June rainfall makes Edmonton wettest month on record, mosquitoes surge back

Climate change has thrown a weather boomerang at Edmonton. After several years of drought, the past June became the city's wettest on record, meaning abundant standing water and the return of Edmonton's least favourite bloodsuckers.

Edmontonians have been largely spared from mosquitoes in recent years, but this summer they're back with a vengeance. The surge reflects a significant shift in the city's mosquito control program. Since 2022, the city stopped aerial sprays of outlying wet areas with the larvicide Bti by helicopter. The city also phased out Dursban in 2016, with chlorpyrifos—a pesticide using the same active ingredient—used until 2019. Chlorpyrifos has been linked to respiratory problems and disruptions to cognitive development in children. Edmonton was the final municipality in North America to use it.

Mayor Andrew Knack explained the reasoning: a significant part of the sprayed area was outside city limits, costing $507,000 annually. "We would use taxpayer dollars to spray for mosquitoes outside our city limits," Knack said. "I was on the council that said we should stop doing that. I had a real tough time justifying why I'm using City of Edmonton taxpayer dollars to provide a service outside our city limits."

A coordinated regional spraying program existed until 1993, when then-premier Ralph Klein cut funding. Edmonton ratepayers have footed the bill ever since. Two-thirds of the former spray budget has been reallocated to ground treatment, with the remainder supporting mosquito predators like dragonflies.

West Nile Virus has been detected in Alberta—people over 50 face the biggest risk of complications, though statistically 80 per cent of infected people develop no symptoms. Carrying a portable fan is a solid defence: mosquitoes can't bite if they can't land. Clearing eavestroughs and removing standing water from containers can also reduce breeding pools.