Pesticide concentrations in bees and other matrices collected from sunflower fields (with and without a neonicotinoid seed treatment) near Sacramento, California

Hybrid sunflower production occurs near Sacramento in Northern California where seed treatments are commonly used. In this study, four locations were sampled in 2016 as matched pairs; half of each field was sown with thiamethoxam treated seed and half without. In addition to the thiamethoxam seed treatment, all seeds were coated with two fungicides, fludioxonil and mefenoxam/metalaxyl. Both wild bee and honey bee pesticide exposure was assessed by analyzing field soil, sunflower pollen and nectar, honey bees (pollen and nectar foraging) and a sunflower specialist wild bee, Melissodes agilis. Samples were extracted via pressurized liquid extraction (except nectar which underwent a room temperature solvent extraction) with an organic solvent followed by solid phase extraction cleanup. Samples were analyzed for 168 pesticides and degradates using both gas and liquid chromatography-tandem mass spectrometry. While only one of the three seed coating pesticides (thaimethoxam) was detected, 25 other pesticides and degradates were also measured. In total, 5 insecticides, 9 herbicides, 7 fungicides, and 5 degradates detected across all matrices. There were 7 pesticides and degradates detected in M. agilis, 4 in honey bees, 6 in nectar, 6 in pollen, and 23 in soil. These results indicate the bees visiting sunflower fields are exposed to more pesticides than those used as seed coatings including those pesticides applied to other nearby crops (e.g., rice, tomatoes and walnuts).