Automated long-term field monitoring reveals diel and seasonal activity patterns of Drosophila suzukii.

Drosophila suzukii is a globally invasive pest causing substantial losses in soft fruit production systems. While diel activity has been studied under laboratory conditions, long-term high-resolution field data remain scarce. Here, we present a multi-year automated monitoring dataset from four field sites in South-West Germany (2017-2019) using traps sampling at 3-hour intervals, combined with high-resolution environmental data. Across the study period, D. suzukii exhibited strong seasonal dynamics, with low activity in winter and early spring, increasing in late spring and summer, and declining in autumn. Diel activity patterns were not constant but varied with seasonal abundance and environmental conditions. During periods of high activity, captures were concentrated in daylight hours and often showed bimodal peaks in the morning and late afternoon. In contrast, during low-abundance periods, diel patterns were weak or absent. Temperature effects on capture rates were season-dependent, showing positive associations in late spring and autumn but negative associations in summer. Rain consistently reduced capture rates across all seasons, whereas wind showed weaker and less consistent effects. Overall, our results show that diel activity of D. suzukii emerges under specific seasonal and environmental conditions rather than being a fixed behavioural trait. The custom-built automated trapping system proved reliable for high-frequency field monitoring and provides a scalable approach for other small insect monitoring systems. These findings emphasise the importance of considering both temporal resolution and environmental context when interpreting trap data and designing pest management strategies.