More hot and sunny weather will kill off what remains of Winnipeg's nuisance mosquitoes - but cooler and wetter weather will bring more bugs.
The weather will determine whether Winnipeg's Insect Control Branch will need to fog for mosquitoes for the first time in three years, city entomologist Taz Stuart told reporters today.
The city-wide average trap count for adult female mosquitoes is 15. The city-wide average needs to be 25 or higher for two consecutive days - and one quadrant needs an average of 100 or more - before a fogging program may commence.
In 2012, warm and dry weather killed off a spring emergence of adult nuisance mosquitoes, which tend to die off when the temperature exceeds 25 C.
On Monday, the average trap count in Winnipeg was 21 adult mosquitoes, according to the city's insect control branch. On Friday, the citywide average trap count was four mosquitoes.
Nuisance mosquito species such as Aedes vexans are not known to transmit diseases to people. The last time the city fogged for nuisance mosquitoes was 2010, an unusually buggy summer when the malathion-fogging program ran from June 19 to Sept. 6.
If trap counts rise high enough to warrant fogging this year, the city will test a product called Pyrocide ULV 7067, a biological alternative to malathion, an organophosphate that's toxic to a wide spectrum of invertebrates.
Pyrocide is reputed to have a smaller impact on the environment because it breaks down more quickly and can 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.
Pyrocide is also twice as expensive as malathion by volume, however. The insect control branch will apply it to one quarter of the city's insect management areas if a fogging program is warranted and compare the effectiveness to areas treated by malathion.
Malathion must still be used for all areas of the city this summer if the province orders a fogging program to combat West Nile virus, which is carried by species such as Culex tarsalis.
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