Sterilized mosquitos helping with notable drop in Southern California nuisance
By Dean Fioresi, Nicole Comstock
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LOS ANGELES, California (KCAL, KCBS) — A pilot program aiming to reduce the massive invasive mosquito population in Southern California seems to be working so far, making for a notable decrease in the nuisance so far this year.
For the first time in a decade, experts have seen a drop in “ankle-biters,” more formally known as the aedes aegypti mosquito. The program releases millions of sterilized mosquitos — meaning they’re unable to reproduce — in some of the biggest trouble areas.
“It’s very exciting,” said Dr. Solomon Birhanie, the scientific director for the West Valley Mosquito and Vector Control District.
He says that they’ve seen notable drops in population across the region so far in 2025, after a yearly incline dating back to 2015, when it was first detected in Southern California. On top of limiting the nuisance associated with mosquitos — itchy, swollen bites and buzzing — it should also help prevent the spread of disease. ‘
When they do reproduce, mosquitos can lay millions of eggs at a time, usually in bodies of standing water as small as a bottle cap or a garden drain. As areas like this are tough to reach for mosquito control agencies, and most mosquitos are resilient to common pesticides, they decided to try and implement the new method.
Male mosquitos are raised in a lab and then zapped by X-ray machines, which makes them become sterile and unable to bite or spread disease. Instead, officials say that they’ll mate with the female mosquitos when they’re released into the wild.
“Those females mate with one of our sterile males; any sperm she collects, she will then store for all of her batches of eggs. But, if she’s mated with one of our sterile males, any sperm that she collects, she will then store for all of her batches of eggs. If she’s mated with one of our males, then any of those eggs that she lays will not be viable,” said Greater Los Angeles County Vector Control District director Steve Vetrone in May last year when the program was announced.
In some especially dense areas in San Bernardino County, the aedes population has dropped by 44%, while in the Suland-Tujunga area they’ve seen a remarkable 82% drop.
So far, Dr. Birhanie says that they’ve received interest from multiple agencies, but scaling targeted programs like this to large areas requires time and resources.
Los Angeles County officials say such a program could cost homeowners approximately $20 per person a year, while medium-sized areas wouldn’t require as large of a budget.
Some other regions have resorted to introducing mosquito fish to water, which resulted to a 65% reduction in some Inland Empire regions like Rancho Cucamonga.
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