Say what you will about the emerald ash borer and the damage it has wreaked during two decades of munching millions of North American ash trees, you have to admire its cold-weather tenacity.
At minus-10 Celsius, the bug just hunkers down into deep dormancy. At minus-20, it can hang in indefinitely until a thaw kisses it back to life. Only when temps drop below minus-34 will the pernicious pests give up – and die. That fact offers some hope that nature itself could bite back to control the ash borer in places such as frigid Winnipeg, which recently reported its discovery of the invasive species.
As large swaths of Canada and the U.S. Midwest sink into a deep freeze, a Western research team is testing emerald ash borers’ temperature tolerance looking to provide clues as to what may eventually kill the invasive species.
“In minus-30, they’re mostly OK. In minus-34, mostly all of them are going to be dead,” explained Biology professor Brent Sinclair. “The problem is, the temperature in a lab is not the same as the temperature inside the tree bark.”
Originally from Asia, the emerald ash borer (Agrilus planipennis) is an invasive species found this region and in cold-weather areas from Moscow to Sweden to Minnesota. Likely hitchhiking to North America in packing crates in the 1990s, the critter was first detected in Michigan in 2002 and has since spread to three provinces and more than two dozen U.S. states.
Its voracious appetite and unchecked reproduction have meant, in some areas, the ruination of ash trees, which were once one of the most populous and commercially important tree species on the continent.
Attempts at widespread control have been virtually ineffective: chemical treatment – expensive; a firebreak near Tilbury – both futile and politically fraught; and predator wasps – although starting to show promise, difficult to scale up.
Postdoctoral scholar Meghan Duell is working with Winnipeg and with the Canadian Forest Service, based in Sault Ste. Marie, to figure out what the borer is doing in the Manitoba capital city.
Testing in the lab’s incubator indicates an insect extremely cold-tolerant – a sort of Schrodinger’s bug, both alive and not-alive at the same time. “We’re finding super-cooling points – how low can they go before cold kills them?” Duell said.
At super-cold temperatures, ash borers have three survival strategies: generating anti-ice proteins in themselves; forming a thick layer of wax to protect against ice crystallization in their host trees; and filling their cells with gooey-thick glycerol, a natural antifreeze.
“They have so much glycerol that is sometimes too viscous to pipette,” Duell said.
Winnipeg has shipped borers to Western labs where Duell is building models of how temperatures affect them at each stage of development. She is exploring whether they have adapted to that region’s different climate during their northwestern migration.
“Our model suggests they shouldn’t be in Winnipeg,” Sinclair said. “But there are a few things at play. The first thing is that, yes, it’s really cold there. But perhaps it’s no coincidence that emerald ash borer has only just arrived there, after a number of warmer-than-average winters.”
Duell is working with a number of scenarios:
- How long and at what temperatures can the emerald ash borer remain dormant?
- What real temperatures are beneath the tree bark where they spend the winter?
- How do their lifecycles and tolerance differ from those in warmer southwestern Ontario?
- How does their cold tolerance change during a sudden cold snap?
Some lab tests show a mid-winter plummet from 15 Celsius to minus-20, for example, is enough to kill them. But that’s in the lab.
“As it turns out, that never happens in real life outside the lab,” Sinclair said.
Some have recently suggested Minnesota’s extremely cold snap could zap its ash-borer problem for good – but Duell and Sinclair aren’t buying it. Somehow, the beetle has survived in Moscow and Sweden and now at least a few years in Manitoba. So it’s adept at adapting.
“It doesn’t really matter if it’s really cold out,” Duell said. “If the tree is warm, it doesn’t really matter.”
Instead, real-life variables include temperature differences between the outside and inside of a tree, between upper branches and lower limbs and even between north- and south-facing sides of a trunk.
Sinclair, who studies cold tolerance in a variety of insects, said Winnipeg’s infestation is relatively recent, so this work is particularly timely. “Winnipeg is the poster child for taking care of their trees and that’s why they found emerald ash borer there early.”
The Canadian Food Inspection Agency announced last week it has updated its regulated areas to reflect the spread of ash borer to Manitoba and a wider area of Quebec. Moving firewood – including logs, branches and woodchips – is restricted in regulated areas in Winnipeg, Thunder Bay, all of Southern Ontario from Windsor to Sault Ste Marie, most of southern Quebec and a small corner of New Brunswick.
In the United States, various regulations about emerald ash borer are in effect in 35 states.