Hamilton Conservation Authority hopes to avoid spraying to keep caterpillar outbreak in check
HCA terrestrial ecologist Lesley McDonell says she first wants to see the results of winter monitoring of LDD caterpillar egg masses before deciding whether to recommend a spraying of the biological insecticide Btk next year. - Metroland file photo
The Hamilton Conservation Authority’s terrestrial ecologist says she’s hoping mother nature will keep an outbreak of the LDD caterpillar in check next year and avoid the need for another aerial spraying of the biological insecticide Btk.
Lesley McDonell said although parts of the Dundas Valley, Iroquoia Heights, Westfield and Borer’s Falls conservation areas have seen trees defoliated by infestations, there are signs the insects are succumbing to a natural virus.
“We call them the silent LDD moth killers,” she said in a presentation to authority directors at their July meeting.
McDonell said a fungus can also kill the caterpillars — formerly known as gypsy moths but now called by the acronym for their Latin name — but it requires a wet spring, unlike this year’s dry one.
“But we are seeing quite a bit of the virus passing around through our caterpillar population,” she said, noting the identifying sign is that they hang in a V-shape. “They pass it to each other and it kills them quite rapidly.”
The authority sprayed about 113 hectares in five areas of the Dundas Valley with Btk in 2018, and then a smaller area in 2019 in conjunction with the city, she said. Prior to that, it had last sprayed in 2008.
Asked by authority chair Lloyd Ferguson if staff plans to recommend joining a potential city spraying program in 2022, McDonell said she first wants to see the results of winter monitoring of egg masses.
She said cold winters used to kill them off, but climate change is affecting that natural threat while also making “it tricky” for trees to survive hotter, drier conditions.
“I’d like to go out and take a look at the (egg) levels and see where we’re at because we’ve seen so much of the virus and the bacteria impacting our populations,” McDonell said.
“Spraying is an expensive endeavour and it requires us to really review what we think the impacts will be for all things.”
McDonell said staff have used other methods to kill the caterpillars, like scraping egg masses off bark and banding, on significant landscape trees at Christie Lake and Valens, but it’s difficult to do so on a wider scale.
“We did really impact the population quite significantly,” she said. “Since those are important infrastructure in those conservation areas, we thought that was a good route to go.”
