Voracious caterpillar here to stay, ecologist says

No matter what you call them, the caterpillars that become LDD moths are here to stay and expected to once again defoliate leafy trees across the city this year, the Hamilton Conservation Authority’s terrestrial ecologist says.

Lesley McDonell said the voracious insects formerly known as the gypsy moth — a name now considered offensive — have become endemic throughout southwestern Ontario, rather than an infestation that flares up about every 10 years.

That means aerial spraying with a biological pesticide, as the authority did on 113 hectares of forest in the Dundas Valley in 2018 and by the Loop Trail in 2019, won’t keep them in check, she said.

“In the past few years, the LDD moth numbers have climbed again,” McDonell told members of the authority’s conservation advisory board, who endorsed her recommendation against spraying this spring.

“It’s here to stay, it’s not going away, so we have to deal with this continuously. It’s nothing that’s going to leave us and then come back in 10 or 15 years,” she said.

“We’d have to spray on a tight cycle over a wider area to be effective and we’re just saying this is neither ecologically nor economically effective.”

McDonell said surveys of LDD egg masses on authority lands indicate there will be severe defoliation this spring and summer in the Dundas Valley, Valens, Westfield, Borer’s Creek, Iroquoia Heights and Felker’s Falls conservation areas.

She said the authority will once again scrape egg masses and use burlap banding to protect select oak and other trees along trails, a strategy that has worked well in recent years.

But it will mostly rely on the moths’ natural enemies, including a bacterium, virus and parasitic wasps that feed on the caterpillars, she said, adding weather can play a key role.

“Widespread spraying doesn’t make sense in an area with natural predators,” she said.

“Let’s pray for a wet spring because that really drives the virus to attack the LDD moth and the bacteria survive much better.”

She said most trees can survive repeat defoliation, but the Dundas Valley has two significant areas where large oak trees died even though they were in sprayed in 2018.

Widespread spraying doesn’t make sense in an area with natural predators.

LESLEY MCDONELL HAMILTON CONSERVATION AUTHORITY