The emerald ash borer:
tiny, green, deadly
By Dan Blouin

OTTAWA — The emerald ash borer seems just like a plain old bug. It looks a bit like a grasshopper. It's bright green and no bigger than a penny.

But this bug has cost Canadian and U.S. forest industries millions of dollars — it's the focus of many lives. Including Ken Marchant’s.

Marchant is a plant protection officer with the Canadian Food Inspection Agency. His job description says it all — he protects plants. And for the past three years, he's been trying to do it by chasing a tiny green bug around Southern Ontario.

The bug is winning.

"It's certainly the zebra mussel of the land," he says. "Beetles like this just are not supposed to be killing trees like this. It is a classic alien invasive species."

It began a few years ago, when people in Michigan started noticing that a lot of healthy ash trees were suddenly dying.

And no one knew why.

But then in 2002, forestry officials found a little green bug. One that no one had ever seen before.

"...where did this thing come from?" he says. "That was one of those things that tweaked us at the beginning...eventually a specimen was found in a Czech insect institute."

The insect, they learned, was called the emerald ash borer and is found all over eastern Asia. Marchant says locating it here in North America was — and still is — a real problem.

"It is extremely difficult to detect," he says. "It doesn't have any pheromones. We still don't know after three years how it finds the ash. It's a fairly cryptic little guy, it doesn't fly around in big swarms, so it's hard to miss it."

Marchant says the ash borer probably came over to North America in packaging materials. He says shipping crates are often surrounded with wood chunks or chips to prevent them from sliding around on ships. New laws require wood coming into Canada and the U.S. to be fumigated and heat-treated, which would kill any dormant eggs. Marchant admits, however, that it's impossible to inspect every stick of wood.

But to find out how to stop the ash borer now, Canadian scientists needed to learn more about what made it tick. So they went to the source.

"We sent teams of scientists to China to look at the problem. And there's virtually nothing in there...it is simply not a problem there."

What they did learn was bad news. The ash borer lays it eggs in the bark of the tree where they hibernate over winter — so Canadian cold won't kill them. When the larvae hatch in warmer months, they eat the outer wood under the bark, forming tunnels that disrupt the movement of water and nutrients inside the tree. After two or three years, the tree dies.

Emerald Ash Borer gallery

The ash borer larvae burrow through the softer layers of the tree, forming galleries like the one shown here. (Photo courtesy of the Michigan Department of Agriculture)

So why wasn't it a problem in Asia?

Barry Lyons, a research scientist with the Canadian Forest Service, says it's all about natural resistance.

"Lots of plants produce what are known as secondary chemicals that are produced in response to insect pests . . . and when insects evolve with a host plant, there's kind of an escalating arms race going on. The plant produces a new chemical and the insect develops a resistance to it and so on."

Lyons says these natural insecticides force these kind of insects to be opportunists — they can only infest trees that are already weak or dying and can't produce the chemicals.

But North American trees only develop resistance to North American pests. Asian insects like the borer aren't affected by their natural chemicals. It's the same way smallpox devastated Aboriginal populations during Western colonization — without natural resistance, even the healthy get sick and die.

"The ashes here just don't have the natural blend of chemicals to fight them off that a tree that had developed alongside it would have," he says.

Another problem with foreign pests is that native predators — like woodpeckers or wasps — don't recognize the borer as being edible. With time, they may develop a taste for the bugs, but Marchant says only about two per cent of the ash borer population is being killed by other animals right now.

So this means the ash borers are free to breed and grow and spread. Stopping that spread is Marchant's main goal — to halt its progress until they learn more about the ash borer and how to kill it.

The stakes are fairly high. According to the Oct. 14, 2003 edition of the U.S. Federal Register, Michigan has lost over $13 million in wood sales alone. Replacing lost trees could cost up to $11.7 billion. The register estimates up to $25 billion in losses if the ash borer spreads to other eastern states.

And it is already coming north.

When the CFIA started fighting the ash borer, the first step was a quarantine. In October 2002, the CFIA banned the movement of ash into or out of the Windsor area. That would ideally stop humans from unknowingly spreading the borer, but it would continue to do so on its own.

Canada had an opportunity the Americans couldn't take advantage of. The borer was moving east from Windsor through Essex County, and was spreading north into the rest of Ontario. But first it would have to pass through a relatively thin stretch of land between Lake St. Clair and Lake Erie. It was there that the CFIA decided to make its stand.

