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The Mountain West has trended towards a decrease in mosquitos, but disease risks remain

Salt Lake City Mosquito Abatement District biologist Nadja Reissen examines a mosquito in Salt Lake City in a lab on Aug. 26, 2019. Cooler temperatures in the spring and early summer have meant that there have been fewer mosquito days in much of the Mountain West but scientists warn people should still be cautious about diseases such as the West Nile Virus when outdoors.
Rick Bowmer
/
AP
Salt Lake City Mosquito Abatement District biologist Nadja Reissen examines a mosquito in Salt Lake City in a lab on Aug. 26, 2019. Cooler temperatures in the spring and early summer have meant that there have been fewer mosquito days in much of the Mountain West but scientists warn people should still be cautious about diseases such as the West Nile Virus when outdoors.

Summer is here, which means mosquitoes are on the hunt. Though you may be lighting those citronella candles more than ever, recent data shows that compared to other parts of the country, the Mountain West is experiencing fewer days with mosquitoes. However, when it comes to mosquito-born diseases, the public might not be out of the woods.

Climate Central looked at how many days were “mosquito days” in 2022 and defined a mosquito day as a day with the perfect humidity of 42% or higher and a perfect temperature range of 50-95 degrees Fahrenheit. The study determined that throughout the Mountain West, the annual number of mosquito days in most cities have decreased since 1979.

Denver saw the biggest decrease in mosquito days out of all the cities measured in the Mountain West, with an average of 24 fewer days annually since 1979. Most other cities had anywhere from 3 to 18 fewer days, on average. Boise, Idaho, was the only city in the region that saw an increase, with an average of 6 more mosquito days.

This trend suggests that the West might also see a decrease in mosquitoes this year. Dr. Nina Fefferman, a professor of ecology and evolutionary biology at the University of Tennessee-Knoxville, said there’s a few factors that go into mosquito hatching. A warm habitat combined with humid weather and shallow water for breeding has to be present. The timing of when that habitat is available is crucial to the equation as well.

“If you have a tiny population of mosquitoes early in the spring and you get a lot more rain than usual early in the spring, it may not change how many mosquitoes you have by the end of summer,” she said. “There are more opportunities to lay eggs in places, but there aren't the females there to lay the eggs.”

That’s why in some parts of the Mountain West, even though there was record rainfall, the conditions were not right to create more mosquitoes.

But Fefferman said that’s not the case on the East Coast – those cities will have more mosquitoes due to having a warm winter and a warm spring, allowing mosquitoes to start breeding earlier. She compared it to compound interest in your bank account.

“If you have an extra month of interest to compound, you're meaningfully richer at the end of the year than if you only had 11 months of interest to compound, even if it's only compounding monthly,” she said. “But if it's compounding daily, which mosquitoes are…oh, that's a lot of money.”

Despite the late start to the warm temperatures in many parts of the Mountain West, Fefferman predicts that due to climate patterns, people can expect bigger mosquito populations in the future.

While most of these mosquitoes are harmless, some still carry diseases. The CDC reported 5 cases of malaria nationwide late last month. With more people traveling domestically, someone could visit and spread the disease to that area with one mosquito bite.

“Even if the mosquito populations are unaltered or in fact lower in the western parts of the country, there might still be an increased risk based on the likely introduction of infection into the community by people traveling from higher prevalence areas because of higher mosquito populations,” Fefferman said.

According to Fefferman, it comes down to when mosquitoes are biting and when people will be exposed. For instance, there could be a ton of mosquitoes outside, but if it’s too hot for people to be outside and they go indoors, less bites will occur, she said. Additionally, even within the same city, depending on where people live, some populations may have an increased risk of getting bitten over others.

“It doesn't matter as much how many mosquitoes are out there, it's still bad,” she said. “But if humans just aren't interacting with mosquitoes in ways that allow them to be bitten, it's not as bad.”

People can protect themselves by wearing lighter-colored, long-sleeved clothing and bug repellant, as well as dumping out any standing water that’s in the backyard, like in a bird bath or cup. Fefferman said citronella candles and mosquito control efforts do work, but they are not as effective in the long-run.

Fefferman emphasized that having an elevated risk of disease is different from being at risk for disease. Yet, it’s important to stay alert.

“No one should be scared, but it really helps everyone if everyone is a little cautious, because if everyone is a little cautious, all of our risks are reduced,” she said.

This story was produced by the Mountain West News Bureau, a collaboration between Wyoming Public Media, Nevada Public Radio, Boise State Public Radio in Idaho, KUNR in Nevada, KUNC in Colorado and KANW in New Mexico, with support from affiliate stations across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting.

Copyright 2023 KUNC. To see more, visit KUNC.

Emma VandenEinde

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