Could predatory flies provide early season control of spotted wing drosophila in red raspberry?

May 22, 2017
By Beverly Gerdeman

Featured BIOAg research: Potential for early season control of spotted wing drosophila by predatory flies (Scathophagidae) as a secondary benefit of manure amendments in red raspberry

Spotted wing drosophila on raspberry [male in focus (L), female out of focus (R)]. Photo: B. Gerdeman

Spotted wing drosophila (SWD), Drosophila suzukii, is considered the most important pest of soft fruit in Washington State. Current control methods require weekly insecticide applications, which are unsustainable. So far however, no effective biological controls have been identified. Large numbers of yellow dung flies were observed in a Whatcom County red raspberry field following an early spring manure application. This prompted an investigation into the potential of yellow dung flies to impact SWD populations by feeding on overwintering females returning to berry fields early spring.

In 2016, I received a grant from CSANR’s BIOAg program to investigate the potential of yellow dung flies as a biological control for SWD. Overlapping with a USDA NCRS-funded project that examined the impacts of a variety of manure-based amendments in berry production, this study investigated the attraction of dung flies to two types of soil amendments in

Predatory yellow dung fly in a hunting pose. Photo: B. Gerdeman.

raspberry: by-products of anaerobic digestion (AD) and liquid manure. Results indicated dung flies were only attracted to fresh raw manure and not to the AD by-products. Dissections and cage studies confirmed dung flies would capture and feed on SWD. Molecular tests detected presence of SWD DNA in dung flies prior to the cage studies, suggesting they had fed on SWD prior to collection.

Raw manure treatments to fresh market crops remain restricted because of potential food-borne illnesses. However if AD by-products could be tweaked to attract dung flies, they could replace risky manure applications while attracting these predators to the fields when overwintering SWD return. Dung flies feeding on these founder females could significantly impact SWD field populations during the fruit harvest period. For more information on this BIOAg project please visit, http://bit.ly/Gerdeman.

This article is reprinted from the CSANR 2016 Annual Report.

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