Mosquito abatement crews went door to door Wednesday in two neighborhoods -- one in Clovis, the other in Madera -- hoping to trap a pesky daytime mosquito that likes to bite humans and can carry potentially deadly tropical diseases.
But by the end of the day, the experts couldn't answer a key question that has evaded them for weeks: how did the insect get here?
For the first time, the invasive Aedes aegypti, aka the yellow-fever mosquito, has invaded the Valley. Typically, it is likes hot, humid tropical areas, like the southeastern United States, Mexico, and Central and South America.
Those facts worried Emilio Hernandez, who lives in the Madera neighborhood where 200 of these mosquitoes have been trapped.
"I wonder if I should let my kids play outdoors?" he said Wednesday.
Rhonda Snyder, who lives in a Clovis neighborhood where the mosquito has also set up camp, echoed similar thoughts: "Should I spray my kids (with insect repellent) before they go outside?"
The abatement crews have been tracking the mosquito since June 9, when it bit a woman living near the Arbor Vitae Cemetery in Madera west of Highway 99.
Since then, the crews have trapped 200 of the mosquitoes in a 10-block area around the cemetery, said Leonard Irby, manager of the Madera County Mosquito and Vector Control District.
"We're doing everything we can," Irby said. "This mosquito has the potential to do a lot of harm if it gets established here."
In Clovis, the mosquito was discovered a week ago in a neighborhood near Shaw and Temperance avenues. Since then it infested several homes, said Steve Mulligan, manager of the Consolidated Mosquito Abatement District.
More traps are being set up to determine how far the mosquitoes have spread, he said. "We have to eradicate it now or we could be in big trouble," Mulligan said.
The mosquito that carries the West Nile virus typically attacks birds -- humans and horses are second choice -- and does so at dawn and dusk. But the Aedes aegypti mosquito is aggressive during the day and it likes human blood, Mulligan said.
More worrisome, the mosquito is a carrier of yellow fever, dengue and chikungunya -- tropical diseases whose symptoms include fever, severe headaches and body aches. In severe cases, the diseases can lead to death.
So far, there have been no cases of these mosquitoes carrying the diseases, Mulligan said, so eradicating the pest before it can get a toehold in the area is a top priority.
The Aedes aegypti is dark brown or black and has distinctive white markings.
Local mosquito expert Charlie Smith said they pose a difficult problem because unlike mosquitoes that like stagnant swimming pools, a female Aedes aegypti can lay eggs in any open container -- a planter, a bucket, a bird bath, an unused dog dish, or empty beer bottle -- as long as it has water.
The female mosquito also lays up to 200 eggs several times a season, Smith said.
They prefer to lay eggs just above the water line of the containers. The eggs then survive for months, even if the container dries out. Once the eggs are flooded, they hatch into larvae and within a week develop into adult mosquitoes. These mosquitoes can then lay more eggs, Mulligan said.
"If you seen any water in a container, dump it out," Mulligan said.
He also said people with pets should fill their dish with fresh water at least twice a week, so the mosquito doesn't make its home there.
In Madera, crews have twice sprayed a mosquito-killing fog in the infected neighborhoods, hoping to eradicate adult Aedes aegypti, Irby said. The fog is organic and not harmful to residents, pets or plants, he said.
Thursday, crews plan to fog the neighborhoods again, but with a mist of larvacide in hopes of killing immature mosquitoes breeding in containers, Irby said. The fogging will be from 3 a.m. to 8 a.m. and also is not harmful to residents, pets or plants, he said.
In Clovis, crews will continue to go door to door and spray insecticide in infested areas, Mulligan said.
Once the mosquito was discovered in Madera, the California Department of Public Health was notified and a statewide alert was issued to other mosquito abatement districts in California, Mulligan said.
With eradication efforts in full gear here, one question still haunts Mulligan, Smith and others on the front lines: the Aedes aegypti tends to stay near its home and it travels less than a quarter mile. "So how did it get from Madera to Clovis, which is 35 miles away?" Smith said. "That's the $64,000 question."
Mulligan said abatement crews will do everything they can to hunt for the mosquito, but the only way it will be eradicated is with the public's help.
"These mosquitoes could be in other cities," Mulligan said. "We won't know until someone gets bitten and reports it to us."
How to avoid mosquito bites
• Dump standing water in backyards
• Wear mosquito repellent when possible
• Wear long-sleeved clothing to protect from bites
• Make sure doors and windows fit tightly
What to do
Madera residents can report daytime mosquito bites or schedule a home inspection by calling (559) 662-8880. Clovis residents can call (559) 896-1085. For more information go to mosquitobuzz.net.