A Plethora of Mosquitoes

Blame it on El Nino: Mosquitoes will swarm this year.

Although mosquito season doesn’t begin until early May, officials are gearing up for a bumper crop of the pesky insects as soon as warm weather arrives.

Puddles of stagnant rainwater are everywhere, giving mosquitoes many places to lay their eggs through October.

“It’s safe to say the season is starting. We’ll be in the full throes of it by May,” said Gail Van Gordon, public health entomologist for the Los Angeles County Department of Health Services.

More mosquitoes increase the chances of mosquito-transmitted St. Louis encephalitis and Western equine encephalitis, according to state officials. Most cases are mild and undiagnosed; people tend to recover quickly from the flu-like symptoms. However, severe cases can cause permanent brain damage, coma or, in rare instances, death.

Here are some ways to protect against mosquitoes:

Genus: Culex

Species: tarsalis

Quarter-inch long, slender, with a long, needle-like “beak” and narrow wings. Males, which live from seven to 10 days, feed on plant juices and do not bite humans. Females, which live 30 days or more, obtain protein needed to lay their eggs from the blood of birds and mammals, transmitting encephalitis in the process.

Range

Mostly in Western states.

Breeding

The female mosquito makes a high-pitched sound with its wings to attract a male. Mate only once in a lifetime. Prefer clear, sunlit water for breeding, such as abandoned swimming pools and roadside ditches.

Prevention

* Don’t let containers--paint cans, wheelbarrows, wagons--accumulate water; empty them of standing water.

* Look for pools of water in less than obvious places, such as children’s toys that have been left outside.

* Check birdbaths and horse troughs.

* Keep sandboxes covered.

* Maintain swimming pools with proper chemicals, circulation and filtration.

* Level or repair easily flooded areas.

Life Cycle

Between 100 and 300 eggs are laid on water or damp ground in an arrangement that looks like a small raft. Hatching occurs in two or three days in warm weather.

Larvae feed on small aquatic plants and animals, then molt into active pupae.

Adults emerge two to five days later at surface from floating pupae.

Your Pet

A mosquito found throughout Los Angeles County, Culiseta incidens, has been shown capable of developing and transmitting heartworm, which can be fatal in dogs and cats. Although mosquitoes generally don’t attack cats as often as dogs, preventive medicine is available to protect both from heartworm.

Natural predators

Dragonflies

Water bugs

Damselflies

Back swimmers

Mosquito fish

Aquatic stage

Predacious diving beetles

Airborne stage:

Birds, especially swallows

Flying insects

Getting Help

A variety of methods is used by the Greater Los Angeles County Vector Control District to rid swimming pools and ornamental ponds of mosquitoes. During the larval stage, an insect growth hormone that looks like charcoal is put into the water to disrupt the mosquitoes’ development. During the adult stage, a highly refined oil is sprayed onto the pool’s surface. Frequently, 25 to 50 guppy-like mosquito fish that eat mosquito eggs, larvae and pupae are added to the water. The free services are funded through a $2.10 annual property tax assessment paid by each county homeowner.

If you have a problem with mosquitoes on your property or want to report a problem in the neighborhood, call (818) 764-2010.

The Greater Los Angeles County Vector Control District keeps tabs on 5,786 of the San Fernando Valley’s approximately 120,000 swimming pools that have been reported as having mosquito problems. Most are checked annually, but 432 are looked at monthly to keep mosquitoes in check.

Service requests to the Greater Los Angeles County Vector Control District increased 53%, from 125 in March, 1997, to 191 in March, 1998.

Encephalitis

St. Louis encephalitis detected cases statewide (no deaths)

1995-97: None

1994: 1 (Riverside County)

1993: 3 (Orange, San Bernardino and San Diego counties)

1992: 2 (Los Angeles and Ventura counties)

1991: 1 (Los Angeles County)

1990: 2 (Tulare and Los Angeles counties) *

* L.A. County case thought to have been contracted along the Colorado River near the California-Arizona border)

Protection

* Use insect repellent.

* Wear long-sleeved shirts and pants.

Sources: Los Angeles County Department of Health Services, Greater Los Angeles County Vector Control District, California Department of Health Services, staff reports; researched by STEPHANIE STASSEL / Los Angeles Times