Evaluating gene and pollen flow mediated by the alfalfa leafcutting bee (Megachile rotundata) in alfalfa seed production

Cross-pollination by bees is necessary for commercial alfalfa seed production.  To maintain varietal purity in alfalfa, seed producers adhere to spatial isolation standards to minimize or prevent bee flight and subsequent pollen flow between fields.  The increased use of genetically-engineered (GE) crops in agriculture has raised concerns over pollinator-mediated gene flow between transgenic and conventional agricultural varieties. Here, we determine the role of  the alfalfa leafcutting bee (ALCB), Megachile rotundata, in contributing to undesired gene flow between alfalfa fields. Bee-collected pollen and seed were tested for the GE trait from conventional alfalfa seed fields at variable distances from known GE fields, and incorporated into a predictive model of ALCB-mediated gene flow over distance.  It was found that GE trait expression in conventional seed was detected at rates that surpass established thresholds for varietal purity.  Additionally, ALCBs frequently forage at distances which exceed previous estimates of their typical foraging range.  These results suggest that current mitigation practices for gene flow in alfalfa seed production may require revision, and identify a new method to infer pollinator foraging range in an agricultural landscape.