Queensland fruit flies, native to Australia, have over 170 different host plants. (Photo courtesy of the University of California, Agriculture and Natural Resources)

By Natalie Willis, Reporter, Valley Ag Voice

With huanglongbing disease carried by Asian citrus psyllids becoming increasingly prominent throughout Southern California, the state’s citrus industry faces another potential threat from the Queensland fruit fly.

Two Queensland fruit flies were detected near Thousand Oaks, leading to a first-of-its-kind quarantine in the United States, covering 90 square miles. According to Hamutahl Cohen, the University of California Cooperative Extension entomology advisor for Ventura County, the Queensland fruit fly is unique in its ability to withstand different temperatures and conditions, making it difficult to control.

She noted that along with the Queensland fruit fly quarantine, there are six other active fruit fly quarantines in California, including the Mediterranean fruit fly, the Oriental fruit fly — which spans three quarantines — and the Tau fly. Cohen explained that fruit flies generally share the same characteristics in affecting host plants.

“What they do is they lay their eggs under the skin of the fruit, and then the egg hatches into a larva or maggot, which travels throughout the fruit and introduces decay organisms like bacteria that facilitate rot,” Cohen said. “They all have the same life cycle and are hard to control once the populations take root.”

In the past, fruit fly quarantines, as well as associated regulations, have been successful in eradicating fruit flies in California, Cohen explained, and the Mediterranean fruit fly has been eradicated multiple times since 1975.

The Queensland fruit fly has had substantial impacts on the citrus industry in Australia, with the Australian Department of Agriculture, Fisheries, and Forestry explaining that fruit flies cost the country hundreds of millions per year in control measures compiled with lost access to international markets.

While it boasts various host plants, the Queensland fruit fly poses a primary threat to citrus production in the state due to the equally concerning spread of huanglongbing disease.

“Citrus growers are already stressed because they have to monitor for Asian citrus psyllid. They often have to do these area-wide treatments for Asian citrus psyllids depending on what region of California they’re in,” Cohen said. “So, this is another possible threat on top of that, and that’s why it’s troublesome.”

The aptly named Queensland fruit fly is most prevalent in Australia from October to May and is known to target over 170 different fruits, vegetables, and plant commodities. In a press release, the California Department of Food and Agriculture explained that residents within the Ventura County quarantine area should not move any fruits or vegetables from their property.

“This has been a record year for fruit fly detections,” CDFA Secretary Karen Ross said in the release. “The stakes are high. Help us protect our commercial and backyard gardens from invasive fruit flies – please ‘Don’t Pack a Pest’ when you travel, and don’t mail packages carrying unmarked fruits and vegetables to California.”

CDFA is working with the U.S. Department of Agriculture and agricultural commissioners from Ventura and Los Angeles counties to implement a multi-tiered approach to eliminate the fruit fly and prevent future occurrences. If larvae or mated adult females are detected, officials will hand-remove the infected fruit or vegetable within 100 meters.

Properties within 200 meters of the detection will be treated with Spinosad — a natural soil bacterium that can be toxic to insects — to remove any live fruit flies. Traps are also incorporated and equipped with a pheromone lure and insecticide to attract and eliminate adult male Queensland fruit flies.

The spike in fruit flies and other invasive species is evident in California, but there is uncertainty over why the detections are becoming increasingly prominent. But Cohen explained that travel is one of the main pathways for fruit flies in California.

“That’s why we often first find invasive species in urban and suburban backyards and not on farms,” Cohen said. “More Californians are traveling now that we are post-pandemic, which may have resulted in the movement of the fruit fly into California.”

Travelers entering the US are cautioned to visit dontpackapest.com to ensure they are not bringing an invasive species home with them.

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