Invasive gypsy moth caterpillars infest York Region trees

Insect larvae can destroy trees

Yorkregion.com
August 11, 2020

Janesse McPhillips of King City is dealing with a gypsy moth caterpillar infestation on her property. She was told it was too late in the season to spray insecticide. She is holding a caterpillar and a moth. July 15, 2020 - Steve Somerville/Torstar

Janesse McPhillips didn’t realize, at first, that her oak tree was infested with gypsy moth caterpillars.

“The first evidence of a problem wasn’t even the caterpillars. It was our pool deck and in the stonework we saw these black pellets everywhere,” McPhillips said. “I looked it up and saw that it was actually the waste of the caterpillars.”

That’s when McPhillips, who lives in King City, started looking at her trees and realized there were what looked to be several hundred gypsy moth caterpillars.

Gypsy moth caterpillars are considered an invasive species in Canada that eats leaves, which can damage the tree.

The moth originated in Europe and was introduced to North America in the late 1800s. It was first detected in Ontario in 1969.

Gypsy moth caterpillars are insects characterized by a yellow head, black markings and red and blue bumps on their back.

Male gypsy moths are light brown with large wings and the female is almost white with black markings on its wings, according to the Canadian Wildlife Federation.

“We started to realize that where they were, the whole section of the tree actually had lost a lot of its leaves,” she said.

At that point, McPhillips called an arborist who said it was too late in the caterpillars’ life cycle to spray the trees with any pesticide.

Gypsy moth eggs hatch in the spring and the caterpillars begin feeding on leaves. By mid-July, the feeding stage is usually complete and the caterpillars develop into moths after a few weeks of pupation in cocoons.

The female moth lays large masses of between 100 to 1,000 eggs on tree trunks, branches and crevices in hidden places such as garbage cans and firewood piles. They are characterized by brown fuzz and are a few centimetres wide and a few centimetres long.

Kevin Reese, York Region’s program manager, forest conservation, natural heritage and forestry and environmental services, said residents have been dealing with high numbers of the gypsy moths this year, but it’s an issue across southern Ontario.

“Their numbers can drastically change from year to year,” Reese said. “It’s very cyclical. Some years it will be difficult find a gypsy moth caterpillar and other years there may be areas where trees are heavily defoliated.”

The caterpillars prefer oak trees but will feed on a number of other tree species, Reese added.

As gypsy moth populations start to rise, birds, squirrels and other insects prey on the caterpillars and cause the population to collapse, Reese said.

“It’s hard to predict with certainty but we can build a bit of an estimate by counting the egg masses that we see,” Reese said.

Most trees can withstand several years of gypsy moth infestation, but Reese said the concern is when the trees put out extra foliage to make up for what the caterpillars ate, it uses its resources, which can cause stress to the trees.

When the caterpillars are active and feeding, Reese said there are a few methods of reducing their numbers, including tying burlap around the trunk with a rope. The caterpillars tend to hide out during the day and feed at night, so under the burlap is a good place to hide. Residents can regularly inspect the burlap and destroy any caterpillars there.

When life cycle is in its egg stage, Reese suggests looking for the egg masses and destroying them to reduce the caterpillar numbers the following year. When leaves fall off the trees in the fall it’s easier to spot the egg masses.

Dawn Bazely, biology professor at York University, said there are several species of plants and animals that are considered invasive, including the gypsy moth.

“Invasive species, they’re here. Many of them we have introduced accidentally. Many of them we have introduced intentionally because we think they’re going to help us,” Bazely said.

Even if a species isn’t native, it doesn’t mean it’s invasive. An invasive species is one that is spreading in ways that is not planned and is having unwanted environmental and economic consequences, Bazely said.

“It’s a value judgment; we decide which species are invasive based on economic, cultural and environmental factors,” Bazely added.