CA Endures Worst Mosquito Season In Years. When Will It End?

LOS ANGELES, CA — If it seems like the mosquitoes are getting worse in California, that’s because they are.

An uninvited houseguest is plaguing homes up and down California. It’s the Aedes aegypti, better known as the ankle-biter mosquito, one of the most vicious little bloodsuckers to invade the Golden State. At the same time, human cases of the mosquito-born West Nile Virus are spiking across the state, prompting counties from Alameda and Riverside to spray entire neighborhoods.

It’s been more than three weeks since Hurricane Hilary dumped record August rain on California, and the rare summer storm’s impact on the mosquito population is hitting home, literally. The ankle biter population is soaring along with complaints from residents who are being bitten in their own homes. The invasive species is more aggressive than native mosquitoes, more likely to bite its victims over and over again, more likely to bite at all hours of the day and more likely to sneak indoors for a meal.

“These ankle biters they follow us so closely and can come under your front door,” said Susanne Kluh, General Manager of Greater Los Angeles County Vector Control District. “As you walk in they just fly right in.”

They also bite their victims five or six times for one blood meal, leaving people with swollen, red and itchy bumps all over their feet and calves.

“This is something that is a lot different for people. People say to me, ‘I've lived in San Diego for 20-odd years, and I have never had mosquito problems. So what is going on?’' said Chris Conlan, Supervising Vector Ecologist for the County of San Diego Vector Control Program. “The behavior of these guys is definitely different than native mosquitoes that breed in the backyard.”

Leave a bucket of water in your yard for mosquitoes to breed in, and the native species called southern house mosquitos will go after birds for a meal, which is how the West Nile Virus is spread, explained Conlan. However, it’s a different story with the Aedes.

“You breed a bucket full of Aedes, and pretty much all those mosquitoes are coming after you,” he said. “They are very adept at getting inside homes and navigating through the home.”

Conlan said the number of mosquito complaints coming into the county has doubled in the last two weeks.

“Everybody is suffering the after-effects of that rain,” he said.

In neighboring Orange County, cases have skyrocketed.

“Right now we have a super huge uptick of Aedes,” said Brian Brannon, public information officer for the Orange County Mosquito And Vector Control District. “Mosquito control is a shared responsibility. We need everyone to do their part.”

In the last week, Aedes mosquitoes were found in Orange County traps at more than six times the normal rate for this time of year, a sign that the rest of the mosquito season could be a bloody one.

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Residents can expect the season to last until early November typically. The mosquitoes breed in water and thrive in heat. When the temperatures finally cool, the mosquito population recedes.

In the meantime, as county vector control officials around the state battle the invasion of the ankle biters, they're also dealing with an even more pressing concern — the rapid spread of West Nile Virus, a mosquito-borne virus on the rise in the aftermath of the storm.

As of September 8, human cases of West Nile Virus infections were already double the state’s five-year average for this time of year.

This month, Los Angeles County recorded its first West Nile Virus death of the year.

Normally at this time of the year, county vector control agencies would have gotten most abandoned swimming pools treated to control the common house mosquito that spreads the West Nile Virus, and they'd be shifting their attention to the ankle biters that thrive later in the summer and fall, said Kluh, Los Angeles County’s vector control general manager. But with the August rain, the pools filled up again, creating conditions ripe for the common house mosquito.

In the aftermath of the storm, the county went back and treated more than 2,500 abandoned pools that had filled up with rainwater again, she said.

“The storm delivered so much water, it was really unusual,” said Kluh. “Usually, it’s not as widespread as Hilary was or as much water. With Hilary, it was a lot of water and very widespread.”

West Nile Virus is now endemic in California, making efforts to halt its spread a priority for vector control and health officials alike. While the native Southern House Mosquito is a primary vector for the virus, the Aedes is still a major concern because it’s capable of spreading diseases that plague other parts of the world including encephalitis, Dengue Fever and Zika.

Concerned about what the future holds, officials are studying new approaches to control the spread of mosquito-borne diseases, said Kluh.

One approach would be to release sterilized males much like a similar, successful approach to managing the fruit fly population. Male mosquitoes don’t bite. It’s the females that bite to provide blood meals for their eggs.

“In Los Angeles and Orange counties, we have partnered up to assess whether we can irradiate male mosquitoes and release those to mate with wild females, resulting in sterile eggs,” she said.
That and similar approaches for reducing the mosquito population are a ways off from becoming a reality, said Kluh. However, Kluh said researchers are optimistic about the approach if it can be scaled to have widespread impact.

For now, the best way for people to save themselves from pesky mosquito bites is to deprive them of their breeding grounds: stagnant water.

The Aedes don’t tend to travel far, so if people keep their yards clear of stagnant water and help their neighbors to do so, they can pretty much rid themselves of the ankle biters, according to the experts. Residents can also call their county vector control to come out and identify and treat the source for free.

Tips for protecting your home from mosquitos:

• Walk your yard and look for breeding sites - namely anything that can hold a quarter inch of water. Dump out any standing water and remove the source - plant saucers, dimpled tarps, buckets, trashcan lids, etc. If you don't remove the source, check weekly for standing water to pour out.
• Empty bird baths weekly.
• Stock ponds with mosquitofish, apply larvicide or filter the water.
• Clean gutters.
• Rinse out pet water bowls weekly.
• Empty the toilet bowl brush holder.
• Flush unused toilets weekly.
• Use mosquito repellent on clothes and exposed skin.
• Wear long sleeves and light, loose-fitting clothes while outdoors.