An invasive insect that attacks hemlocks is expanding its range in Ontario
Hemlock woolly adelgid (HWA) is an aphid-like insect that only feeds on hemlock trees. First found in British Columbia a hundred years ago, and in Virginia in the 1950s, the insect eventually kills the trees. While cases of HWA were found in Ontario as long ago as 2012, all were contained in the Niagara Peninsula. Of the two cases this year, one was in Pelham within Niagara, while the other was in Grafton in Northumberland County.
Hemlock is an important tree for fish and wildlife as well as the forestry industry. The trees assist
with temperature regulation in streams, which allows cold-water species like brook trout to survive. It also provides cover for deer and birds in the winter.
“The impacts to wildlife would include the loss of winter cover for deer, moose, and birds as
well as a reduction in food source for forest animals,” said Alison Morris, coordinator of Ontario’s
Invading Species Awareness Program. “The dense branches of hemlock are a great source of shelter and used as bedding sites for white-tailed deer.”
Signs of an HWA infestation include dieback of twigs and branches on a hemlock tree. The
insects are tiny, less than a millimetre in length in the nymph stage, and the adults look like aphids.
Eggs are amber in colour and contained in a woolly, white sack at the base of the needles from
November to May.
As a result of the latest cases, the Canadian Food Inspection Agency has placed a restriction
on any movement of hemlock tree materials, and firewood of all species, from the City of Niagara Falls, the Township of Wainfleet, and the Town of Fort Erie.
Any suspected cases of HWA should be reported by calling the Invading Species Hotline
at 1-800-563-7711, or by visiting EDDMapS.org or iNaturalist.org.
– Jeff Helsdon