Return time for a 99 percent emerald ash borer (EAB) prepupae mortality event as predicted by the probability of −35.4 °C underbark temperatures given by a Newtonian cooling model relating daily air temperature minimum to underbark temperature for annual winter minimum temperatures from 1993–2013. In addition to return times, areas where air temperatures cold enough to cause underbark temperatures colder than −35.4 °C have been observed at least once between 1993 and 2013 (light blue). Circles indicate major urban centers in Canada considered. Purple line gives range of four major Fraxinus species in North America as indicated by Little (1971). Graphic: Cuddington, et al., 2018 / Biological Invasions

17 May 2018 (University of Waterloo) – More Canadian cities will experience damage from the emerald ash borer than previously thought. As a result of climate change and fewer days of extreme cold, the beetle may eat its way further north than originally estimated.

Kim Cuddington, a professor of biology at the University of Waterloo, led the team that produced a probability map for North America showing where the emerald ash borer is likely to kill trees.

“We ran specific predictions to help Canadian cities decide if they need to make plans before they’re affected,” said Cuddington. “Calgary is likely to experience damage, as are Thunder Bay, Prince George and Winnipeg. Edmonton and Saskatoon are less likely, but they should remain vigilant.”

So far, the wood-boring beetle has wiped out tens of millions of ash trees and will likely cost municipalities $2 billion. Still, people expected Canada’s extremely cold temperatures to stop the species’ rapid migration.

“This should be a wake-up call for how we think about invasive species,” said Cuddington. “We need to develop preemptive measures as well as mitigate potential impacts. By the time we see the damage, it’s almost too late.”

According to previous studies, prepupae can survive in temperatures as low as -34ºC. Cuddington and her group confirmed the temperature found under the bark where the insect overwinters is warmer than the outside.

“We took a different approach from traditional range maps and charted the statistical probability of under-bark temperatures being above this lethal limit for at least six years,” said Cuddington. “That’s just long enough for the insect to kill its host tree.”

This is one of the first studies to couple an extensive empirical data set with measures of climate variability using a mechanistic modelling approach. Cuddington says researchers need to think more carefully about how a changing and unpredictable climate relates to the biology of an invasive species and their risk of doing damage, both economically and ecologically.

The research appears in the journal Biological Invasions.

Climate change broadens threat of emerald ash borer

ABSTRACT: Emerald ash borer (EAB; Agrilus planipennis, Coleoptera: Buprestidae) causes large economic costs by killing ash trees (Fraxinus spp.): a process that takes several years of infestation. We suggest that the most important prediction regarding this species is not whether EAB can persist indefinitely in a new region, but whether it can persist long enough to kill trees. We use a mechanistic model of overwintering mortality of EAB prepupae to identify Canadian cities and more generally, those areas of North America at risk of impact. Although we have previously used a Newtonian cooling model to predict underbark temperatures of ash from meteorological data, we show that a linear regression model has smaller errors for the low winter temperatures relevant to EAB mortality. Using this regression model we generate distributions of predicted underbark temperatures which we then use to predict the return time of weather events cold enough to cause either complete (99%) or partial (75%) mortality of overwintering EAB prepupae. We find that most of North America does not experience extreme cold events frequently enough to prevent ash mortality from EAB (i.e., more frequently than every 6 years), and therefore conclude that large economic impacts are likely throughout the continent. However, if relatively frequent partial mortality events are sufficient to reduce ash mortality, there is a possibility of northern refugia for ash species, and some northern Canadian sites may escape the costs of this non-native pest.

Probability of emerald ash borer impact for Canadian cities and North America: a mechanistic model



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