Exotic Beetles Put
Ontario Trees at Risk

November 19, 2003

By Rachelle Cooper

Prof. Gard Otis holds a piece of bark from a tree that has been ravaged by the emerald ash borer.
Photo by Grant Martin

Trees in southern Ontario are in danger, says Prof. Gard Otis, Environmental Biology. Ash, maple, birch, willow, elm and fruit trees are all at risk because of two exotic beetle species that have made their way to North America, he says.

One of the pests, the Asian longhorned beetle, was recently discovered in Toronto, and it's hoped the insect can be contained to a small region of that city, says Otis. But another Asian beetle, the emerald ash borer, has already killed thousands of ash trees in the Windsor area.

Working with graduate student Nicole McKenzie, Otis is helping to detect and contain emerald ash borers before they spread across the country.

"When I heard about the borer, I saw it as a research opportunity," he says. "I was lucky and got linked with Canadian Forest Service researchers who are spearheading a number of projects to understand everything we can about the beetle."

Most people barely notice dead trees, let alone take the time to stop and look at what may have killed them. That's why both species went undetected for several years.

"For both these beetles, until the adults emerge and there is an exit hole in the tree or trees are dying in large numbers, there is little evidence they are infested," says Otis. Only if you look closely for symptoms and peel back bark will you see their mark.

"The discovery of the Asian longhorned beetle in Toronto came as a huge surprise," he says.

One of the people called on to help diagnose the bug during the initial outbreak was Otis's colleague Prof. Steve Marshall, who has overseen Guelph's insect collection since 1982.

The Canadian Food Inspection Agency (CFIA) is now co-ordinating a survey of the areas infested in Toronto. "If the beetles get into the nearby forests along the Humber River, it's going to be really hard to stop them or detect them," Otis says.

He notes that the current development stage of the pests is buying the CFIA some time. "Luckily, the beetles are done flying for the year. The CFIA has the winter to complete the survey and figure out what to do."

There are only two ways to destroy the beetle: cut, chip and burn affected trees, or inject the trees with insecticides that kill the beetle larvae as they feed. Otis says the city of Chicago has been successful in containing the beetle through cutting and chipping trees, but new infestations continue to be found around New York City.

It's vital to find a solution to the problem before spring, when adult beetles emerge from trees and take flight, says Otis. "Because they're not very host-specific, longhorned beetles could have a big impact. The effects on shade trees, forests and the maple syrup industry could be devastating."

In contrast to the relatively slow decline of trees attacked by the longhorned beetle, trees infected with the emerald ash beetle have been dying rapidly in Windsor and southeastern Michigan.

"Trees in Windsor that were healthy in spring were dead by fall," Otis says.

There has been a general decline in ash trees for a number of years, referred to as "ash decline." It was only in May 2002 that unusual D-shaped holes were noticed in dead ash trees in Michigan.

"As soon as inspectors started looking under the bark, extensive galleries, distinctive larvae and small bright green beetles about one centimetre long were found," says Otis. "They put two and two together and realized that these insects were at least partly involved in what was affecting ashes."

An estimated six to 10 million trees in Michigan have died as a result of this beetle. Many thousands of trees in Essex County have died as well.

"By fall, it's difficult to tell a live ash from a dead ash, so surveying them is really quite difficult and not very efficient," says Otis. "Inspectors look for holes, swellings and cracks on the bark as well as crown dieback. If you find the distinctive galleries under the bark or D-shaped holes, then the presence of the emerald ash beetle is confirmed."

One focus of his research has been the ash beetle's mating behaviour.

"If we knew there was a sex attractant, then it might be possible to develop lures for more efficient detection and survey. Although our observations failed to provide evidence of sex pheromones, they suggest that we may be able to use green decoys to attract beetles to sticky traps."

Left to their own devices, neither of the Asian beetles disperses very rapidly. The biggest problem is their almost instantaneous dispersal through humans moving firewood. Despite signs on the 401 and at border points stating that it's illegal to import firewood into Ontario or remove it from a quarantine zone, people are still moving firewood. On the 2003 Victoria Day weekend, more than 300 people were stopped from bringing firewood into just three provincial parks in southwestern Ontario, says Otis.

"If you translate that to the number of people who moved firewood to their cottages and other parks, I think it's pretty hard to believe that there are no outlier populations far from Windsor."

Although he believes Canada is being proactive in its fight against these pests, he predicts that in one to two years, emerald ash borers will be found throughout much of Ontario as they come across the border from heavily infested counties in Michigan and as people inadvertently transport them on firewood.

Otis says that by killing ash trees, these beetles could have a huge impact on the environment. "Ashes are very important along streams and as a food source for wildlife. Right now, it's unclear how the loss of ashes will filter down through the system."

As with the destruction caused by Dutch elm disease and the Asian blight fungus that wiped out American chestnut trees, U of G researchers will likely play a role in the recovery of trees. Henry Kock, the Arboretum's interpretive horticulturist, has been leading an elm recovery project since 1998. With the public's assistance, he's found more than 100 surviving mature white elms in Ontario and has used them to create a living gene bank. Some of the seedlings from this population are likely to exhibit resistance to Dutch elm disease.

Profs. Brian Husband, Botany, and Greg Boland, Environmental Biology, have conducted a survey to locate chestnut trees growing in southern Ontario as part of the World Wildlife Fund's chestnut recovery program.

"We hope to find patterns where trees are healthier in certain areas than others to determine how to bring the chestnuts back to past levels," Husband says.

As for the beetle pests, other than not moving firewood, there's little that can be done to contain them, says Otis. He adds, however, that researchers in China are now searching for biological agents to control the bugs.

"To find effective biological control agents, you go to the area where the insect came from to see what organisms are keeping things in check. Once a pest species has been established and eradication is impossible, biological controls offer the best permanent solution."