The state's first Oriental fruit fly infestation of the year has broken out in San Diego County, where workers began spraying pesticides on about 4,200 trees and telephone poles over a 7-square-mile area Wednesday.
Four of the destructive flies were discovered in traps--three in Mira Mesa and Scripps Ranch and the fourth in Hillcrest--in recent days, prompting a coordinated state-county effort to eradicate the pest.
"They turn into real monsters," said Bill Routhier, the state Department of Food and Agriculture's area manager for Southern California.
On Wednesday, about 20 county workers placed 200 additional traps in the target area while a three-member state team started applying bait that attracts male Oriental fruit flies with a fly sex aroma mixed with pesticide.
The lure is squirted on trees and utility polls at 10 to 12 feet above ground; no aerial spraying is involved. The pesticide, naled, is commonly used in household no-pest strips, flea collars and to kill flies at poultry ranches.
"There's no health hazard" to humans or pets, according to Bill Snodgrass, assistant agricultural commissioner for the county.
Agriculture officials hope the quick attack will control the fast-multiplying, yellow-striped fly before it turns the budding infestation into a full-fledged crisis.
The county's multimillion-dollar citrus and avocado crop is especially vulnerable to the Oriental fruit fly. Females deposit up to 100 eggs under the skin of the fruit. Maggots then hatch and destroy the fruit.
Officials are encouraged that no larvae has been discovered so far, and the traps will reveal over the next week or two whether the peril has been quashed.
"At this point," Snodgrass said, "if we only find four (flies), we have caught it at its first emergence."
However, officials are worried, pointing out that the Oriental fruit fly is as potentially harmful as Mediterranean and Mexican fruit flies.
San Diego County learned that lesson in 1973, when the state's first major Oriental fruit fly infestation covered 120 square miles, Routhier said. The county has had other visitations, but usually only one Oriental fruit fly at a time.
This new discovery is technically an infestation, the only one in California so far this year, said Carl DeWing, spokesman for the state Department of Food and Agriculture.
In 1991, 81 Oriental fruit flies were found over 133 square miles of San Bernardino County and were only recently declared to have been eradicated, DeWing said.
Much of the success in containing the fly is given to the fly-sex lure. "This is definitely a weak link in their defense," Routhier said.
The lure is being placed on trees and polls in the Mira Mesa and Scripps Ranch area, but not in Hillcrest at this time, officials said. The treatment will be repeated every two weeks for about 60 days, long enough to ensure the flies don't reproduce.
Nobody knows how the Oriental fruit flies arrived in San Diego County, but Snodgrass said "we suspect it's been brought in on fruit from Hawaii or Southeast Asia. Mangos are a prime host."
The four flies were found in traps placed in citrus trees to serve as an early warning system.