Gypsy moth outbreaks grow larger

June 3, 2021 · 0 Comments

Written By Sam Odrowski

The presence of gypsy moths (L.D.D moth) is rising around Dufferin County and all of southern Ontario following a relatively mild winter.

Ontario currently has a “severe” outbreak of the invasive species, which means there’s more than 6,000 gypsy moth egg masses per hector, while last year’s was deemed “moderate”.

This year’s increase in numbers is concerning to environmental groups like the Credit Valley Conservation Authority (CVC), as gypsy moths do have the potential to cause deforestation, especially after years of repeated infestations, with the greatest immediate threat to coniferous trees. Fortunately, the moths tend to be attracted to Oak trees and other deciduous trees, which hold up better against the pest, often able to last three to five years of defoliation.

But sadly, it appears that the issue of gypsy moth infestations won’t be going away anytime soon.

Freyja Whitten of the CVC told the Citizen a contributing factor for gypsy moth outbreaks is climate change causing milder winters.

“Because we’re not getting those consecutive -20°C days in the winter, there’s a potential that we could see more of this,” said Whitten. “Multiple days of -20°C is what leads to a reduction in the survival of the egg masses, which obviously we are not seeing in these last few winters, with all our warm winters going on.”

While there’s methods to combat the pest, there is currently an issue with finding the supplies due to the incredible demand created by the size of this year’s outbreak, impacting so many people, over such a large area.

Placing burlap around a tree can provide protection, or the Entomophaga maimaiga fungus is a natural way to kill gyspy moths, and the Nuclear Polyhedrosis Virus can also be used to exterminate their larvae.

“Those two things usually kind of help to start the population collapses,” said Freyja Whitten of the CVC. “As the Gypsy Moth population increases, then you get more of the fungus, more of the virus, and predation by birds and mammals and other things are also likely going to increase.”

“We’re on the upcycle, but hopefully some of those factors will kick in,” she added.

The gypsy moth caterpillars, which cause the defoliation, should hatch into moths later this month and into July, no longer causing harm to trees.

By the end of the summer, the species is generally gone completely.

From an ecological perspective, gypsy moths are a great food source for birds and other insects, but in addition to defoliating trees, they also have some human health impacts. Some people are allergic to their hairs and have adverse reactions when breathing them in or having them land on their skin.

Gypsy moths are native to Europe and arrived in Ontario in the late 60s after they were shipped to Boston as a potential silk producer and escaped. However, wide spread defoliation of trees didn’t happen until 1981.

“Like a lot of the invasive species, they were brought over for other reasons, and then they go, ‘hey, I don’t have any predators. There isn’t anything to keep me in check. I like these conditions, and I’m going to take off,’” said Whitten.

“Fortunately, there are some predators, but obviously it’s not enough to keep the [gypsy moth] populations in check all the time… luckily the viruses have come along and the fungus, so we do at least have some natural control options.”

To learn more about gypsy moths and the threat they can pose to your property, visit: https://cvc.ca/your-land-water/tree-planting-and-habitat-restoration-services/invasive-species/invasive-species-spotlights/forest-pests-and-diseases/gypsy-moth-lymantria-dispar-dispar/