The mosquitoes are out, and they're looking for blood.

Claude Watson, manager of the Modesto-based East Side Mosquito Abatement District, said the early-season mosquito population is high this year. Late rainfall is one reason. Another is an early irrigation season, the result of warmer-than-usual spring weather.

In Sacramento County, with acres of flooded rice fields providing prime breeding ground, officials say the mosquito count is up as much as 500 percent over last year.

Watson and Jerry Davis, manager of the Turlock Mosquito Abatement District, say the biggest concern right now is the tree-hole mosquito, a small but vicious variety that breeds in diseased branches or other hollow parts of trees.

The good news, Davis said, is that tree mosquitoes breed only once and should be gone in two to three weeks.

Both officials recommend emptying wading pools, buckets, barrels and other containers of standing water, to eliminate mosquito-breeding sources.

"A little concern by the resident usually takes care of the problem," Davis said.

Added Watson: "We also try to discourage farmers from using excess irrigation water during the breeding season."

The East Side district has a staff of 16 seasonal control assistants, and the Turlock district will have 18 workers in the field by May 1.

"We can answer every call in 24 to 48 hours," Davis said.

District workers regularly spray gutters and storm drains in urban areas and check standing water and other breeding sources that have created problems in past years.

They regularly check mosquito traps throughout the districts to make sure the population is under control.

The districts provide mosquito fish on request to people who want to put the fish in home garden ponds.

Lavonne Larsen, a communicable-diseases nurse with the Stanislaus County Health Services Agency, said mosquitoes can carry yellow fever, malaria and encephalitis, "but, thanks largely to the abatement programs, that's something we just don't see around here."

Larsen said the only local cases of those diseases she knows about have involved visitors from other countries.

Mosquitoes also carry canine heartworm, and veterinarians recommend preventive vaccine for all dogs.

For information or to request services, call the East Side Mosquito Abatement District at 522-4098; the Turlock Mosquito Abatement District, 634-1234; the Merced County Mosquito Abatement District, 722-1527; or the San Joaquin County Mosquito and Vector Control District, 982-4675.