Tropical mosquito found in San Gabriel Valley

It started when an El Monte woman called to report an unusual pest: tiny mosquitoes that she said were biting her in the middle of the day.

The complaint last week raised red flags for technicians at the San Gabriel Valley Mosquito & Vector Control District, who know that common mosquitoes typically attack during morning and evening hours.

When a worker arrived at Dodson Street, one of the insects landed on his partner, so he trapped it in a plastic jar.

“He took a close look at it, and he realized we might have a problem,” said Kelly Middleton, a district spokeswoman.

It was an Asian tiger mosquito, an aggressive, nonnative species that has caused outbreaks of tropical viruses in other states. Authorities worry the insects, about half the size of normal mosquitoes and named for their distinctive black-and-white striped markings, could spread disease if they gained a foothold in Southern California.

So they are hoping to wipe out the blood suckers.

Two dozen pest control workers started going door-to-door Wednesday in a half-square-mile area around the infestation site to warn residents. They posted signs, passed out fliers, inspected yards and patios for standing water and set out traps — black cups filled with water — to determine how far the invaders have spread.

On Friday, crews will begin spraying pesticides in the neighborhood to eradicate them.

The insect, Aedes albopictus, is native to Southeast Asia and can transmit viruses the common mosquito cannot, such as yellow fever, chikungunya and the sometimes-fatal dengue fever. They also can spread parasites that cause heartworm in cats and dogs.

Unlike typical mosquitoes, which favor large bodies of water like marshes and ponds, the Asian tigers have adapted to urban life. The insects are sometimes called “container mosquitoes” for their preference to lay eggs in small pools of water that collect in buckets, old tires, the wrinkles in plastic tarps — even the dishes under potted plants.

To the chagrin of city dwellers, they are also vicious biters that seek blood to feast on night or day. And they aren’t easily deterred by swatting hands, Middleton said.

“If they sense any humans, or any mammal really, they’ll just go for it,” Middleton said.

Maria Salas, who spoke with pest technicians as they canvassed the Glen Elm mobile home park she manages, said she’s been itching from the bites of mosquitoes that have been pricking her day and night.

On the advice of the pest inspectors, she tossed the water out of the bird bath in her front yard. And she pointed them to what she suspects is a source of the infestation: a pool of dirty, stagnant water that sits in a gutter down the street.

“I don’t want to take any chances,” Salas said. “I have two daughters, and I don’t like to let them go outside. I don’t even come outside, because I’ve been bitten.”

Tiger mosquitoes are relative newcomers. First detected in the United States in 1985, they have since spread throughout the Southeast and are responsible for recent outbreaks of dengue fever in Florida, Texas and Hawaii. Pest controllers have struggled to stamp them out in Washington, D.C., New Orleans and Memphis.

It’s a mystery how they got to El Monte.

The exotic insects didn’t appear in California until 2001, when they were discovered in shipments of ornamental “lucky bamboo” plants that made their way from ports in Los Angeles and Oakland to nurseries in Chino and Gilroy.

They haven’t been documented in the San Gabriel Valley since then, Middleton said, because extermination measures kept them from taking hold. “We’re working very hard to keep it that way.”

tony.barboza@latimes.com