Degree-day models reveal divergent flight phenology of invasive ambrosia beetles: implications for areawide management

Invasive ambrosia beetles present a severe threat to ornamental nurseries, particularly during spring months. However, divergent flight periods among species can create a continuous threat from early spring through mid-summer, making it critical to understand species-specific flight seasonality to optimize management. The primary objective of this study was to model the seasonal flight phenology and multi-generational dynamics of invasive ambrosia beetle species. A grid of ethanol-baited traps was deployed from April to September 2022 and 2023 within ornamental nurseries in Ohio. We used occurrence data to develop species-specific 5 and 10 °C degree-day (DD) models. We quantified 10 species of ambrosia beetles, including the predominant invasive species Xylosandrus germanus, followed by Anisandrus maiche, and then Xylosandrus crassiusculus. Xylosandrus germanus exhibited a comparatively short lag phase that corresponded to rapid trap captures early in the season. Xylosandrus crassiusculus showed a moderate lag, or slow initial accumulation phase, while A. maiche exhibited a prolonged lag phase before trap captures increased rapidly. Of the three key pest species, X. germanus reached 10% of trap captures at 11 DD, X. crassiusculus at 107 DD, and A. maiche at 477 DD. These results demonstrate that with the introduction of A. maiche, the window of infestation risk has broadened into a prolonged spring-to-summer threat due to their divergent flight phenologies.