Progress report for ONE20-365
The spotted wing Drosophila (SWD), Drosophila suzukii, is a highly invasive insect pest widely distributed throughout the Northeast (and much of the continental USA). Current SWD management recommendations for the Northeastern region lean heavily upon consistently scheduled chemical applications throughout the harvest season. Both the ecological and economic costs of chemical dependence are well documented (e.g. pesticide resistance, non-target organisms, etc.) and are a valid concern. The recent success of a novel food-grade, biodegradable SWD attractant, developed by researchers at Oregon State University, represents a great opportunity to add a new and potentially highly effective alternative to the currently available tactics. Recent preliminary studies from early prototypes deployed on Oregon berry farms suggest these attractant baits can significantly affect SWD behavior and last for up to 21 days. Developers of this innovative tool estimate that these baits exhibit the potential to reduce pesticide dependency “by at least 50% during the cropping season”.Our project seeks to assess the utility and economic viability of this recently developed low-tech tool for the management of spotted wing Drosophila and develop appropriate protocols to best adapt this technology for use on Northeastern berry farms. In concert with our field trials we will also develop a robust outreach program in line with our participatory action research (PAR) agenda. Our educational program will rely upon research site field days, presentations, individual and remote consultations, and extension workshops to best disseminate our results and inform growers of the most appropriate SWD management options.
This project seeks to assess the utility of a recently developed low-tech attractant bait, “Decoy" fruit, for the management of spotted wing Drosophila (SWD) within berry crops on Northeastern farms.
Specifically, our project will look to answer two research questions: 1) How does the application of “Decoy” fruits within berry orchards affect the egg-laying behavior of SWD in berry crops located in New England? And 2) What is the potential of this novel approach for reducing SWD impact on average marketable yields and net revenue for growers with significant investments in berry crops?
This project will provide northeastern growers direct information on the potential of this novel management strategy for reducing SWD damage within berry crops. Furthermore, if our field trials exhibit comparable results to those documented by our collaborators in the Pacific Northwestern growing region of the USA, we will look to develop region specific protocols for the successful use of this novel technology. Ideally this project will add to the currently available IPM tactics for susceptible growers looking to reduce their dependence on chemical controls.
The spotted wing Drosophila (SWD), Drosophila suzukii, is a highly invasive insect pest widely distributed throughout New England (and much of the continental USA). First discovered in the western continental United States in 2008, the SWD rapidly expanded its geographic distribution to include the Pacific Northwest and Southern Canada (Asplen et al. 2015). By 2010 Florida berry growers reported incidences of SWD damage and by the autumn of 2011 select New England growers began to experience significant losses from SWD (Lee et al. 2011, Dean et al. 2013). Since its arrival within the region, SWD has established itself as the primary insect pest of most berries and stone-fruits crops (Farnsworth et al. 2017). While SWD can be found on many plants, its preferred hosts include grapes, cherries, peaches, blueberries, raspberries, strawberries, and other soft-flesh fruits. Unlike the majority Drosophila species, which generally infest over-ripe, rotted or fermenting fruits, SWD adult females exhibit a saw-like ovipositor allowing them to attack fruit during the early stages of ripening(Lee et al. 2011, Asplen et al. 2015). Once infested, larval feeding typically results in extensive fruit rot and/or the loss of fruit integrity. Because SWD is a generalist fruit fly, infestations in New England easily persist throughout much of the late season harvest as populations move across fruit crops that are phenologically staggered(Asplen et al. 2015).
Current SWD management recommendations for the Northeastern region lean heavily upon consistently scheduled chemical applications throughout the harvest season (Beers et al. 2011, Loeb et al. 2013, Van Timmeren and Isaacs 2013). As a result, non-target organisms (e.g. pollinators, natural enemies, etc.), found within the local landscape, are often exposed to both lethal and non-lethal doses of chemical toxins, potentially leading to long-term agroecosystem instability (Belzunces et al. 2012, Stanley and Preetha 2016). Pesticide resistance is also emerging as a major issue for growers utilizing pesticides as a primary management strategy for addressing SWD pressure. This is particularly a concern for organic growers as chemical options are limited and the most effective (and popular) organically certified option for chemical control, spinosad, is already exhibiting reduced efficacy stemming from resistance (Gress and Zalom 2019). A recent study out of central California revealed that fly populations previously exposed to spinosad “exhibited LC50 values 4.3– 7.7 times higher than those from [an] untreated location and 11.6–22.4 times higher than previously reported susceptible baselines” (Gress and Zalom 2019). Though this is the one of the first studies to document the emergence of spinosad resistance in invasive SWD populations, it underscores the potential risk of pesticide resistance emerging in other growing regions.
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This project will begin March 2021.
Hypothesis: Application of “Decoy” bait stations significantly affect the incidence of spotted wing Drosophila in, and the marketability of, various berries grown in the Northeast.
Treatments: Experimental treatments will include plots baited with “Decoy” baits (hemp fiber with an attractive gum) compared to untreated control plots (hemp fiber alone).
