Bug battle subsides after spongy moth population declines in York

Outbreak of lymantria dispar dispar moths at an end, region says residents need not use burlap or other measures this year

newmarkettoday.ca
May 23, 2023

Newmarket residents can be assured they will likely not find their trees covered in caterpillars this year after a decline in the spongy moth population.

The insects --- also known as lymantria dispar dispar --- have infested York Region trees for the past couple of years, prompting efforts to curtail their population and prevent them from defoliating more trees. But due to a natural virus, York Region saw a crash in the insect's population last year, with no significant amount of the insects expected this year.

Dayna Laxton, York Region invasive species specialist, said residents need not take any preventive measures this year.

“The natural controls in our environment took effect and the population crashed,” she said. “It looks like we’re going to have little to no defoliation in York Region.”

Newmarket and other municipalities responded in force to address the outbreak the past few years, providing free burlap to residents to wrap around their trees to help capture the insects. Now, Laxton advises taking down any burlap, with it not being necessary and potentially harmful to trees in the long term.

The insects have outbreaks in cycles, with the nucleopolyhedrosis virus controlling the population after it spikes every six to 10 years. Laxton said the virus is largely responsible for the crash in population in the past year, and natural predators will likely control any remaining population.

Still, the insects have spent the past few years defoliating trees throughout York Region. Trees have adapted to the caterpillars, Laxton said, but added that some older trees could have more lasting damage.

“Not to say the trees will necessarily die,” she said, “they just may be stunted in growth or look a little ugly for a few years. Nature is resilient.”

There is no preventing another outbreak in six to nine years, with the moth being an established species now, she said. But York Region and other authorities will continue to monitor the population. When the moths return in significant numbers, she said the region will take similar steps to control the population and the damage to vulnerable trees.

“We’re able to keep our fingers on the pulse,” Laxton said. “So we can start communications as early as we start to see the population build.

“Unfortunately, it’s something we have to live with,” she added.