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Heavy rains, warmer weather bring increase in mosquitos
west nile
Infected mosquitoes spread West Nile Virus to humans and other animals when they bite. - photo by Photo courtesy of CDC

If your idea of mosquito repellant is to slap them dead, then it’s going to be a brutal season for you

Local mosquito abatement districts caution that 2023 will be a challenging year for the area due to the heavy rainfall, creating many opportunities for mosquitoes to breed.  

With the abundance of water and increasing temperatures, the mosquito population will be increasing and with it the risk of contracting a potentially deadly disease such as West Nile Virus and Saint Louis Encephalitis Virus. Both the Turlock and Eastside Mosquito Abatement Districts are reminding residents to take precautions to prevent mosquitoes and mosquito‐borne diseases.

In 2022, mosquitoes were responsible for causing 209 human and 16 horse cases of WNV in California. Of the WNV cases in California, there were 15 human and one horse case in Stanislaus County. There was also an additional human case of St. Louis Encephalitis Virus in Stanislaus County.

The Districts urge residents to “Dump and Drain” standing water around their properties to prevent mosquitoes from becoming established around their homes and to protect themselves and their families. Dumping outstanding water is particularly important with the county’s newest species, Aedes aegypti, which likes to live near homes and is an aggressive daytime biter of people. This species only needs 4 to 5 days to complete its lifecycle and their eggs can last up to a year before they hatch. Since they like to lay their eggs on the sides of containers, it is recommended that anything holding water that can’t be completely removed such as a pet bowl, should be scrubbed every three days to remove the eggs before adding fresh water.  

Aedes aegypti is very difficult to control and will require the help of all residents to reduce their population each season, according to the abatement districts. Aedes aegypti mosquitoes, which are invasive for the region, are capable of transmitting viruses such as chikungunya, dengue, yellow fever, and Zika.

“Take a moment to look around your property and dump and drain any items with standing water that can allow mosquitoes to develop. Aedes aegypti only require a bottlecap full of water to start the next generation,” said David Heft, general manager for Turlock Mosquito Abatement District.

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 Districts also anticipate challenges with larger amounts of water from neglected swimming pools and flooding along the rivers. The Districts monitor and treat neglected swimming pools which can produce numerous mosquitoes capable of carrying West Nile Virus. In addition to the neglected pools currently being monitored, many pools that were empty will now have water in them so they may begin to breed mosquitoes.

The Districts will maintain surveillance of current and future flooding along river corridors, which based on past history, will also produce an abundance of mosquitoes. As snowmelt releases continue through the spring into summer, residents often experience problems with mosquitoes traveling away from the rivers towards adjacent urban areas. The Districts will inspect and treat those areas as needed.   

Help reduce mosquitoes and mosquito diseases by following these guidelines:

·         Dump and drain containers or other items holding standing water

·         Remove saucers under pots

·         Repair leaky faucets and broken sprinklers

·         Dump and scrub (every 3 days) any outdoor containers holding water: pet dishes, birdbaths, fountains, kiddie pools, etc.

·         Cover trash cans, bins, buckets, and tubs with fitted lids and make sure they drain well

·         Remove old tires, tarps, buckets, junk, and miscellaneous containers that can hold water

·         Re‐direct sprinklers so containers do not fill with water

·         Clean out rain gutters and drains in the yard  

·         Use well‐fitted door and window screens

·         Avoid overwatering yard and plant overgrowth

·         Defend yourself against mosquitoes using repellents containing DEET, Picaridin, or Oil of Lemon Eucalyptus.

·         Properly cover (screen) or remove rain barrels

·         Report neglected swimming pools to your local mosquito and vector control agency.


Mosquitoes become infected with West Nile Virus when they feed on infected birds. Infected mosquitoes can then spread West Nile Virus to humans and other animals when they bite, according to the Centers for Disease Control.

Approximately 1 in 5 people who are infected with West Nile Virus will develop symptoms such as fever, headache, body aches, joint pains, vomiting, diarrhea or rash. Less than 1 percent will develop a serious neurologic illness such as encephalitis or meningitis (inflammation of the brain or surrounding tissues). About 10 percent of people who develop neurologic infection due to West Nile virus will die, according to the CDC. People over 50 years of age and those with certain medical conditions, such as cancer, diabetes, hypertension, kidney disease, and organ transplants, are at greater risk for serious illness.

There are no medications to treat or vaccines to prevent West Nile Virus infection. People with milder illnesses typically recover on their own, although symptoms may last for several weeks or months. In the neuroinvasive forms, patients can suffer severe and sometimes long-term symptoms.

People 50 years of age and older have a higher chance of getting sick and are more likely to develop serious illness when infected with WNV. Studies also indicate that those with diabetes and/or hypertension are at greatest risk for serious illness.

Reporting and testing of dead birds are important steps in preventing West Nile Virus. A confirmed case of the virus in dead birds or mosquito samples helps to identify areas that need treatment to reduce mosquito activity. To report a dead bird, call the California State hotline at 1-877-WNV-BIRD or report it online at Birds of particular interest are crows, ravens, magpies, jays and raptors (hawk or eagle).

There are two mosquito abatement districts to serve residents in Stanislaus County. Residents north of the Tuolumne River should contact the Eastside Mosquito Abatement District at (209) 522‐4098. Residents south of the Tuolumne River should contact the Turlock Mosquito Abatement District at or (209) 634-1234.