San Mateo and Santa Clara County officials are inspecting areas in Palo Alto, East Palo Alto and Menlo Park after two male peach fruit flies native to southern Asia were found in Palo Alto, with plans to begin eradication treatments this Thursday.

County officials trapped the bugs in Palo Alto on June 28 and July 2, then began placing insect traps in a 4.5-mile radius from the discovery sites.

The flies were found in the area of Embarcadero Road and U.S. Highway 101 west of the freeway and the area of Alma Street and El Verano Avenue, according to a map provided by Santa Clara County.

"These finds are the result of early detection trapping which is key to finding and eradicating exotic pest infestations before they can become widely established," San Mateo County Agricultural Commissioner Fred Crowder said in a statement.

Currently, the treatment plan to eradicate peach fruit flies in the Midpeninsula cities won't affect private properties and no one will be under quarantine. Starting Thursday, trained applicators from the state Department of Food and Agriculture will place spinosad, an organic pesticide, on trees, light poles and other far-to-reach, elevated locations about 8 to 10 feet above the ground within a 1.5-mile radius from where the fruit flies were found. The material is known to attract male fruit flies who die after consumption.

Peach fruit flies, commonly found through most of mainland southern Asia and neighboring islands, are known to attack about 50 kinds of fruits and vegetables, San Mateo County officials said in a statement. The produce becomes spoiled when a female peach fruit fly lays eggs that hatch into larvae.

The invasive bugs behave like regular fruit flies, but are considered a threat to native wildlife. San Mateo County currently has over 4,250 "exotic pest detection" traps countywide. Other bugs in the category include the gypsy moth, Japanese beetle, and a range of non-native fruit flies.

According to San Mateo County officials, exotic pests usually hitchhike on fruits and produce transported illegally from other countries.

The two counties, the state Department of Food and Agriculture and the U.S. Department of Agriculture will assess the bugs' spread and use organic pesticide for extermination.

What to know about this pest

The peach fruit fly, recently found in Palo Alto, has the potential to thrive in this area due to the mild year-round climate, which offers both an abundance of fruit and no harsh winters that would kill the fly.

"We use insect traps to monitor what's coming in. We found this one before a few years back. It's a tropical insect and has a fast reproductive life cycle. It's easy to quickly get a large infestation," said Santa Clara County Agricultural Commissioner Joe Deviney.

He said that so far, trapping has not caught any pregnant females, which would point to a more serious problem: "Then we'd know that we have a population and they're breeding." Deviney also said that the treatment program now underway eradicated the flies previously found.

With the flies' recent detection in this area, here are some things to know if you grow fruit:

What trees and produce are at risk?

Despite the name, the peach fruit fly has no preference for its namesake. "I'd call it a common name. It will go for anything around," Deviney said, noting that there's about 50 species, including stone fruit and citrus, that the fly attacks.

What kind of damage do the flies create?

The female fruit fly pierces the fruit's skin to lay eggs, but the damage isn't obvious until you open an affected piece of fruit: It will have maggots inside.

What should you look for in your yard?

It's tricky. The flies themselves look unremarkable to the average person. And because female flies leave no marks on fruit when they lay their eggs, the flies are difficult to detect — except for the aforementioned evidence. "If you open up a fruit and it's filled with maggots, give us a call. That would be the telltale sign if they've gotten established," Deviney said. If you see evidence of peach fruit flies, call the California Department of Food and Agriculture Pest Hotline at 1-800-491-1899.

What can you do to minimize risk to your fruit trees and produce?

Deviney emphasized not giving invasive insects a chance to get here in the first place. "We don't know how it got here, but it shouldn't be here, So this is a perfect reminder: Don't bring things back, or ship things, or ask relatives to send you things unless it's been checked and cleared by [agricultural authorities," he said.

When will we know if the current treatment has been effective?

Officials will continue to closely monitor traps. "We will do the treatment one full time and then maybe a second time," Deviney said. "If we go a couple of life cycles and we haven't caught any more, then we'll know we've got them. That's what our hopes are, that we're responding early enough."

For more information, call the County of Santa Clara Agricultural Commissioner's office at 408-918-4600.