Researchers in the hottest city in the U.S. are investigating how mosquitoes are surviving and adapting to help curb the spread of West Nile virus and other vector-borne illnesses.

What's happening?

Researchers at Arizona State University are studying Culex mosquitoes across Phoenix to see how this West Nile virus-carrying species can withstand the city's intense heat. ASU News summarized their work, which has involved logging temperatures at 24 microhabitats, such as well-watered plant nurseries and murky park drains. 

The team collects mosquito larvae at each site. They rear them in the lab, where they determine their critical thermal maximum — the highest temperature they can survive — and compare it to the temperatures found at each site. Then, they compare this to the city's weather station data.

Among their findings so far is that the temperatures at mosquito collection sites are cooler than the city's weather station data, which is typically collected at places like the airport. This nugget of information helps to give a more accurate picture of why mosquitoes are thriving, ASU News explains.

Still, "these hearty little creatures are living on the edge of their critical thermal maxima," Assistant Professor Kelsey Lyberger says, adding that they can adapt through acclimation or evolution.

The researchers' work will eventually be used to predict mosquitoes' seasonality and to inform local vector control and public health agencies about where and when disease transmission will occur.

Why is this research important?

"The mosquito landscape has changed," Lyberger says. "They have increased in abundance, and we can attribute this to warmer climates and weather events like Arizona monsoons."

Arizona is not the only place to deal with these changes. Across the board, warmer temperatures and more humid conditions are helping to expand mosquito habitats into more northern parts of the globe and to higher altitudes, while also extending their active seasons in many areas.

With this increased abundance of mosquitoes comes increased risk for the diseases they spread, including West Nile virus, dengue, malaria, and others.

In fact, several U.S. health departments issued warnings in 2025, as they saw West Nile arriving earlier in the season. Colorado officials, for one, warned that the disease was starting earlier than usual on the state's Front Range in 2025, although they added that they weren't yet certain if this would translate into higher infection rates. Likewise, Massachusetts officials discovered the state's first West Nile-carrying mosquitoes two weeks earlier than last year. 

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West Nile is typically asymptomatic, but more severe cases can result in fever, headache, body aches, vomiting, diarrhea, and rash, according to the Centers for Disease Control and Prevention. In rare cases, the virus can turn deadly. 

What's being done about West Nile virus?

The best way to avoid contracting West Nile virus is to avoid being bitten, according to the CDC. The agency recommends preventative actions such as using an Environmental Protection Agency-approved insect repellent, wearing long, loose-fitting clothing, avoiding the outdoors during dawn and dusk, and using screens on windows. 

Many communities also have active mosquito control programs to help reduce their numbers and monitor them for disease. For instance, Maricopa County Vector Control traps mosquitoes once a week year-round, testing them for West Nile, St. Louis encephalitis, chikungunya, dengue, and Zika viruses, depending on the species. To control populations, the department utilizes fumigation and other methods.

Meanwhile, some communities are using more creative means. For instance, officials in one Florida county are using X-rays to kill invasive mosquitoes, and one Manila neighborhood is paying people to turn over any mosquitoes they can capture.

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