Bugs bite back with a vengeance after local downpours
Mosquito eggs can lay dormant for years then hatch after a heavy rain
The City of Edmonton’s mosquito squad is on a mission to destroy larvae before they develop into full-grown bloodsuckers.
“With this most recent rainfall we are seeing hatching in pretty much every habitat where we can find water still standing,” said Mike Jenkins, a biological sciences technician with the mosquito control program.
“The good news is that, because it was a slow, sort of soaking rainfall rather than one big torrential downfall, a lot of that moisture has actually been sucked up by the ground or by the vegetation,” said Jenkins.
While mosquitoes are pollinators for some plants and a food source for some birds, bats and dragonflies, “there’s very little that absolutely depends on mosquitoes,” Jenkins said.
The mosquito control program primarily uses Vectobac 200G to take out mosquito larvae. The product contains Bacillus thuringiensis israelensis or Bti, which affects mosquitoes but not other organisms.
Crews using helicopters, trucks and specialized backpacks target ideal mosquito-breeding habitat for treatment — ditches, fields and other places where temporary bodies of water collect for about a week, Jenkins explained.
An area is treated with Bti if 65 per cent or more of the pools in an area are producing larvae.
Mosquitoes can develop in significant numbers because they take advantage of habitat where there are few predators, Jenkins said.
When adult mosquitoes emerge, the females will leave to find a blood meal before returning to that semi-permanent water body and laying their own eggs in the vegetation around the pool.
Those eggs can lay dormant for up to a decade before they hatch, depending on whether that pool of water fills up again, how warm the water is, and whether it contains the right amount of dissolved oxygen.
Once they’re activated, though, it can take less than a week for those eggs to transform into adult mosquitoes.
Early spring mosquito counts were low, Jenkins said. But that might not mean much, as the numbers can shift quickly and dramatically.
The year before last, for instance, mosquito numbers were low until the end of July. But that all changed when torrential downpours activated a lot of dormant eggs, he said.
The Weather Network is forecasting warmer than normal temperatures and near-normal levels of precipitation for the Edmonton area this summer.
Doug Gillham, a Weather Network meteorologist, said Edmonton can expect a “changeable pattern” of weather.
“There are really some conflicting signals for this summer,” he said. “We’ve got the developing La Nina, which argues for a cooler summer in the west, but then you have warmer water in the North Pacific west of B.C., and that argues for more of a summer like the past couple of summers.”