USU Ecologists Receive CDC-Supported Grant to Study Insecticide Resistance in Mosquitoes

Utah isn’t among the worst U.S. states for mosquitoes, yet the pesky fliers make themselves at home in the Beehive State and can be a significant public health threat to people and animals. Utah State University ecologists were recently awarded funding to bolster state efforts to keep mosquito numbers in check.

“Several species of mosquito are prevalent in Utah and some are disease vectors,” says USU doctoral student researcher Emily Calhoun. “The focus of our study is the species Culex pipiens, a common house mosquito, which can spread West Nile virus and St. Louis encephalitis in humans, as well as avian malaria in birds and heartworm disease in dogs.”

Calhoun and her faculty mentor, Norah Saarman, assistant professor in the Department of Biology and the USU Ecology Center, received a one-year, $25,000 training grant from the Centers for Diseases Control and Prevention’s Pacific Southwest Regional Center of Excellence in Vector-Borne Diseases, based at the University of California, Davis.

The research funding will support the USU team’s efforts with the Salt Lake City Mosquito Abatement District and the South Salt Lake County Mosquito Abatement District to monitor levels of larvicide resistance in the county’s catch basin system. The districts provided $3,500 in matching funds to further support Calhoun’s project.

“Catch basins throughout Salt Lake County collect runoff from creeks, streams and irrigation, and are ideal breeding habitat for mosquito larvae,” says Calhoun, an ecology major and trainee in USU’s National Science Foundation-funded, interdisciplinary Climate Adaptation Science program.

The abatement district includes the larvicide Bacillus sphaericus in its arsenal of “modes of action” to reduce mosquito populations.

“Bacillus sphaericus or ‘Bs,’ as it is known, is a widely used, cost-effective and fast-acting approach to mosquito abatement,” Calhoun says. “Safe for humans and animals, it is applied in pellets or granules to water catchment areas, where mosquito larvae feed on the larvicide, which binds to receptors in the larvae’s midgut cells and kills the young mosquitoes.”

A drawback? Mosquito larvae evolve resistance to the larvicide. Monitoring the level of resistance, and where it’s taken place, is a management challenge. Collection and analysis are time-consuming and costly chores. The process requires personnel to collect larvae samples from catchment areas using cups attached to long sticks. Samples are then transported to a lab for bioassay analysis.

“Our goal is to streamline this process so managers can better identify where resistance is occurring, how widespread it is and how long-lasting its effects are,” Calhoun says. “We will assess published methods that could allow faster testing and investigate a more targeted and time-effective approach to resistance monitoring.”

Does this past winter’s extraordinary snowpack and robust runoff portend an extra-bad mosquito season for Utah?

“That remains to be seen,” Saarman says. “On the one hand, fast-moving water (from snowmelt) inhibits mosquito habitat. On the other hand, water may linger in areas that would dry up quickly in a drier year. There’s also the question of irrigation. In a dry year, more use of irrigation promotes mosquito habitat.”

Whatever the next few weeks and months bring, West Nile virus is an annual presence in Utah. Saarman says the disease occurs in cycles, with the Utah Department of Health and Human Services reporting an average of 25 human cases of the virus per year in recent years, along with a surge of 158 cases during a high transmission event in summer 2008.

“The relatively small number of cases may not capture the virus’s serious level of the threat to humans,” she says. “West Nile virus is a neuroinvasive disease that can progress to dangerous and lingering complications, including meningitis, encephalitis and Acute Flaccid Paralysis.

Three Utahns died from the illness in 2021.

“That may seem like a small number, but it warrants vigilance,” Saarman says. “Our focus is on preventing vector-borne disease in the safest, most cost-effective and environmentally friendly ways possible.”