Bee bread collected by honey bees (Apis mellifera) as a terrestrial pesticide biomarker to complement water studies

Background: Pesticides in aquatic environments are frequently studied, yet those in terrestrial environments remain relatively unexplored. This study monitored bee bread collected from two apiaries located in a typical agricultural environment in Switzerland from March to August 2022 as a proxy for terrestrial pesticide inputs. The temporal appearance of the selected pesticides was compared to their profiles in the water of a small catchment within this area. Results: Overall, 62% (31 of 50) of the targeted pesticides were detected in bee bread, with occurrences in both apiaries largely overlapping (23 pesticides), demonstrating a similar agricultural landscape across the region. Furthermore, nine pesticides were detected in bee bread and water, two pesticides were detected only in bee bread, and two additional pesticides were detected only in water. Comparative temporal analysis revealed that pesticides with moderate-to-high movement potential [Groundwater ubiquity score (GUS) ≥ 2.19] appeared simultaneously in bee bread and water (azoxystrobin, boscalid, flufenacet and terbuthylazine). However, pesticides with low movement potential (GUS ≤ 1.86) showed different profiles in both matrices (cyprodinil, prosulfocarb, tebuconazole and thiacloprid), indicating the difficulty of predicting their fate, given that they adhere to soil particles and cannot be covered by current water monitoring programmes. Conclusion: Our findings present bee bread as a viable biomarker for monitoring pesticides by complementing the conventional water monitoring, and permitting a more comprehensive assessment of the exposure of terrestrial organisms to pesticides. Bee bread allows immediate recording of the applied pesticides and promptly reflects the seasonal variation in pesticide use. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.