Why invasive moth caterpillar infestation breaks records in central Canada

During the record outbreak, an invasive moth caterpillar was stripping trees in southern Ontario and most of Quebec and pouring feces from the canopy. This is why their population has exploded and what can be done with them.

What are these moths and what do their adults and caterpillars look like?

The moth is called “LDD” moth because of its scientific name Lymantria dispar disparLDD moth is the preferred name of the Ontario Invasive Species Project, which stated that its original generic name “Gypsy Moth” was derived from a culturally offensive slander.

The caterpillar grows to six centimeters long. They are hairy and can be identified by five pairs of blue dots and six pairs of red dots on the back.

Adult male moths are brown and will fly around. Adult females are larger, white and cannot fly.

Female LDD moths are white and cannot fly. Males can fly and are brown. (Emily Chung/CBC)

Where did they find it?

At this point, they are found throughout most of southern Canada.

They are native to Europe and Asia, but were introduced near Boston in the United States by astronomer and amateur entomologist Étienne Trouvelot in the 1860s. He wanted to test their potential for making silk.They escaped and became an invasive species

According to David Dutkiewicz, an entomology technician at the Invasive Species Centre, a non-profit organization based in Susan, they first arrived in southern Canada in 1969. Mary, Ontario is a conservation organization focused on the prevention, detection, response and control of invasive species in Canada.

The current population explosion has mainly occurred in southern Ontario, but Quebec has reported outbreaks in the Montrégie area and near Montreal (Boucherville, L’Île-Perrot, National Park Dumont-San Bruno) and the Outaouais area. The Mauricie region and the vicinity of Quebec City are less populated.

What kind of damage can these moths cause?

Unlike many other picky caterpillars, these moth caterpillars have a large appetite and eat a wide range of food, including oak, birch, poplar, willow, and maple. Toronto Forest Health Inspector Joel Harrison-Off said they eat about twice the number of native caterpillars during a period of the year. Although they are eaten by some birds and mammals, their consumption is not enough to really reduce the population.

When it broke out, they could strip the leaves of the trees completely, just like they did with the oak trees in Toronto High Park.

As of mid-June, the caterpillars had almost completely stripped the leaves of the oak trees in Toronto High Park. (Oliver Walters/Canadian Broadcasting Corporation)

Generally speaking, trees can be restored. But some tree species, such as oak trees, have a harder time to regenerate their leaves.

Harrison-Off said that the stress and energy required by trees, especially under stressful weather conditions such as drought, make it more difficult for them to resist pathogens.

“These trees, due to fallen leaves, some of them will begin to die in the next few years.”

How serious is the epidemic this year?

These moth outbreaks are cyclical, leading to outbreaks or infestations every ten years or so, lasting one to three years. In years with good weather conditions, the numbers will rise, and then fall due to fungal or viral infections that spread among the population. Previous outbreaks occurred in 1985, 1991, and 2002.

The current outbreak in Ontario began in 2019, and the following year, moth caterpillars lost more than 580,000 hectares of leaf-a record. “What you see is the size of Prince Edward Island, basically the leaves that fell last year,” Dutkiewicz said.

He said that this year’s final statistics will not be released until August, and now, we are expected to see a similar number of fallen leaves and “another record-breaking year or close to it.”

Watch | “For many people, trees look dead”:

Alistair MacKenzie of Ontario Parks said he is not too worried that LDD moth caterpillars will destroy one of the province’s rarest ecosystems. 2:37

In contrast, 1985 was the worst outbreak before, with 350,000 hectares of fallen leaves at its peak.

Harrison-Off said that this year, LDD moths were found in parts of Toronto that have never been seen before, including people’s property: “We have received a lot of responses and people are working hard to respond and understand [LDD] Moth. “

Why is it so bad?

Part of the reason is natural circulation. But the weather conditions this year are also ideal, Dutkiewicz said-a warm winter, and then a dry spring.

Moths cannot survive long-term in environments below -20 degrees Celsius, which is why they are limited to southern Canada. The wet spring helps to grow fungi that kill them.

“We have not had these types of natural events… in order to reduce the population,” he said. “This is really a series of perfect weather events.”

Will climate change make the situation worse?

David Featherstone, a senior ecologist at the Nottawasaga Valley Conservation Agency, about 100 kilometers north of Toronto, predicts that these moths will begin to spread northward to central Ontario.

He added that droughts and extreme storms also put pressure on trees and forests, making them unable to withstand the leaves peeled off by LDD moths and having to grow again.

What can be done about LDD moth infestation?

Some cities in Ontario For example, London, Ontario, spraying bacterial insecticide Call BTK to control the epidemic. Dutkiewicz said that some conservation authorities also carried out targeted spraying to protect “high-value trees.”But Ontario Park says it is Let nature go with the flow.

Joel Harrison-Off, a forest health inspector in the City of Toronto, said the city uses targeted treatments to deal with LDD moth infestations, including vacuuming eggs and spraying or injecting pesticides Protect specific trees. (Oliver Walters/Canadian Broadcasting Corporation)

Harrison-Off said that BTK has the potential to kill many beneficial native caterpillars in environmentally sensitive areas such as High Park.

On the contrary, the City of Toronto does have targeted on-site treatment.

“We vacuumed away millions of eggs,” he recalled. Some trees, such as oak trees, were injected with pesticides or sprayed alone. As part of the public education campaign, the city also mailed 40,000 pamphlets about this pest.

He pointed out that moths are mainly spread by humans because they don’t fly well (females can’t fly at all). For example, people may attach eggs to cars when visiting a city park, and these eggs may hatch in their huts or other places.

Can you do something to them on your property?

Dutkiewicz recommends that people dispose of moths on a small number of trees on their own land. A technique can also be used, which involves tying burlap about chest height around the tree trunk. The caterpillars like to hide there under the shade of trees until mid-July. Afterwards, they can be taken off and poured into a bucket of soapy water.

Watch | Volunteers work hard to stop invading moth caterpillars in Hampton Park, Ottawa:

Resident Sharon Boddy said that many trees in Hampton Park are threatened by LDD moth caterpillars, forcing volunteers to capture and remove as many of them as possible. 1:45

After Labor Day, when the adults lay their eggs, you can also find their eggs and scrape them into soapy water with a butter knife or a painter’s spatula. Dutkiewicz said they are brown, similar in texture to the skin of a tennis ball, and can be found under branches or in tree crevices.

But the biologist interviewed by CBC News for this article pointed out that because these moths do not usually kill trees, they are actually less harmful than many other invasive species and are the species we will have to coexist with. .

“They won’t disappear anytime soon,” Featherstone said. “And we just need to adapt to humans and ecosystems.”

Female LDD moths have egg masses that can be scraped from trees to control their numbers next year. See a pupa in the lower left corner. (Emily Chung/CBC)

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