Pests are destroying Canada’s trees — and a warming climate threatens to send more insects north

Terry Hoover first noticed the fuzzy brown clumps on his maple trees in the winter of 2019. Each one was about the size of a quarter, and there were at least 10 on every tree of his 50-acre sugar bush outside Atwood, Ont. Had they always been there? In all his years making maple syrup, he’d never noticed them before.

Hoover has been tapping maple trees since 1967, when he was eight years old and terribly allergic to nearly everything else on the family farm. His asthma kept him off the fields through most of the year, except in the winter and early spring when the cold killed off all the goldenrod and ragweed, and he was free to tromp between the thawing trees and collect the flowing sugar. He would boil the maple water down for hours over a little outdoor fire — a great excuse for a young boy to be playing with matches, which were otherwise forbidden.

Over the years, this hobby would turn into an obsession; what insiders call the sugars.

“It’s a terminal disease,” he jokes. “Once you have the sugars, you have to keep doing syrup year after year.”

These days, Hoover and his wife Diane own and operate their own organic tapping company, Hoover’s Maple Syrup. They’ve seen the industry go through a multitude of changes, from rechargeable cordless drills (“fantastic!”) to climate change.

Though he didn’t realize it yet, the fuzzy brown clumps in Terry’s sugar bush were egg masses of the voracious, leaf-eating LDD moth (formerly known as the gypsy moth), which have been on this continent for over a century. Their numbers have skyrocketed in tandem with a warmer climate and extended feeding season. The affected area in Ontario alone has jumped from 47,203 hectares in 2019 to 1.77 million in 2021, slightly larger than the state of Connecticut.

According to Environment Canada, the overall economic impact of invasive species in Canada, including plants and living creatures, is staggering: about $7.5 billion annually, and the ballooning cost of pests isn’t unique to North America. Studies show the annual global cost of invasive insects has exhibited a consistent threefold increase per decade since 1970, with the latest “grossly underestimated” cost in 2016 being US$70 billion.

Hoover didn’t do anything about the egg masses in 2019. He and his wife almost never went into the sugar bush during the summers, when the mosquitos are out in full force and the trees aren’t producing any sugar. If they had, they might have noticed a few more warning signs: leaves pockmarked with a distinctive shotgun-spray pattern of nibble holes or the tap-tap-tap of feces falling like rain to the forest floor.

By the time they finally returned to the bush in the winter of 2020, the number of clumps had tripled: 30 to a tree, at least.

Each egg mass holds 100 to 1,000 eggs, and come spring, caterpillars would emerge and crawl up into the canopy, stripping away roughly 50 per cent of Hoover’s bush. The canopy is usually so thick that driving through the forest requires headlights, but there was no need in the summer of 2020. There was plenty of sunlight streaming through the skeletal remains of the maple leaves.

“It was scary to look at,” Hoover recalls. “Only 25 per cent of the leaf was there. The rest was all eaten away, with little veins sticking out like fingers.”

A particularly indiscriminate eater, a single LDD caterpillar can devour one square metre of oak, pine, spruce, maple or birch leaves in a single season. Hardwood trees like maple can handle a couple of years under attack, but they’ll be more vulnerable to other infestations and diseases, and sustained populations of this magnitude could spell the end for many small maple syrup producers, including me.

My family owns a small hobbyist sugar bush just off the island of Montreal, in a neighbourhood that used to be flat pasture land. The slow resurrection of the forest has wooed back much of the natural wildlife. We tap our maple trees among flocks of irascible turkeys and herds of deer, stalked by occasional coyotes and my own hopeful dog, Goose.

One fall morning, my sister and I joined David Dutkiewicz, an entomology technician with the Invasive Species Centre (ISC), on a “pest tour” in Limerick Forest just south of Ottawa. Dutkiewicz and his colleague, Derissa Vincentini, led a small group of concerned tappers and farmers through the park, pointing out various signs of infestation and handing out wood samples.

At the start, Dutkiewicz held up a wood and glass display case of his own making, with an Asian longhorned beetle pinned inside. The beetle posed a serious threat to Canadian sugar maples when they were first sighted in 2003, and then again in 2013. After the second sighting in Ontario, all the maple trees within 800 metres of Toronto’s Pearson International Airport were cut down to slow the spread, and wood pallets coming into Canada from overseas must now be heat-treated. The pest is currently considered eradicated, though federal agencies still keep a close eye out.

Since the 1950s, temperatures in Canada have risen twice as fast as the global mean, about 1.7 C overall. Where our cold Canadian winters have long acted as a barrier to entry, warming climates have allowed many enterprising bugs to creep in, like the hemlock woolly adelgid and spotted lanternfly.

Provincial groups like the ISC rely heavily on local reporting to keep track of invasive insects. The centre investigates tips that come in over a dedicated hotline, answering questions and, in some cases, alerting the federal Canadian Food Inspection Agency (CFIA) to suspicious findings.

Dutkiewicz, who personally answers some calls, remembers one man inquiring about a set of wooden wind chimes he’d brought back from the Dominican Republic with “bugs coming out of it.” Dutkiewicz told the man to seal the wind chimes inside a plastic bag and wait for a federal agent to arrive.

The assigned agent later identified the bugs as invasive bark beetles, and the souvenir and its unwelcome hitchhikers were summarily destroyed.

The ISC and the CFIA also monitor social media websites like Reddit and Facebook for mentions of problematic species. Partner apps like iNaturalist use artificial intelligence to flag suspicious photos uploaded by users, and teams of passionate amateurs and professionals crowdsource these findings to build tracking maps and share information, hoping to catch pests before they can establish themselves.

