What does it look like? Aedes aegypti is a small, dark mosquito with distinctive white markings on its body and legs. It is an invasive species that is now established in many areas of California, including throughout San Joaquin County.
When and where does it bite? Unlike many of our native mosquitoes, Aedes aegypti is an aggressive daytime biter. It prefers to live close to people and can bite multiple times. It is commonly noticed biting around the legs and ankles and can follow people indoors or into vehicles.
How far does it fly? Not very far. Aedes aegypti generally stays close to where it developed, often traveling only a few hundred feet during its lifetime. If you are being bitten around your home, there may be a development source with water on your property or nearby.
Where does it lay its eggs? Females lay individual eggs on the sides of containers and other surfaces just above the waterline. They often spread their eggs among multiple locations throughout a yard and may also lay eggs in items indoors. Eggs stick tightly to surfaces and can survive for many months without water. When water returns and covers the eggs, they can hatch.
Even very small amounts of standing water can produce mosquitoes, as little as a bottlecap! Common sources include plant saucers, buckets, toys, pet bowls, yard drains, tarps, clogged gutters and other water-holding items around the yard.
How does it spread to new areas? Because Aedes aegypti does not naturally fly very far, long-distance spread can occur when its drought-resistant eggs are unintentionally transported in containers or other items that hold eggs. Adult mosquitoes may also be transported in vehicles.
What diseases can it transmit? Aedes aegypti is capable of transmitting dengue, Zika, chikungunya and yellow fever viruses. These diseases occur in various parts of the world, and dengue has also been locally transmitted by Aedes aegypti mosquitoes in Southern California in the summers of 2023-2025.
To date, none of these diseases have been locally transmitted by mosquitoes in San Joaquin County.
Aedes aegypti is not a competent vector of West Nile virus. In San Joaquin County, West Nile virus is transmitted by Culex mosquitoes. Aedes aegypti in San Joaquin County The invasive yellow fever mosquito, Aedes aegypti, was first detected in California in Madera and Fresno counties in 2013 and has since spread as far south as San Diego County and north as far as Jackson County, Oregon, along the Oregon-California border. Ae. aegypti was first detected in San Joaquin County in 2019 within the Stockton-Brookside neighborhood in response to a service request for day-biting mosquitoes. The District has since expanded the invasive Aedes surveillance program. As of 2024, Ae. aegypti has been identified in every incorporated city of San Joaquin County and has continued expanding its populations.
In 2019, the Brookside Ae. aegypti population was quickly suppressed to low levels after its initial discovery. The District utilized all available control methods and received strong support from residents, who allowed yard inspections and actively followed recommendations. Many homeowners continue to regularly eliminate even the tiniest water-holding items in their yards—an essential effort given that this mosquito species needs only a small amount of water to develop. In 2024, surveillance data showed that this population remains relatively low and has not expanded beyond the initial range. This case demonstrates that invasive Aedes can be managed if the population is detected early and addressed immediately while it is still confined to a small area, with active community participation. However, the District utilized a plethora of resources and all available methods to achieve these results for a single neighborhood. As Ae. aegypti became widespread in other cities, the labor and resources required to contain the species became overwhelming and unsustainable for the District.
Multi-year surveillance data from the cities of Escalon, Ripon, and Manteca reveal a three-year pattern in the establishment of Ae. aegypti populations: in the first year, some eggs and/or a few adults are detected; in the second year, eggs and adults become widespread at low levels; and by the third year, multiple populations of varying levels are established. Ae. aegypti was first detected in Lodi and Tracy in 2023, and Lathrop and Mountain House in 2024. Assuming the three-year pattern, the District expects to see increasing adult activity in these cities over 2025 and 2026.
In addition to its day-biting behavior, Ae. aegypti is a vector of yellow fever, chikungunya, Zika, and dengue. Dengue prevalence, in particular, has increased globally over the past decade. In 2025, four travel-related cases were reported in San Joaquin County and 13 were reported in 2024. While San Joaquin County has had no local dengue transmission, Southern California has reported locally-acquired cases in 2023-2025. With Ae. aegypti becoming more widespread throughout San Joaquin County and with increased travel-related cases, the risk of local dengue transmission rises accordingly. Controlling Ae. aegypti is crucial to reduce the risk of acquiring these diseases.
