Modeling the seasonal activity and infestation risk of <i>Drosophila suzukii</i> (Diptera: Drosophilidae) in U-pick blueberry orchards in Indiana, USA

Drosophila suzukii (Matsumura) is an important pest affecting small fruit crops worldwide. Given its short generation time and multiple, overlapping generations annually, population monitoring remains a critical integrated pest management strategy to detect and track population dynamics throughout the season. In this 3-year study, we leverage adult D. suzukii trap captures from Scentry monitoring traps to develop a degree-day model for this invasive fly in small (<25 acre) U-pick blueberry orchards in Indiana. Three common blueberry varieties ('Bluecrop,' 'Blueray,' and 'Elliott') were also examined to identify berry characteristics known to influence D. suzukii infestation. A two-parameter generalized logistic model explained ≥ 80% of the variance between cumulative degree days and the cumulative proportion of adults captured in monitoring traps in 2021, 2022, 2023, and across all 3 years combined. Based on the combined degree-day model, monitoring traps should be deployed in early June, as the first detection of D. suzukii typically occurred in mid-June. Additionally, the model predicts that peak activity, marked by 50% of cumulative trap capture, will occur by late July. The late season 'Elliott' berries were more susceptible to infestation, while firmer berries had lower infestation rates, regardless of blueberry variety. This research improves the predictability of D. suzukii activity and infestation risk in Indiana blueberry production.