This design was implemented based on the assumption that volatiles from treatment plots may be blown or diffuse beyond treatment plots. Berries were brought to the laboratory to determine number of eggs in fruit for each of the plots using a dissecting microscope. All soft or damaged fruits were excluded when assessing presence of eggs. In some cases, at first fruit color, laboratory-reared D. suzukii flies were released in each plot with the intent to create a relatively even pest pressure in all plots. Colonies of D. suzukii used in field studies consisted of seasonally collected wild adults from multiple field sites in the Willamette Valley, Oregon, and Oxnard, California. Collected adults were released into plastic cages and reared at 24°Cand 70% relative humidity, with a 16:8 h photo period before being released in the respective field trials. Flies were constantly provided with water and artificial diet that served as both a food source and an oviposition medium. Before their use in experiments, blueberry container all flies were allowed to mate for 8 d in mixed-sex cages. Some small fruit varieties were numbered since this information is proprietary.
A replicated field trial on drip-irrigated Pinot noir winegrape was conducted in Yamhill County, Oregon, USA from 10 to 18 October 2019 on ~2.6 hectares. Vines were spaced at 1.5 by 5 m, and trellised on a standard four wire trellis system, supporting a ~2 m canopy. Rows were oriented along a north-south direction on an east facing slope. Three treatments , were included with ~0.056 ha plots. No pesticides were applied during the experimental period. Here, there were 28 GUM and buffer plots each and 18 UTC plots. GUM dispensers were applied on 10 October and ten berries were collected from each plot on this date. Sampling dates were 11, 14, and 18 October 2019.Trials were conducted in a commercial sweet cherry orchard located at the Mid-Columbia Agricultural Research and Extension Center , Hood River, Oregon, USA. A 1.12-hectare orchard was divided into twelve plots . UTC, buffer, and GUM plots were replicated four times. The GUM dispensers were deployed on day 0 . No insecticides were applied to the orchard for the duration of the experiment. Here, an additional 200 mated 8- to 12-day-old D. suzukii were released in the center of each plot on a weekly basis on 23 June, and 1, 8, and 15 July 2020 . Data were collected for 35 days from 16 June through 22 July 2019. Because of relatively large canopy size of cherry trees compared to the other crops, ten cherries were collected from the lower , middle , and upper portions of the central two trees in each plot weekly.
The trial was conducted in an organic highbush blueberry planting on 23.76 hectares in Independence, Oregon, USA . The experiment began on 9 July and continued through 11 September 2020. There were three treatments: UTC , grower standard , and GUM. Grower standard applications targeting D. suzukii at the registered field rate included spinosad , peroxyacetic acid and Chromobacterium subtsugae . Each treatment had 12 plots, and each plot was ~0.66 hectare. GUM dispensers were deployed on 9 and 13 July , and on 9 and 22 August 2019. Blueberries were collected every two days for the duration of the experiment. One fruit sample was collected in each of the respective 36 plots. Collected samples were at least 20 m from the edge of the crop and each sample contained 10 blueberries collected from the interior of the bush at ~0.75 m from the ground.Trials were conducted in 1.8 hectare of highbush blueberry plants . The experiment ran from 6 October to 15 October 2020. There were three treatment levels i.e., UTC , buffer , and GUM. The GUM plots were located directly next to the buffer, followed by UTC plots of equal size. Plots were each ~0.05 hectares . Spinosad was applied on 6 October on the UTC and buffer areas. Insecticide application and GUM deployment occurred only on 6 October. On 8, 10, 13 and 15 October, one fruit sample consisting of 10 berries was collected from each of the 36 plots. Samples were collected at least 20 m from the edge of the crop and at ~0.75 m above the ground.This trial was conducted in Oxnard, California, USA on highbush blueberry plots during 2020. Plants were irrigated with three drip stakes per plot ten times a day for ten-minute intervals delivering 1.1 liters of water per hour. Screenhouses were fully enclosed with screen material to prevent insects from entering.
