Heavy rain in Edmonton area has driven ‘a lot of mosquito hatching’: pest expert

After the large amount of rain that fell in Edmonton and the surrounding areas last week, it’s time to get out the mosquito repellent.

So far this year, the mosquito population as been relatively low. But after the Edmonton area received about 65 millimetres of rain over a 72-hour period last week — between noon on June 12 and noon on June 15 — that’s about to change.

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“In recent weeks, we’ve had considerable rainfall and that has driven a lot of mosquito hatching. A lot of habitat is out there producing mosquito larvae now,” said Mike Jenkins, the City of Edmonton’s pest management coordinator.

“We are expecting to see an increase in the number of mosquitoes in the next week or so.”

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Jenkins said crews are out reducing numbers of mosquito larvae in roadside ditch and ground areas, to decrease the number of adult mosquitoes that emerge.

“We do have our ditch trucks that are going out and treating roadside ditch habitat both within the city and extending into surrounding counties. Those roadside ditch habitats are really significant development sites for mosquitoes — probably 50 per cent of our mosquito population comes out of those roadside ditches,” he explained.

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But because the city eliminated its aerial mosquito control program last year, Edmonton and surrounding areas will likely see more mosquitoes emerge.

“A lot of the habitat that we are seeing out there now is in the areas that were formerly treated by the aerial program. We are seeing development of larvae in those habitats,” Jenkins explained.

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“So we are expecting mosquitoes to be emerging from those habitats, making their way into the city. So there will be an increase in mosquito numbers compared with if we did have the helicopter program. It will be noticed probably most in the peripheral areas around the city.”

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Jenkins added that mosquitoes can fly up to 25 kilometres from where they emerge, particularly if they’re drawn in by the city lights at night.

“We could see some of those showing up in the city as well,” he said.

The mosquito forecast for the rest of the summer is largely dependent on how much more rain the city receives, as mosquito larvae thrive on stagnant water to survive.

Shift from aerial pest control to education/biological interventions

Earlier this year, city council voted 7-4 in favour of doing away with the aerial mosquito control program, which uses a helicopter to drop pesticides into temporary and stagnant water bodies in control areas around Edmonton. The goal of that program is to kill the larvae before they hatch, reducing the pesky adult biting populations.

Instead, the city will use the $507,000 annual cost of the program on education and other biological interventions to help control the mosquito population.

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“Probably the most effective means of reducing the mosquito population, in terms of the biting, is the use of those biorational insecticides that we use still in our ground and ditch program, and that we used in the aerial program,” Jenkins explained.

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“And it is pretty much the only way to target a lot of those mosquito larvae that are developing in temporary habitats. There’s no predators or anything to take advantage of those.

“But overall, if you can get the more balanced ecosystem going, have more natural enemies, fewer habitats for the mosquitoes to actually develop in, then you don’t have the development of the mosquito population in the first place. And that’s sort of where we’re aiming with a lot of these biological control programs.”

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After council’s decision to eliminate the aerial program in April, city administration was asked to develop education and biological pest control measures to manage Edmonton’s mosquito population.

In a report going to a council committee next week, administration outlines that the majority of the funding will go towards personnel and monitoring-related costs (approximately $388,000), with the rest going towards alternative biological control activities (approximately $65,000) and enhanced communication and educational efforts (approximately $45,000).

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In the report, administration said it must consider a number of factors in the development of alternative biological control measures for mosquitoes, outlining there are three broad types of biological controls where human input is involved: conservation, classical and augmentation.

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Conservation controls work to ensure the conservation of existing natural enemies already present. For example, ensuring good habitat for native mosquito predators like bats.

Classical controls introduce natural enemies to a new locale. For example, the use of Bacillus thuringiensis israelensis (Bti) products, which are made from naturally occurring soil bacteria toxic to mosquito larvae.

Augmentation is the supplemental release of natural enemies to increase existing populations. Raising and releasing additional native bats to increase local populations is an example of an augmentation biological control.

“Any biological control requires careful consideration of ecological and biodiversity impacts since there are human interventions involved,” reads the city report.

Read more: Edmonton city council eliminates aerial mosquito control program

Administration said it will also look at mosquito control programs from other municipalities as part of the Edmonton program development. Evaluation and reporting will be done annually for all mosquito program activities.

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An enhanced communications and education plan will be used to engage and inform Edmontonians on the work that is being done by the city related to mosquito control.

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The city will use data collected from monitoring, along with feedback from 311 inquiries to inform the public messaging, according to administration.

At the end of 2022 season, an analysis of the program’s effectiveness will be completed to determine if changes need to be made for 2023.

According to recent feedback from Edmontonians through 311 and public engagement done in 2018, residents said pest management is an important service to be provided by the City of Edmonton.

What about wasps?

Last year Edmonton experienced a high number of yellowjackets, due to hot, dry weather conditions. Will the city see that again this year? Jenkins said the nests from last year sent out queens, so there is large population starting out this year.

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But how successful they are will be dependent on the weather, he said.

“If it’s cool and rainy — the sort of things that mosquitoes prefer — that doesn’t work so well for the yellowjackets. So we won’t see as much development of yellowjackets,” Jenkins said.

“So it’s kind of a balancing act. If you get lots of mosquitoes, you get fewer yellowjackets. But if you get no mosquitoes then you get more yellowjackets.”

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