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Late summer is the time to watch for mosquitoes

It might seem like the end of the summer means the end of the mosquito season, but Minnesota Mosquito Control District employees caution against putting that bug spray away just yet.

This summer hasn't been bad, as far as mosquitoes go. Though most yards could have used a little more rain, the lack of rain means fewer mosquito eggs have hatched and that means fewer of the blood sucking pests.

But late summer is when a different type of mosquito starts to reproduce more abundantly. And that type is the dangerous one. It's the one often blamed for spreading the West Nile disease. That's why MMCD inspectors are out patrolling the community's ponds these days. They're taking samples and spraying, trying to control the mosquito population.

Preventing the pests

MMCD public information officer Mike McLean says Minnesotans put up with more mosquitoes than they realize. The MMCD treats for about 15 specific species "because those are the ones that spread disease and bite," McLean said.

Each breed carries with it little nuances, like where the female prefers to lay eggs, under what conditions those eggs hatch and how much of a pest the breed is going to be to humans, animals or birds.

The mosquitoes that bite people the most are referred to as "floodwater mosquitoes," because that's where they prefer to lay their eggs -- near the pools of water that form after a rainfall. Places where puddles form are often attractive breeding grounds for the floodwater species. Some will lay their eggs on the ground right next to an area where water pools, like a gutter. When it rains, the water pools up, triggering the eggs to hatch.

Dakota County and the Farmington area have had a few good rain showers in the past few weeks, McLean said, which is why MMCD staff have been patrolling the area, looking for signs of egg nests that can be destroyed. But the dry summer has had its benefits, too.

"When you have a rainfall, that's where floodwater mosquitoes are produced," McLean said. "The broods of mosquitoes have been lower this year than we usually see, but people are starting to see more activity now because of the rain we've received lately."

Late summer

The Minnesota Mosquito Control District changes its focus come mid- to late July, though, from trying to really track down the floodwater mosquitoes to tracking the ones that carry the West Nile disease.

The Culex mosquito lays its eggs on permanent water, like ponds. In particular, shallow "stinky" ponds, where vegetation has had a good chance to grow over the summer are attractive to the female. The female lays eggs in a raft-like fashion and they float on top of the water for a brief time before hatching.

Places where water gathers and sits undisturbed for a period of time are also attractive to the Culex mosquitoes, McLean said. An abandoned child's sandbox toy or old tires stacked outside provide a place for pools of water to form, and to grow warm -- a perfect host for the eggs.

"We pay attention to different types of sites at different times of the year," McLean said. "Late in the summer we start being more focused on permanent water ponds and standing water. We do a lot of neighborhood maintenance, too."

The Culex mosquitoes, for the most part, prefer to bite birds, rather than mammals. Bird blood, McLean said, is richer, and that is what attracts the Culex breed. But not just any bird is affected. For the most part, birds native to Minnesota are not affected by the bites. But some birds, like crows, blue jays and birds of prey, are particularly susceptible.

"When you start seeing dead crows, it's a pretty good sign the West Nile disease is present," McLean said.

The Culex Tarsalis mosquito is maybe the most problematic, because it is content to feed on birds until mid-July or early August, but then switches its feeding habits to mammals. It's something MMCD officials call the bridge factor. And a lot of times, that is where the West Nile can be transferred to humans. The mosquito bites a bird carrying the disease, then bites a mammal.

Taking precautions

Though people typically let their guards down later in the summer and into the fall, that is the time some people also contract the West Nile disease. With the bug spray put away, people aren't as diligent about protecting themselves from the mosquito bites.

"The chances really kind of go up, especially if they're doing any kind of camping," McLean said. "This is the time of the year where it's worth paying attention to the mosquitoes and trying to avoid those mosquito bites. Even though the population may be way down, the risk goes way up."

For its part, MMCD inspectors will be more visible around the community the next few weeks, he added. Mostly what residents will see are inspectors going out in waders and using dippers to collect eggs. Those eggs are being analyzed, and if the results show there is an area of concern, the MMCD can take steps to kill off the species in those locations.

As the days get shorter, the eggs can "sense" the change, he added. Eggs will actually go dormant for an entire season, and can survive the freezing winter temperatures, only to hatch in the spring. Floodwater eggs can lie dormant for as long as five years.