Spotted-wing drosophila, Drosophila suzukii (Matsumura), an economically damaging invasive species of numerous fruit crops, was first detected in Minnesota in 2012. High fecundity, and short generation times facilitated a rapid rise in the global pest status of D. suzukii, particularly in North America and Europe. To date, the majority of crop injury research has focused on fruit crops such as blueberries, raspberries, and cherries. However, little is known regarding the impact of D. suzukii on the wine grape industry in the upper Midwest region of the United States. Field trials were conducted in Minnesota during the summers of 2017–2018 to examine season-long phenology of D. suzukii in wine grape vineyards and wineries, and to assess the efficacy of exclusion netting for control of D. suzukii. Four treatments were evaluated, 1) open plot check (control), 2) open plot treated with an insecticide, 3) exclusion netting, and 4) exclusion netting, with artificial infestations of D. suzukii adults. Exclusion netting was applied at véraison and removed at harvest. On each sample date, 20 berries (10 intact and 10 injured) were collected from each plot for dissection. The number of larvae and adults were recorded for each berry to determine infestation levels. As shown by mean larval infestations and injured berries across treatments, exclusion netting provided a significant reduction in the level of D. suzukii infested berries when compared with the untreated check. These results indicate that exclusion netting could provide an effective alternative management strategy for D. suzukii in wine grapes.

No abstract

Popillia japonica (Newman), is a highly polyphagous, invasive species, first recorded in the U.S. in 1916, and detected in Minnesota in the late 1960s. Historically, research on this pest in the Midwest U.S. has focused primarily on ornamental and turf crops, with little attention placed on adult feeding damage to fruit crops. Recently, wine grape producers in the region noted substantial increases in defoliation from P. japonica feeding, confirming concerns for this perennial high value crop. To address these concerns, studies were conducted during the summers of 2020–2021 to understand the impact of P. japonica foliar feeding on the quality and yield of wine grapes. Trials utilized vines of the wine grape variety, ‘Frontenac.' In addition to open plots, whole vines were caged within fine mesh netting and infested with P. japonica at 0, 25, 50, and 100 beetles per meter-row of vine. Beetles used for infestations were collected from natural field populations of P. japonica and left to feed until grapes were ready for harvest. During harvest, data collection included leaf samples for obtaining average percent defoliation, cluster weights, and berry subsamples for soluble solid content, pH, titratable acidity, and phenolic compound measurements. Results from these studies demonstrated that as beetle population density and defoliation per m-row increases, at-harvest measurements of quality parameters are significantly and negatively affected (P < 0.05) when compared with uninfested vines. The negative impacts to fruit quality exhibited in these studies will be important in the development of future management strategies for P. japonica in ‘Frontenac.'

Japanese beetle, Popillia japonica (Newman), was first detected in the United States in New Jersey in 1916. The beetle gradually spread to the Midwest U.S. region, and was first confirmed in Minnesota in the late 1960’s. Popillia japonica has subsequently become a major invasive insect pest in turfgrass and several agricultural crops. As P. japonica continues to spread throughout the U.S., and other countries, it is important to develop efficient ways to monitor adult populations, and where possible, forecast the phenology of adult population dynamics. During 2019-2021, field trials were conducted to develop a degree-day model that can be used to forecast P. japonica adult phenology under Minnesota, and Midwest summer climatic conditions in. We used commercially available traps and lures to monitor adult flight phenology, specifically beetle trap-catch, along with weather data at four locations in Minnesota, to relate ambient field temperatures to population phenology. The concordance correlation coefficient (CCC), an index of both precision and accuracy, was used to develop a final degree-day model. Model development included evaluation of simple and sine-wave degree-day calculation methods, start dates between 1 Jan. and 1 April, and a range of lower (0-15 °C) and upper (20-37 °C) thresholds. The optimum model was found to be a simple degree-day calculation, using a biofix date of 1 Jan, and lower and upper thresholds of 15 and 21.7 °C, respectively, for predicting 10% beetle trap-catch. The model will aid in future integrated pest management (IPM) and regulatory strategies by providing a tool for prediction of P. japonica adult flight phenology.

Acknowledgments: The authors thank Adam Toninato, Sarah Holle, and Izzy Bur (UMN Fruit & Vegetable lab) for assistance with data collection and treatment applications. A special thanks to John and Jenny Thull and Drew Horton (UMN Horticultural Research Center) for sharing their knowledge and expertise in winegrapes and assisting with data collection and trial processes.