Invasive species threatens Haldimand trees
Hemlock woolly adelgid is difficult to spot, measuring less than one millimetre in its active ‘crawler’ stage
A pilot project using 3D-printed traps is tracking an invasive insect species threatening woodlots in Haldimand County and throughout southern Ontario.
Hemlock woolly adelgid is difficult to spot with an untrained eye, measuring less than one millimetre long in its active “crawler” stage.
The aphidlike insect can be detected through woolly egg masses, called ovisacs, that resemble the tip of a cotton swab. The ovisac is typically found on the underside of hemlock tree branches, at the base of the needle and along the stem.
Native to East Asia, the insect was detected in Haldimand last summer through the hemlock woolly adelgid monitoring network, a partnership between the Canadian Forestry Centre, the Invasive Species Centre and the Canadian Food Inspection Agency.
The 2023 pilot project deployed 50 3D-printed traps across southern Ontario resulting in a new detection in a Haldimand woodlot.
The traps include a microscope slide dipped in petroleum jelly that captures the adelgid at the crawler stage. The slides are returned by mail to the Canadian Food Inspection Agency to confirm the presence of adelgid.
Victoria Derry, a forestry health biologist at the Great Lakes Forestry Centre, said hemlock woolly adelgid was confirmed in a Haldimand woodlot last summer through the pilot project, following a visual inspection and DNA extraction.
The invasive species was found in the Niagara region in 2019, but last year’s pilot project was the first confirmed detection in Haldimand.
“It was great and successful to show that the program works, but also not wonderful to see that we had another site found,” Derry said in an interview.
Trees infested with adelgid will display foliage loss, discoloration and premature needle loss. The insect consumes sap from the tree at the base of the needles, leading to needle loss and dieback over time.
Derry noted hemlock woolly adelgid can be spread by birds or through human interaction.
Following one of the mildest winters on record in southern Ontario, she anticipates an earlier adelgid season this year.
“It didn’t get cold enough to see significant cold mortality,” said Derry, noting a lack of consistent -20 C temperatures needed to freeze out the pest.
Last year, researchers spotted the first ovisacs in the Niagara region in late April, Derry said.
“This year we started seeing eggs in the Niagara area about midMarch. So it’s about a month and a half ahead right now. That’s kind of what I was expecting with how weirdly mild our winter was.”
Property owners can apply to join the hemlock woolly adelgid monitoring network through the Invasive Species Centre at invasivespeciescentre.ca. Sites will be prioritized based on the number of hemlocks in the tree stand, with an emphasis on southwestern Ontario.
You can also report hemlock woolly adelgid sightings directly to the Canadian Food Inspection Agency, through the agency’s website or the Survey 123 app.
Madison Sturba, program development co-ordinator for the Invasive Species Centre, urges anyone visiting a stand of hemlock trees to take precautions against spreading the woolly pest.
In an interview, Sturba noted ovisacs spun on trees in the fall can be spotted in the spring. The waxy and woolly ovisacs protect eggs over the winter, allowing the species to reach the crawler stage in warmer temperatures.
“These insects will kill hemlocks within three to 15 years and, in the more severe infestations, you can see that foliage discoloration, premature needle loss, dieback and thinning crowns,” said Sturba.
If you’re walking through a stand of hemlocks, you can flip over the branches to look for the woolly ovisacs or check twigs that have fallen, Sturba added.
To avoid spreading the pest through human interaction, Sturba recommends carrying a lint roller to clear your clothes and hair of the tiny insects or eggs found in the ovisac.
“Survey 123 is a great tool to report hemlock woolly adelgid sightings,” said Sturba.
Even if there are no apparent issues, property owners can help researchers track the presence of hemlock woolly adelgid by reporting both healthy and unhealthy hemlock trees.
“So it really helps everyone to know where hemlock woolly adelgid is, but also where it’s not,” Sturba added.