Data from: Honey bee dietary neonicotinoid exposure is associated with pollen collection from agricultural weeds

Neonicotinoid insecticides have been linked to bee declines. However,
tracking the primary exposure route for bees in the field has proven to be
a major logistical challenge, impeding efforts to restore pollinator
health in agricultural landscapes. We quantified neonicotinoid
concentrations and botanical species composition in 357 pollen samples
collected from 114 commercial honey bee colonies placed along a gradient
of agricultural intensity between June and September. Neonicotinoid
concentrations increased through the season, peaking at the end of August.
As a result, concentrations in pollen were negatively associated with
collection from woody and crop plants that flower early-mid season, and
positively associated with collection from herbaceous plants that flower
mid-late season. Higher clothianidin and thiamethoxam residues were
correlated with samples containing a greater proportion of pollen
collected from agricultural weeds. The percentage of agricultural land
within 1,500 m was positively correlated with thiamethoxam concentration;
however, this spatial relationship was far weaker than the relationship
with the proportion of pollen collected from herbaceous plants. These
results indicate that both plant species identity and agricultural
dominance are important in determining honey bee neonicotinoid exposure
through the pollen diet, but that uncultivated plants associated with
agriculture are the source of the greatest acute exposure.