Natural Resources Canada Forest Service scientists accidentally discovered the outbreak of the woolly adelgid, which they say had gone unnoticed for some time, this summer while collecting data on hemlock trees in southern Ontario. Chris MacQuarrie, a researcher with Natural Resources Canada, says the Cobourg find is concerning because it is much deeper in Ontario than the only other known active population of the species in the Niagara region. “This is hundreds of kilometers away from other places where we know the insect is,” MacQuarrie said. “We think it’s been there for a long time because it was big enough and easy enough to see, and it’s already started killing trees.” Hemlock woolly adelgids are aphid-like insects that attack hemlock trees by sucking sap from the base of their needles, draining the trees of their energy and killing them. Their egg sacs look like cotton balls or clumps of snow, making them difficult to spot. HWA poses no threat to humans, but is extremely destructive to hemlock trees, which are used for firewood, lumber and other wood products. Hemlock trees are also indicators of a healthy forest, provide shade for aquatic ecosystems in streams, help deer navigate their trails in winter by blocking snow, and are scenic fixtures in rural Ontario. MacQuarrie noted that the find is quite close to an area where the abundance of hemlock trees is beginning to become apparent. He said there were a large number of dead hemlock trees in the surrounding area, indicating the bug has been there for years, as it usually takes four to six years to kill a tree and may have spread beyond the infected zone. The invasive species can be spread by wind, animal and human movement from saplings, logs, firewood and other wood products. MacQuarrie said the contamination likely spread to some parts of Ontario and Nova Scotia by birds. “In those places, especially in southern Nova Scotia, it’s killed quite a few trees,” he said. “It went unnoticed for a while and so it had a chance to be created.” The bugs were likely introduced to North America in the 1950s from Japan via infected nurseries, according to the Invasive Species Center. It was first discovered in Virginia in the 1950s and has since spread along the east coast of the continent, the Sault St.-based nonprofit wrote on its website. Marie. One factor contributing to HWA’s ability to invade is the fact that it reproduces asexually for most of its life cycle, MacQuarrie said. All it takes to create a population is one female. “So you have a small insect that is hard to find and doesn’t need to mate to reproduce. Those are the conditions to build up the population very quickly,” he said. MacQuarrie said the insect arrived in Canada several times in the early 2010s when it was accidentally introduced to horticultural trees, but populations were later discovered in southern Nova Scotia in 2018 and in the Niagara region of Ontario in 2019. “We can look at the east coast of the US and southern Nova Scotia for examples. Those are places where the insect has been around a little bit longer and where there’s a fair amount of hemlock,” he said. “There was a lot of tree mortality in that area.” Following the discovery of the Cobourg outbreak, the Canadian Food Inspection Agency will survey the surrounding area for any other outbreaks, according to MacQuarrie. He said anyone spotting HWA should contact the CFIA for confirmation and handling. This report by The Canadian Press was first published on September 5, 2022.
