Fungicides are often used to manage diseases in Michigan orchards at the same time that bees are providing crop pollination. New research suggests that fungicides have sub-lethal effects for honey bees, such as synergism with other pesticides, decreased immune function, gut microbe interference, and increased larval and colony mortality. Quantifying field-level fungicide exposure to honey bees and understanding how bees interact with orchard crops during bloom is important for developing management practices that protect orchard crops and the bees that provide pollination. At each of three sites (two orchards and one non-orchard), we sampled eight commercial honey bee hives for nurse bees, foragers, larvae, pollen, bee bread, and wax over three consecutive years. Samples were analyzed for the presence of common spring fungicides to assess exposure levels at different time intervals centered around tart cherry bloom. Pollen was identified using DNA sequencing to determine important floral resources and identify possible sources of pesticide exposure. Our results suggest that honey bees that are within foraging range of cherry and apple orchards are exposed to fungicides in the spring, even if the hives are not being rented for pollination. Many of the detected fungicide residues are at levels known to cause negative health effects for honey bees based on previous lab studies. Possible implications on honey bee health based on the detected residue levels are discussed. New and refined best management practices to reduce fungicide exposure to bees during bloom are suggested for orchard growers and beekeepers who rent their hives for pollination services.
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