Rebuilding Integrated Pest Management: Advances in Spotted-Wing Drosophila Control

Monday, February 3, 2025

 


Berry interesting take aways from the Nova Scotia Horticultural Congress 2025

The 2025 Nova Scotia Horticultural Congress featured a review of the best management techniques for Spotted-Wing Drosophila (SWD). Dr. Cesar Rodriguez-Saona, Professor and extension specialist at Rutgers University, shared the latest advancements in Integrated Pest Management (IPM) strategies, focusing on biological control, insecticide application, adjuvants, and repellents.

SWD, an invasive pest from Asia, was first detected in California in 2008 and has since spread across North America. Unlike common fruit flies, female SWD possess serrated ovipositors, allowing them to lay eggs in fresh, ripening fruit. Their rapid reproductive cycle and broad host range (including strawberries, raspberries, cherries, and blueberries) make them a major threat to fruit growers. Wild plant species in wooded areas can also serve as SWD hosts, increasing their persistence in agricultural landscapes.

 

SWD Larvae on fruit maked by arrows
Photo credit: University of New Hampshire

Efforts to introduce natural predators against SWD have seen mixed results. Researchers have explored several parasitoid wasps, including Pachycrepoideus vindemiae and Trichopria drosophilae, with limited success. These species have a broad host range but show low parasitism rates (0-10%). More promising candidates, such as Ganaspis kimorum and Leptopilina japonica, are being introduced in North America, with release trials in New Jersey showing potential for SWD suppression. In 2022, 5,000 adult wasps were released in five sites, followed by 10,000 additional releases in 2023 and 2024. While parasitism rates remain variable, these efforts mark a significant step in biological control integration.

Chemical control remains an essential tool for managing SWD, with extensive testing conducted across multiple U.S. states. A 2020 efficacy ranking included results from 10 states and 19 crop combinations, identifying the most effective insecticides. Dr. Cesar Rodriguez-Saona included an excellent slide in his presentation, ranking the effectiveness and grouping the insecticides tested into their IRAC group.   The take away from this for Nova Scotia growers was that all the products registered for SWD in Canada had a rating of good to excellent. However, repeated applications pose risks such as insecticide resistance, residue accumulation, and outbreaks of secondary pests. Dr. Cesar Rodriguez-Saona indicated that there was a resistance issue with Entrust in California where organic growers may have overused this product. This will mean that Success will also be ineffective in the affected area.  Growers were cautioned to maintain a good rotation involving multiple IRAC groups in order to maintain effectiveness of all currently registered products. Organic growers in California were looking at including Pyganic in their spray rotation in order to slow the spread of resistance to Entrust.  Pyganic has an efficacy rating of fair when tested in the US.  In Canada, Pyganic is not registered on SWD despite being registered on highbush blueberry for other pests.    To maximize efficacy, researchers recommend applying any insecticides at dawn and dusk when SWD activity is highest.

An emerging approach in SWD control is the use of adjuvants like Combi-Protec (a product similar to molasses), a feeding stimulant that enhances insecticide effectiveness. Field trials in highbush and lowbush blueberries, as well as raspberries in states like Oregon, New Jersey, Maine, and New York, demonstrated its potential. Cage field trials involving 100 released SWD flies per treatment showed reduced egg-laying and adult survival when Combi-Protec was mixed with some insecticides (Imidan, Delegate) while other insecticides did not show a great improvement in control when it was added (Up-cyde, Malathion). 

Beyond killing SWD, researchers are investigating ways to repel them. Previous studies identified compounds such as 1-Octen-3-ol, Geosmin, and 2-Pentylfuran as potential repellents. New research has focused on volatile organic compounds (VOCs) released from diseased fruit. Botrytis cinerea (grey mold) and Colletotrichum fioriniae (anthracnose fruit rot) were found to emit odors that naturally repel SWD. Experimental trials using Ethyl Butyrate, Ethyl Crotonate, and 2-Pentylfuran in controlled environments showed significant reductions in SWD oviposition. A multiple-choice assay demonstrated that certain volatiles consistently deterred SWD from laying eggs, marking an exciting avenue for non-lethal pest management.

Dr. Rodriguez-Saona emphasized that a single control method is insufficient. Instead, an integrated approach combining cultural, chemical, behavioral, and biological strategies is essential. Farmers are encouraged to:

-Monitor SWD populations using effective baits and attractants before infestations occur.

-Time insecticide applications during peak SWD activity.

-Incorporate adjuvants to enhance control efficacy.

-Remove alternative host plants from surrounding wooded areas to reduce SWD reservoirs and prune to increase spray penetration and reduce favorable (humid, calm air) environment within the field.

-Dispose of infected fruit approprately so that the crop is not reinfected

I would like to thank Dr. Cesar Rodriguez-Saona for taking a great deal of time out of his busy schedule to travel to Nova Scotia to present at the Horticultural Congress. I’m hoping he returned home safely between the storms.