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Holes, or ‘exit wounds,’ in the trunk or branch of trees are a sign of infestation. (Charles Harrington/Associated Press)
Holes, or ‘exit wounds,’ in the trunk or branch of trees are a sign of infestation. (Charles Harrington/Associated Press)

WILDLIFE

Will the Asian long-horned beetle ravage the GTA's trees? Add to ...

It’s been a tough year for Mississauga’s trees: they were battered by extreme winds during last July’s rain storm and their branches were dismembered in December’s ice storm. Now they face quieter, but far more diabolical opponents.

They are harbouring insect visitors, which likely arrived from Asia after larvae, each less than half a centimetre long, burrowed into the wooden pallets of shipping containers bound for Canada’s busiest airport. Upon arrival, they probably munched their way out, matured into adult Asian long-horned beetles and set up camp in a few maples, from there expanding their base, leaving behind dozens of damaged, weakened trees.

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Some observers hoped the cold weather associated with the polar vortex would kill off the pest, but it boasts a range of superhero-like biological defences against bitter Canadian winters and has survived the worst of the season. Now, all three levels of government are co-ordinating efforts in a race to eradicate it before June, when it is expected to emerge from hibernation, multiply and wreak even more havoc on the region’s tree population.

“It’s going to be several thousand trees,” said Gavin Longmuir, Mississauga’s manager of urban forestry.“The hope is to have all of the trees removed by then and chipped up and processed, and that eliminates the ability of the beetle to exit the tree and fly and move on.”

The Asian long-horned beetle is among the urban forester’s worst enemies: a female chews a hole into the bark of a tree and lays her eggs, which hatch into larvae. The larvae gnaw their way to the core of the tree, turn into pupae, emerge as adults and munch their way back out. They feed on the layer of woody tissue under the tree’s bark, which interrupts the transport of water and nutrients between the roots and the tree. With their extensive tunnelling, they compromise the tree’s structural integrity.

Asian long-horned beetles first showed up in Canada – Toronto and Vaughan, specifically – in 2003, and the Canadian Food Inspection Agency battled them for a decade, surveying and then cutting down 27,000 trees at a cost of $33-million, before declaring the species eradicated last April. But the celebration was short-lived.

In August, a Mississauga resident found an adult Asian long-horned beetle on his car and emailed a photo of it to the CFIA, which positively identified it in its Ottawa lab, said Ben Gasman, an inspection manager with the CFIA. The beetles are distinctive creatures: their black bodies are usually two to four centimetres long and covered in rows of parallel white spots. Their name comes from their long, curly black-and-white antennae.

Dozens of CFIA workers were deployed to scour a 2.5-kilometre area in Mississauga’s Malton area and a small segment of western Toronto for signs of infestation: some climbed trees looking for “exit wounds” – holes in the trunk or branches, others examined treetops in cherry pickers, looking for leaf damage, Mr. Gasman said.

The urban areas of Southern Ontario are particularly vulnerable to pests such as the Asian long-horned beetle because they are where the majority of containers arriving in Canada are opened, said Taylor Scarr, a provincial forest entomologist with Ontario’s Ministry of Natural Resources based in Sault Ste. Marie.

They’re hardy creatures, he explains. The Asian long-horned beetle, like its beetle cousins, probably uses a combination of strategies to prevent freezing in the winter: producing an internal antifreeze (a sugar alcohol), forming a protective wax on its exoskeleton that repels water and shedding some of the water content in its body when the temperature drops. It is also protected from the elements deep within trees in the winter.

All the maple, willow, poplar and birch trees in the regulated area will likely be removed, Mr. Longmuir said. Included in that is Wildwood Park, the only significant green space in what is a largely industrial part of the city. It could easily be a decade before all the tree-planting is done to replace the loss, and the city will have to avoid all 10 types of trees prone to attack by the Asian long-horned beetle.

Being strangers in a strange land actually makes it easier for them to proliferate here, Dr. Scarr said.

In China, trees and beetles “have evolved together almost like in an arms race, when one tries to get ahead of the other, the other reacts.” So while trees in the beetle’s native environment have developed defences against them, the resistance level of Canadian trees “is a lot lower, their ability to fight off insects like Asian long-horned beetle is greatly reduced.”

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