University of Florida doctoral student wins award for work with spotted wing drosophila

Although it is no longer a new pest, spotted wing drosophila continues to be a bane for small fruit—especially organic—growers. To help both organic and conventional growers fight the pest, a University of Florida doctoral student examined several pest management options and has won a regional award for her research.

Lindsy Iglesias

Lindsy Iglesias, who will graduate from the University of Florida in May with her Ph.D., discovered some novel and more efficient ways to scout and control spotted wing drosophila, or SWD, that will work for both organic and conventional growers. She won a Friends of Southern IPM Graduate Student Award from the Southern IPM Center for her work.

Blueberry growers who use conventional pest control methods have been able to control SWD adequately through weekly insecticide sprays. Organic growers, on the other hand, have only one biorational insecticide that works and have been having difficulty managing the pest as a result. Because of the possibility of insecticide resistance, Iglesias wanted to find more ecological ways to control the pest as well as more efficient methods of scouting so that growers could use control methods more efficiently.

To figure out how to control SWD, scientists first must understand it and its host preferences. Unlike other drosophila, SWD prefers ripening fruit over rotting fruit, making it more of a threat to production and more vital to manage effectively.

Iglesias collects captured SWD from a trap in a strawberry field

Iglesias and other researchers at the University of Florida examined berry characteristics and plant variety, but no one characteristic or variety stood out in terms of a favorite for the pest. Iglesias then looked at patterns in the field.

Working on a certified organic blueberry farm, she discovered that flies congregated outside of the field in unmanaged wild areas and along the field edges. Yet, blueberries infested with SWD eggs were randomly distributed throughout the field. . Inside the field were large gaps of no flies, which showed up more prominently when Iglesias mapped out where she found the pest.

“We didn’t know why they were in these areas,” she said. “We looked at the cultivars in the field, but there was no difference in fly captures.”

SWD were entering the field from these adjacent wild areas, she found. Although searches to discover where in those areas SWD was laying eggs were inconclusive, she did find that focusing treatment along the border of a field controlled the pest while reducing the amount of insecticide needed.

“Border sprays can reduce SWD, especially in the beginning of the season,” she said.

In addition to the border sprays, Iglesias and Extension entomologist Oscar Liburd tested the effectiveness of soil tillage on SWD reduction. SWD pupate in the soil, so Liburd and Iglesias hypothesized that tilling the soil might upset the pest’s life cycle. Although initial experiments have been inconclusive, they are continuing to explore tilling to see if pupa burial will have any effect.

SWD on blueberry

To give organic growers more to fight the pest with, along with giving conventional growers other tools to relieve pressure on the pyrethroid sprays, Iglesias tested the effectiveness of several biorational compounds that organic growers can use. From the trials, she found three compounds that showed promise: Chromobacterium subtsugae (trade name Grandevo), sabadilla alkaloids (Veratran D) and pyrethrins plus azadirachtin (Azera). Growers are currently using Grandevo and Azera. Although Veratran D shows promise, it is not currently labeled for SWD. Spinosad, an organic insecticide that had previously provided some control of SWD, showed reduced control in the trials.

Iglesias hopes that another graduate student will continue the research into the SWD populations in wild areas.

“We continue to find populations throughout the winter in wild, non-crop areas in Florida,” she said. “It would be useful to see how far south these flies have their resting stage, whether winter-caught flies are still laying eggs. It could have implications for early-season management.”

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