Integrating manure-based amendments with pest control: Potential of predatory flies (Scathophagidae) as a secondary benefit of manure amendments, for early season control of spotted wing drosophila in red raspberry
CSANR Project 160
Yellow dung flies, Scathophaga stercoraria are associated with dung of large mammals. They are predatory on other flies particularly drosophila and are attracted to red raspberry fields following manure applications in early spring. We investigated their potential to provide season-long impact on spotted wing drosophila populations (Drosophila suzukii, SWD) in red raspberry by feeding on returning founder females in early spring, coinciding with the manure treatments. Due to the risk for human pathogens associated with raw manure, their attraction to anaerobic digestion by-products was also evaluated. Weekly timed counts were taken for each of the treatments. Dung flies exhibited lekking behavior and were only attracted to fresh raw manure. Despite high numbers of eggs laid on the manure slurry, no flies emerged. Laboratory studies included dissections of the dung flies, which confirmed the presence of highly sclerotized prestomal teeth, capable of predation on SWD. Presence of thoracic holes and total loss of body fluids and red eye pigmentation in SWD housed with the dung flies in cage trials provided forensic evidence of predation. Molecular analyses detected presence of SWD DNA in field-captured dung flies, suggesting SWD are a regular component in their diet. While the anaerobic digester by-products were not attractive to the dung flies in their current state, additional research may identify ways to increase attractivity of these less-risky soil amendments, enabling growers to utilize these predators to help control SWD in red raspberry.
In prep - Morphological, forensic and molecular evidence of dung fly predation on Spotted wing drosophila, Drosophila suzukii
Beverly Gerdeman1, Lydia Tymon2 and G. H. Spitler3
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Impacts and Outcomes
The expected short-term impacts are Awareness by farmers of the presence of these fly predators in their fields that can provide an unexpected valuable service by reducing SWD populations. Growers and dairymen attending the above outreach activities received firsthand information on the study.
Intermediate-term impacts include grower awareness of these beneficial flies and efforts to maintain their populations on their red raspberry farms through timely applications of selected insecticides that may reduce negative impacts on the population. Growers are concerned about the overuse of insecticides and we are currently working on ways to reduce insecticide applications but thus far nothing is as effective as the broadspectrum insecticide sprays and so these intermediate goals have not yet been met.
Long-term impacts include the potential for active management of dung flies using manure-based amendments as attractants, coinciding with early founder-female SWD and further potential for season-long control of subsequent generations of SWD. The biodigester by-products were not attractive to the dung flies, only the raw manure slurry was attractive. Growers may not want to take the risk of applying raw manure to their berry fields in light of the new FSMA restrictions however there remains potential for dung flies to play a role in SWD control programs (see Recommendations for future research).