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Trial this summer for non-chemical mosquito killer

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Winnipeg will test out a biological alternative to the chemical insecticide malathion this summer if mosquito trap counts are high enough to warrant fogging.

The city's insect control branch is itching to test out an insecticide called Pyrocide ULV 7067 to see whether it's just as effective as malathion, an organophosphate used to kill adult mosquitoes in Winnipeg for decades.

Although malathion is approved for use as a fogging agent in Canada, environmental groups and anti-pesticide activists consider it undesirable because it kills many species of insects indiscriminately and breaks down into potentially more harmful components.

The city intends to phase out malathion completely by the end of 2014. But first, the insect control branch must field-test the use of Pyrocide, a biodegradable product reputed to be effective in smaller concentrations.

According to a product monogram, Pyrocide's active ingredients are one part pyrethrin -- a neurotoxin derived from chrysanthemum plants -- and five parts piperonyl butoxide, a sassafras derivative that increases the killing power of insecticides by turning off the enzymes that help mosquitoes fight off chemical attacks.

City entomologist Taz Stuart said Pyrocide promises to have a lower impact on the environment because less of it needs to be used and it also breaks down very quickly.

"It's almost immediate," Stuart said Thursday after announcing the start of the city's annual insect-control program. "When I started in Winnipeg, the intention was to get away from malathion."

If conditions warrant a nuisance-mosquito control program this summer, one quadrant of the city will be fogged with Pyrocide and the other three will be treated with malathion. Stuart and his colleagues will then monitor trap counts to test the effectiveness of the biological agent, which is twice as expensive as malathion by volume.

The city was ready to test out Pyrocide in 2012, but the relatively mosquito-free summer meant there was no need for any fogging last year. The city has had no need to fog for adult mosquitoes since 2010, an election year that saw politicians make several attempts to loosen up restrictions on pesticide-free buffer zones.

While it's too soon to tell whether fogging will be required this year, the initial prospects for a mosquito-free spring look good. Cool, dry weather means mosquito development has been slow, delaying the start of the city's annual larviciding program.

While some overwintering adult mosquitoes are flying around, the average city-wide trap count is zero and the prospects of a significant emergence of adult mosquitoes is extremely low over the next three weeks, Stuart said.

"This type of spring is the best kind of spring," he said.

On May 1, the insect control branch began treating bodies of standing water in and around the city with the biological agent BTI, the bacterium bacillus thuringiensis israelensis. Since some bodies of water remain too cold and too deep for mosquito larvae to emerge, a lot more larviciding has yet to come, Stuart said.

At this time of year it takes two to three weeks for mosquitoes to mature. Once the weather warms, maturation can occur in three or four days. The potential for a major emergence of mosquitoes this summer cannot be predicted this early, as warm weather and heavy rains can change conditions very quickly, Stuart said.

bartley.kives@freepress.mb.ca

Republished from the Winnipeg Free Press print edition May 10, 2013 A9

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