OSU researchers prepare for a new emerging pest

By Oregon State University Extension Office,

CORVALLIS, Ore. – Recent warm weather has prompted more than spring fever. As temperatures have climbed over 50 degrees, a potentially devastating insect pest has been detected in western Oregon and Washington.

Last fall, the spotted wing drosophila, an invasive vinegar fly native to southeast Asia, first flew onto the radar of fruit growers from California to British Columbia. Damage from the fly was rapid and intense. California lost about one-third of its cherry crop; Willamette Valley growers lost up to 20 percent of their blueberries and raspberries and up to 80 percent of their late-season peaches.

Since then, researchers from Oregon State University, U.S. Department of Agriculture-Agricultural Research Service and Oregon Department of Agriculture have joined colleagues in California and Washington in a multi-state, multi-agency effort to combat the tiny fly that threatens much of the West Coast fruit industry.

In recent weeks, researchers have seen evidence of overwintered adult spotted wing drosophila in a few monitoring traps in the Willamette Valley. The team now has launched a regional management plan, and is presenting this information in workshops throughout Oregon, California and Washington.

With the appearance last fall of tiny white maggots in a handful of blueberries, OSU researchers identified the spotted wing drosophila, a pest never before documented in Oregon. Immediately, the research team scoured agricultural records from Japan to estimate the fly’s damaging potential. In field and laboratory tests, they studied the fly’s overwintering habits, its reproduction rates and its preferred fruits, and they have tested a variety of baits, traps, and controls.

“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 OSU horticultural entomologist who oversees a rapidly expanding compendium of information online for growers and researchers. See the Spotted Wing Drosophila Web site.

The stakes are high, and both growers and scientists are concerned. 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. And 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 to10 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.

The research team is presenting training sessions to growers throughout the Pacific Northwest. A public session will be held on March 30, from 1 to 5 p.m., at the Airport Sheraton Hotel in Portland. Presentations and hands-on activities focus on the fly’s life cycle, field identification and monitoring, and evolving options for control. Pre-registration is not required.

For more information on upcoming workshops, see the Spotted Wing Drosophila Web site.

By: Peg Herring
Source: Amy Dreves, Vaughn Walton

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