High in the tops of some of Nova Scotia’s largest trees, a black speck no bigger than a sugar crystal is wreaking havoc.
The hemlock woolly adelgid, first seen in the province in 2017, is an invasive insect moving rapidly through Nova Scotia’s hemlock forests, leaving ghostly trees in its wake. By sucking sap from the base of hemlock needles, the adelgid can kill a tree in less than a decade. The insects leave behind a white substance that looks like wool, giving them their name.
On the campus of Acadia University, scientists are investigating what it will take to find a solution.
A research project led by Acadia is investigating the effects of insecticidal treatment that are being used to control the hemlock woolly adelgid. They’re also establishing a biological control facility that will be used to keep adelgid populations in check.
“For me, the urgency is very obvious,” said Kirk Hillier, a biology professor at the Wolfville, N.S., university and lead researcher on the project. “I’ve seen the dead trees — I’ve seen what we call the grey ghosts of dead hemlocks. So it’s a significant threat.”
Researchers say measures needed to counter a fast-moving danger
The project has two elements. First, it is working to assess the effects of adelgid infestation on biodiversity, as well as the impact of insecticides.
Hemlocks are now treated with two types of insecticide, either by injecting it into the tree or spraying it on the bark.
“This is an unfortunate but necessary element to keeping trees alive, because without insecticide protection these trees will perish,” said Hillier.
In other contexts, such as agriculture, scientists have found potential impacts on pollinators from these types of insecticides. But in Nova Scotia, these potential impacts have to be weighed against the effects of losing the hemlocks entirely.
To assess this, the research will be trapping insects and birds to determine whether there are changes to biodiversity from trees dying in infested areas, as well as the relative risks of insecticides to birds, insects and salamanders.
Acadia researchers are also doing lab work to investigate the impact of insecticides on ground-nesting bees.
A major hurdle for insecticides is that they’re expensive and time-consuming to apply. Despite the efforts of volunteers, private individuals and government agencies, only about 600 hectares of hemlocks have been treated with chemical controls in Nova Scotia.
To help guide treatment to where it’s needed most, the project is testing funnel-shaped traps to detect the adelgid at very low levels, using molecular tools.
“Basically what we’re looking for is not necessarily the insect, but DNA that comes from the insect,” said Martin Williams, genomics research scientist with the Canadian Forest Service, which is partnering on the project.
Without these traps, researchers search for hemlock woolly adelgid in the canopy using pole pruners and slingshots, which is labour-intensive. With molecular tools, traps are left out for two weeks to pick up the traces of insects that fall in. Contents are then DNA-tested in the lab.
“Once you get to a certain point in the infestation, there really is nothing you can do,” said Williams. “If you can do early detection, especially in an urban centre, for example, then you can manage … that location, to slow it down.”
Long-term biocontrol necessary
In the long term, traps will also help detect hemlock predators — an important step, since scientists say saving hemlocks depends on the hemlock woolly adelgid’s natural enemies, including a small, black beetle named Laricobius nigrinus. Since 2023, the Canadian Forest Service has painstakingly collected roughly 12,000 of the beetles in British Columbia and released them in Nova Scotia.
Acadia researchers aim to expand those efforts, using a greenhouse on campus as a rearing and testing facility.
“The longer-term vision is to develop this facility where we can release multiple different insect species to manage this insect pest without the need of insecticides,” said Hillier.
The biocontrol facility will allow researchers to collect a secondary predator that’s present in B.C. called a silver fly.
“[The silver fly] really works in concert with the beetles,” said Hillier.
This requires using the greenhouse to bring in foliage from B.C. that’s infested with the western strain of hemlock woolly adelgid; that foliage also contains silver flies, which will be raised in the lab.
“What that does is it’s a much less expensive, much more high-volume way of actually collecting predators and releasing them.”
Eventually, Hillier hopes the facility could get to the point of releasing 50,000 to 60,000 predators a year in the province.
They also aim to investigate another predator, Laricobius osakensis, which comes from Japan. Laricobius osakensis is an especially effective predator, but needs more safety testing, as it’s a more exotic species. That research will take place at Acadia.
Ultimately, Hillier said, the biocontrol facility will be able to provide predators not just for Nova Scotia, but for other parts of the country, as the hemlock woolly adelgid spreads in other provinces.
‘It’s the morally right thing to do’
Donna Crossland, a forest ecologist who’s been involved in protection measures for hemlock since first learning about the threat when working for Parks Canada in 2017, said it’s important that the project is considering the short- and long-term measures to control hemlock woolly adelgid.
Like many ecologists, she said she was initially fiercely resistant to the idea of using insecticides to protect hemlocks. Over time, she came to see it as a necessary tool, until biocontrol can be implemented.
“It’s a last resort,” she said. “We will not receive any benefit from a biocontrol program in hemlock if we don’t use some chemical control in the interim.”
Crossland commends scientists for getting a biocontrol facility started, but said she’s concerned the province has not yet made a funding commitment to fund a biocontrol program for the long term.
“We need that desperately,” she said.
In response to a question about long-term funding for biocontrol, a joint response from the Department of Natural Resources and the Department of Environment and Climate Change said that the province has committed $3 million to treat high-value hemlock stands, and that Natural Resources is working with Acadia to build the biocontrol facility.
Crossland said government leadership is needed to keep that program running and ensure it doesn’t fall through the cracks in the future.
“It’s the morally right thing to do to conserve something that’s been here in Nova Scotia for thousands of years, and we’re going to lose it at the near blink of an eye.”
Hillier said the pace of that change is why he’s continuing to push for public awareness, and for operational funding for a biocontrol program, because the longer it takes to get that program established, the fewer trees will be left to save — a reality that has direct resonance for many Nova Scotians.
“I’ve worked on a lot of different projects in my career, and this one is actually something that is unique for me because I can look at my living room window, I can walk behind my house, and there are hemlocks everywhere, and I know that many of those trees are doomed. So it’s something that is not esoteric at all — it’s something that is very fundamental.”