There were three 70 m x 5 m screenhouses with GUM or UTC treatment randomly assigned to the north or south end of each screenhouse for a total of 6 plots. Within each screenhouse, treatment plots contained twelve plants in two rows, and plots were separated by 45 m. one-hundred flies were released in each plot four times, once per week. Three GUM deployment plots were compared with three UTC plots. GUM dispensers were installed in every other plant with irrigation stakes placed directly through the pads. The GUM application was completed on 14 April. Plots were sampled every seven days from 14 April to 12 May. One sample consisted of 50 berries.Ten field trials were conducted from September to November 2020 across multiple coastal production regions in California, USA , at different ranches and on multiple varieties being grown under high tunnels. Each location was a replicate consisting of two plots and were randomly assigned at each ranch to GUM or to UTC. Plots within a ranch received similar irrigation, fertilizer, and insecticides. Each plot received a minimum of four spinosad sprays timed 7-10 days apart during the cropping period and based on monitoring trends from fruit collections. Additional peroxyacetic acid applications were applied at 2-3 day intervals after each spinosad application, followed by a C. subtsugae application 1-2 d after each peroxyacetic acid application. Throughout the experimental periods, GUM dispensers were distributed evenly throughout each plot and replaced every 21 days. GUM dispensers were staked directly under the drip line in soil plots, and irrigation stakes were placed directly through the dispenser in substrate plantings. Six fruit samples were collected from each treatment plot every week for 4 to 12 weeks. Samples were collected at least 2 m from each edge of the tunnel as well as from the center of the tunnel approximately 20- 30 m from the edge of the tunnel and at ~0.75 m from the ground. Each sample consisted of 50 berries. Sample berries were incubated at room temperature for 2-4 days to allow for larval growth and facilitate detection. Samples were evaluated by crushing fruit and submerging them in a saltwater solution . The crushed fruit solution was then poured into a tray where D. suzukii larvae subsequently floated to the top of the solution and were counted. A trial was conducted in a 4.85 ha blackberry field with cultivar Prime-Ark® 45, in Salinas, California, USA in 2020 . Each treatment consisted of 7 plots: UTC, , GUM, or GS + GUM. Each plot was approximately 0.23 hectares. Two insecticide treatments were applied on 19 and 25 September in the GS and GS + GUM plots. The GUM dispensers were deployed on 21 September 2020, three days before the first sampling, and reapplied on 8 October 2020 in the GUM and GS + GUM treatments. The gum was placed under drip emitters. Blackberry samples were collected twice per week with one pre-treatment collection occurring before the insecticide treatments and gum deployment. Each sample consisted of 300 blackberries for each plot. Biweekly collections continued for 5 weeks after the pretreatment count. Samples were evaluated 3 to 4 days after collection to allow larvae to develop and the number of D. suzukii eggs and larvae were counted under a stereo-microscope .The current study supports findings from previous laboratory and small-scale field cage trials. Here we show through field collected and modeled data that food-grade gum use can reduce D. suzukii fruit damage . The aim of this work was to acquire detailed knowledge about limitations of food-grade gum in a range of commercial cropping systems including growing blueberries in container, blackberry, cherry, raspberry, strawberry, and winegrape. These studies were conducted in two key production regions i.e., California and Oregon in the USA.
The overall results supported initial findings and provided additional evidence that this tool can reduce D. suzukii crop damage especially when applied together with the grower standard. Both field-collected data and model simulations indicates that there is a synergistic effect of food-grade gum when used in combination with a conventional insecticide. For most of the experiments , field plots receiving the food-grade gum resulted in either numerical or statistical differences in D. suzukii damage compared to untreated control plots. This was not recorded for the cherry, strawberry, and blackberry trials. Reasonable hypothesis about these data are discussed below. In trials where D. suzukii infestations were measured in buffer plots , there was evidence of a reduction in damage, but not at the same level as in plots treated by the food-grade gum. Overall, considering all the trials, crop damage was reduced up to 78% over a period of up to 21 days post application of the food-grade gum. The results from the current study indicate that the food-grade gum can be used in combination with standard insecticides , and in some cases as a stand-alone treatment to reduce the infestation level of D. suzukii. Similar reductions in D. suzukii damage were reported under laboratory and controlled semi-field conditions , suggesting that the food-grade gum resulted in lower damage due to oviposition. These findings support earlier results where the effects of semiochemical volatiles emanating from the food-grade gum resulted in significant behavioral changes . In several trials, data lower oviposition and fruit infestation in the presence of the food-grade gum under field conditions. Reasons of why in multiple trials a statistical difference was not reached, can be explained by multiple parameters observed by scientists and growers such as animals removing the cottons pads, water-irrigation issues, and wind. These factors are addressed in a future publication . In the Hood River cherry trial, constant windy conditions may have resulted in dispersion of volatiles, ultimately resulting in impacts that were less pronounced. There is little doubt that efficiency of the food-grade gum can vary depending on production conditions and crop . Host preference of D.suzukii was ranked 4th for cherry, followed by blueberry and winegrape . Such differences in host preference should be considered when applying food-grade gum. Synthetic blends can be less attractive compared to the actual fruit; thus, additional adjustments may be required to minimize egg-laying in the fruit. Results showed that the application of the food-grade gum in grape shows clear impacts to protect berries from D. suzukii attack. Considering the vulnerability of several winegrape cultivars towards D. suzukii and the encouraging results collected, we have reasons to believe that the food-grade gum can be a useful tool for the winegrape production. For the food-grade gum applications in blueberry in open field experiments, the infestation rate for the food-grade gum and grower standard were 70% and 85% lower than that for untreated control respectively, with the food-grade gum treatment resulted in a significantly lower infestation rate compared with the control. Open and semi-field experiments conducted in California provide similar outcomes to those in Oregon. Blueberry experiments conducted in California within a screenhouse provided 45.5% egg reduction. There were sequential applications with differing timing and the results indicated that early applications resulted in lower egg reductions . A potential hypothesis for this phenomenon could be related to environmental conditions including temperature and humidity that could significantly change the emission of plant volatiles . Egg reduction in raspberry and blackberry varied from 42-90% and 24-70% respectively. Two cultivars of raspberry have been subjected to the trial and in both cases there was reduction in egg infestation. Results were consistent between the different locations. For strawberry, in several cases results showed numerically increased larval levels compared in the food-grade gum treatments. A potential hypothesis for this phenomenon could be related to either unreported production practices or environmental conditions that could significantly change the emission of plant volatiles or the food-grade gum. Other reasons that can justify the negative results, range from lack of irrigation to rodents removing food-grade gum within a day of placement .