LA CROSSE, Wisconsin (WXOW) – Earlier this week, temperatures in the Coulee Region dropped between -15 and -30. While this didn't equate to record breaking cold in most areas, it may still have some interesting impacts.
Rob Venette is a Research Biologist with the US Forest Service in St. Paul, MN. He's been studying the cold hardiness of emerald ash borer larvae since 2009: an invasive insect that has killed millions of ash trees since its discovery in North America. In 2011 it was discovered in La Crosse County.
"We've been monitoring the conditions of the larvae starting in the fall and then going into the winter," said Venette, "measuring their cold tolerance, specifically what temperatures they freeze at and what temperatures they die at. It turns out that with this insect, if they freeze they die."
In the winter, emerald ash borer larvae go into hibernation under the bark of ash trees. During this time, they produce a chemical that prevents their bodies from freezing. But the study suggests this natural anti-freeze has limitations.
"When temperatures get between -20 to -30 we start to see fairly significant impacts on populations of emerald ash borer," said Venette. "And by significant I mean that mortality in the population increases from anywhere from 50% to approaching 90%."
This means there's a good chance that the cold this week put a dent in the emerald ash borer population. But all that's expected is a dent.
"Temperatures have not been cold enough to get rid of this insect," said Venette. "In fact, we have not seen temperatures anywhere yet that we would feel confident that it would completely eliminate emerald ash borer. But we do feel confident that it is going to slow the spread of the insect in areas where it currently occurs."
Unfortunately, Venette does not think this slow down will last long.
"This is a time to first of all, appreciate the fact that a little extra time has been given," said Venette. "But we're not talking a lot. We're talking about two years is an optimistic estimate."
The emerald ash borer larvae that survive the winter are expected to emerge as adult beetles in early July. Venette suggests people to use the next year or so while the insects' population regroups to take inventory on the number of ash trees in their community.
"A number of cities really haven't been able to do careful tree inventories," said Venette, "and so they don't really fully appreciate how many ash trees might need to be removed or managed."
He also encourages communities to create programs to systematically look for trees with signs of emerald ash borer and discuss both short term and long term management options.
"This is a good opportunity to think about maybe diversifying the number of trees in an area and perhaps building a more resilient urban forest in the long run."
To learn more about the emerald ash borer you can visit the City of La Crosse website or the UW-Madison Emerald Ash Borer Information Page. You can find more about Rob Venette's research at the USDA Forest Service website.
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