Ken Carlson

Mosquitoes may breed early in north San Joaquin Valley

Owing to warmer-than-normal temperatures, residents could be scratching after they dry out from this weekend’s rainfall.

Dave Heft, general manager of the Turlock Mosquito Abatement District, said conditions should be right for mosquitoes to breed in puddles, flowerpots and trees in residential areas of the Northern San Joaquin Valley.

“If it’s in the 60s or 70s, we will see mosquitoes,” he said. “We have a winter crew that we keep for weed control, but we do answer mosquito complaints.”

Vector control experts always are watching for the northern house mosquito, which may carry West Nile virus, although the insect is not considered a serious threat until the spring.

Some species are fairly active during cooler months. One variety is called the “tree hole” mosquito because its eggs are laid in cavities of tree bark. When the crevices fill with water, the larvae hatch.

Tree hole mosquitoes are carriers of heartworm, a potential health problem for dogs and cats, though felines are not as susceptible.

The most risky period for dog heartworm runs from March through August, according to the Mosquito and Vector Control Association of California, but the pests could get an early start on breeding this month.

Heft said the Turlock district began surveillance last year for yellow fever mosquitoes. That species and Asian tiger mosquitoes can emerge in winter if temperatures around homes are warm enough.

The two species are historically linked to deadly yellow fever, but experts are concerned they could introduce dengue and another human illness that is rampant in Central America. Yellow fever mosquitoes have been detected in Madera, Fresno and San Mateo counties, and it may be a matter of time before they are here, Heft said.

“They can breed indoors in a vase or a bucket under the kitchen sink,” Heft pointed out.

The National Pest Management Association warned that the storms in California will deliver much rain in a short time, leaving standing water that won’t easily evaporate or soak into the ground.

The association recommended taking precautions by eliminating standing water around homes, screening windows and doors, and minimizing activity between dusk and dawn. Residents worried about mosquito activity can call a pest control business or local mosquito abatement district, the association suggested.

In Stanislaus County, residents south of the Tuolumne River may call Turlock Mosquito Abatement District at (209) 634-1234. Others may contact Eastside Mosquito Abatement District at (209) 522-4098.

Bee staff writer Ken Carlson can be reached at or (209) 578-2321.