Glow Better: Students and Faculty Collaborate to Study Fruit Pest

Wednesday, August 21, 2013

PHILADELPHIA (August 20, 2013) ­— Kristina Orbe has spent the past two summers thinking about flies. But rather than consider the dragonflies or houseflies that are so prevalent at this time of year, Orbe is interested in an invasive fruit fly species from Japan that is causing widespread damage to soft-skinned fruit crops. Called Drosophila suzukii, the fly is also known as spotted wing Drosophila (SWD) because of its distinctive black spots on the wings of the male.

Orbe received a Summer Scholar grant both this year and last to study SWD. Saint Joseph’s Summer Scholars Program gives students the opportunity to work collaboratively with a faculty mentor on an independent research project. Participants receive a stipend of $3,200 and are required to write about their work and present it publicly.

This summer, Orbe worked with two mentors, Jonathan Fingerut, Ph.D., associate professor of biology, who studies how insects disperse in environments, and Scott McRobert, Ph.D., professor of biology, a geneticist who also studies animal behavior. Concurrently, John Braverman, S.J., assistant professor of biology, an evolutionary biologist who studies genetic variation in a variety of organisms, is investigating the biodiversity of Drosophila with his students. 

“I've been studying the genetics and behavior of Drosophila for over 30 years, but this situation with SWD is a rare scientific opportunity,” says McRobert. “Since D. suzukii is an invasive agricultural pest (unlike most Drosophila species), our work can be directed at finding a solution to an environmental problem. Dr. Fingerut, Dr. Braverman and I are planning a long-term collaboration to attack this problem from three perspectives: ecology, molecular biology and behavior. In that way, we hope to gain a detailed understanding of D. suzukii and possibly find ways to reduce the damage it causes.” 

First discovered in California in 2008, SWD is related to more common fruit fly species, but it harbors a menacing difference. The female’s serrated ovipositor, the organ she uses to deposit her eggs, is razor-sharp, allowing her to lay her progeny under the skins of unripened blueberries, raspberries, strawberries, cherries and other fruits.

“The fruit is inedible after the eggs are laid,” says Orbe, a rising senior biology major. What happens next is “pretty disgusting,” she adds. “The larvae develop and eat the fruit from the inside, causing it to collapse and turn to mush.”

SWD infestations are bad news for agriculture. According to a University of California study, 2009 yield loss estimates in California alone range from negligible to 80 percent.  The tiny invader, which is about 3 mm in size, is now on the East coast, having made its way to New Jersey blueberry fields by June 2011. It has also been found in Pennsylvania, Maryland and New England. Fr. Braverman and graduate student Philip Freda conducted a study documenting the presence of SWD on Saint Joseph’s campus (July-December 2011 and March 2012), which was published in Entomological News, May and June 2013.

“We want to know how SWD interacts with and moves about within the environment so that we can develop a trap that could help to control their numbers,” says Fingerut.

Understanding the flies in the wild entails running release and recapture studies. “We knew we had to come up with an effective way to tag the flies that we released to distinguish them from the flies already in natural populations,” says Fingerut.

According to Orbe, a common tagging practice is to “shake and bake” the flies by putting them in a bag with micronized dusts that attach to thoracic hairs, but she wanted to find a less invasive technique to minimize the chance of affecting their behavior. Orbe experimented last summer on D. melanogaster, which she used as a test model for SWD, and discoverd that the best approach was adding powdered fluorescein, a non-toxic dye that glows green under blue or UV light, to food media. Several hours later, the solution produced flies with glowing abdomens.

“Kristina was quite successful with that stage of the work,” says Fingerut. “It’s easy to distinguish the flies that have ingested the fluorescein. Their bellies light up very nicely.”

This summer, Orbe worked on developing an attractive bait for D. simulans, which was used to fine tune the protocols. “The simulans flies found fermented blueberries more enticing than apple cider vinegar and even grape wine, among other choices,” says Orbe, who will continue her research into the fall semester by running experiments with SWD stocks instead of the analogue species. “It’s very rewarding to be engaged in research that may have an impact on a real-world problem,” she adds.

Media Contact

Patricia Allen, Senior Associate Director of University Communications, 610-660-3240,


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