L.A. released thousands of mosquitoes last year. They could be helping prevent infectious disease.

In 2023 and 2024, some districts in Southern California announced a plan to reduce the number of invasive mosquitoes: they would breed the insects, subject the males to radiation, and then release them.

The results continue to trickle in, and are so promising that other districts now want to launch similar programs.

The operation works by releasing radiation-sterilized male mosquitoes into the ecosystem. Males do not bite, and females who mate with sterile males lay eggs which will not hatch.

The West Valley Mosquito and Vector Control District, which operates in the Inland Empire, found a 44% reduction in the female mosquito population after a year of its trial. The Greater Los Angeles County Vector Control District established a similar program in the Sunland-Tujunga neighborhood, but the results are not yet available.

As a result, other municipalities have attempted to start their own trials. Mission Viejo plans to release over 100,000 mosquitoes per week from May through November. 

However, a proposal to do the same in all of L.A. County may require an extra $20 per year to be levied in annual property taxes.

Pest control officials have targeted mosquitoes in the genus “Aedes,” which are invasive in California. These pests can spread dengue — which is in the midst of an “unprecedented” surge in L.A. — as well as yellow fever, Zika, and other diseases.

Aedes mosquitoes fly low to the ground. They are unable to travel for long distances in one stretch, but pause to rest periodically. Because of this, they are known to bite at ankles during the summer.

Climate change has allowed Aedes mosquitoes to spread from the tropics and establish a home in California. They lay eggs in miniscule bodies of standing water, including small puddles left over after rainfalls. As a result, they are difficult to exterminate directly. Initiatives like the release of sterilized males may offer a more promising alternative.