Taking a Bite Out of Breeders : Mosquitoes: The battle is on to control the pests, reproducing by the millions in pools and puddles.

Orange County has launched a battle against the mosquito, fighting an airborne foe with bacteria-laced kernels of corn.

From a helicopter 100 feet above the Bolsa Chica salt marshes, the anti-mosquito forces are dropping the corn into the brackish water to avert what otherwise would be a near-apocalyptic hatch of mosquitoes this month.

“If we let it go without treating the marshes, Huntington Beach would be uninhabitable,” said Gil Challet, manager of the Orange County Vector Control District.

Because of recent rainstorms and the peaceful puddles they left, mosquito eggs laid by the millions in marshes and back yards are hatching swarms of the blood-sucking insects.

“It is shaping up to be a good year for mosquitoes,” said Ron Elliott, foreman for the vector control district, who was at the marsh on a recent morning.

“Anywhere where water collects, mosquitoes will find it. And right now, everything is breeding.”

Officials at the district, which is responsible for insect and rodent control in the county, said that every two weeks they treat the marshy breeding grounds along the county coastline with bacteria fatal to larval mosquitoes but harmless to humans and animals.

The bacteria, Bti, discovered in Israel about 20 years ago, rupture the inner lining of the pest’s stomach. Corn is used as a convenient method of delivery.

At the Bolsa Chica marshes last week, the helicopter dangled a bucket of kernels as it strafed 600 acres in a couple of hours. From the marsh edge, district officials judged the coverage by watching the kernels splash in the prime breeding grounds. They returned Monday to check the results.

“We went back and found no larvae or (only) dead larvae,” said Larry Shaw, district foreman. “That should take care of it for maybe the next two or three weeks when another crop may hatch.”

Twenty-one species of mosquito live in the county. The female mosquito sucks blood to feed its eggs. Every two weeks, a new life cycle starts and ends.

Seeking prey around the clock, three of the 21 mosquito types strike primarily during the day, while the rest are night-biters, officials say. Some only bite during the winter, but most do their work during the spring and summer.

All of them breed in fresh water or the slightly salty waters of coastal marshes. Officials estimate that a puddle the size of a tabletop can breed thousands of mosquitoes within weeks.

“In the last good rain in 1983, inspectors missed a pond that was about 20 feet wide and 30 feet long,” Challet said. “We ended up getting 170 complaints from residents living near the marsh.”

Mosquitoes are more than just a nuisance. They can transmit diseases to humans from birds. The most common mosquito-borne diseases in Southern California are two strains of encephalitis--St. Louis and Western equine. In the vast majority of cases, the disease causes flu-like symptoms that go away in a few days. But in severe cases, it can lead to inflammation of the brain lining, possibly coma and even death.

There has not been a human case of the disease in the county since 1984. But last fall, 16 sparrows and finches, mostly from Huntington Beach, tested positive for St. Louis encephalitis, and samples of mosquitoes in Pomona, Torrance and Malibu were found to be carriers of the disease. Officials warned residents to wear repellent and long-sleeved clothing.

After this winter’s storms, marshes and back-yard pools have again accumulated enough rainwater to transform them into mosquito hatcheries.

There are about a dozen marshes throughout the county that are key monitoring sites for the district. Officials say the Bolsa Chica marsh receives the most attention. The San Joaquin marsh near the UC Irvine campus and a marsh owned by West Newport Oil company in Costa Mesa are also major breeding grounds.

The district monitors mosquito infestation at these locations and dozens of others in the county by counting dead mosquitoes collected in traps. Their numbers jump dramatically after rain.

Besides treating the marshes and the puddles in more than 300 miles of flood control channels, the district responds to about 2,000 calls each year from residents.

During the winter, the district checks about 1,000 pools for floating leaves or weeds to which the female mosquito attaches her eggs. Regular pool skimming can curb the problem.

At residents’ request, the district will stock infested pools with 2-inch-long mosquito fish to devour mosquito larvae, Challet said.

In the summer, the district hires a crew to spray a highly refined oil into street gutters and catch basins where mosquitoes breed. The oil suffocates the mosquito in its pupa stage and then evaporates.

