The fight against invasive mosquitoes is underway behind the recent surge in localized spread of dengue fever in Southern California. The authorities may have unlocked a powerful tool to win the day.
Two vector controlled districts – local agencies tasked with controlling disease-spraying organisms – released thousands of infertile male mosquitoes in certain areas, one starting in 2023 and the other the following year.
The idea is, infertile men should not hatch. And, as only female mosquitoes bite, unleashing men does not lead to infection with diseases like dengue, a fatal viral infection.
The data so far has been encouraging.
One agency serving large Swas in Los Angeles County found that invasive aegypti mosquito populations fell by nearly 82% in the Sunland-Tujunga release area last year, compared to the control area.
Another district covering the southwest corner of San Bernardino County released sterile men last year and recorded an average 44% decline in several serious locations sterilized last year compared to pre-intervention levels.
Overall invasive mosquito counts fell 33% across the district. This marked the first time in about eight years, rather than growing population.
“We were on the scene and not only were we actually seeing good cuts, but we were calling. People were calling to complain,” said Brian Risingter, community outreach coordinator for the Inland Empire’s West Valley Mosquito and Vector Control District.
However, the challenges remain. Overnight expansion of interventions at the level necessary to create dents in the vast areas provided by the LA County district does not occur overnight, and requires homeowners to pay up to $20 per year on the property tax bill.
Climate change is allowing mosquitoes in Aedes aegypti and the diseases they spread.
“We’ve seen a lot of people who have had a lot of trouble with the LA County Public Health,” said Dr. Eiman Harai, director of Vector-borne Disease Unit.
Small tragedy, big threat
The murine egiput mosquito was first detected in California about a decade ago. Originally from Africa, this species can infect yellow fever, Zika, Chikungunya as well as dengue fever.
Another invasive mosquito, Aedes albopictus, arrived early, but its numbers have declined, making it less likely to spread diseases such as dengue.
The black and white striped aegyptiformes cannot fly to the distance of about 150-200 yards, but they can somehow roam. Low-flying, chewing mosquitoes exist in more than a third of California counties, including Shasta County in the far north.
Mosquitoes known for pinching their ankles prefer to bite humans by animals. Insects that arrived in California about 10 years ago can transmit diseases such as dengue fever and deer.
(Orange County Mosquito and Vector Control District)
Aedes aegypti loves to bite people. In many cases, it is rapidly multiple times in a row. As insects spread throughout the state, the patio and backyard transformed from rest to dangerous territory.
However, it turns out to be difficult to close the bug. They can lay eggs in small water sources. And they might put some in the drains, such as a tray of plants. Eliminating the invaders is not easy if it is difficult to find all breeding spots or if it is difficult to access all yards where breeding is rampant.
That’s one of the reasons why liberating sterile men is so attractive. They are naturally experienced in finding their kind.
Mosquitoes and mosquitoes
Releasing sterile male insects to combat pests is a proven scientific technique that has been around since the 1950s, but using it to control invasive mosquitoes is relatively new. This approach appears to be catching up in Southern California.
The West Valley area has pioneered the release of sterile male mosquitoes in California. In 2023, the Ontario-based agency launched its pilot program before expanding the following year. This year, the number of sites available is increasing.
The Greater Los Angeles County Vector Control District began its own pilot effort in 2024, with plans to target roughly the same area this year.
Starting in late May, the Orange County District will continue its lawsuit with scheduled releases of 100,000 to 200,000 sterile male mosquitoes per week in Mission Viejo until November. The Coachella Valley area is hampering the development of its own programme that could potentially descend from the ground next spring.
Vector officials in LA and San Bernardino County said residents are asking them when they can bring a batch of men zapped into their neighborhood. But experts aren’t that easy for large population centers.
“I answered this morning to one of the residents who was saying, ‘Can I take this anywhere this year?’ And that’s of course because Rome wasn’t built in one day,” said Suzannekul, general manager of the Vector Control District, Greater Los Angeles County.