These viruses are not currently transmitted by mosquitoes in San Joaquin County.
Due to its cryptic (prefers small hidden sources) nature and desiccation-resistant eggs, the invasive Ae. aegypti is a difficult species to control.
The District has utilized a matrix of control methods, including wide-area larvicide spray (WALS) and adulticide treatments, premise inspections, and source reduction. All these methods have limitations - for larvicides and adulticides, only a few formulations are available on the market. Property inspections for treatment and breeding-source reduction are notably effective for controlling Ae. aegypti. However, thorough property inspection is time-consuming, labor-intensive, and often unfeasible when Ae. aegypti is present across wide areas with difficult-to-access properties. To achieve a sustainable county-wide Ae. aegypti control program, it is imperative for the District to seek and utilize new control technologies and methods, such as sterile insect technique (SIT), and to educate and promote public participation.
https://www.cdph.ca.gov/Programs/CID/DCDC/pages/Aedes-aegypti-and-Aedes-albopictus-mosquitoes.aspx
Aedes aegypti, or Yellow Fever mosquito, is a small, dark mosquito with stripes forming a harp shape on the thorax and white banded legs. They often bite low and from behind—commonly on ankles and elbows. Spread throughout San Joaquin County.
Aedes albopictus, or Asian Tiger mosquito, is a small black mosquito with a bright white stripe on the thorax and white banded legs. It is an aggressive, rapid daytime biter. Not currently found in San Joaquin County.
For in-depth information on mosquito-borne diseases, visit:
* References: The Biology and Control of Mosquitoes in California (1996), Mosquito and Vector Control Association of California; CDPH; Best Management Practices for Mosquito Control in California (2012), CDPH
Watch Video
Learn where Aedes mosquitoes commonly develop and how to prevent them.
Invasive Aedes, District Inspection Locations
The District is not currently using Sterile Insect Technique (SIT) methods in 2026.
What to Know About Our Pilot Release of Sterile Male Wolbachia Mosquitoes Within One Neighborhood of Ripon in 2025
For more information
Aedes aegypti is an invasive mosquito species
Aedes aegypti, the Yellow Fever Mosquito, and its relative Aedes albopictus, the Asian Tiger Mosquito, are invasive mosquitoes in California. They can be a major annoyance and a public health threat. These mosquitoes are potentially capable of transmitting several diseases, including Zika, dengue, chikungunya, yellow fever, and others.
Apply EPA-registered insect repellents such as those containing DEET, picaridin, IR3535, or oil of lemon eucalyptus when outdoors. Please follow label instructions.
Inspect your yard weekly for hidden sources of standing water, then dump or drain Are you being bitten by mosquitoes during the day or experiencing an unusual number of mosquitoes?
Request an inspection at 209-982-4672 or 1-800-300-4675 or visit www.sjmosquito.org
THERE IS NO CHARGE FOR DISTRICT SERVICE.
7759 S. Airport Way Stockton, CA 95206
Monday-Friday 7:00 am - 3:30 pm
www.sjmosquito.org
Date/Time________________ Technician___________________
Service Request #______________________________________
Please call the District to schedule an inspection
We were unable to inspect your property
We inspected your property
Found invasive Aedes adults larvae
Found common mosquitoes adults larvae
No mosquitoes found
Plant saucers
Buckets
Bird Baths
Yard clutter
Rain barrels
Septic tanks
Tires
Toys left outside
Remove saucers under plants or fill with sand
Cover bins, buckets, and tubs with fitted lids
Remove miscellaneous containers from yard
Remove old tires from yard
Screen yard and patio drains
Re-direct sprinklers so containers are not filled
Keep recyclables in covered container(s) that drain
Properly modify (screen) or remove rain barrels
Empty birdbaths/fountains (every 3 days)
Empty/refill pet drinking water (every 3 days)
Clean out/drain rain gutters and drains in the yard
Remove plants that hold old water in yard
Keep potential sources dry when not in use
Comments:
Please call the District at 209-982-4675 or 1-800-300-4675 or visit www.sjmosquito.org
San Joaquin County Mosquito & Vector Control District is committed to providing vector surveillance and control services to protect public health. As an independent special district, our funding is through property taxes and benefit assessments. We cover all of San Joaquin County, including cities!
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