Health Care

April 11, 2014

Even in drought, mosquitoes find dirty water needed to breed, hatch in Valley(video)

It's shaping up to be a hot and dry spring in the central San Joaquin Valley, but the drought hasn't stopped mosquitoes from hatching.

It's shaping up to be a hot and dry spring in the central San Joaquin Valley, but the drought hasn't stopped mosquitoes from hatching.

Mosquitoes have plenty of places to breed in backyards -- from neglected swimming pools to flower pots. And they breed faster in warm weather.

"It's typically a week from hatching to flying this time of year," said Tim Phillips, manager of the Fresno Mosquito & Vector Control District.

Spring is the time to check around homes for places where mosquitoes can breed, he said. Two kinds found in the Valley last year can carry diseases that, in extreme cases, can be fatal.

As in past years, neglected swimming pools are an ongoing problem, Phillips said, although this year, calls from people reporting them have tapered off.

But mosquitoes don't only use dirty pools to multiply.

In a typical backyard, they can find enough water, said Steve Mulligan, manager of Consolidated Mosquito Abatement District, which includes Clovis. "Even the dishes that collect water under flower pots are attractive for mosquitoes to lay eggs."

And fighting mosquitoes is a backyard-to-backyard battle that Mulligan said takes the public's cooperation to win.

Mosquitoes are more than pests to be swatted away, he said. In the Valley, they can carry West Nile virus, a disease that affects the central nervous system. Most often symptoms are mild, but the disease can cause neurological problems and the infection can be fatal.

Mosquitoes that carry the West Nile virus are commonly known as the southern house mosquito and the encephalitis mosquito. They bite at dusk and dawn.

Last year, there were 372 cases of West Nile virus in California and 14 deaths. There were no deaths in the Valley, but Fresno County reported seven illnesses. Tulare had five illnesses, Madera had three and Kings County had one.

Valley mosquito control managers also are concerned about the Aedes aegypti mosquito, a species not native to California that was found last year in Madera, Clovis, Fresno and Fowler.

The mosquito is brown with white markings. An aggressive day-biter, it is commonly found in hot, humid tropical areas, like the southeastern United States, Mexico and Central and South America.

The mosquito is capable of transmitting deadly yellow fever, dengue and other diseases, said Mulligan, who is president of the American Mosquito Control Association, a national nonprofit organization.

So far, none have spread disease in the Valley, he said.

Eradicating the Aedes aegypti mosquito has become a priority since its discovery last spring.

Vector control agents went door-to-door last year warning residents to empty all standing water. And agents sprayed insecticide that's been approved by the federal Environmental Protection Agency for use in and around infested homes.

So far this year, six of the species have been trapped in Clovis and a female Aedes aegypti mosquito has been caught in a Madera trap. There's no indication of disease in the mosquitoes, Mulligan said.

The Aedes aegypti mosquito acquires yellow fever and dengue from infected humans, then transfers the infections to other people. Dengue is a virus that can cause headache, body pains and a rash similar to measles. Extreme cases can be deadly. Yellow fever is a virus that causes severe flu-like symptoms and sometimes jaundice. It also can kill.

It's too early for predictions, but Mulligan said "as the weather warms up, we anticipate we may have another resurgence of that mosquito in this area."

Last year, the Aedes aegpyti mosquito was first found in a trap near the Madera cemetery on June 9. Making sure it doesn't get a foothold this year will require the public's help, said Leonard Irby, director of the Madera County Mosquito and Vector Control District.

The mosquito requires very little water to breed -- a teaspoon of water is enough to produce eggs. A female Aedes aegypti can lay eggs in any open container -- a planter, a bucket, a bird bath, an unused dog dish or an empty beer bottle. The female mosquito lays up to 200 eggs several times a season, and prefers to lay eggs just above the water line of the container.

The Madera vector control district is urging anyone experiencing mosquito bites during the day to "dump anything holding even the smallest amount of water," and to survey property for unneeded containers, cans, buckets, and tires that can retain water. "This mosquito is even known to lay eggs in water-filled holes in asphalt and concrete," Irby said.

Madera County voters in October voted down an assessment for mosquito prevention and control, Irby said. Last year, the district spent $350,000 to fight the Aedes aegypti mosquitoes.

This year, Irby said: "We don't have the resources to provide as much prevention or control. We're asking homeowners and residents to help us out by eliminating the water sources."

Protect yourself

• Apply insect repellents that contain DEET, picaridin, oil of lemon eucalyptus or IR 3535 according to label instructions.
• Use repellent, especially in the early morning and in the evening.
• Make sure that doors and windows have tight-fitting screens to keep out mosquitoes. Repair or replace screens that have holes.
• Use mosquito netting over infant cribs, carriers and strollers.
• Eliminate standing water and containers that can hold water from around the home. Yellow fever mosquitoes lay eggs in water-holding containers.
• Get free mosquito fish for backyard ponds or water features from mosquito abatement districts.

For more information

• Consolidated Mosquito Abatement District: Call (800) 821-1577 or visit
• Fresno Mosquito & Vector Control District: Call (559) 268-6565 or visit
• Madera County Mosquito and Vector Control District: Call (559) 662-8880 or visit

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