On August 30, My Muskoka Now reported a sighting of the invasive gypsy moth in Ontario’s Parry Sound. Originally found throughout Europe and Asia, this deciduous-destroying insect was brought to North America in the late 1860s by Leopold Trouvelot, a French artist and amateur entomologist, in an attempt to establish a silk industry in the United States. But the insect escaped from Trouvelot’s laboratory in Boston, Massachusetts, thriving and multiplying in the nearby hardwood ecosystem. Eventually, the moth made its way north to Canada.
“They’re pretty well distributed across Southern Ontario and as far north as Sault Ste. Marie,” says Kate Powell, a terrestrial biologist with the Ontario Federation of Anglers and Hunters. Gypsy moths were first detected in Ontario in 1969, but the devastating effects of their defoliation didn’t take place until 1981.
The preferred host of the gypsy moth is the oak tree. Over the winters, they will hatch their eggs on the barks of trees. Gypsy moths reproduce quickly and abundantly, and with few predators, their numbers are often left unchecked.
In the spring, the larva hatch. “During their larval stage, so when they’re caterpillars, they feed on the foliage, so that’s when they do the most damage,” Powell says. Caterpillars devour foliage, often leaving trees bare. Initially, the caterpillars feed during the day, but as they mature, they begin feeding at night, making it difficult to identify an infestation. While the trees are able to produce new leaves over the summer, the damage can affect photosynthesis, causing significant loss to the tree’s growth.
By July, the caterpillars will have finished eating and “later on in the summer, they’ll pupate and you’ll see them as the adult version of the moth,” Powell says. The male moths have light brown, slender bodies, while the females have white, heavy bodies.
Gypsy moth outbreaks occur every seven to 10 years and pose a serious threat to cottagers with deciduous trees. A good way to stay up-to-date on the prevalence of gypsy moths in Ontario is by using the Ministry of Natural Resources and Forestry’s annual forest health survey. According to the 2018 survey, gypsy moths were on the rise in Southern Ontario.
Powell says once you’ve identified an infestation, there are ways to manage it. “You can remove the caterpillars when you see them,” she says. “You can also attach burlap sacks around the trunk of the tree. The caterpillars take refuge under these and then you can destroy them that way.” Powell adds that there are also some over-the-counter pesticides that are effective. “BTK is a natural fungus that can help control them.”
If you see the adult versions of the moth then there will be egg sacks present. Powell says “that’s a good time to take as many of those off the tree as possible to reduce further establishment next spring.”