Study Offers New Insights on Invasive Fly Threatening U.S. Fruit Crops

Humans aren’t the only species with a sweet tooth. Research from North Carolina State University shows that the invasive spotted-wing vinegar fly (Drosophila suzukii) also prefers sweet, soft fruit – giving us new insight into a species that has spread across the United States over the past four years and threatens to cause hundreds of millions of dollars in damage to U.S. fruit crops.

“Because we know that D. suzukii prefers softer, sweeter fruit, we can focus our research efforts into which wild fruits may serve as reservoirs for this species and help identify new crops that might be at risk,” says Dr. Hannah Burrack, an assistant professor of entomology at NC State and lead author of a paper on the research. “These findings may also be a starting point for plant breeders interested in developing new fruit varieties that are more resistant to D. suzukii.”

Originally from east Asia, D. suzukii were first detected in California in 2008. They have since spread to states from Wisconsin to North Carolina to Florida. The female flies use serrated blades on the tip of their abdomens to cut through the skin of ripe fruit and lay their eggs. The eggs hatch into larvae that feed on the flesh of the fruit until they reach maturity – ruining the fruit in the process.

Sellers go to great pains to remove infested fruit before it reaches the marketplace, so consumers won’t notice a difference in fruit quality. But infestations can cause significant economic problems for fruit growers. For example, researchers estimate that D. suzukii has the potential to destroy 40 percent of blackberry and raspberry crops in the eastern U.S., which would affect berry prices and availability.

D. suzukii already causes tens of millions of dollars in crop damage annually to cherries, raspberries, blackberries, blueberries and strawberries. But researchers estimate that losses could climb into the hundreds of millions of dollars per year if the pest can’t be controlled.

While ongoing studies explore pesticide-based approaches to control D. suzukii, the new research from NC State should help scientists and farmers with other control options.

For example, the study found that D. suzukii are more likely to infest certain varieties of raspberries and blackberries. This means growers may be able to limit crop damage by planting more of the varieties that D. suzukii tend to avoid. Similarly, this information allows farmers to focus pesticide treatment on varieties that are most susceptible to infestation.

The three-year study evaluated D. suzukii impacts in commercial blackberry and raspberry crops in North Carolina, and also encompassed laboratory experiments to help researchers determine which characteristics made fruits more likely to be infested. The work was supported by the Southern Region Small Fruit Consortium, North Carolina Tobacco Trust Fund Commission, North Carolina Department of Food and Agriculture, U.S. Department of Agriculture and North Carolina Blueberry Council.

The paper, “Variation in selection and utilization of host crops in the field and laboratory by Drosophila suzukii Matsumara (Diptera: Drosophilidae), an invasive frugivore,” was published online March 14 in Pest Management Science. Co-authors are Dr. Gina Fernandez, a professor of horticultural science at NC State; Taylor Spivey, an undergraduate at Brevard College; and Dylan Kraus, an undergraduate at NC State.

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Note to Editors: The study abstract follows.

“Variation in selection and utilization of host crops in the field and laboratory by Drosophila suzukii Matsumara (Diptera: Drosophilidae), an invasive frugivore”

Authors: Hannah J. Burrack, Gina E. Fernandez and Dylan A. Kraus, North Carolina State University; Taylor Spivey, Brevard College

Published: online March 14, 2013, Pest Management Science

Abstract: BACKGROUND: Drosophila suzukii, a pest of soft-skinned berries and stone fruits, has recently rapidly expanded its global range. The impacts of D. suzukii infestation and subsequent fruit damage in North America and Europe have been profound. The aim of the present work was to assess host selection of D. suzukii in the field and laboratory, with an emphasis on hosts commonly grown in the southeastern United States, where D. suzukii has been established since 2010. RESULTS: Raspberries were infested at a greater rate than blackberries in the field, and varieties within both species were infested at different rates. Primocane-fruiting blackberries were often the least heavily infested. Further, blackberries and raspberries grown under high tunnels were infested at lower rates than those grown outside. Fruit and artificial substrates with a lower surface penetration force were more heavily infested than firmer substrates in the laboratory; no eggs were laid in artificial substrates exceeding 52.00 cN surface penetration force. CONCLUSION: Infestation rates differ between species and varieties within species of Rubus in the southeastern United States. Fruit penetration force is one potential measure of host susceptibility, but host attractiveness will likely depend upon additional factors, such as soluble sugar content.