Partway through the tour, an LDD egg mass was spotted high up in a looming maple tree. A spongy brown patch that blended right into the bark. Vincentini, who helps run the centre’s annual Egg Mass Scraping Contest, patted herself down looking for something to remove it with.

“If you spot an egg mass, scrape it into soapy water and leave it for 72 hours, then throw it out,” she said. A paint scraper or butter knife will do the trick.

That is, unless you own a sugar bush with thousands of infested trees, with 30 or more masses each, like on the Hoover Farm in Atwood in 2020.

Terry Hoover ultimately paid a local aircraft company to spray his property with Btk, a bacterial agent toxic to LDD caterpillars. The service cost him about $100 an acre, though prices can go as high as $250. He spent $5,000 for the whole bush.

“It was a lot of money,” he muses. But it worked: this summer, the canopy was completely closed with no defoliation at all.

Hoover says it’s difficult to quantify exactly how much money they lost to the bugs in 2020 because last year’s haul was already so poor after a warmer-than-average winter. What he can do is look over the fence at his neighbour’s bush, where they haven’t sprayed any treatment and the trees are still largely defoliated.

In my family’s case, I wouldn’t be able to afford the spray required to save our bush if the moths invaded. Though it may not be up to me, as these treatments have gotten harder to come by. Zimmer Air, the company that sprayed Terry’s property, felt an “overwhelming strain” in 2021 after an explosion in demand, and it has had to put its services to smaller bushes on hold.

Christian Messier, a professor of forestry at the Université du Québec en Outaouais, says homogenous forests are largely to blame for such unrelenting pest outbreaks in sugar bushes and other forests. Maple tappers often cut all but the sugar maples from their bush, but Messier’s research shows mixed forests with many tree species are far more resilient.

“Managed forests tend to be less diversified, more homogenized over large areas,” Messier says. He estimates a quarter of the forests in Canada, almost all of the southern boreal and British Columbia, have essentially been turned into tree farms: dense, simplified forests that are perfect targets for fire and pest infestations.

Municipalities suffered the same folly in the 1950s and 1970s, when neighbourhood streets across Canada were left bald after Dutch elm disease swept through the country on the backs of invasive beetles, infecting elm trees wherever they went.

An annual injection of fungicide is required to salvage an infected tree, and many municipalities opted not to invest. Untreated trees died and were cut down en masse, and roads where nothing but elm trees had been planted — in a uniform style alien to actual forests but quite vogue in residential areas — were suddenly barren.

In their place, ash trees were planted. Of matching age and species… You probably know where this is going.

Enter the emerald ash borer in 2002, a wood-boring beetle with a singular focus. It attacks all species of ash tree, killing 99 per cent of those it infests, leaving behind mesmerizing, serpentine galleries in the bark of its victims. Its distinctive D-shaped exit hole is about the size of the D in “Canada” on the loonie.

Around Hoover’s bush and my own house, the solid carcasses of infected ash trees have been allowed to fall slowly over time, consumed into the forest without much intervention. But densely populated cities can’t afford to be so laissez-faire. Dead trees pose a risk to the surrounding area and are cut down as soon as they’re noticed. In Montreal’s parks alone, millions of trees have had to be removed after the city failed to inoculate them in time.

One of the most expensive pests in Canada is the mountain pine beetle, which killed an estimated 50 per cent of British Columbia’s commercial pine between 1998 and 2009. A recurring pest, its population has historically been balanced by local predators and winter climates.

However, warming weather over the past decade allowed the beetle to migrate over the Rocky Mountains and much further north into B.C. and Alberta, where they’ve made quick work of local forests with little natural defence against them.

Prof. Allan Carroll, an insect ecologist and professor of forest entomology at the University of British Columbia, says that when the insect reaches epidemic levels, it will kill the vast majority of the mature pine trees over a landscape extremely quickly.

This is exactly what began happening in Jasper National Park in 2016. Striking aerial images of the park, which has lost over 163,000 hectares to the beetle, show a sickly reddish-brown scar of dead trees winding its way through the otherwise lush pinewood forest.

The greatest danger after such a massive incursion, Carroll says, are high-intensity fires fuelled by the large tracts of uniformly old, dead trees left behind.

Total eradication of an invasive species is rarely possible, but educated communities and proper forest management practices can help manage the damage.

“The best defence is vigilance,” Dutkiewicz told our little group at the end of his invasive pest tour in Ontario. Colourful info packets were handed out, with pens and magnets with the Invasive Species Centre’s hotline number prominently displayed.

The next day, I decided to investigate my own sugar bush. Warily, fact sheet in hand, I tried to spot any of the LDD moth warning signs I’d just learned about: clumps of fuzzy brown egg masses, skeletal leaves, dying trees.

Losing my family’s maple trees would be devastating to the property, but our 30-odd taps are small potatoes in the grand scheme of things. Canada produces about 75 per cent of the world's maple syrup, with exports valued at $515 million in 2020. The vast majority of this comes out of Quebec, which is the world's largest producer.

More than that, maple trees and syrup have been intrinsic parts of Canada’s identity for centuries. To say nothing of the flag, sweet syrup was valued and used extensively by Indigenous peoples long before the arrival of European settlers, and tapping has helped many amateurs get outdoors as a popular pandemic hobby.

“When you sit down and you put the syrup that you made on your pancakes, there’s a real gratification there,” says Hoover. “You managed the whole process, right from the beginning through to the end when you put it on your plate.”

After a couple of hours poking around, I didn’t find any evidence of the moth in our bush. It’s only a temporary relief. With everything I’ve learned, I know it’s only a matter of time.

If you’ve seen a suspicious-looking bug, consider calling it in to your local agency.