It looks like emerald ash borers will continue to be a problem in Manitoba, despite the extremely cold weather we had in the Southeast.

Many people were hoping the twin polar vortexes that brought nearly a month of frigid weather would drive the invasive species extinct within the province. Unfortunately, Manitoba Sustainable Development says this will not be the case.

“What we do know is that the cold weather will kill some of the ash borers,” says Pest Management Biologist Fiona Ross “but we also know that it will not kill them all.”

The emerald ash borer is roughly the diameter of a penny and can burrow underneath the bark of trees.

According to Ross, recent in-lab testing shows that roughly 75% of the ash borers die at temperatures colder than minus 30. However, she acknowledges that in a real-world scenario that number is likely much lower.

Ross indicates that the ash borer tends to bed down beneath the bark of trees during the winter months, providing them with some insulation and total protection from the wind.

“Often when we think about cold Manitoba weather we think about the wind," says Ross, "but windchill is not a factor that affects the insects inside of the trees.”

In addition to this, Ross notes that the beetles are not total strangers to harsh winter conditions.

“Though these insects are invasive to Manitoba, they do come from other areas that are also extremely cold, so they are tolerant to some of these temperatures.”

Even if 75% of the insects did perish in the cold, Ross says that their numbers are already great enough that they would still pose a significant threat.

So why are emerald ash borers so bad in the first place?

Being an invasive species, the pests have no natural predators in Manitoba. Similarly, local green and black ash trees have no defense mechanisms against the insects. Without these natural barriers, Ross indicates that the beetles can easily lay their eggs inside of ash trees. Once the eggs hatch, the larvae bore into the tree and feed on its essential tissues.  

“They are slowly killing all of the ash trees in Canada,” Ross states. “And now they are in Manitoba, so all of our ash trees are at risk now.”