While we were experiencing subzero weather over the past few weeks, the question of whether these temperatures can kill the emerald ash borer has come up in conversation. It’s common knowledge within the green industry that many overwintering insects die off in such cold temperatures. But what about an insect like the EAB that lives inside the tree, under the bark?
After doing a little research, I found the answer in a state that is much colder than ours – Minnesota. Minnesotans posed the question in comments to a blog by Minnesota Public Radio Chief Meteorologist Paul Huttner. So he posed the question to Dr. Lee Frelich, director of the University of Minnesota’s Center for Forest Ecology. Here is a concise, edited version of Dr. Frelich’s response:
“Winter mortality for emerald ash borer is definitely temperature dependent. The larvae can supercool to a certain point, but they die if they freeze, and there is variability in tolerance among individual insects. A recent study from the Forest Service in Minnesota showed that 5% of the insects die at 0F, 34% at -10F, 79% at -20F and 98% at -30F.
“However, there is the question of what temperatures the insects actually experience, since they spend winter under the bark of trees, and some of them close to the ground, where they may be insulated by the bark itself and possibly by the snow.
“This insulation effect can have a substantial effect if overnight minimum temperatures take a brief plunge and recover quickly. In such cases minimum temperatures under the bark can be 2-7F warmer than air temperature.”
As you can see from the temperatures that Dr. Frelich is quoting, it is unlikely that a significant number of emerald ash borer larvae were killed by our cold temperatures. When spring comes, I recommend continuing your prevention or control regimen for this difficult pest.
For more on the Emerald Ash Borer, click here.