Agrochemical occurrence on colocated wildflowers and wild bees collected near beef cattle feed yards and row crops

It is well established that agrochemicals can pose significant threats to native pollinators; however, relatively little is known about pollinator risks associated with agrochemicals that are used on beef cattle feed yards. Recently, feed yard-derived agrochemicals and those from row crop agriculture were quantified on wildflowers growing on the High Plains, USA. To better characterize pollinator risks on the High Plains, we collected colocated wildflowers and foraging bees across three field seasons for analytical determination of residual agrochemicals. Agrochemicals were detected and quantified on the majority of wildflowers (85%) and nearly half of bees (49%). Permethrin was the most frequently detected analyte on wildflowers (32%) and bees (17%). Flower hazard quotients and flower hazard indices were calculated to deterministically evaluate risk to foraging pollinators. Mean flower hazard quotients exceeded one for 5/16 analytes (31%), and flower hazard quotients calculated for 30% of wildflowers were greater than 50. Flower hazard quotients for clothianidin exceeded 400 for 14% of wildflowers, which portends conditions conducive to frequent bee mortalities. Flower hazard indices were greater on wildflowers from mid-July to mid-September as compared with wildflowers collected earlier in the summer, which coincides with row crop planting and increased prevalence of feed yard flies. Hazard quotients and hazard index values calculated from agrochemical residue data suggest that pollinators frequenting wildflowers near beef cattle feed yards and row crops on the High Plains are at risk from both individual sources, and more so when considered in combination. (C) 2021