As if fear of West Nile virus weren’t enough, folks in San Joaquin County are being warned to take precautions over the Labor Day weekend against a ravenous — and potentially dangerous — breed of mosquito.
The more catchy name for the invasive Aedes aegypti is the “yellow fever mosquito.” That dreaded disease is most famous for having killed U.S. soldiers during the Spanish-American War and terrorized workers during the building of the Panama Canal in the late 1890s and early 1900s. The mosquito can also carry dengue and Zika.
From a modest start in Stockton in 2019, the presence of these blood-suckers has grown across the county, the Mosquito and Vector Control District said in a news release this week.
“This mosquito is a relentless biter and quite a nuisance,” the district said in a statement. Plus, it’s prolific. The insects lay eggs on the sides of buckets, open jars or even something as small as a bottle cap. Several generations of mosquitoes can hatch after a single laying of eggs.
Aedes aegypti made its California debut in Madera and Fresno counties in 2013. It would take six more years before the species would reach San Joaquin County, having been first detected in Stockton’s Brookside neighborhood. It has since spread as far south as San Diego County and north as far as Jackson County, Oregon.
At first, county officials said they were succeeding in combating the insect by pouring eradication efforts into a relatively small area. Since then, though, that strategy has become been unsustainable.
To illustrate how fast Aedes aegypti has propagated in the county, the Mosquito and Vector Control District used surveillance data from Escalon, Ripon and Manteca showing a three-year cycle. The mosquitoes laid eggs the first year they were discovered in those cities, established small populations in the second year and had become more widespread — though at relatively low levels — in the third year.
But then they moved into Lodi and Tracy in 2023 and Lathrop and Mountain House in 2024.
“As (Aedes) aegypti became widespread in other cities, the labor and resources required to contain the species became overwhelming and unsustainable,” the district said.
Officials expect the breed to become a bigger problem countywide, both this and next, as the mosquitoes follow that three-year pattern.
What’s worse, the little buggers can’t be controlled by homeowner spraying alone. The district said the insects can only be eradicated with larvicide treatment, meaning wide-area spraying aimed at eliminating eggs. Those efforts are in addition to normal low-volume mosquito spraying.
The district said it will inspect homes for the presence of mosquitoes but asks that residents provide a sample of one of the pests in order to identify the breed.
In the meantime, residents should eliminate any sources of standing water around their homes to prevent mosquito breeding grounds.
The mosquito wars in San Joaquin County heated up earlier this summer, as they always do. In June, mosquitoes that tested positive for West Nile virus were detected in two ZIP codes, officials said.
By mid-July, the county’s Mosquito and Vector Control District’s laboratory surveillance and disease testing system had found infected mosquitoes for four consecutive weeks in and around Tracy.
At the time, 80% of the mosquitoes found to be carrying West Nile virus in the county were detected in Tracy. Since then, the district is warning that the threat is countywide.
West Nile virus circulates between mosquitoes — primarily Culex species, according to the U.S. Centers for Disease Control and Prevention — and birds. But people can become infected when mosquitoes who have fed on infected birds bite them. I
There have been 22 human cases of West Nile virus this year in California, including one fatality, according to the state Department of Public Health. No human infections have been reported in San Joaquin County, but there have been five dead birds that have tested positive for the disease, as well as 78 samples of mosquitoes.