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First Invasive Aedes Mosquito Detected In Stanislaus County
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To report mosquito-breeding problem areas, Stanislaus County residents should contact one of the two mosquito abatement districts that serve the county. For Stanislaus County addresses north of the Tuolumne River, residents should call the Eastside Mosquito Abatement District at 522-4098 ( and all others should contact the Turlock Mosquito Abatement District at 634-1234 (

The East Side Mosquito Abatement District and Stanislaus County Public Health have jointly announced the first detection of invasive (non-native) Aedes aegypti mosquitoes in the county. Aedes aegypti mosquitoes have been detected previously elsewhere in California, but never before in Stanislaus County. Aedes aegypti is capable of transmitting viruses such as chikungunya, dengue, yellow fever, and Zika that are not transmissible by the native Culex mosquitoes.

Aedes aegypti mosquitoes pose a threat in that returning travelers may contract these viruses elsewhere, and Aedes aegypti in infested areas may pick them up and transmit to others. While the Aedes aegypti mosquito has the potential to transmit deadly viruses, none of these viruses are currently known to be transmitted locally in California.

Aedes aegypti mosquitoes were recorded by the District, initially in a trap located in Modesto just north of the intersection of Lakewood Avenue and Scenic Drive on July 25, 2019 and in another trap nearby on July 31, 2019.

“We found two male Aedes aegypti in traps within 100 meters of each other, which is indicative of an established breeding population in the community. It is our responsibility to locate and control them,” said J. Wakoli Wekesa, Ph.D., General Manager at East Side Mosquito Abatement District.

District staff will be conducting enhanced surveillance in the area including more trapping to evaluate the extent of the infestation. Mosquito control technicians will be doing door-to-door inspections searching for standing water sources where mosquitoes lay eggs and breed, which will encompass an area about a quarter mile radius from the index location. The technicians will be carrying out inspections and control activities in residents’ yards as needed and educating residents on how to prevent mosquito breeding.

In contrast to the native amber-colored Culex mosquitoes, whose peak biting times are dawn and dusk, Aedes aegypti mosquitoes are black and white, bite aggressively during the day, and feed almost exclusively on humans. Additionally, the larvae of Aedes aegypti mosquitoes require much less water. Females lay their eggs just above the water line in small containers and vessels that hold water, such as dishes, potted plants, bird baths, ornamental fountains, tin cans, or discarded tires. The eggs can survive for up to eight months after the water dries out.

The public plays a critical role in helping to control the spread of this mosquito population.

“This mosquito species breeds in small containers in and around homes. To get rid of it, people need to be aware of it, and then prevent its establishment by eliminating standing water in and around their homes,” added Wekesa.


Prevent Aedes aegypti development in your yard:

Inspect yards for standing water sources and drain water that may have collected under potted plants, in bird baths, discarded tires, and any other items that could collect water.

Check your rain gutters and lawn drains to make sure they aren’t holding water and debris.

Check and clean any new potted plant containers that you may bring home from areas that may have Aedes aegypti. The eggs can remain viable under dry conditions for months.


Prevent mosquito bites:

Apply repellents containing EPA registered ingredients such as DEET, picaridin, oil of lemon eucalyptus, or IR3535 to exposed skin and/or clothing (as directed on the product label). DEET can be used safely on infants and children two months of age and older.

Wear long sleeve shirts, long pants, socks and shoes when outside.

Be sure window and door screens are in good repair to prevent mosquitoes from entering your home.


Residents experiencing mosquito bites should report them immediately to the Mosquito Abatement Districts in Stanislaus County. If you are sick with fever, headache, and joint or muscle pain after returning from an area where dengue, chikungunya, or Zika occurs, contact your doctor and stay indoors as much as possible to avoid mosquito bites and help prevent possible spread of the virus.