Owing to its warm climate, Florida has a unique, early-season blueberry market valued over $84 million. Spotted wing drosophila (Drosophila suzukii Matsumura), a global, invasive pest of small, soft-skinned fruits, has become a significant pest of Florida’s blueberries over the last decade by rendering ripe fruit unmarketable. Currently, heavy pesticide use is the only feasible and effective control for this pest. The high cost of pesticides and the development of resistance threaten to collapse Florida’s niche blueberry market, and excessive pesticide use endangers farm workers and non-target organisms like pollinators, beneficial insects, fish and wildlife.
This project’s aim is two-fold: to thoroughly map seasonal timing and patterns of SWD migration from woodlands into blueberry fields; and to evaluate the efficacy of SPLAT (Specialized Pheromone and Lure Application Technology), a new attract-and-kill product containing a SWD-specific fruit volatile-based attractant and a low-risk, naturally derived pesticide, to control SWD populations. Understanding spatio-temporal patterns of SWD migration and utilization of attract-and-kill technology can facilitate more targeted pesticide application, reducing the amount of pesticide used, reducing costs for farmers, limiting pesticide exposure, and improving environmental quality.
Objective 1: Monitor season-long adult SWD population density and map migration phenology along a woodland-to-cropland gradient on two Florida blueberry farms (one conventional, one certified organic).
Objective 2: Compare adult and larval SWD population density in fields treated with SPLAT to untreated fields on two Florida blueberry farms (one conventional, one certified organic).
Objective 3: Monitor and identify athropod natural enemies in fields treated with SPLAT and compare to untreated fields on two Florida blueberry farms (one conventional, one certified organic).
Objective 4: Compare adult SWD mortality and larval infestation using choice and no-choice cage experiments between SPLAT-treated and untreated blueberry plants.
Objective 1 (seasonal monitoring): Three Scentry traps containing SWD lures (Scentry Biologicals, Inc. Billings, Montana) were placed along three 25 m transects beginning at the woodland margin and extending into the blueberry field, 8.5 m apart. This plot design was replicated four times in individual fields on two separate sites, a conventional farm and an organic farm. Trap catch samples are currently being collected and drowning solution replaced weekly. Lures are being replaced monthly. Samples are refrigerated and processed during the week of collection. We have been recording numbers of male and female SWD, other drosophilids, other common blueberry pests, and natural enemies. Collection began in early February and will continue until early May. We hope to observe seasonal changes and timing of SWD migration into cultivated fields.
Objective 2 (SPLAT evaluation): We will apply SPLAT (0.25% spinosad) at a rate of 1.5L/acre to two 5-acre plots, each with three replicates. Treatments will include SPLAT application every 1) 7 days, 2) 14 days, and 3) no SPLAT (control). A total of nine plots will be used at each of the two farms. Each plot will contain two Scentry traps with lures and one yellow sticky card. Trap samples and sticky cards will be collected and processed weekly, and the same taxa as outlined in Objective 1 will be recorded. Lures will be replaced monthly. This experimental design will be repeated once at a conventional farm and once at an organic farm for comparison. We will collect approximately 1.9 L ripe blueberries from each replicate in all plots on weeks three and six of the SPLAT trials. Three quarters of fruit volume will be incubated for 2-3 weeks to quantify adult emergence. One quarter will undergo a salt test to quantify larval infestation. Larval infestation data will be compared to adult trap captures to evaluate the potential of each monitoring method to predict in-field SWD populations.
Objective 3 (effect of SPLAT on natural enemies): Yellow sticky cards will be collected weekly from SPLAT and control plots, and all parasitoids will be identified to family. Any SWD or common blueberry pests will also be recorded. Through this data, we will observe any changes in natural enemy density and composition in treatment versus control plots.
