Student uses prism traps across Halifax to research invasive beetle

·4 min read
A prism trap shown in an ash tree in Bedford's Fish Hatchery Park on July 26, 2022.  Researcher Alexandre Caouette is using the traps to study the emerald ash borer before more trees are affected.  (Brian MacKay/CBC - image credit)
A prism trap shown in an ash tree in Bedford's Fish Hatchery Park on July 26, 2022. Researcher Alexandre Caouette is using the traps to study the emerald ash borer before more trees are affected. (Brian MacKay/CBC - image credit)

Halifax residents may think they are seeing bright purple and neon green lanterns or kites around the city.

But they are prism glue traps, and they are part of new research into an invasive species.

Alexandre Caouette, a master's student from the University of New Brunswick, is the one who put the traps in the tops of some of the city's ash trees for samples of the emerald ash borer.

"I've had a lot of people come up to me and think I was setting up for some kind of festival or something like that because of all the colour," Caouette said with a laugh.

The invasive species has been in the city since 2018, but is native to parts of Asia.

The jewel beetle likely got to North America in shipments of goods, he said. When the beetle is introduced to a new environment, the trees in that area often have no defence, allowing the borers' population to grow quickly.

Brian MacKay/CBC News
Brian MacKay/CBC News

The larvae feed on the tree's nutrients as they grow, he said, effectively cutting through the circulation system used to transport water and fuel throughout the tree's body. Infested ash trees usually die within seven years, he added.

The traps, shaped like a prism, use a pheromone blend that works like perfume to the beetles, and mimics the scent of an ash tree under attack, he said. He also has traps in locations in New Brunswick.

To the eye of an emerald ash borer, the green traps represent the leaves of the tree and are likely to attract male beetles that tend to land on leaves.

The purple traps attract the female borers and represent the bark of the tree, Caouette said, because they're likely to land on the bark to lay their eggs.

By trapping both female and male beetles, he said he'll be able to gain insight on "how successful beetles are at mating in those specific areas where we're measuring."

Brian MacKay/CBC News
Brian MacKay/CBC News

Caouette, who's specializing in population ecology, said the borers aren't widespread in the city, but he's looking to get insight into the beetles before more trees are affected.

"One of the hopes is that bringing this information is going to give us a better idea of what is happening to emerald ash borer populations when they're first establishing."

They aren't easy to find when population levels are too low, but the emerald ash borer leaves noticeable signs on ash trees they've infested.

Affected trees will usually have fewer leaves as well as small holes in the bark from where fully grown beetles have emerged.

And under the bark, galleries formed by the larvae moving through the tree can be seen, he said.

Dylan Jones/CBC News
Dylan Jones/CBC News

Already, the bugs are changing the landscape of some city parks. The municipality began removing some 80 ash trees from DeWolf Park in Bedford last week, since many of the trees are dead or dying due to damage caused by the beetles.

Jeffrey Ogden, a provincial forest entomologist, said Nova Scotia is using its own set of prism traps across the province to keep an eye on the beetle in "areas of high risk."

"We have traps set up … to see the spread of the beetle within [DeWolf] park," Ogden said. "We've been doing tree sampling, looking for the insects within the tree ... and we continue to do that as this population explodes."

He said the only place the beetles have been detected so far is in the Bedford area. The province is looking into ways to mitigate the growth and spread of the borer population, Ogden added.

Brian MacKay/CBC News
Brian MacKay/CBC News

"There's fungicides that you can put in a trap; the beetle will fall into the trap, grab these fungicides and then fly off and spread that fungus to other populations of emerald ash borer," as well as parasites that can be released that would feed on the beetle, Ogden said.

"It's a combination of tools.... Maybe this fungicide, maybe some pesticide treatment and then hopefully the biocontrol ones ... can keep the population down to a level where the trees won't succumb to the beetle."

Caouette said he'll be analyzing the data this fall and hopes to have results by sometime next spring. In the meantime, he said that if residents are concerned about the beetle's spread, they should make sure they're not moving any firewood.

"There's a few different ways that emerald ash borers can actually travel, and oftentimes it's in untreated, dead wood," he said.

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