News Column

Medfly Spreading Through California Crops

August 8, 2013

Reed Fujii

Mediterranean fruit fly, commonly known as the Medfly (photo: Alvesgaspar, Creative Commons)

Researchers at the University of California, Davis, and in Greece have concluded that several species of invasive tropical fruit flies, including the notorious Medfly, are now permanent residents of California and are slowly spreading.

The presence of the destructive pests threatens exports of California fruit, vegetables and nuts -- which amounted to $7.7 billion in 2011 -- to countries seeking to protect their own farmers.

But state farm officials and agricultural industry experts said there was no immediate cause for alarm, noting that the new research must still be vetted by the larger scientific community and that existing programs to contain and eradicate fruit fly infestations have worked well for more than 30 years.

Scott Hudson, San Joaquin County's agricultural commissioner, said Wednesday he's sure none of the exotic crop pests are within his jurisdiction and its $2 billion-a-year commodity value.

"We put out nearly 30,000 traps in the county for fruit flies and other invasive pests throughout the year," he said.

That system most recently -- in 2011 -- identified the presence of the Oriental fruit fly in north Stockton, triggering a months-long program that eradicated the pest.

Hudson said foreign agricultural experts often visit San Joaquin County to check its pest-trapping and inspection programs.

"They are satisfied with them, and they are satisfied that they are an indicator that we do not have the pests," he said.

However, James Carey, a UC Davis entomology professor and co-author of the study, said the fruit flies targeted by such efforts frequently reappear in some locations, even annually, and are gradually spreading.

The study, he said, "definitively rebuts the hypothesis that the multiple detections of many species of fruit flies in California each year are the result of repeated new introductions. ... What we are detecting here are low-level, established populations."

Jay Van Rein, a spokesman for the California Department of Food and Agriculture, said Carey had previously argued that invasive fruit flies had become endemic in the state and that his new data will be considered by the agency's scientific advisory panel.

And Van Rein defended existing fruit fly control programs.

"We have long-standing support for these programs, not just from our farmers but from our international trading partners as well," he said Wednesday.

"For the sake of argument, even if we assume the claims that are made by the paper (are correct), the tools that we have ... in place have kept fruit flies out of cropland and have satisfied the needs of our trading partners for decades."

Barry Bedwell, president of the California Grape & Tree Fruit League, echoed those thoughts.

"We certainly have to give any of this type of study a thoughtful review," he said. But he also questioned whether the study was relevant, given the record of fruit fly control.

"Really, what we need to concentrate on is the progress we've made in controlling (these pests)," Bedwell said Wednesday. "That's something all of us in agriculture, as well as our trading partners, can take confidence in."

Carey argued that the pest-control efforts, while managing to eradicate localized, high-density concentrations of fruit flies, allow low-level populations of several species -- including the Mediterranean, Mexican, Oriental, melon, peach and guava fruit flies -- to remain undetected.

In an email Tuesday, when the study was announced, he said there's a "need to develop a new strategic plan, involving trapping efforts in key agricultural areas that are 10-, 50-, maybe even 100-fold greater than current. Traps are extremely insensitive, so the only way to increase overall efficiency is to increase numbers in a big way."

"This would ... keep fly populations suppressed far more than they currently are," he wrote.

With the fruit flies present and slowly spreading, Carey also said that in the long term, the "CDFA and (U.S. Department of Agriculture need) to do better job of protecting individual growers who face financial ruin with some of these quarantines that are certain to increase in frequency."

The research done by Carey; lead author Nikos Papadopoulos; an entomologist at the University of Thessaly, Greece; and Richard Plant, a UC Davis professor emeritus of plant sciences and biological and agricultural engineering, was published Tuesday in the international journal Proceedings of the Royal Society B.

Contact reporter Reed Fujii at (209) 546-8253 or


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