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. In 2024, surveillance data showed that this population size remains relatively moderate and has not expanded beyond the initial range. This case demonstrates that invasive Aedes can be managed sustainably if the population is detected early and addressed immediately, while the population is confined to a small area. 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 2024, 13 travel-related dengue cases were reported in San Joaquin County, up from 4 in 2023. While San Joaquin County has had no local dengue transmission, Southern California reported 18 locally-acquired cases in 2024. 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.
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
These viruses are not currently transmitted by mosquitoes in San Joaquin County or California.
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
What to Know About Our Pilot Release of Male Wolbachia Mosquitoes for 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 or lemon eucalyptus when outdoors. Please follow label instructions.
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
Cemetary vases
Rain barrels
Septic tanks
Tires
Toys left outside
Remove saucers under plants
Cover bins, buckets, and tubs with fitted lids
Remove miscellaneous containers from yard
Remove old tires from yard
Fill rims of pots with sand
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 report online at 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!
or online at westnile.ca.gov
Sign up to receive email updates including news releases and spray updates.