Pesticides distribution and chronic honeybee colony exposure in Swiss agricultural landscapes

Due to their foraging behavior, honeybees interact with the environment. In agricultural landscapes, honeybees play a crucial role as pollinators collecting pollen and nectar from mass-flowering crops, orchard and vineyards which provide important resources for honeybees. Therefore, pesticide contamination of bee products is a widespread phenomenon. In the agricultural landscapes of western Switzerland, an ultra-trace level determination of neonicotinoid analysis was performed. A total of 200 honey and pollen samples from 30 apiaries over three years were analyzed based on efficient modified quick, easy, cheap, effective, rugged, and safe extractions (QuEChERS) followed by a UHPLC-MS/MS quantification. Furthermore, brood size and pollen stocks area were evaluated using ColEval method to assess the sublethal chronic honeybee colonies exposure. 94% of our samples contained at least one of the targeted neonicotinoids, 63% of the samples were contaminated by doses greater or equal to 0.1ng/g and 62% of the samples contained two or more neonicotinoid. Thiacloprid and acetamiprid were the most frequently detected molecules. Also, this study found traces of banned or highly regulated neonicotinoids, suggesting their persistence in the environment. The incidence of contamination was higher in honey than in pollen samples, indicating a more frequent occurrence. The prevalence was higher in pollen samples, suggesting higher levels of contamination per samples. The fact that pollen samples were grouped by period ensured greater consistency than honey samples for long-term analysis of pesticide residues. Samples from apiaries located in crop-dominated landscapes were found to be more contaminated than samples from grassland-dominated landscapes. Finally, this study showed that a cumulated concentration of neonicotinoid found in spring pollen samples reduced the surface area of further pollen stocks and brood size. These results may argue in favor of the deleterious effects of larval exposure to a mixture of neonicotinoid and other pesticides on the foraging capacity of newly emerged bees. Moreover, these results might indicate a deleterious indirect effect of contaminated pollen on nurse bees’ foraging. Further efforts should focus on monitoring honeybee colonies exposure to a mixture of pesticides in agricultural landscapes and could integrate farmers’ practical management as a reference for sampling.