San Mateo County agricultural officials announced they’ve found an unwelcome visitor and are urging travelers to refrain from illegally bringing fruit and vegetables into California.

For the first time in more than two decades, a Mediterranean fruit fly was found in San Mateo County. The pest can devastate a range of agricultural crops if left unmanaged and officials are in the midst of an extensive delimitation survey to determine whether this is a single incident or if a breeding population needs to be combated, according to the county.

The fly was caught in a trap placed in Half Moon Bay Nov. 14 and experts believe it was brought in, perhaps on fruit carried over from Hawaii, said the county’s Agricultural Commissioner Fred Crowder. The county announced on Monday that genetic tests determined the fly was indeed wild, not a sterile fly currently found in Solano County for an eradication project up north.

With state crop values in the billions of dollars and numerous residents enjoying backyard fruit trees, there’s much at risk should the Mediterranean fruit fly spread, Crowder said.

“It’s really important that people are aware and keep from bringing these bugs home,” Crowder said. “They’re very pesky, they infest about 250 different kinds of fruits and vegetables, and these are common fruits and vegetables, plums, oranges, apples.”

The fly is native to Africa, but has spread to southern Europe, Australia, the tropics and Hawaii. It was first trapped in California in 1975, according to the county.

The last time the fly was found in San Mateo County was in 1994 and Crowder noted it’s more common for these pests to appear during summer and spring. The timing and thus far having only captured a single fly has Crowder predicting the insect was brought on a plane or in the mail on a smuggled piece of fruit. The county is continuing to work with the California Department of Food and Agriculture to set out and regularly check traps over 17 square miles around the Half Moon Bay residential property where the fly was discovered.

The Mediterranean fruit fly is known to infest the widest range of host plants of any pest fruit fly and is consider one of the most important agricultural pests in the world. The flies lay eggs inside the ripening host fruit or vegetable. The eggs hatch into maggots and bore their way out while making the fruit inedible, according to the county.

The Mediterranean flies are uncommon in San Mateo County, however, officials have documented several cases of Oriental fruit flies in the last four years, Crowder said. The Mediterranean flies are typically found in urban and suburban areas where fruit trees or other host plants are grown. Early detection and rapid response to control the fly is critical to preventing it from affecting residents’ backyard fruit trees, larger agricultural operations as well as trade, Crowder said.

California produces nearly $50 billion a year in agricultural commodities and about $11 billion of that is at risk to Mediterranean fruit flies, Crowder said. It can also have a significant impact on organic growers who don’t have as many treatment options to combat the flies, he explained.

“It affects your backyard fruit, your farmers and growers who produce the food we eat, and it also affects trade when those commodities go out of state or overseas,” Crowder said.

With much at risk, he noted the county and state as well as federal officials don’t take the Mediterranean fruit fly lightly.

The county frequently sets out traps, about five per square mile throughout areas where host plants are grown. Since a Mediterranean fruit fly was found, they flooded the area with an additional 200 traps that will be checked daily for a week. If no other flies are captured, they will scale back to a “core area” and watch those traps daily for about a month. Only if a second fly is found will it prompt eradication or treatment efforts, Crowder explained.

Crowder noted the “fruit fly wars” of the 1970s and 1980s when large-scale aerial sprayings were common. However, those are not the methods typically used nowadays and instead Crowder said treatments may include stripping or removing all the fruit from trees, and ground treatments.  

But prevention is ultimately the preferred method and officials have implemented educational “don’t pack a pest” outreach programs as well as stepped-up enforcement at places like the San Francisco International Airport. People are urged to not bring or mail fresh fruit, vegetables or soil into California unless agricultural inspectors have cleared it beforehand. Studies have shown for every dollar they spend deterring the flies, it saves between $10 and $15 on eradication efforts, Crowder said.

“An ounce of prevention is worth a pound of cure,” Crowder said.

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