Methods: Field trials will be conducted at four partner farms: Arbor Farmstead in Grand Isle, VT, Last Resort Farm in Monkton, VT, The Farm Between in Cambridge, VT, and Adam’s Berry Farm in Charlotte, VT in 2021 and 2022. We will use a Randomized Complete Block Design, whereby randomly assigned plots will be assigned to an untreated control dispenser of hemp fiber alone (with no gum) or an experimental treatment of hemp fiber and gum dispenser (Figure 1 found in Other Relevant Research Information). Treatments will be applied by placing the hemp fiber dispensers beneath the berry plants. Five control plots and five experimental plots will be established at each of the four partner berry farms. The specific type of berry will vary depending on the site, thus the exact plot composition will also vary depending on plant architecture. Previous research at Oregon State University (Tait et al. 2018) has shown that the appropriate density of deploying Decoy is 50 dispensers/acre, the equivalent of placing them every 20-30ft within the berry rows. As such, plots will be spaced at least 30ft apart (see Figure 2 found in Other Relevant Research Information). The dispensers will be placed prior to the coloring period of fruit, and remain in place through harvest. To ensure the effectiveness of the attractant, the dispensers must be wetted at least 2 times daily (if berries are not drip-irrigated) and will be changed every 21 days to ensure they remain attractive throughout data collection.
Data Collection and Analysis: Berries will be scouted weekly at each of the four field sites throughout the season to confirm the presence of SWD in the research plots. When berries have ripened, we will randomly subsample 50 berries from each plot and the number of SWD infected berries, and SWD eggs per berry, will be counted. For statistical analysis, the number of infected berries/plot and eggs/berry will be designated as dependent variables, and differences among treatments will be determined via a generalized linear model for both dependent variables. Dispenser treatment will be considered the single fixed factor. Farm site, trial year and their associated interactions will be considered random effects.
Field Season 2021
- Low SWD pressure at Adam's Berry Farm
- High variability in the amount of SWD pressure on the selected berry farms
- Reduced numbers SWD larvae in berries selected from plants with decoy baits (not statistically significant)
- Small plot sizes and field variability may have contributed to the consistency in our results across plots and farms.
As part of our field research we harvested 5 replicates of 10 berries for each treatment (control & decoy bait) at each farm. Our sampling included four consecutive weeks starting with the onset of berry ripening. The mean number of larvae per sample (10 berries) varied significantly over the course of the sampling period and among farms. The blueberries sampled from the decoy treatment plants did exhibit a reduced number of larvae. Though not statistically significant, the trend was consistent across all farms except Adam's berry farm (see figures below). The high effect variance of the treatments is likely the result of both the limited number of berries sampled and the relatively small plot sizes. To best address these limitations we consulted with Dr. Vaughn Walton of Oregon State (the primary investigator that developed the baits) to decide upon any modification to our methods. Dr. Walton advised that we try to increase our plots sizes and perhaps consider shifting to a more susceptible berry type (i.e. raspberries) to decrease the variability. We are currently in the process of reaching out to raspberry growers within Vermont to add new farms to increase our replication.
Education & Outreach Activities and Participation Summary
Our research team includes two UVM educators/PAR researchers and four participating farm partners. As members of the greater UVM Extension community and Plant and Soil Science Dept, the project leaders are well positioned to access all of the available communication channels associated with UVM Extension, including the network of extension professionals who collaborate with our research team (e.g. Cornell Cooperative Extension, UNH Cooperative Extension, UMaine, UMass Extension, Penn State University Extension, etc.) on various other projects.
Our outreach curriculum will focus upon adaptable information to aid farmers in applying sustainable IPM tactics both new and old for the management of SWD within susceptible fruit crops. Learning outcomes for this curriculum will be divided into two general categories: knowledge building and skill development.
Knowledge Building: Growers participating in our educational program will receive detailed and practical knowledge on a variety of relevant topics. These topics shall include: 1) the ecology and biology of SWD; 2) currently available control tactics for SWD management; 3) descriptions of the general ecology of plant volatiles and their contribution to plant defense; 4) general chemical ecology theory applied in the development of the attractant; and 5) any results stemming from our research trials.
Skills Development: Growers will be trained in the proper deployment of various low-impact and ecologically based IPM tactics for SWD management. Though comprehensive in nature, these training will focus on the proper deployment of the novel tool being tested in our field trials. Farm demonstrations and field days at our partner sites will provide growers the opportunity to directly observe the basic protocols for deploying and maintaining the efficacy of the technology.
Instructional Methods: Research site field days (2 events X 20 participants = 40), individual and remote consultations (~10 participants), and extension workshops will directly support our educational curriculum (~40 participants). Farmer-to-farmer communication will also be facilitated through farm demonstrations (~20 participants), PAR meetings (~12 partner farms) and postings to northeastern Veg and Fruit Listserves where partner farmers and growers interested in the novel technology will communicate about the protocols, benefits and challenges of using the tool (~350 subscribing members). Results from our trials will also be posted on the www.uvm.edu/agroecology (~100 subscribers), and www.uvm.edu/extension/cropsoil/ websites. In addition, we will present the results of this project at regional and national conferences including: regional NOFA conferences (~20 participants), Entomological Society meetings (~20 participants), and Vegetable and Fruit Grower meetings (>200 participants).
Due to covid restrictions at our field sites, we refrained from conducting our 2021 field days. Also, due to the inconclusive results we have opted to collect a second year of data before sharing results with the appropriate stakeholders.