Objective 4 (SPLAT evaluation cage trials): No-choice experiments—50 SWD (1:1 ratio of F:M) were released in 4 x 2 x ft. mesh cages. Each cage contained two two-year-old blueberry plants with one plant at each longitudinal end of the cage. Five mesh satchels, each containing five store-bought, organic blueberries were randomly hung from each plant. Both plants per cage either had one SPLAT plastic hangtag per plant (SPLAT treatment) or no hangtag (control). Two grams of SPLAT were applied to each hangtag. Each cage will contain one 500 mL plastic Tupperware container of water with cotton wicks. A white sheet covered the cage base and white paper discs will cover soil surface of each plant to facilitate observation of dead flies. Every 12 hours after introduction of flies, dead flies were removed by hand and counted. After 72 hours, berry satchels were removed from plants, and berries were incubated for three weeks to compare adult emergence between treatment and control cages. SPLAT treatment and control plots will each be replicated ten times.
Choice experiments—all aspects of experimental design and protocol were the same as described for no-choice experiments, but each cage contained one SPLAT (treatment) plants on one longitudinal end of the cage and one control plant on the other end.
Both choice and no-choice experiments were recently completed, and data have not yet been statistically analyzed.
ANOVA with repeated measures will be used to evaluate mean adult SWD captures per trap across weeks, treatments, and farms in seasonal monitoring studies and SPLAT field trials. Differences among male and female densities per trap and differences among larval infestation rates will also be analyzed. We will separate means using Tukey’s HSD when required. We will utilize geostatistical analyses to observe seasonal migration in the monitoring studies. ANOVA will also be used to compare mean fly mortality and larvae per gram of fruit in cage experiments.
Note: This report is based on findings from preliminary research activities performed last season (2018) that were not funded by this southern SARE graduate student grant but evaluated similar objectives.
Preliminary data from our 2018 SPLAT field evaluation suggests that SPLAT provides significantly better control of SWD larvae when added to the grower’s standard management program compared to the grower’s standard only (control) (figs. 1-2). Although we did not observe an effect of SPLAT on adult trap catch (fig. 3), we consider larval density to be a better measure of pest pressure and blueberry injury. Adults are highly mobile and are not responsible for most berry injury. We did not observe an effect of application frequency on the level of larval control provided by SPLAT (figs. 1-2), meaning growers can apply SPLAT biweekly and achieve the same control compared to weekly applications.
Seasonal monitoring data (2018) and natural enemy data from the 2018 SPLAT evaluation have not yet been statistically analyzed. SPLAT cage trials funded by this SARE grant (2019) were completed last week, and have not yet been analyzed. All other research funded by this grant is currently underway.
Educational & Outreach Activities
We provide regular consultation to our participating growers and keep them abreast of current on-farm SWD pest pressure and findings from our research. I presented preliminary SPLAT field findings (2018) at the Entomological Society of America Southeastern Branch annual meeting in March 2019 and discussed SWD trapping methods and efficacy at a University of Florida Doctor of Plant Medicine Program event called Natural Area Teaching Lab Trap Day.
Preliminary data suggests that SPLAT provides significantly better control of SWD larvae when added to the grower’s standard management program compared to the grower’s standard only (control). Because SPLAT is applied to a localized area, specifically attractive to SWD, and utilizes an OMRI-approved reduced-risk insecticide, we believe it has a lower overall impact on non-target organisms, environmental health, and poses less health risk for farmers and farm employees compared to a traditional foliar spray. Because SPLAT provides added SWD control, growers will see higher yields and more stability in Florida’s valuable, niche blueberry market. We also observed that biweekly SPLAT applications provide the same level of SWD larval control as weekly applications, which can save growers time, money, and labor.
Preliminary data (2018) from the attract-and-kill component of this project suggests that SPLAT is a tool that my advisor and I can recommend to growers for increased control of spotted wing drosophila (SWD) larvae. While researching the monitoring component of this project, I learned how to effectively deploy and service traps for SWD, identify and count SWD, and analyze trap data. In investigating the SPLAT component of this project, I learned the importance of a multi-faceted management program for sustainable blueberry production.
Options for future study include evaluation of SPLAT for SWD control alone, in absence of the grower’s standard. Because the SARE-funded research is currently underway, the final report will share results from the other objectives of this project.