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Gypsy moth caterpillars bare trees and rain canopy droppings down across much of southern Ontario and Quebec, amid record outbreaks. Here’s why their populations have exploded and what can be done about them.
What are gypsy moths and what do adults and caterpillars look like?
Gypsy moths are also known as the “LDD” moth because of their scientific name. Lymantria dispar dispar. LDD Butterfly is the name preferred by Ontario’s Invasive Species Program, which says its original common name is derived from a culturally offensive insult.The caterpillars are up to six centimeters long. They are furry and can be identified by the five pairs of blue dots and six pairs of red dots on their backs.
Adult male butterflies are brown and fly. Adult females are larger, white, and cannot fly.
Where are they found?
At this point, they are found throughout much of southern Canada.
They are native to Europe and Asia, but were introduced to the United States near Boston in the 1860s by amateur astronomer and entomologist Étienne Trouvelot, who wanted to test their potential for making silk. They escaped and became an invasive species
They first reached southern Canada in 1969, according to David Dutkiewicz, entomological technician at the Invasive Species Center, a nonprofit based in Sault Ste. Marie, Ontario, a conservation organization focused on the prevention, detection, response and control of invasive species in Canada.
The current population explosion is located mainly in southern Ontario, although Quebec reports outbreaks in the Montérégie region and near Montreal (Boucherville, L’Île-Perrot, parc national du Mont-Saint-Bruno ), as well as in the Outaouais region, as well as smaller populations in Mauricie and near Quebec.
What kind of damage do gypsy moths do?
Gypsy moth caterpillars have a voracious appetite and eat a wide range of foods, including oak, birch, poplar, willow, and maple, unlike many other caterpillars that eat more difficultly. They also feed for one time of year about twice as long as many native caterpillars, said Joel Harrison-Off, City of Toronto Forest Health Care Inspector. And although they are eaten by some birds and mammals, none of them consume enough of them to really reduce the population.
When there is an epidemic, they can completely strip the trees of their leaves, just as they did the oaks in High Park in Toronto.
Usually trees can recover. But some tree species, such as oak, have a harder time regenerating their foliage.
Harrison-Off said the stress on trees and the energy they need, especially if climatic conditions such as drought are also stressful, make it more difficult for them to defend against pathogens.
“These trees, some of them will start to die back in the next few years due to defoliation. “
How serious is this year’s epidemic?
Gypsy moth epidemics are cyclical, resulting in an epidemic or infestation every ten years or so and lasting one to three years. The numbers increase in years with good weather conditions and then decrease due to fungal or viral infections spreading in the population. Previous epidemics occurred in 1985, 1991 and 2002.
The current outbreak in Ontario began in 2019 and in 2020, gypsy moth caterpillars defoliated over 580,000 hectares, a record. “You look at the size of Prince Edward Island, basically, which was defoliated last year,” Dutkiewicz said.
He said this year’s final tally will not be released until August, and at the moment we are on track to see a similar amount of defoliation and “another record year or close to a record year”.
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