The Kluh district has a budget of nearly $24 million and is responsible for nearly 6 million residents in 36 cities and unincorporated areas. West Valley’s budget this year is around $4 million, with the district serving around 650,000 people across six cities and surrounding county regions.
The approach between the two districts varies in part due to the size they work.
West Valley is targeting what is known as hotspots. This is an area with a particularly high mosquito count. Last year, before peak mosquito season, we released about 1,000 sterile men every other week on each site. The district then hit a maximum of 3,000 on certain sites during a peak period that lasted from August to November. The idea is to outperform wild men by 100 to 1 for the program. The program’s equipment cost around $200,000, and the district hired full-time staff to support this year’s $65,000 effort.
West Valley Science Director Solomon Billhoney said the district doesn’t have the resources to attack large-scale land and therefore uses the resources it has efficiently. Focusing on problem sites has been shown to be sufficient to affect the entire service area, he said.
“A lot of medium and small districts are interested in using our approach right now,” he said. Because “there is evidence that it can be incorporated into a repeal program without hiring highly skilled personnel or asking for more budgets.
Solomonville Honey, director of science at the West Valley Mosquito and Vector Control District, looked at a container of mosquito larvae in the lab in March 2024. The Ontario-based district has pioneered the release of sterile male mosquitoes in California.
(Allen J. Scheven/Los Angeles Times)
In the first study last year, the LA County district unleashed an average of 30,000 men a week in two Sunland-Tujunga districts between May and October. They want to be superior to 10-1 wild men.
Kluh said more funding is needed to bring the program to a larger area of the district. Authorities offer up to $20 per year for each detached house. This is in addition to paying for services already offered by the $18.97 district homeowners now pay for the agents.
If the investigation sent to a sample of owners supports the new claim, they will vote in the fall, as requested by Proposal 218, Kluh said.
There are five vector control districts covering LA County. The land of Roun County is the largest district, stretching from San Pedro to Santa Clarita. It covers most of the city of LA, except for coastal areas, and does not serve San Gabriel or Antelope Valley.
Zinc plating due to illness
Last year, there were 18 local dengue cases in California. This means that they were infected with a viral disease in the community, not while traveling.
Fourteen of these cases were in Los Angeles County. This includes at least seven that are tied to a small outbreak in Baldwin Park, an eastern city in Los Angeles.
The year before, the state confirmed the first locally acquired cases in Long Beach and Pasadena.
Most people with dengue fever do not have symptoms, but it can cause severe body pain and fever, and in rare cases, it can cause death. That alias, “Breakbone Fever,” gives you a stern glimpse into how it can feel.
More than a third of LA County’s dengue cases last year required hospitalization, according to Harai.
Mosquitoes pick up the virus after biting an infected person and bite and spread the virus.
Hope and the harsh truth
Mosquito control experts advertise that it is sterilized to be environmentally friendly as it does not involve spraying chemicals, and staff could potentially use it to target other disease spreaders, such as the local native Culex Mosquito, a carrier for the deadly West Nile virus.
New technology continues to be online. Last summer, the California Department of Pesticides Control approved the use of male mosquitoes that had infected a specific strain of a bacteria called wolbachia. Eggs fertilized by those men also do not hatch.
Despite the promising innovation, some aspects of the tragedy ignore local management.
He said that since starting in California with mosquito control almost 26 years ago, insect seasons have become longer as winters go. At the time, authorities worked in late April or early May, closing in early October. Now, native mosquitoes can appear as early as March, and invading insects can stick in December.
“If things are going as they are now, we can always circulate some dengue fever,” she said.
Last year, dengue fever recorded the worst year in the world, with more than 13 million cases reported in the US and the Caribbean, according to the Centers for Disease Control.
Many countries still report higher than average dengue fever. This means that travelers are getting more opportunities to take it home.
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