Long-term trends in migrating Brassicogethes aeneus in the UK

The pollen beetle (Brassicogethes aeneus) causes significant yield loss in oilseed rape (Brassica napus). Predicting population changes remains a scientific challenge, especially since its phenology and abundance varies dramatically over space and time. We used generalized additive models to investigate the long-term trends in pollen beetle annual, seasonal and monthly counts from Rothamsted 12.2 m suction-traps. We hypothesised that the beetle's abundance is positively related to the area of oilseed rape at a national and regional level. We used random forest models to investigate the inter-generational relationship within years.

Although Brassicogethes aeneus annual counts and area of oilseed rape grown in the UK both increased by 162% and 113%, respectively, over the time period studied, they were not significantly related. The size of the immigrating pollen beetle population (up to 1 June) can be explained both by the size of the population in the previous summer and prevailing winter temperatures, indicating a positive feedback mechanism.

Currently, pollen beetle numbers continue to increase in the UK, meaning that control issues may persist. However the relationship between counts in spring, during the susceptible phase of the crop, and counts in the previous summer indicates that it may be possible to forecast the counts of the spring migration of Brassicogethes aeneus a few months in advance using suction-trap samples, which could aid decisions on control options. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.