Variable pesticide exposure in pollen collected by honey bees and bumble bees during blueberry bloom: risk from crop and non-crop sources

Exposure to pesticides can result in diminished health and productivity of bees. Managed bees that are brought into agricultural fields for pollination are at risk from pesticides used to control crop pests such as fungal diseases and insect pests. However, for many crop systems we do not have a good understanding of the identity, levels, or sources of pesticide exposure for managed bees. To address these issues, during highbush blueberry bloom in Michigan, we collected pollen from foraging honey bees and bumble bees used for pollination. Farms in the study ranged in pest management intensity including untreated, organic, and conventional fields. We then screened the pollen for 260 pesticide compounds and identified the floral sources of the pollen through morphological identification. Higher concentrations of pesticides were found in the pollen from organic and conventionally managed farms compared to untreated farms. For both honey bees and bumble bees, the most products detected were fungicides. However, the greatest concentrations in honey bee pollen came from fungicides, while insecticides made up the largest concentration in bumble bee pollen.  Spray records from all farms were used to determine the degree of correlation between management activity and residues in the pollen, revealing bee exposure to highly toxic insecticides coming from outside the focal farms. The influence of landscape composition on pesticide residues was also determined, further highlighting the importance of surrounding landscapes for the pesticide exposure of managed bee hives. Our results will guide development of Best Management Practices to mitigate pesticide exposure to bees.