New mosquito-control agent kills it during its first real Winnipeg test

After waiting three summers to wage war on mosquitoes with a new chemical weapon, Winnipeg's insect control branch is pleased with the results from its first use of deltamethrin.

In July, the city's bug-fighting units sprayeda handful of parks and cemeteries with deltamethrin, a synthetic insecticide that has replaced malathion asthe mosquito-killing agent of choice.

While the city started stockpiling deltamethrin in 2017, adult nuisance mosquitoes didn't emerge in sufficient numbers that summer to warrant a fogging program. The following summer proved just as mosquito-free.

This summer, the combination of warm weather and heavy rain created sufficiently buggy conditions to conduct a limited fogging program in nine parks and cemeteries.

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Deltamethrinwas successful in reducing the number of adult nuisancemosquitoes for a few days in places such as Kildonan Park and BrooksideCemetery, said Ken Nawolsky, the superintendent of the insect control branch.

"We only did it in parks and open spaces where the mosquito numbers were higher than normal," Nawolsky said. "We didn't want the mosquitoes to spread into [nearby] residential areas."

"We've been waiting three years to use the product just because, you know, it's been very dry. So it was kind of a little bit of an excitement to start using it," Nawolsky said.

Nawolsky said deltamethrin proved to be as effective,if not more so,than malathion, which the city no longer has a license to use. Malathion was declared"probably carcinogenic" to humans by the World Health Organization in 2015.

More expensive, likely more effective

While deltamethrin's success didnot come as a big surprise other North American cities have been using the chemical for years the insect control branch was not sure precisely how it would work in Winnipeg.

This city has some unique characteristics when it comes to mosquito control, said University of Winnipeg entomologist Rob Anderson, who has been contracted to analyze when and where deltamethrin should be deployed in order to optimize its use.

Unlike malathion, which belongs to a family of pesticide known as organophosphates, deltamethrin is a pyrethroid, a group of synthetic insecticides with chemical similarities topyrethrins, which occur naturally in chrysanthemum flowers.

"The objective of our work is not to say whether the product works in an an urban mosquito-control setting. That case has been made," said Anderson, citing the work of graduate student Jennifer Pawluk, who reviewed academic studies of deltamethrin use in a number of cities.

"There's lots of evidence to show that it's at least, if not more, efficacious than malathion."

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While deltamethrin is more expensive than malathion, smaller quantities of the newer chemical are needed to kill adult mosquitoes. Deltamethrinis also believed to be less toxic than malathion after it breaks down in the environment, he said.

The chemical is also spread in a way intended to reduce harm to other organisms.

"The tiny little droplets that kill mosquitoes are not poisonous enough to kill large-bodied insects," said Anderson, who nonetheless acknowledged it could kill smaller flying bugs, such as midges.

Should the city require a full-scale residential fogging program in the future, residents may not even be aware deltamethrin is being deployed, Nawolsky said.

Unlike malathion, deltamethrin has no odour.

"What we found from people who livedby the areas where we did the fogging, they were going, ' We didn't smell anything. Did you do anything?' " Nawolsky said. "That was kind of the biggest surprise."