The borer would have stopped its progression in Canada

After 20 years of devastation, the progression of the emerald ash borer outside already infested areas seems to have stopped, says the Canadian Food Inspection Agency, the federal agency responsible for plant protection. The last territorial expansion was in February 2020 when the insect appeared in several counties in southern New Brunswick.

Pierre Gingras
Special collaboration

In Quebec, several regions such as Charlevoix, Côte-Nord, Gaspésie or even Abitibi are still spared, but ash populations are usually smaller than in already invaded areas. Same situation in Ontario, Nova Scotia and Manitoba, where only the regions of Halifax and Winnipeg are affected.

Several scientists interviewed by Press remain skeptical, however. They maintain that the onset of an invasion is very difficult to detect and that progression should resume eventually. The agency retorts that several traps installed at strategic locations did not capture the borer. The two citizen observation blitzes carried out in August, this year and last year revealed no damage. However, the organization could not specify the number of people who participated in the surveillance.

“This is good news,” says Mireille Marcotte, Acting Director of the Plant Protection Scientific Services Division.

The agency therefore intends to maintain its quota policy. Since last January, the American federal government for its part put an end to its quarantine policy, because the measure has not slowed down the progress of the insect which can easily move on its own. Washington is now focusing on biological control and the planting of resistant hybrids. Ash tree species are the subject of a very important forest industry in the United States, unlike in Canada.

Mature ash trees condemned

Isabelle Aubin has been following the fate of ash trees since the borer was detected in Windsor, Ontario, in 2002. Last summer, the researcher at the Great Lakes Forestry Center in Sault-Sainte-Marie, a division of the Canadian Service des forests, visited the plots it monitors across Ontario.

This progressive disappearance on a continental scale does not mean, however, that the 16 species of North American ash trees (including 3 in Quebec) will disappear. The catch is that after infesting larger trees, the borer attacks young stems as soon as they reach nearly 2 cm in diameter, explains M^me Aubin. The original forest gradually disappears to make way for a myriad of immature shrubs. The impact is significant on the water cycle and on that of nutrients, which directly affects flora and fauna. This is particularly the case of black ash: there are around 71 million in Quebec, one of the rare tree species adapted to wetlands.

Pests and promising hybrids

However, Canadian and American scientists are betting on these trees which take the longest time to die to obtain hybrid ash trees. They could possibly regenerate part of the original forests. Nathalie Isabel, from the Laurentian Forestry Center in Quebec City, dissects the genes responsible for this temporary resilience in these trees. We are talking about one tree in 10,000. Many hybrids are currently being tested, as part of a 10-year project.

A researcher specializing in pest management at Natural Resources Canada, Christian MacQuarrie is working on the introduction of parasitoids. These little wasps parasitize borer larvae with their eggs.

In the United States, tens of thousands of wasps have been successfully released over the years, but parasitoids often take time to have a noticeable impact on the borer. In Quebec, wasp releases have taken place in several municipalities, and one species is already well established in Montreal. “Raising borer in the laboratory to feed parasitoids is extremely complex,” he explains. Then, we must make the releases in kind at the appropriate time. Again, it is very complicated. And the big challenge remains to measure the real impact of these introductions. ”

For Mr. MacQuarrie, these little wasps are unlikely to save the mature trees of today, but should have an effect on the next generation ash trees.

Ash trees, chestnut trees, elms: similar destinies

Introduced accidentally from Asia in the early 1900s, fire blight, a fungus, wiped out as many as 4.5 billion chestnut trees in just a few years, wiping out a thriving forest industry in the United States. The species still exists (around 431 million individuals), but most specimens are small and considered unsustainable in the long term. This is because the disease strikes before the tree has time to flower and reproduce.

Of the nine billion mature ash trees on the continent, hundreds of millions have already died.

Survive only stems emerging from dead tree stumps, which in turn are attacked before they can produce seeds.

However, the impact of Dutch elm disease was different. The American elm is still ubiquitous in our environment, despite its fungal predator. This is because the evil usually strikes older specimens which have had time to reach large sizes and produce a lot of seed.