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Michigan's mosquito population plummets during hot, dry summer

The Aedes aegypti mosquito is one of two types thought to be capable of carrying and transmitting the Zika virus.
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The Aedes aegypti mosquito is one of two types thought to be capable of carrying and transmitting the Zika virus.

Mosquito populations are down in Michigan this summer. Michigan State University microbiology and entomology professor Ned Walker said they are only 10% of what they were last year. He said that is probably due to this summer's hot, dry weather.

Walker's team monitors disease-carrying species. He said the lack of rain is making it hard for aquatic larvae to develop. There are more than 65 mosquito species in Michigan, including ones that carry West Nile virus, dengue, and eastern equine encephalitis. Statewide testing efforts have shown those diseases are down this season as well.

Climate change is changing Michigan's mosquito season in two noticeable ways that are intertwined, Walker said. Hatching season is longer because Michigan's spring and fall temperatures are getting warmer, and species are expanding their ranges, establishing in Michigan where they previously had not.

Michigan has a mix of mosquitos that can thrive in warm climates and those that are cold-tolerant. That's because of the state's traditionally moderate temperatures, Walker said. Over the past 15 years, five different southern species usually found in Alabama, Texas, and other warm states have established in Michigan, he said. Meanwhile, northern species that can withstand harsh winters are retreating to higher latitudes. That's because climate change brings an early end and late start to Michigan's frost cycle.

Walker said the mosquito population can increase quickly. More rain usually means more bugs. "Seven to 10 days after a heavy rain event, here come the pest mosquitoes," he said.

But this year, that hasn't been happening. Walker said recent rainfall was sucked up by the ground because it's been so dry.

And Walker said the season is still young. With a longer warm season, this summer could still see mosquitos being a problem late into October.

If mosquitoes do get worse in the coming weeks, Walker said to plan ahead with water drainage systems, use bug spray, and wear pants and long-sleeve shirts.

Katheryne Friske is the weekend morning host and producer for All Things Considered.
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