Environmental conditions influencing seasonal population dynamics of Drosophila suzukii (Diptera: Drosophilidae) in mid-latitude organic farms

The local population dynamics of an invasive species are important for determining proper management. Temporal and spatial distribution can influence monitoring and treatment decisions, and understanding climatic influences on population size can help predict peak numbers. Drosophila suzukii (Matsumara, 1931) is an invasive fruit pest, and its seasonal dynamics vary across its range. We conducted a three-year trapping study with various modelling approaches to determine the environmental variables influencing D. suzukii population dynamics across all seasons in Kentucky, a temperate state with overwintering D. suzukii. Male and female flies were active in all seasons, visiting traps located on the ground and at plant height. Most flies were caught in the wooded edge habitat in all seasons, and crops only had more catches than the forest during summer. Population size was best predicted by a general additive model that included the average temperature 8 weeks before sampling and relative humidity in the two weeks before sampling, which differs from other models that have extremely low temperature as the most predictive weather variable. Our results indicate that the factors influencing D. suzukii population dynamics in Kentucky differ from those at higher or lower latitudes. We recommend monitoring average temperature leading up to fruiting to predict pest pressure. Further, our results suggest that the optimal time to monitor is when average temperatures exceed 21°C. Broadly, our findings highlight the need to investigate these factors on an appropriate scale to develop region-specific monitoring and management recommendations.