Owing to its warm climate, Florida has a unique, early-season blueberry market valued over $84 million. Spotted wing drosophila (Drosophila suzukii Matsumura; “SWD”), 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 ACTTRA SWD, a new attract-and-kill product containing an 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 ACTTRA to untreated fields on two Florida blueberry farms (one conventional, one certified organic).
Objective 3: Monitor and identify hymenopteran parasitoids in fields treated with ACTTRA 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 ACTTRA-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 at three distances from the woods: 0m (woods edge), 20m (field edge), and 40m (mid-field) These distances represented our three treatments. This plot design was replicated four times in individual fields at site 1, a conventional farm, and replicated two times at site 2, an organic farm. Trap catch samples were collected and drowning solution replaced weekly. Lures were replaced monthly. Samples were transported to the University of Florida Small Fruit and Vegetable IPM Laboratory, immediately refrigerated, and processed during the week of collection. The number of male and female SWD, other drosophilids, other common blueberry pests, and natural enemies were counted in each sample. Collection began in early February and continued until mid-May in 2018 and 2019.
Objective 2 (ACTTRA evaluation)
During the 2019 field season, this study took place at a USDA Certified Organic commercial blueberry farm in Hawthorne, Florida. ACTTRA was applied at a rate of 1.5 L/acre in two of the three treatments. Treatments included: a) ACTTRA applied once every 7 days in addition to the grower’s standard (suite of conventional products including bi-weekly applications of organophosphates and pyrethroids) (ACTTRA-7d), b) ACTTRA applied once every 14 days in addition to the grower’s standard (ACTTRA-14d), and c) no ACTTRA applied (grower’s standard only; control). Plots were approximately 2.7 hectares (6.5-6.68 ac.) with four replicates. ACTTRA was applied to the bases or lower canopies of bushes, away from berries, using hand-pump backpack sprayers. The first application was made on 12 April, and the final application of all treatments was made on 10 May.
Adult D. suzukii density was evaluated using Scentry traps and lures (Scentry Biologicals, Inc., Billings, MT). Lures were replaced on the third week of the trial. Tap water with several drops of unscented dish soap was used as a drowning solution in each trap. One trap was deployed randomly in each treatment replicate. The contents from each trap were emptied into a collection jar, labeled, and stored in a cooler each week before transporting to the University of Florida Small Fruit and Vegetable Integrated Pest Management (SFVIPM) Laboratory for processing. The drowning solution was replaced weekly, and the number of D. suzukii per trap sample was counted by sex under a dissecting microscope.
To measure adult emergence, 100 ripe blueberries were randomly collected weekly from each replicate, stored in plastic containers, and incubated in an environmental chamber for three weeks at 24°C, 64% RH, 16:8 L:D cycle.The number of D. suzukii adults that emerged from each sample were counted by sex under a dissecting microscope.
Objective 3 (effect of ACTTRA on parasitoids)
One yellow sticky card (Great Lakes IPM, Vestaburg, MI) was deployed randomly in each replicate of the ACTTRA 2019 study and collected and replaced weekly. Any parasitoids caught on these traps were identified to family by Dr. Elijah Talamas at the Florida Division of Plant Industry. Using this data, we will observe any changes in natural enemy density and composition in treatment versus control plots.
Objective 4 (ACTTRA 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 ACTTRA plastic hangtag per plant (ACTTRA treatment) or no hangtag (control). Two grams of ACTTRA were applied to each hangtag. Each cage contained one 500 mL plastic Tupperware container of water with cotton wicks. A white sheet covered the cage base and white paper discs covered the 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. ACTTRA treatment and control plots will each be replicated five times.
Choice experiments. All aspects of experimental design and protocol were the same as described for no-choice experiments, but each cage contained one ACTTRA (treatment) plant on one longitudinal end of the cage and one control plant on the other end.
ANOVA with repeated measures was used to evaluate mean adult SWD captures per trap across weeks, treatments, and farms in seasonal monitoring studies and the ACTTRA field study. Differences among male and female densities per trap and differences among adult emergence rates were analyzed. We will separate means using Tukey’s HSD when required. Differences in parasitoid family composition among treatments in the ACTTRA study will be analyzed using principal components analysis. ANOVA will be used to compare mean fly mortality and adult emergence by treatment in cage experiments.
Preliminary data from our 2019 ACTTRA field study suggests that ACTTRA does not provide significantly better control of SWD larvae when added to the grower’s standard management program (fig. 1). This is in opposition to data collected in a similar field study in 2018 performed on a conventionally managed farm, in which we observed significantly fewer SWD adults emerge from blueberry samples collected in ACTTRA-treated plots (fig. 2). We did not observe a significant effect of ACTTRA on total adult trap catch (males and females) or female trap catch (figs. 3-4), but we did see a significant difference in the number of males trapped by treatment (fig. 5). In 2018 adult emergence data and 2019 male trap catch data, we did not observe an effect of application frequency on the level of larval control provided by ACTTRA, suggesting growers can apply ACTTRA biweekly and achieve the same control compared with weekly applications. More research must be done at multiple sites to confirm these findings.
Seasonal monitoring data, parasitoid data from the 2019 ACTTRA evaluation, and ACTTRA cage studies have not yet been statistically analyzed.
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 ACTTRA 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. 2019 ACTTRA evaluation data will be presented at the Entomological Society of America national meeting in November 2019.
Data is inconclusive as to whether ACTTRA provides significantly better control of SWD larvae when added to the grower’s standard management program. Because ACTTRA 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. We suspect that growers will see higher yields and more stability in Florida’s valuable, niche blueberry market. In 2018, we observed that biweekly ACTTRA 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 ACTTRA is a tool that my advisor and I can recommend to growers for increased control of spotted wing drosophila (SWD) larvae. However, more field studies on both conventional and organic farms should be performed to confirm these findings. 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 ACTTRA component of this project, I learned the importance of a multi-faceted management program for sustainable blueberry production. I also found that Florida’s commercial blueberry farmers are eager to adopt emerging technologies that can reduce their insecticide use.
Options for future study include evaluation of ACTTRA 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.