Pesticide risk to honey bees in sweet cherry, white clover, meadowfoam, and carrot seed production of Oregon

Risk assessment for pesticide side effects to honey bees (Apis mellifera L) assumes exposure entirely originates from the crop where the pesticide is applied. Yet, colonies in agricultural environments forage on a wide range of surrounding crops and wild plants. Consequently, the actual risk of a pesticide to colonies pollinating a specific crop may vary considerably from risk-assessment predictions, depending on how much foraging activity is devoted to the treated crop and how much toxic pesticide residue is on adjacent crops or wild-flowering plants.

In order to test the adequacy of current risk assessment assumptions around honey bee exposure to pesticides, we investigate pesticide residues in pollen collected by honey bees pollinating four Oregon crops from March to August of 2020; sweet cherry, white clover, meadowfoam, and carrot seed. In total, thirty-one agricultural sites were monitored for pesticides to understand pesticide risk. Sixty-three pollen samples—collected at early, peak, and late bloom for each crop—were analyzed for over 250 pesticide residues. We then sorted composite pollen samples and identified the major plant species within each color of pollen. These sorted samples were then tested again for pesticides and compared to the original composite test, allowing us to identify species of plants which disproportionately contribute pesticide risk to the composite sample. We then determined the extent that current risk-assessment assumptions of exposure, sourced primarily from bee-pollinated crops, aligned with our data. These results point towards a more comprehensive framework to assess risk of pesticides to honey bees in agricultural systems.