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County to Conduct Treatments to Eradicate Non-Native Mosquitoes in East San José

The treatments are necessary to protect public health and residents’ quality of life from Aedes aegypti, an invasive mosquito that is known to carry Zika virus and other pathogens

SANTA CLARA COUNTY, CALIF. — The County of Santa Clara Vector Control District will conduct a series of treatments to eradicate Aedes aegypti (pronounced AY-dees ah-JIP-tie), an aggressive mosquito that is known to spread diseases such as Zika, before it can establish a permanent population.

The treatments will take place in a neighborhood in East San José surrounding Machado Lane.

The district has discovered 12 of the day-biting mosquitoes in that area since early April. The district has not been able to eliminate the mosquitoes using its first level of response, which includes applying larvicide to potential sources of mosquito habitat on private properties, with assistance from residents.

The first treatment will occur around 8:30 a.m. on Wednesday, May 29. The district will likely conduct several treatments in the area over the next few months. The treatments are necessary to protect public health from an invasive species that is capable of spreading the viruses that cause Zika, dengue fever, yellow fever and chikungunya. These potentially fatal diseases have caused significant public health problems in places such as South America and Africa where Aedes aegypti is established.

A pickup truck carries a mosquito-treatment machine.
A County Vector Control District truck carries equipment to conduct Wide Area Larvicide Spraying.

If Aedes aegypti gains a foothold in Santa Clara County, it would negatively affect our quality of life. These mosquitoes are highly aggressive and active during the day, unlike native mosquito populations, which are most active in the morning and evening, when temperatures are cool.

Aedes aegypti is a significant public health risk and a threat to our quality of life, and we need to do everything in our power to prevent it from establishing itself in our community,” said Edgar Nolasco, director of the County of Santa Clara Consumer and Environmental Protection Agency. “Treating the area where Aedes aegypti has been found is necessary to protect public health, and it is safe for residents, their pets, and wildlife.”

The treatment, known as Wide Area Larvicide Spraying, lasts about two hours. It involves a truck-mounted mist sprayer that uses a bacterial insecticide which targets mosquito larvae. The naturally occurring bacteria is nontoxic to beneficial insects and other forms of wildlife as well as humans. 

Wide Area Larvicide Spraying differs from the adult-mosquito-control treatments the district conducts to control mosquitoes that carry West Nile virus in a few important ways: It uses a different pesticide, takes place during the day, and targets larvae instead of adult mosquitoes.

County officials from the Vector Control District and Public Health Department will hold a community meeting on Tuesday, May 28, to inform residents about the treatments and answer their questions. The meeting will take place at 6 p.m. at the Alum Rock Branch Library in San José.

To assist with the eradication campaign, the district urges residents in East San José to inspect their properties for standing water, which provides breeding habitat for mosquitoes, and remove it. 

This is the second time Aedes aegypti has been detected in Santa Clara County. The district carried out a successful eradication plan the first time, when the non-native insect was detected at an industrial facility in North San José in the fall of 2022.

This incident is more serious. The number of mosquitoes is greater, they are spread across multiple properties in a residential area, and we have entered the warm months of spring and summer, which is the peak season for mosquito activity.

District staff do not know how the mosquitoes arrived in East San José. It’s likely that mosquito eggs were unknowingly transported into the area. Aedes aegypti eggs are able to survive without water, in a period of dormancy, for a year or more. 

Close-up photo of an aedes aegypti mosquito
Close-up photo of an Aedes aegypti mosquito.

Though it is not native to California, Aedes aegypti is present in 19 counties throughout the state, mostly in the Central Valley and Southern California. Zika and other viruses that Aedes aegypti is known to transmit are not endemic to California, but there have been occasional cases of these diseases being spread by travelers returning from parts of the world where the viruses are prevalent.

Aedes aegypti is about a quarter inch in size with black and white stripes on its back and legs. It does not fly long distances, venturing less than 500 feet from where it hatches. The mosquitoes are “container breeders,” preferring to lay their eggs just above the water line in small, artificial sources of water such as buckets, pet dishes, fountains and bird baths, plant pots and saucers, and old tires. 

The public plays a critical role in controlling the spread of this mosquito as well as native mosquitoes. Residents throughout Santa Clara County should look around their property and dump out even the smallest amount of standing water. Cleaning and scrubbing bird baths, pet dishes and other containers is a good way to remove any lingering Aedes aegypti eggs, which are about half a millimeter in size and look to the naked eye like tiny bits of dirt.

Residents should also:

  • Properly screen rain barrels, cisterns and irrigation drains to prevent mosquito access.
  • Fix leaky water faucets and broken sprinkler heads and avoid overwatering lawns and plants.
  • Ensure window and door screens are in good condition with no holes or tears and are tight-fitting.
  • Make sure the water level of swimming pools is adequate for proper circulation and filtration.

To protect yourself from mosquito bites:

  • Apply insect repellents containing EPA-registered ingredients such as DEET, picaridin, IR3535 or oil of lemon eucalyptus, always following label instruction.
  • Wear long-sleeve shirts, pants, socks, and shoes when mosquitoes are most active. 
  • Make sure your window and door screens are in good condition. 

Residents experiencing mosquito bites during the day should report them immediately to the Vector Control District at (408) 918-4770 or [email protected].

If you are sick with fever, headache and joint or muscle pain after returning from an area where dengue, chikungunya, yellow fever or Zika occurs, contact your doctor, and stay indoors as much as possible to avoid mosquito bites and help prevent the possible spread of the virus. 

To reduce the population of Aedes aegypti, the district uses pesticides that are approved by the Federal and State environmental protection agencies and are widely used by vector control agencies throughout California. 

The County of Santa Clara Public Health Department monitors the occurrence of viruses transmitted by Aedes aegypti and any unusual disease in partnership with local medical providers and laboratories, who are required to report certain diseases and conditions to Public Health authorities.

For more information or frequently asked questions on Aedes aegypti, visit the district’s invasive mosquitoes webpage or the California Department of Public Health’s Aedes aegypti and Aedes albopictus webpage.


The County of Santa Clara government serves a diverse, multicultural population of 1.9 million residents in Santa Clara County, making it more populous than 14 states in the United States. The County provides essential services to its residents, including public health protection, environmental stewardship, medical services through the County of Santa Clara Health System, child and adult protection services, homelessness prevention and solutions, roads, park services, libraries, emergency response to disasters, protection of minority communities and those under threat, access to a fair criminal justice system, and many other public benefits.

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