The spotted wing drosophila, Drosophila suzukii, an invasive vinegar fly native to southeast Asia, first appeared on fruit crops from California to British Columbia last fall.
In the fall of 2008, the first reports emerged of an unfamiliar fruit pest in the Watsonville area of central coastal California. In June 2009, spotted wing drosophila were trapped over a wide area in northern California including Santa Clara, San Benito, Santa Cruz and Monterey counties.
In 2009, California lost about one-third of its cherry crop to infestations of the invasive fly. In Oregon, Willamette Valley growers lost up to 20 percent of their blueberries and raspberries and up to 80 percent of their late-season peaches.
The first Florida detections of this fly were made on August 4, 2009 in rural Hillsborough County where a single male fly was captured in each of two separate multi-lure traps located about three miles apart.
With the appearance last fall of tiny white maggots in a handful of blueberries, Oregon State University researchers identified the spotted wing drosophila, a pest never before documented in Oregon.
The fly was first observed on Japan's Honshu Island in 1916. It also occurs in parts of China, India, Thailand and Korea and has been established in Hawaii since at least 1980.
Spotted wing drosophila flies are small beside a dime. (Photo by Mike Reitmajer, Walton Lab)
This year, researchers from Oregon State University, the federal Agricultural Research Service and the Oregon Department of Agriculture have joined colleagues in California and Washington in a multi-state, multi-agency effort to combat the fly.
Managers are combating the fly with a multi-state management plan being presented in workshops throughout Oregon, California and Washington.
"This effort involves a big network of cooperators, including scientists of many disciplines, growers of many kinds of fruit, and state, provincial and federal agencies, all working together to monitor and control this fly," explained Vaughn Walton, an Oregon State University horticultural entomologist who is compiling information online for growers and researchers.
The stakes are high, worrying growers and scientists alike. Tests have confirmed that the spotted wing drosophila will feed on a wide range of grapes, berries, cherries, peaches, pears and plums grown commercially in Oregon, California and Washington. Unlike other vinegar fly species, the spotted wing drosophila prefers ripe ready-to-harvest fruit.
The fruit industry is a multi-million dollar enterprise in Oregon. The farm gate value of Oregon wine grapes is about $68 million, according to Oregon Department of Agriculture. Berries are valued at about $100 million; Oregon pears at $80 million.
"Since the fly is new to North America, we are learning as fast as we can," said Amy Dreves, an OSU research and extension entomologist who is helping to design an integrated pest management strategy. "We are studying all aspects of its biology and testing tools such as monitoring, trapping, sanitation, and efficient timing of effective chemicals."
This is not a problem that can be wiped out with a barrage of chemical sprays, according to the researchers. Controls must not harm pollinating insects or other beneficial organisms that are necessary for healthy orchards and fruit fields. In addition, chemical resistance is a problem when combating any insect with up to 10 generations a year, as has been reported for this fly in Japan.
Both field and lab studies have found that these flies thrive in cooler areas and are most active at temperatures of 68 degrees. Much of western Oregon's growing season would seem to favor these flies, according to Dreves. And because Oregon has a variety of crops that ripen at different times during the season, the spotted wing drosophila could move from one crop to another as the season progresses, and populations could build up to high numbers in many crops.
The research team is developing effective traps in Oregon and California to monitor fly activity and they are testing organic bait sprays that may be effective early in the season in reducing numbers of flies before they lay eggs in the ripening fruit. Field sanitation practices may be especially critical, to reduce habitat for overwintering flies.
Last month, the research team received $225,000 in emergency funding from the Oregon Legislature to implement a broad-based monitoring and education plan. In addition, the scientists have applied for a grant from the federal government to expand their research and outreach to growers.
Click here for more information on fighting the spotted wing drosophila.
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