Experiment looks at reach of mosquito fogging

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This article was published 21/06/2011 (5291 days ago), so information in it may no longer be current.

The City of Winnipeg plans to conduct a mosquito-fogging experiment in a small patch of East Kildonan to finally settle the question of how far malathion travels.

The city’s insect control branch has asked Manitoba Conservation for special permission to spray the mosquito-killing agent around a square kilometre of East Kildonan for one to four nights this summer, even if nuisance mosquitoes are not present in large numbers.

The experiment is part of the city’s effort to reduce the size of the buffer zones placed around homes where residents object to the application of pesticides. The size of buffer zones has not changed since 1983, when the Clean Environment Commission set the zones at 100 metres, based on earlier Winnipeg research on malathion drift.

But in recent years, especially during exceptionally buggy summers, the size of buffer zones has led to conflict in neighbourhoods where some residents support fogging and others do not.

Last summer, city council asked the province to reduce the size of buffer zones as part of a package of changes to the way the city controls nuisance mosquitoes such as Aedes vexans, which are not known to transmit West Nile virus to humans.

“On this issue, intuitively, my sense is the buffer zone is too big. I know it causes huge problems in neighbourhoods,” St. Vital Coun. Gord Steeves, one of the main drivers behind the move, said on Monday.

The province responded by tossing the political hot potato back to the city, asking the insect control branch to propose a new buffer-zone size — along with scientific research to back up the proposal.

In response, city entomologist Taz Stuart conducted a review of existing scientific literature about malathion dispersal and also began planning an experiment that may start within weeks.

His literature review came up with two 1996 malathion-drift studies that are applicable to residential neighbourhoods in Winnipeg, according to a letter from Stuart to Tracey Braun, Manitoba Conservation’s licensing director.

A study in Saginaw County, Mich., found malathion droplets drifted 91.4 metres, although the highest concentrations were found within 7.6 metres. Another study in Panama City, Fla., found the droplets drifted 42.8 metres, but the most droplets were found directly in front of the house that was fogged.

“The overall consensus for all the studies is that dispersal decreases with distance, regardless of the habitat type, and that droplets travel further in open environments, compared to non-open environments,” Stuart wrote.

The Winnipeg experiment has been planned for a square kilometre of an East Kildonan neighbourhood Stuart describes as “indicative of many of the normal neighbourhood sites that the insect control branch treats during an adult nuisance-mosquito control program,” as it has “linear, parallel streets lined with mature American elm trees and back lanes between streets.”

Although the test neighbourhood is not specified in his letter, an aerial satellite map provided to the province appears to correspond with part of the Rossmere neighbourhood that sits west of Watt Street.

The city declined to confirm the location or comment on the experiment. But in the letter to the province, the city promised to notify affected residents 15 days before the experiment.

The city has previously warned the results of the study may not be determined in time to reduce buffer zones this season.

“I’m not blaming anybody, but that’s disappointing. I was hoping we’d move through this a little faster,” said Steeves, adding he hopes the study will allow the city to noticeably reduce buffer zones. “What I hope is we’re working toward some sort of reasonable average in terms of dispersal. I hope we’re not talking the worst-case scenario, with high winds and wide-open territory, because if you do that, you’ll end up with the buffer zone we have now.”

bartley.kives@freepress.mb.ca