been found in 48 out of 87 counties in the state. They originated in Asia, and they feed just below the bark of ash trees.

"As they feed, they basically girdle the tree, and eventually kill it," Venette said.

Girdling is when the flow of nutrients from the crown to the roots is blocked because the vascular part of the bark, called cambium, is damaged in a band all the way around the trunk. This technique is used to kill trees while leaving the wood standing.

In Asia, the insect and the ash trees have co-evolved, with the trees becoming resistant to damage. However, that hasn’t happened here.

An iridescent green insect is seen resting on bark.
An emerald ash borer, which is an invasive pest responsible for killing ash trees, is showing up in more Minnesota counties.

This winter's effects

Venette explained that when temperatures reach minus 20 degrees, about 50% of emerald ash borers die off. At minus 30, 90% die. However, recent research has pushed those temperatures a bit colder, down to minus 32, to get that 90% death rate.

John Latimer stated that it has not reached minus 20 degrees at his house near Grand Rapids all winter.

"The emerald ash borer is certainly not immune to the cold, but when we have a winter like this one, they're just not getting the cold that's going to cause a lot of death," Venette said.

What can be done to stop the spread of the emerald ash borer?

The most important thing Minnesotans can do is avoid moving firewood around. If you are going camping, for example, get your firewood at your destination.

The Minnesota Invasive Terrestrial Plants and Pest Center has been working on other solutions too. There are tiny parasitic wasps that will feed on emerald ash borer. Scientists have been studying them carefully, to make sure that they will only attack emerald ash borers.

“We're not just releasing insects willy nilly, but it's a promising prospect,” Venette said, noting that there is no “silver bullet” solution at this time.

Woodpeckers are also important, for two reasons. They eat emerald ash borers, and they help researchers find the pests, thanks to the holes they leave behind in trees.

Are you concerned?

Do you live in a county that has seen emerald ash borers? Email us.

Listen to the full conversation from the KAXE Morning Show above.

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Jennifer has worked at Northern Community Radio since 2006 and spent 17 years as Membership Manager. She shifted to a host/producer position in 2023. She hosts the Monday Morning Show and is the local host of National Public Radio's "All Things Considered" a few days a week. She also writes public services announcements and creates web stories.
As a mail carrier in rural Grand Rapids, Minn., for 35 years, John Latimer put his own stamp on a career that delivered more than letters. Indeed, while driving the hundred-mile round-trip daily route, he passed the time by observing and recording seasonal changes in nature, learning everything he could about the area’s weather, plants and animals, and becoming the go-to guy who could answer customers’ questions about what they were seeing in the environment.