Residents in Los Angeles County were anticipating a break from the pesky mosquitoes responsible for a recent rise in dengue fever. Typically, these invasive mosquitoes, known as Aedes aegypti, go dormant from winter until early May in the area.
This year, however, complaints to mosquito control agencies have surged, indicating that they haven’t disappeared as expected. “We have not seen them go away altogether like they have in previous years,” noted Susanne Kluh, who manages the Greater Los Angeles County Vector Control District.
This unusual situation has intensified efforts in a shipping container located in Pacoima, which is being readied as a nursery for thousands of mosquitoes. In May, the district plans to release sterilized male mosquitoes—individuals that don’t bite—across Sunland-Tujunga. Previous years showed some success, with female mosquito populations in treated neighborhoods declining by over 80%. However, local business owners have expressed reluctance to finance an expansion of this program, complicating officials’ plans to extend it throughout their service area, which covers 36 cities and unincorporated regions.
“Unfortunately, that’s going to be a rather expensive endeavor,” Steve Vetrone, an assistant general manager for the district, commented. “I can tell you right now that’s not something that we can do with our current operating budget.”
A need, an ask and a disappointing answer
Aedes aegypti are a recent addition to the local ecosystem. Originating from Africa, these mosquitoes first appeared in California in 2013 and in L.A. County the following year. They’ve rapidly proliferated, spreading to nearly every city in the district and much of Southern California. Kluh emphasized the danger they pose: “Despite our best efforts, they’ve been able to just outpace us.”
In search of solutions, various vector control districts, including those in Orange and San Bernardino counties, are attempting the sterile insect technique. This involves releasing sterilized males at a ratio of 10 to 1 or even 100 to 1 against wild males to prevent them from mating successfully and producing viable eggs. Kluh’s district sterilizes males using X-rays, though other methods exist, such as genetic modification.
This technique, while potentially effective, requires both time and funding. In California, property owners typically cover pest control costs, including an annual benefit assessment. To introduce a fee for wider mosquito control, officials need approval from homeowners and businesses, following Proposition 218. They seek to impose an extra fee of up to $20 annually for households, alongside the existing $18.97 charge for service. Earlier this year, 50,000 sample ballots were distributed to gauge support for this increase, but only 47% of responses were favorable. Kluh noted that while homeowners showed support, many businesses didn’t see the cost-benefit rationale.
Puzzlingly, businesses often hold more weight in votes, which can complicate such initiatives. Commenting on this situation, Times readers expressed support for combating mosquitoes, with one saying they would willingly spend $20 to reduce their numbers. Officials remain hopeful and plan to conduct another ballot later.
Making mosquitoes that can’t reproduce
During a recent visit to the Pacoima insectary, Nicolas Tremblay, a senior vector ecologist, showcased a container filled with about 6,500 mosquito eggs mixed with bovine liver powder. These capsules are added to water-filled trays, enabling the eggs to hatch and larvae to thrive on the powder. It takes roughly nine days for them to develop into adults, which are then transported for sterilization before being released back into the environment.
The district launched a pilot program in 2024 and successfully released nearly 600,000 sterilized males in two neighborhoods, resulting in an average 82% reduction in female populations compared to a control area. This success came at a critical time, as California saw a sharp rise in locally acquired dengue cases.
Having conducted similar efforts last year, the district observed further drops in mosquito activity, although natural variations may have influenced this decline. Inside the insectary, researchers are studying mosquito behavior, exploring preferences for different blood types—a factor potentially influencing reproduction rates.
A highly adaptive foe
The tenacity of Aedes aegypti is notable; they can breed in tiny amounts of water, which means everything from a bottle cap to a crevice in a food package is suitable for them. Additionally, this species has developed resistance to many common pesticides. Recently, Kluh noted that it appears they may have altered their hibernation behavior, remaining active during winter due to climate change.
Although some community members are enthusiastic about the new control methods, others express concerns about the ecological implications. “There are folks that are in favor, and then there are folks that are just absolutely opposed because it’s like, ‘You’re playing God,’” Vetrone acknowledged.
