2010 Annual Report

Spotted wing drosophila damaged these cherries. Photo by L. L. Strand

Spotted wing drosophila targets soft-flesh fruits

UC scientists are helping growers identify and manage spotted wing drosophila, a new pest in California. This fruit fly was identified in 2009 and recently has been found in many California counties infesting soft-flesh fruits, particularly ripening cherries and caneberries.

This new pest has been found in the San Francisco Bay Area, in the Sacramento Valley, in some sites in the San Joaquin Valley and the Sierras, and along the Southern California coast.

Damage occurred to both backyard and commercial cherries, causing fruit to soften and turn brown. Spotted wing drosophila has the potential to become an important pest, because it attacks ripe, undamaged fruit as well as damaged or rotting fruit—unlike other Drosophila species that it resembles.

Soon after the pest was found, UC IPM organized a meeting so scientists from California, Washington, and Oregon could discuss what needed to be done. Strong research collaborations grew out of the fall 2009 meeting including a $5.7 million grant from USDA’s Specialty Crops Research Initiative (SCRI). UC researchers Frank Zalom, Mark Bolda, Bob Van Steenwyk, Bill Coates, Janet Caprile, and David Haviland are studying the insect’s biology and how best to monitor and manage it.

After the first year of study, researchers still are learning about spotted wing drosophila’s life cycle in California; however, like other vinegar flies, it appears to have a short life cycle and as many as 10 generations per year. This rapid rate of development allows the fruit fly to grow quickly to large numbers and inflict severe damage to a crop, rendering fruit unmarketable.

Spotted wing drosophila’s rapid growth also makes it easy to study in the field and lab.

“We are trying to determine what trap captures mean and where spotted wing drosophila pupate in the field to determine if there is a way to use this knowledge in their management,” Zalom said about research he’s conducting with his graduate student Kelly Hamby. “We are also working with how pesticide resistance might occur in spotted wing drosophila and how it can be managed before it occurs in the field.”

Spotted wing drosophila adult male.
Photo by L. L. Strand.

To get the word out to growers and pest control advisors, authors of the UC IPM Pest Management Guidelines for caneberry, cherry, and strawberry have added what they currently know about monitoring and controlling spotted wing drosophila. Growers can monitor the pest with a variety of traps, and UC researchers continue to test management strategies. A management plan for urban audiences has been developed as well, since the fly also infests backyard fruits. These management plans continue to be updated, as researchers develop new information they can stand behind.

UC Cooperative Extension advisors are kept informed of new findings through a UC ANR Collaborative Tools group that UC IPM operates. Advisors can add information they collect straight from the field to a group of their fellow researchers. UC IPM Content Development Supervisor Tunyalee Martin also gathers new information from California researchers, plus those in Oregon and Washington, and posts it for the group.

“It’s important that the UCCE farm advisors know about any information we have, because we don’t know much about its biology in California yet and even where and in which crops it will show up,” added UC IPM Advisor Carolyn Pickel.

Now that the SCRI grant has been funded, the team involved with the project anticipates making considerable progress in learning about the biology and management of spotted wing drosophila.

“I am especially excited, because there is the opportunity to learn about this insect at the fundamental level by applying the work that has been done with Drosophila melanogaster in the past and using that knowledge to solve a real-world problem,” Zalom said.

Unlike other vinegar flies that occur in California, spotted wing drosophila attacks healthy ripening fruit as well as damaged or rotting fruit. The female ovipositor is very large and serrated, so it is able to penetrate the skin of soft-skinned fruit and lay eggs just beneath the skin, creating a small depression or “sting” on the fruit surface. Eggs hatch and the maggots develop and feed inside the fruit, causing the flesh of the fruit to turn brown and soft; sunken areas that exude fluid often appear on the fruit surface. Damage can provide an entry site for infection by secondary fungal and bacterial pathogens.

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