Winnipeg mosquito larviciding crews look for 'wrigglers' in the water

On a sunny May morning, a City of Winnipeg larviciding crew prepares to spray a ditch in the Fort Garry neighbourhood.

Brendan Warren operates the sprayerwhile Courney Clark drives the white insect control branch pickup truck. The two were hired as part of the city's annual mosquito larviciding program, which began in early May.

The treatment of the ditch along Hervo Street followed one of the few heavy rain storms to hit the city.

Branch superintendent David Wade demonstrated how the crew searches for the mosquito larvaeusing a white cup on the end of a stick, which he used to scoop out water and inspect it for the telltale signs of the adolescent insects.

"Mosquito larvae have a very distinct movement in the water," Wade said.

"They're sometimes called 'wrigglers,' because they do wriggle around in the water body. They also have a siphon tube that helps them breathe at the surface of the water. Those are the key features."

The product they use to kill the larvae isn't a chemical, but a bacteria. The compound Warren sprayed into the ditch contains Bacillus thermogenesis israelensis, or BTI, which produces a toxin in the gut of the larvae.

"It's specific to biting fly larvae so mosquito larvae and certain midge larvae and it only kills those organisms and leaves the other organisms," Wade said.

Wade can't predict what this year's mosquito season will be like.

Given last winter's below-average snowfall and relatively dry spring, he says we likely won't see much mosquito action in the next couple weeks.

"But a lot can change between now, and all it takes is a heavy one-inch of rain and everything changes."

WATCH | TheCity of Winnipeg does battle with mosquitoes:

Larviciding for mosquitoes

1 year ago

Duration 2:21

City workers are hitting the ditches, spraying biological larvicide to prevent swarms of mosquitoes from growing up this spring.

Wade estimates about half of the areas where standing water collects within the city boundaries are on municipal land. The rest are on private properties.

Few mosquitoes at Assiniboine Park

In Assiniboine Park, people were out enjoying the mostly-mosquito free space on Monday.Penny Bilquist and Lorne Stadnyk, both from Flin Flon, Man., were visiting The Leaf gardens.

"Haven't found one yet, so that's good," said Bilquist.

Stadnyk noted it's been a "dry season."

Peter Synychych visits the park as much as he can.

"We've been here probably for about an hour and a half at The Leaf garden, absolutely beautiful, and no mosquitos."

Stephen Douglas was the only person CBC News spoke to who had found a mosquito.

"I've killed two so far, but I haven't found any more.Walking through the park, I haven't seen very many mosquitos at all."

The most recent City of Winnipeg adult mosquito monitoring program report from May 29 noted low levels of activity, with city-wide average trap counts of 15.

The city's larviciding program continues from now until September.

Any time it rains, crews will head out to check on standing water to look for potential mosquito breeding grounds, and if they find them, they'll spray again.

Athletic fields, parks and golf courses will be closed 20 minutes before spraying.

City staff will also post signs 24 hours in advance that show the date and time of the planned treatment, and try to schedule the treatments as early as possible in the morning.