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Funded Project

Funding Program: IPM Enhancement Grants

Project Title: Does the invasive pest Drosophila suzukii manipulate the microbiome of its fruit hosts? Implications for management and ecology

Project Directors (PDs): Hannah Burrack [1] Marc Cubeta [2]

Lead State: NC Lead Organization: North Carolina State University

Undesignated Funding: $30,000

Start Date: Mar-01-2018 End Date: Feb-28-2019

No-Cost Extension Date: Jul-30-2019

Pests Involved: Drosophila suzukii

Site/Commodity: Baneberries, blueberries, strawberries, etc

Area of Emphasis: using basic biology to inform management

Summary: This proposed project seeks generate knowledge about the interactions between Drosophila suzukii, commonly referred to as the spotted wing drosophila (SWD) and the plant microbiome in order to develop new management tactics. SWD is a devastating invasive pest of soft-skinned fruit crops native to eastern Asia. Since detection in 2008 in both California and Italy, SWD has since spread to all fruit growing areas in the United States, Europe, and much of South America. Unlike other Drosophila species, female SWD prefer to lay their eggs in ripening and ripe, rather than rotting, fruit. Developing larvae cause loss by directly damage fruit and contaminating shipments, and egg laying alone may make fruit more susceptible to pathogen infestation (Rombaut et al. 2017). Blueberries, blackberries, raspberries, cherries, strawberries, and grapes have been the most impacted by SWD. There is zero tolerance for SWD infestation in fruit, which means that the detection of even a single larva can result in complete crop rejection. The potential annual crop losses due to SWD in the United States alone has been estimated at greater than $700 million, and this high risk has prompted both conventional and organic growers to dramatically increase prophylactic pesticide use. Although SWD egg laying behavior and larval feeding niches differ from other flies in the genus Drosophila, they also share common traits. In particular, both SWD and other drosophilid adults are strongly attracted to odors associated with microbial products (yeasts, wines, vinegars, etc., Keesy et al. 2015). Fungi, particularly yeasts, serve as a food source and influence which hosts are used. Species-specific yeast strains are often intentionally introduced at the same time as eggs are laid (Gilbert 1980). SWD adults appear to contain their own specific microbial community including yeasts as determined via culture dependent methods (Hamby et al. 2012) and bacteria including some known to associate with other drosophilds (Chandler et al. 2014). It is likely that, similar to other drosophilids, SWD also influences the microbial community of its host plants and use these microbes to enhance survival. We are, therefore, interested in understanding how SWD influences the microbial community in host crop plants over time. We believe that understanding the microbial profile of SWD infested plants will provide us with new routes of potential control. Though they are capable of infesting many crop and non-crop hosts, SWD prefer certain plant species (Lee at al. 2011, Burrack et al. 2013, Poyet et al. 2015). We have selected three host crops in which to track spatial and temporal progression of fungi and bacteria, two preferred hosts (raspberry and blackberry) and one less-preferred host (blueberry). This seed money, will allow us to generate hypotheses about ways to exploit these microorganisms for management purposes, either through enhancing attractants or identifying deterrents. As a byproduct, we may also identify plant pathogens of these high value crops that may be of economic concern to growers. Objectives: Objectives. Our proposed project seeks to understand how SWD modifies the plant microbial community and to use this information to guide future management efforts. Our specific objectives are to: 1. To describe the bacterial and fungal communities found on three fruit species throughout the growing season, before, during and after infestation by SWD, and 2. Identify microbes in the community that may deter or attract SWD. Previous fruit phytobiome studies have done snapshot sampling at a single point in time, have been conducted on postharvest products in search of food-borne pathogens (Leff and Fierer 2013), or have studied the yeast communities of wine musts (Bokulich et al. 2014). We expect the microbiome of infested and uninfested fruits will differ in both species and abundance (following Hamby et al. 2012, Chandler et al. 2014). We predict that over time, fungal and bacterial diversity will increase following SWD infestation and will increase further in overripe fruit. We expect similar yeast species will be consistently present in all fruit species with SWD infestation and that these yeasts may include species previously observed in the western United States (Hamby et al. 2012). Finally, we expect that microbial communities present in overripe fruit will include members that will be unattractive or repellent to SWD. Our will be the first longitudinal study to use culture-independent methods to characterize the microbiome of these economically important crops. This will also be one of the first studies to simultaneously identify both bacterial and fungal species, increasing our knowledge about species interactions, competition and succession at the microscopic level. Beyond our main purposes to relate SWD infestation to the plant microbiome, we believe the information we generate will be valuable to researchers studying pathogenic bacteria and community ecology, and to growers by developing new methods to make disease management decisions.

Final Report:

Outputs This proposed project seeks generate knowledge about the interactions between Drosophila suzukii, commonly referred to as the spotted-wing drosophila (SWD) and the plant microbiome in order to develop new management tactics. SWD is a devastating invasive pest of soft-skinned fruit crops native to eastern Asia. Since its detected during late 2008 in both California and Italy, SWD has since spread to all fruit growing areas in the United States, Europe, and much of South America. Unlike other Drosophila species, female SWD prefer to lay their eggs in ripening and ripe, rather than rotting, fruit. Developing larvae cause loss by directly damage fruit and contaminating shipments, and egg laying alone may make fruit more susceptible to pathogen infestation (Rombaut et al. 2017). Blueberries, blackberries, raspberries, cherries, strawberries, and grapes have been the most impacted by SWD. There is zero tolerance for SWD infestation in fruit, which means that the detection of even a single larva can result in complete crop rejection. The potential annual crop losses due to SWD in the United States alone has been estimated at greater than $700 million (https://swd.ces.ncsu.edu/eastern-us-swd-impacts/), and this high risk has prompted both conventional and organic growers to dramatically increase prophylactic pesticide use. For example, blackberry growers in the southeast typically made two or fewer insecticide applications prior to 2010, when SWD was first detected throughout the region. Since SWD establishment, most blackberry growers now make weekly insecticide applications from fruit ripening through the end of harvest, resulting in at last eight applications directed at SWD alone. Wet weather, dense plant structure, incomplete harvest, and poor post harvest storage all increase infestation risk which cannot always be overcome by preventative insecticide use. Although SWD egg laying behavior and larval feeding niches differ from other flies in the genus Drosophila, they also share common traits. In particular, both SWD and other drosophilid adults are strongly attracted to odors associated with microbial products (yeasts, wines, vinegars, etc., Keesy et al. 2015). Drosophila flies have a close, well documented relationship with microbes. Fungi, particularly yeasts, serve as a food source and influence which hosts are used. Fly speciesspecific yeast strains are often intentionally introduced at the same time as eggs are laid (Gilbert 1980). SWD adults appear to contain their own specific microbial community including the yeasts Hanseniasprora uvarum, Issatchenkia terricola, and Pichia kluyveri (as determined via culture dependent methods, see Hamby et al. 2012) and a bacteria including Tatumella, Gluconobacter, and Acetobacter species known to associate with other drosophilds (as determined via molecular identification, see Chandler et al. 2014). It is likely that, similar to other drosophilids, SWD also influences the microbial community of its host plants and uses these microbes to enhance survival. We were, therefore, interested in understanding how SWD influences the microbial community in host crop plants over time. We believe that understanding the microbial profile of SWD infested plants will provide us with new routes of potential control.

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