These mosquitoes don’t wait for nighttime; they bite in broad daylight, going straight for humans, and they love to sneak indoors. Now through November, mosquito control crews in Natomas are walking block by block and doing something that sounds backwards: releasing even more mosquitoes.
Each cardboard tube holds about 600 sterile males. At each stop, technicians crack one open and give it a few shakes, sending a cloud of insects drifting into the neighborhood air. The idea is to shrink an invasive mosquito population over time, reducing bites and the risk of disease.
“That’s why you find them in these urban dense populations, because that’s where the humans are,” said David Smith, a supervisor with the Sacramento Yolo Mosquito & Vector Control District. “A lot of times when we get calls from residents, [they tell us they were bitten] around the ankles, wrists, behind the knees and behind the elbows.”
Aedes aegypti, an invasive mosquito, was first detected locally in Sacramento in 2019. Unlike native species that target birds at dawn and dusk, these aggressively target humans all day long. They can spread dengue, Zika, and chikungunya, diseases already appearing in Southern California.
“They tend to lay eggs in small containers, anything that can hold water, even a bottle cap is enough,” Smith said.
Aedes aegypti eggs can survive for weeks or even months without water, waiting to hatch when a container is refilled. The department’s prevention team urges residents in Natomas to dump and drain standing water every week.
The district says Aedes aegypti is becoming more common across Sacramento and Yolo counties. Eggs from these species can survive dry spells and hatch once water returns, making them especially stubborn.
Science on the sidewalk
The 400,000 mosquitoes being released are all males raised in a Kentucky lab and treated with a naturally occurring bacterium called Wolbachia. When they mate with wild females, the eggs don’t hatch.
“Male mosquitoes don’t bite. They actually feed on nectar,” said Luz Maria Robles, with the Sacramento Yolo Mosquito & Vector Control District. “Their role here is when they mate with wild females, her eggs won’t hatch.”
A view inside this tube shows male mosquitoes clustering along the rim. The district says males don’t bite. Thursday, Aug. 28, 2025, in Natomas.Tony Rodriguez/CapRadio
The insects live about ten days, so crews return each week with fresh releases.
This pilot program covers about 25 acres, which is roughly 200 homes. By the end of November, the district expects to release the entire 400,000 mosquitoes.
Robles said Aedes aegypti arrived in California through bamboo shipments from Asia. The sterile-male approach is brand new for Sacramento but has been tested in places like Fresno and in countries worldwide struggling with the same species.
This pilot program is not aimed at the West Nile virus, which is carried by a different mosquito species common in the region. Those species tend to bite birds and other animals, with people as incidental hosts.
Control for West Nile involves spraying, not sterile releases, since the biology and behavior of the mosquitoes are different, according to Robles.
This has actually been a fairly mild season for West Nile virus,” she said. “But one of the areas we’re really closely monitoring is Yolo County, the city of Davis. The Yolo County Health Department actually just confirmed the first human case of West Nile virus for this year in Davis.”
Behind the scenes, traps are set and checked to track the experiment.
“During this time, they’re actually setting traps, collecting mosquitoes, taking that information back, and then they’ll be able to tell how much of the populations were reduced,” Robles said.
If invasive females show up in lower numbers, the district will know if it’s working. In the meantime, they tell residents to expect more mosquitoes landing on them.
Team effort and community outreach
A sealed tube of sterile males is shown before release on a block with high invasive mosquito activity. Thursday, Aug. 28, 2025, in Natomas.Tony Rodriguez/CapRadioWalking the route makes it clear this is more than science. One technician carries release tubes, while others update maps and chat with residents, handing out flyers about the invasive mosquito.
“To most people, mosquitoes are mosquitoes. They just want to kill it,” Robles said. “It's very important to understand the difference.”
That’s why outreach is built in. The district leaves door hangers, sets up tables at community events and posts reminders online. Flyers remind residents that these males don’t bite, their eggs won’t hatch, and the goal is to mitigate disease.
Releases are just one piece of a larger strategy. Crews continue to spray larvicide in standing water, stock ponds with mosquito-eating fish, respond to service calls, and encourage residents to empty containers that collect even a little water.
According to the mosquito control district, releasing mosquitoes has caused some concern on social media. But the district emphasizes the project is safe and targeted. Sterile-male methods have been used for decades in agriculture to suppress pests like fruit flies, and this release only affects Aedes aegypti.
“During the release, their job is to go and find the ladies and begin their mating process,” one technician joked.
The goal is to reduce bites and minimize the risk of disease. If it works, Sacramento could give the rest of California a model for controlling one of the state’s most frustrating pests.
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