The helicopters are airborne and the ground crews are in the field — it's mosquito-fighting season in Edmonton.
The city's resident mosquito expert, Michael Jenkins, is forecasting a modest mosquito season, consistent with the past few years. He expects it will pale in comparison to the mosquito heyday in the 1980s, a downward trend driven in part by climate change.
The cool nights early this spring have slowed the mosquito larvae's metabolism and stunted their growth.
The longer the larvae take to develop, the longer the city has to target them with bio-pesticides before peak mosquito season hits in July.
The city contracts out helicopters to swoop over mosquito hot spots in the city, dropping pesticides into standing water where larvae are feeding. The bio-pesticide, called Bti, is lethal for mosquito larvae and some related species, such as blackfly and fungus gnat.
"It's virtually non-toxic for everything else," Jenkins said.
The pesticide is granular and embedded into small chunks of corn cob. The helicopters have metal arms, similar to a grain auger, that "sprinkle" the pesticide on ponds, with ground crews using spray backpacks in other areas.
The city gets consent forms from large landowners to spray on private property. The helicopters, meanwhile, have a special low-flight waiver that allows them to hover just 10 to 15 metres above the ponds while they're applying the pesticide.
"It's always disconcerting to the radar operators at the airport, since the helicopter keeps disappearing off their radar and popping back up again," Jenkins said.
The mosquito control program extends beyond the city boundary, and includes partnerships with Leduc County and Enoch Cree First Nation.
The southeast Edmonton area, from Beaumont to Sherwood Park, is a particular hotspot for mosquito larvae, where they thrive in the pools of water created out of the spring thaw in the local valleys.
The program takes about a million dollars from the city's $3.6 million annual budget for Animal Care and Pest Management, Jenkins said.
Climate change driving mosquito changes
Climate change, and drier summers in particular, is partly responsible for a sharp drop in Edmonton-area mosquito populations over the past three decades, according to Jenkins.
Light traps around the city captured upwards of 6,000 mosquitoes in 1980s. But the city's traps have rarely exceeded an average of 2,000 mosquitoes since the 1990s, often recording just a few hundred a week.
In 1982, the city experienced a perfect storm of mosquito mayhem. A shoddy batch of pesticide, coupled with warm nights and lots of rainfall meant the city was trapping upwards of 100,000 mosquitoes a week.
"When people are telling you all the mosquitoes were much worse back when I was a kid — yeah, they're right. They absolutely have been," Jenkins said.
But if climate change continues to warm Edmonton summers, potentially more dangerous mosquito species could take up residence in the city.
The city has trapped the culex restuans species of mosquito several times in the past few summers, which had not been previously recorded in the city, according to Jenkins. It's a carrier for West Nile Virus.
Jenkins said in 50 or 60 years, mosquito species that carry yellow fever, that can't currently survive the winter, could start to migrate to Edmonton if the climate continues to warm.
But Edmonton summers are still brief, and the mosquito control program is about making sure people can enjoy the sunshine sans mosquito, Jenkins said.
"Even though the numbers aren't as high as they were, say, in the 80s, it's still enough to be annoying and a detriment to people's enjoyment of the outside."