Neighbors of Pond Bugged by Mosquitoes : Pests: A recent application of insecticide has brought some relief. Now officials are studying lowering the water level to further reduce the hazard.

The orange and blue can of insect repellent stood alone on a shelf in the Chatsworth Lake Market, a monument to a potentially perilous problem along the shores of the Chatsworth Reservoir.

The problem is mosquitoes. Swarms of the pesky insects have transformed the two-acre reservoir from a bucolic pond into a buzzing nightmare. Nearby residents, fearful of mosquito attacks, said they have been cloistered behind closed doors most of the summer.

“You literally could not go outside at night,” resident Christina Stroh said as she played Wednesday with her 21-month-old daughter in their back yard. “It was that bad.”

Residents said a recent insecticide application, the result of numerous angry calls to state officials, appears to have killed off the worst of the infestation. They hope that a decision this week by the Los Angeles Department of Water and Power to lower the reservoir’s water level will further reduce the hazard.

Stroh and others with small children have been particularly worried because the mosquitoes swarming around their houses could be carrying the potentially fatal St. Louis encephalitis virus, which causes inflammation of the brain and spinal chord. Symptoms can range from flulike conditions to more rare manifestations, including paralysis, coma and even death.

On Wednesday, the Southeast Mosquito Abatement District mailed about 700 trapped mosquitoes packed in dry ice to a state laboratory in Berkeley, where they will be tested for the virus, said Jacquie Spoehel, an entomological assistant with the district.

Although one mosquito with the virus was trapped in June in the Sepulveda Basin, no diseased insects have been found near the Chatsworth Reservoir.

Also Wednesday, the DWP unsuccessfully tried to bring in equipment to lower the pond’s water level. Spokeswoman Dorothy Jensen said the DWP must clear an access road to make room for the oversized pump truck.

DWP workers will also chop down tall tule brushes along the shore that provide an ideal breeding ground for mosquitoes.

The actions come none too soon for those living nearby in new tract houses on winding streets.

“A month ago, it was really bad,” said Gabrielle Vanderpool, who said she suffered from painful dime-sized welts on her arms. “You couldn’t go outside without getting attacked. Even inside the house, we had to lock ourselves in our bedrooms.”

The insects were especially menacing to Norma Ortiz, whose two young children are allergic to their bites. “If we came outside, we’d all be wrapped in towels,” she said.

Last week, a woman at the market carried a baby girl covered with mosquito bites, store manager Denise Gentile said. “The poor kid looked like she had the measles,” Gentile said.

Several residents who recently moved to the area said they would have moved elsewhere had they known about the infestation. Some have coped by hoarding bug spray.

“We keep it under the barbecue and everywhere,” Oriz said. “That’s the first thing guests say--’Where’s the Off?’ ”

Others, such as Jeff Adams, have adopted more creative defensive techniques. On a friend’s recommendation, Adams swallows Vitamin B daily. “It’s just something in your blood that gives off this scent and they don’t go near you,” he said.

The infestation is acute this year because silt from surrounding construction sites has raised the water level to the leaves of the tule bushes. Fish, which normally control the mosquito population, cannot easily snap up insects that settle on the leaves.