Hemlock trees have a new invasive enemy

hemlock woolly adelgid wool balls Courtesy Ontario Ministry of Natural Resources and Forestry

Ontario’s latest forest invader looks like “invasive fluff,” says Canadian Forest Service research scientist Chris MacQuarrie. And really, how scary is that? 

Plenty scary for anyone who values the province’s dense stands of hemlock. 

Despite its fuzzy appearance, the aphid-like Hemlock Woolly Adelgid (HWA) literally sucks the life from its victims—a tiny vampire that “quickly overwhelms the tree’s ability to defend itself,” MacQuarrie says. “It’s another invasive that kills its hosts really quickly and has the potential to change ecosystems.”

The HWA landed in Virginia on Japanese nursery stock in 1951. Since then it has been spreading through the eastern States towards the Great Lakes, riding on infected wood, catching a lift on the wind, or even cruising on migrating birds. In 2017 the HWA was discovered in southwestern Nova Scotia, where MacQuarrie says it’s causing “significant mortality.” 

Nature scrapbook: meet the hemlock tree

Now it’s Ontario’s turn. This past summer researchers found the bugs in hemlocks near Grafton. Infested trees were found within about 40 acres of a mixed woodlot, with many displaying extensive damage, though an exact number of trees killed by the pest is not available. To contain the pest, the Canadian Food Inspection Agency (CFIA) has filed a Notice of Prohibition of Movement on the site, preventing the movement of wood or wood material off the property.

It’s not the first sighting of HWA in Ontario—during the past decade, isolated infestations were wiped out in Toronto and the Niagara Gorge, and another Niagara outbreak is contained by farm fields and development. But the Grafton bugs are close to Ontario’s hemlock heartland, stretching from the Ottawa Valley through Algonquin Provincial Park to the Kawartha Lakes and Muskoka District. If the bugs spread, the ecological impact could be severe: hemlock provide crucial habitat for everything from moose and deer to brook trout and Blackburnian warblers. The trees’ towering foliage also cools riparian areas and buffers shorelines and ravines from erosion. 

Battling invasives with slingshots

So while researchers look for ways to control the bug, MacQuarrie’s asking cottagers and landowners to track new outbreaks by scouting for telltale woolly fluff at the base of the hemlock needles, and reporting sightings to the CFIA or the Ontario Ministry of Natural Resources and Forestry. 

The HWA secretes this waxy, fuzzy coating to protect and insulate itself and its eggs. Infestations usually start near the tops of the tree and work downward. “Be observant if you see declining hemlock,” MacQuarrie says. “Usually once the insect gets down to eye level it has already been there for a while.” 

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