In summers past, Dee Edling has cooled off each evening in her back yard and watched the sun set over the Santa Ana River.
Not this year. Not as long as the mosquitoes are around.
“I’ve just been covered,” Edling said. “I go outside and just get eaten alive.”
Even with the drought drying up some potential mosquito breeding grounds, Norco and Corona officials are mobilizing their biggest assault on mosquitoes in at least six years.
“I don’t let the kids go out after sunset,” Edling said. “And sometimes (mosquitoes) get inside, and I have to get up and spray the house.”
Councilman Steve Nathan, who has lived in Norco for 22 years, says the infestation is “the worst we’ve seen it.”
The most dramatic sign of the mosquito problem came during the last week in July, when the average number of mosquitoes found in mosquito traps climbed from 125 to 379, said Dr. Major Dhillon, an entomologist with the Northwest Mosquito Abatement District. Normally, only about 100 would be found in Norco traps at this time of the year, he said.
In the Greenbriar section of Corona, as many as 800 mosquitoes were found in each trap, Dhillon said, up from an expected 500.
These mosquitoes, the Culex tarsalis and the Culex quinquefasciatus, or quinqs, generally breed in stagnant water along the river and bite at night, Dhillon said. He has been monitoring the population by setting about 45 traps a week. The traps include several pounds of dry ice, which serve as a lure by giving off carbon dioxide.
“That’s how the mosquitoes find their host ‘blood meal,’ ” Dhillon said. “They sense that it is a little bird or animal.”
So far, the cause of the mosquito outbreak is a mystery. Some officials point to the hotter and more humid weather, which provides prime conditions for breeding. Although there has been a drought, water collects when residents water their lawns or wash their cars.
In Norco and Corona, the mosquito abatement district has had trouble getting to some breeding grounds, including jungle-like areas along the Santa Ana River and small duck ponds, exacerbating the problem, Dhillon said.
“I wish I could say that the drought has brought the population down, but I can’t,” said Lino Luna, the manager of the district. “We still have water and that’s where mosquitoes will go. A lot of the problems are man-made.”
The assault on the mosquito is being waged on two fronts. For the first time in half a dozen years, officials have taken to the air and doused about 500 acres along the Santa Ana River, including the bluffs area of Norco and the Greenbriar section of Corona, with a pesticide called Bti, a bacterial agent that attacks mosquito larvae but is harmless to humans and other animals.
The pesticide was sprayed once in May and once last week, Dhillon said.
Even more concentrated efforts to control the mosquitoes are being made at about a dozen dairy farms north and west of Norco. There, district officials fear that a different type of mosquito, the Aedes dorsalis, will get out of control. This so-called “dirty water” mosquito can begin breeding in mud deposits, which are common on dairy farms.
Up until last summer, the Aedes mosquito was seldom found in the district, Dhillon said. This year’s discovery is worrisome because the Aedes can grow into adulthood in about four days, a much shorter maturing time than for other mosquitoes. Even more troublesome, they bite during the day and their eggs can lay dormant for as long as 10 years before hatching, Dhillon said.
Crews are now checking some dairies twice a week and ground-spraying the areas every seven days, he said.
“We cannot tolerate even one of those mosquitoes,” Dhillon said. “If we didn’t control it this year, it would be a real big problem.”
In Orange County, Vector Control District officials are concerned about the threat of an outbreak of St. Louis encephalitis, a viral disease carried by the mosquito that can be transmitted to birds and humans. The virus can cause headaches, flu-like symptoms and, in extreme cases, coma and death.
In July, 19 of 293 birds caught in about a dozen traps throughout Orange County tested positive for the virus, a number 10 to 20 times higher than in recent summers, said Vector Control biologist Jim Webb. Fifteen of the birds that tested positive were trapped in Huntington Beach, he said.
So far, four people in Orange County are being tested by state health officials for the virus, Webb said. In addition, a Moreno Valley man, who is an electrician at Disneyland, is suspected of contracting the virus.
“It’s still debatable whether he got it at Disneyland or in Moreno Valley,” Webb said. “He said that he sometimes sleeps outside on hot evenings.”
Samples were taken of birds at Disneyland, and four of 140 birds, or about 3%, tested positive for encephalitis, he said.
No cases have been reported in the northwest district of Riverside County, Dhillon said.