An invasive species first introduced to North America 150 years ago, gypsy moths have proven tough to eradicate, increasing their range and popping up in large numbers in bad years. This is one of those years.
A bad infestation in Waterloo Region this summer came as something of a surprise.
“We see them here, sort of fairly regularly but they never really amount to much – we’ll see them in a few woodlots here and there for one year, maybe two years, and then the birds will start to get them under control, or if we have a cold winter, a lot of the eggs will die off [and not so many will hatch],” said Albert Hovingh, an environmental and stewardship planner with the Region of Waterloo. “This year, we weren’t expecting quite this many. I think everybody in southern Ontario pretty well was caught by surprise – it was a sort of a major eruption, they call that. So yeah, they’ve been doing a number on the trees.”
It’s in their caterpillar stage that the insects do damage. Gypsy moth caterpillars defoliate host trees, often killing them. A single gypsy moth in its larvae form will eat an average of one square metre of leaves and in large numbers can be particularly destructive to a tree which needs the leaves to survive. As leaves help create food for a tree by turning light into food via photosynthesis, a reduction in coverage can result in a loss of food production. The moths tend to feed on leafy trees, usually choosing oak, birch and aspen in northern regions, while focusing on sugar maple, beech, eastern white pine and blue spruce in southern parts of the province.
Here in Waterloo Region the moths continue to be a problem, with the number taking people in the area by surprise. Normally, the larvae hatch around spring and reach maturity – becoming a full moth – by mid-June to early July.
Hovingh says this problem can be managed by the trees themselves – as they can produce another set of leaves if they are eaten away – but they can only tolerate this for so long.
“A lot of the trees actually will be able to put out another set of leaves… but the trees will continue to function [after being stripped by the moths]. The trees if they’re healthy, they can tolerate this for three, maybe four years, just basically being stripped. Every year, it slows their growth down [and] also makes them susceptible to other diseases and things, but they can tolerate it. So, a little bit [of a] different action than some insects have, but yeah if you get enough of them for enough years, it can have a pretty major impact on your trees,” Hovingh added.
The Grand River Conservation Authority sprayed this year, using a special bacterial insecticide that specifically targets moths like these. The region chose not to do anything as they did not see any major outbreaks at the time when spraying for the pests was necessary. Hovingh says the region may do some “egg mapping” later this year and consult with cities and townships on a course of action for this next year.
The Gypsy Moth was introduced to North America from Europe in 1869 by French artist, astronomer and amateur entomologist Etienne Leopold Trouvelot, who wanted to breed them with silkworms and develop a silkworm industry. His efforts, however, got away from him when the moths he was breeding behind his Boston residence were released accidentally. The resulting error began a century long spread of the invasive species which now sees the destruction of trees across provinces like Ontario, Quebec, and the Maritimes.
At this time in the year it is too late for the public to do anything about the gypsy moth, however, Hovingh says there are some things which can be done in early stages. These things include spraying Btk (Bacillus thuringiensis kurstaki, a bacterium found naturally in the soil) to control and kill the caterpillars, wrapping burlap around the trees and then removing the caterpillars each morning from the tree, or use sticky tape around the tree. People can also remove egg masses from the trees and stop the moths at their source.