The idea was to create a kind of fire break.

"The Americans never got the breakwall up; they could never really find the leading edge (of the spread)," Marchant says. "The Canadian geography was so much of an advantage, with the St. Clair Lake and Lake Erie, and you're dealing with one of the most treeless land zones in eastern North America. . . the place is only about 0.8 per cent tree cover."

The CFIA planned to stop the ash borer in its tracks by eliminating its food supply. In late November 2003, the CFIA announced that all ash trees and materials would be removed from a 10-kilometre-deep swath of land from Lake Erie to Lake St. Clair. The CFIA also ordered that firewood of all types would not be allowed to leave the ash-free zone, to prevent people from confusing one type of firewood with another.

"At the time we thought probably five kilometres is the maximum it could spread by itself," Marchant says. "The initial recommendation was five kilometres, but after looking more at this we decided to go with 10."

The logic is simple. If the ash borer can only fly five kilometres in search of food before it dies, and if it is surrounded on three sides by either water or land without ash, they would only be able to go back the way they came. And Marchant says that Essex County was already beyond saving.

Map of the Ash-Free Zone

The faint yellow area shows where the ash-free zone was cut, all the way across from Lake St. Clair to Lake Erie. (Photo from the Canadian Food Inspection Agency)

"All of the horror stories about what would have happened to Essex if the emerald ash borer got loose all came true. It was one of those things where we would have loved to be wrong," he says.

But they weren't. Marchant says about 80,000 trees were cut down and either burned or trucked out of the zone over the winter. As spring came around, they were on the lookout for any infestations on the other side of the zone.

And they found them. Marchant says some break-jumpers were expected.

"No one ever said this would eradicate the beetle. We expected it to slow the spread and keep the outliers — and we knew there would be some — manageable...in a perfect world, it would have worked."

Things haven't worked out the way they were supposed to. The ash borer has been found in Chatham-Kent County north of Essex and the ash-free zone in populations much higher than expected. He says it's because people ignored the quarantine.

"These were all the result of human activities. Ninety per cent of them at least can be attributed to human activities. There was someone who had been moving and selling firewood in their backyard, and there was a small unregistered sawmill."

The CFIA has since issued another quarantine to Chatham-Kent and another 34,000 trees are supposed to come down before May.

"The actions we're taking now are going to have a major impact on it," Marchant says. "Without it, the population in Chatham-Kent will explode. Seriously explode, based on what we've seen in Michigan and Essex."

John Enright, a forester with the Upper Thames Conservation Authority located north of Chatham, says there haven't been any sign of emerald ash borer infestations in his jurisdiction, but says he keeps up-to-date on the latest news. He adds preparations are in place in case the ash borer is found.

"People have been contracted again to remove those trees and any ash within 500 metres," he says.

Marchant says there is progress being made on pesticides, but it's impossible to rely on them to solve the ash borer problem.

"There's about a billion ash trees in Ontario, that's a conservative estimate, and most of them are forest trees. There's no way you could ever treat them all," he says. "The only real way that this thing is going to come into balance is that there are some resistant trees are going to show, and that's probably just because they won't taste right. . . that or a natural complement of parasites and predators."

When other predators start eating the bug in large numbers and trees develop defences, the ash borer will then be just like any other native species.

Until then, the CFIA is relying on the fire break to slow the emerald ash borer's spread. But unless people obey the quarantine, it could reach other parts of Ontario, leading to another outbreak - this one without the natural barriers the CFIA took advantage of initially.

"The biggest risk is that somebody's going to be visiting their daughter in Essex or whatever, load up their car with firewood and drive back to Lanark," Marchant says. "We won't know until it happens, and almost by the time you find it, it's too late."

Lyons says people just don't appreciate how dangerous the ash borer really is.

"There's nothing exactly comparable to this one. This is a very aggressive tree-killer. It seems to disperse very quickly, whether through its own means or through humans spreading it, and I suspect the latter. . . it's like nothing we've seen before."

He adds people need to understand the wider importance of trees, beyond just the forest industry.

"Trees are incredibly important things. . . All of the things that trees do, sequestering carbon, cooling houses, air pollution controls, all of these things are very important."

"People in the rest of Canada probably have never heard of the emerald ash borer and don't know it's a threat right now."

To them, it's just another bug.