Evidence Edmonton mosquito plague could've been tamed by aerial spraying inconclusive: experts

It's hard to tell if the absence of an aerial spraying program led to plague of mosquitoes early this month in Edmonton, say city pest experts.

Data collected by the City of Edmonton's pest management department shows the population of the blood-suckers peaked in early August -- pest control workers collected 42,000 mosquitoes in traps, compared to just 600 of them a year before.

The city paused its $500,000 program of spraying for mosquitoes by helicopter in 2021. It was subsequently shelved permanently by city council following a motion by Coun. Michael Janz.

City workers still spray for the pests but use handheld pumps to target certain pools of water.

"We’re still spraying in the city," said Janz, who represents south-central Ward papastew. "I want people to know that we’re spending $650,000 (annually) doing spraying within the city of Edmonton."

Ward pihêsiwin Coun. Tim Cartmell, who wanted to keep the aerial spraying program, says he thinks having it would make for a more-pleasant summer but admits it's tough to measure its effectiveness.

"The more you spray, the better it gets, but that has all kinds of limitations to it," Cartmell said Tuesday. "Effectively, we've gone from spraying with a helicopter to spraying with a little handheld pump thing that we're walking through the ditch. It's ridiculous, but at the same time, this year with all this rain ... I remember that the rain has come in big deluges, so water levels rise to a point that I haven't been in years, which activates mosquito eggs that had been laying there for years. I don't know that we would have seen a big difference. But I would sure like to spray more."

Sarah McPike, a senior biological sciences technologist with the City of Edmonton's pest management lab, said the large amount of standing water from rain this summer hampered current mosquito-spraying efforts and led to the skeeter explosion.

"If you have dry years where it’s just eggs and eggs and eggs, and then you have repeated water events ... They call it the egg bank. The mosquitoes cashed in the egg bank this year and there were a lot of mosquitoes," she said.

McPike and her team's immediate concern is the arrival of a new breed of mosquito larvae to the city. The culex pipiens larvae that pest management has been collecting from Edmonton's stormwater catch basins is common in Eastern Canada and is known to carry West Nile Virus. Its breeding habits could mean they city's strategy of killing larvae in puddles and ditches won't work on it.

"It changes everything for our mosquito treatment program because we’ve always targeted those floodwater mosquitoes," McPike said. "Now we have this raft-layer that is a West Nile vector, so we want to stay on top of that."

The city is looking into breeding tiny shrimp-like predators to take on the new mosquito breed and attracting more mosquito-eaters such as bats and dragonflies.

In the meantime, residents are encouraged to pour out and drain any standing water on their property.

"We need our neighbours to be vigilant and make sure you're pouring out your water, make sure your neighbours are doing the same," Janz said. "That's the only way that we're ultimately going to get rid of them."