The City of Winnipeg may end the decades-long practice of fogging for adult nuisance mosquitoes because the pesticide it uses is no longer being made.
A new report to city council says Winnipeg has bought up all the remaining Canadian stock of DeltaGard, the pesticide the city has used for adult nuisance mosquito fogging since 2017, when it replaced malathion.
DeltaGard is a trade name for a product containing the chemical deltamethrin, which is considered less ecologically harmful than malathion. Manufacturer Envu Canada informed the city it stopped producing DeltaGard in 2023.
The city’s insect control branch now has enough DeltaGard on hand — 6,629 litres — to fog for mosquitoes over the next two to four years, depending on weather conditions over the next few summers.
But once that supply runs out, there is no replacement pesticide available to the city to deploy against adult mosquitoes, said David Wade, the superintendent of the city’s insect control branch.
Pesticides approved for use in the United States would have to go through an expensive Canadian licensing process that would make no economic sense for manufacturers, he said.
Winnipeg, which started fogging for adult mosquitoes in 1950, is now the only large municipality that still engages in this practice, he said.
The rest of the Canadian market for adult mosquito fogging is very small, he added.
“It costs hundreds of thousands of dollars to register a product through the government of Canada through the Pest Management Regulatory Agency,” Wade said in an interview outside his office on Waverley Street on Wednesday.
“That’s why some companies are reluctant to do so.”
If another product is not licensed for use in Canada, the city may stop fogging for adult mosquitoes altogether, Wade said.
Improved larviciding, less fogging
Fogging for adult mosquitoes is not the main weapon in Winnipeg’s skeeter-fighting arsenal. The insect control branch tries to kill mosquitoes in the larval stage with larvicides, applied both by people on foot and by helicopter to low-lying areas of the city, where standing water accumulates in the spring.
Improvements to Winnipeg’s larviciding practices, combined with dry weather, have allowed the city to fog for adults less often. The insect control branch has only deployed fogging trucks during three of the past seven years, Wade said.
“I think it’s important that Winnipeggers know that spraying for mosquitoes is a very small portion of the work that the City of Winnipeg does in insect control,” said Coun. Evan Duncan (Charleswood-Tuxedo-Westwood), who chairs city council’s community services committee, which is responsible for insect control.
Nonetheless, Duncan said he would prefer to see Winnipeg find an alternative to DeltaGard before supplies of the pesticide run out over the next two to four years.
“A lot is going to change in that time, and I think that we’ll see a product come to Canada and Manitoba that will be as effective, if not more effective,” he said in an interview outside city hall.
In the event the province of Manitoba orders up a mandatory fogging program because of the public health threat posed by West Nile virus, Winnipeg could receive emergency approval to use a pesticide licensed in the U.S., Wade said.
That is not an option for nuisance mosquito fogging, he added.
Rob Anderson, a University of Winnipeg entomologist, said Winnipeg may have to devote even more resources to larviciding and land drainage if fogging for adult mosquitoes is no longer an option.
But he suspects some Winnipeggers might take pest control into their own hands if the city stops fogging for mosquitoes.
“Many people may just simply start doing it themselves, buying off-the-shelf aerosol applications, pieces of machinery and pesticide products from garden stores,” Anderson said in a telephone interview.
Wade’s report, which goes to city council’s community services committee on April 10, makes no recommendations. He said his main objective was to inform council and all Winnipeggers of the looming shortage of fogging agents.
Despite the relatively dry conditions this spring, Wade said it’s too soon to say what sort of summer Winnipeg will have with mosquitoes. Insect control crews will begin larviciding operations in early May, he said.