Sunday, July 26, 2026

San Gabriel Valley Mosquito District Begins Releasing Sterile Male Mosquitoes in Bassett

The agency that serves Pasadena and Altadena is deploying non-biting males carrying Wolbachia bacteria to curb disease-spreading Aedes aegypti

The mosquito-control agency that protects Pasadena, Altadena and two dozen other San Gabriel Valley communities began releasing tens of thousands of non-biting male mosquitoes last week in the community of Bassett, launching a new effort to shrink the population of an invasive species that can spread dengue, Zika and chikungunya.

The program, called SGV Mosquito Match, is the San Gabriel Valley Mosquito and Vector Control District’s first use of the sterile insect technique against Aedes aegypti.

The district said it will release more than 30,000 male mosquitoes a week from cardboard tubes within a 25-acre section of Bassett for 16 weeks, from July through October. The males carry Wolbachia, a naturally occurring bacterium that, according to the district, makes them unable to produce viable offspring when they mate with wild females — a mismatch the district says will gradually reduce the biting population.

Releases began in an area bounded by East Temple Avenue, Millbury Avenue, Moccasin Street and Vineland Avenue. The district said it chose the unincorporated neighborhood, north of Avocado Heights, because years of surveillance found high numbers of Aedes aegypti there.

The program is run by the same district that serves more than 1.5 million residents across 26 cities and unincorporated areas, including Pasadena and Altadena, and that led the operation to treat thousands of neglected swimming pools in the Eaton Fire burn area last year. The district tests mosquitoes across the valley for viruses including West Nile and evaluates the risk of dengue, Zika and chikungunya.

“As the Aedes aegypti population expands throughout the San Gabriel Valley, the risk for local transmission of dengue, Zika and chikungunya also increases,” District Manager Jason Farned said in a statement. He said the technique “utilizes mosquitoes of the same species to work for us, not against us.”

The mosquitoes are EPA-approved WB1 males reared by the company MosquitoMate, using a Wolbachia strain the U.S. Environmental Protection Agency registered in April 2024 as a tool to suppress Aedes aegypti. Only female mosquitoes bite; males do not bite or transmit disease.

The district said residents may notice more mosquitoes after each release, but that the added insects are harmless males. “While residents may visually see more mosquitoes in the area, Aedes aegypti biting pressure will gradually reduce over time,” said Tristan Hallum, the district’s director of scientific programs. “This program is species-specific and will not affect humans, pets, wildlife, or other insects, like bees or butterflies.”

The district said the releases are meant to supplement, not replace, traditional mosquito control, and urged residents to keep dumping standing water, maintaining pools, changing pet-dish water weekly, and using EPA-approved repellents.

Aedes aegypti, an invasive species that has spread across Los Angeles County since 2011, is difficult to control because it resists many insecticides and breeds in small containers around homes. Other California districts have tested similar methods. The Greater Los Angeles County Vector Control District reported a nearly 82% drop in Aedes aegypti in one release area in Sunland-Tujunga, and districts in the Inland Empire and Sacramento region have run comparable programs.

The district said Bassett is the only neighborhood scheduled for the program this year, and that it will use the launch to measure cost and effectiveness before deciding whether to expand elsewhere in the valley.

Residents can find program information at bit.ly/sgvmosquitomatch or by calling the district at (626) 814-9466.