Abstract
The alfalfa leafcutting bee (LCB) (Megachile rotundata Fabricius) is a solitary, managed pollinator widely used in North American agriculture to produce alfalfa and hybrid canola seed. Despite its economic importance, and known sensitivity to certain pesticides, little is known about the specific pesticide residues LCBs encounter during pollination, and toxicity data for this species remains limited. To determine what residues LCBs are commonly exposed to, we screened larval LCB provisions from nine alfalfa sites during pollination in southern Alberta for 69 pesticide residues. Eight residues amongst three classes of pesticides were detected including four fungicides (boscalid, cyprodinil, fludioxonil, and pyraclostrobin), three insecticides (chlorpyrifos, cyhalothrin lambda, and deltamethrin), and the herbicide Velpar (hexazinone). Using the residue data, we calculated site-specific hazard quotients (HQ) using Apis mellifera L. LD50s to provide context for exposure risk. Sites with residues from multiple pesticide classes tended to have higher-though not always significantly higher-HQs than sites with residues from only one class. These findings provide a regional profile for pesticide exposure for LCBs in southern Alberta and identifies compounds of potential concern for future toxicological testing and pollinator management.