Officials will treat infested pools for free, and a free brochure about combatting mosquitoes is available from the district at (714) 971-2421.

Residents can help by dumping water collected in open containers, old tires and bird feeders.

“We even once found mosquito eggs in a dog dish that someone had left out in their back yard,” Elliott said.

Mosquito Season Arrives

Recent rains have left behind puddles where mosquitoes can breed. Within the span of a week, thousands of new ones can emerge from sources of standing water as small as a bucket. The pests breed year-round, but spring rains lead to peak activity in summer. Their life cycle can be accelerated by warm, humid weather.

1) Eggs Laid (Days 1 and 2): The female mosquito lays 100 to 400 eggs, which hatch into larvae. Local species can lay up to 1,000 eggs in a lifetime.

2) Larvae Grow (Days 3 and 4): Larvae breathe through tubes while remaining below the water’s surface. Long, hairy “mouth brushes” help them sweep up and eat tiny plants and animals.

3) Metamorphosis (Days 5 and 6): A grown larva changes into a pupa, where skin covers a rapidly changing adult. A mature adult emerges after about two days.

4) Adult Mosquito (Day 7): The adult rests until strong enough to fly. Females live up to three weeks in summer and maybe for months in winter, in order to lay eggs in the spring. Males live 10 to 20 days.

How a Mosquito Bites

Only female mosquitoes “bite,” a misnomer since they actually pierce the skin. Blood provides protein for the female’s eggs, which she cannot get by sipping plant nectar.

1) Skin Pierced: Mosquito pushes several needle-like “stylets” through the skin and into a blood vessel. Saliva flows into the bite to prevent clotting. Saliva of some mosquito species will cause an itchy welt.

2) Blood Drawn: Mosquito sips up to 1 1/2 times her weight in blood. Abdomen swells with blood. She leaves behind a droplet from intestines to reduce her weight before flying away.

Source: Orange County Vector Control; World Book Encyclopedia

Researched by DANNY SULLIVAN / Los Angeles Times

Fighting Mosquitoes

Mosquitoes, of which there are 21 species locally, are more a nuisance than a serious health threat. But without control, a large mosquito population could make disease transmission more likely.

Home Control

Mosquitoes breed in about 10% of back yards. Water in one wheelbarrow can spawn up to 15,000 mosquitoes a week. Here are some methods of control and protection:

Dump water from open containers. Keep them covered or turned upside down.

Cover swimming pools or clean every day with filter and skimmer. Chlorine will not kill mosquitoes.

Put mosquito fish in ornamental pools or fountains. The 2-inch-long fish eat larvae and may be obtained free from Orange County Vector Control.

Repair screens.

Avoid working at dusk or dawn, when mosquitoes are most active.

Use personal mosquito repellents cautiously and follow directions.

Back-yard electronic killers don’t work well in destroying mosquitoes.

Contact Orange County Vector Control, (714) 971-2421, for more information and assistance.

County Control

Orange County Vector Control fights mosquitoes with various methods. A “vector” is any creature that transmits diseases to humans.

Chemical pellets: Corn kernels treated with bacteria are dumped into marshes by helicopter. The chemical is fatal to mosquito larvae, harmless to humans and animals.

Oil film: A thin film of oil is applied to large pools of stagnant water, covering the breathing tubes of larvae and pupae.

Mosquito fish: The fish eat larvae, require no special care and breed easily. They are placed in large expanses of water, such as golf course ponds.

Insecticide: Applied along curb gutters where water collects and other places attractive to adult mosquitoes.

Mosquito Diseases

Mosquitoes have killed more humans worldwide than any other living being because some species carry malaria.

Encephalitis is the most common mosquito-borne disease in the western United States. Three cases were reported last year in Los Angeles and Riverside counties. Orange County has had no cases since six were reported in 1984.

Malaria kills more than a million people each year worldwide. Malaria has increased as mosquitoes have become resistant to pesticides. Several cases were reported in San Diego County in 1990.

Source: Orange County Vector Control District; World Book Encyclopedia

Researched by DANNY SULLIVAN / Los Angeles Times