Assessing the impact of alfalfa leafcutting bee (Megachile rotundata) foraging on gene flow in alfalfa seed fields

Cross pollination by bees is necessary for commercial alfalfa seed production.  To maintain varietal purity in alfalfa, seed producers use spatial isolation standards to control bee and pollen flow between fields.   The 2011 deregulation of Roundup Ready (RR) alfalfa by the USDA has sparked public concern and scientific debate over the robustness of current isolation standards. The alfalfa leafcutting bee, Megachile rotundata (ALCB), is a commercially managed pollinator used extensively in alfalfa pollination. Our study evaluates the influence of ALCB on gene flow between RR and conventional alfalfa seed fields.  Five sites were identified in the Touchet valley of central Washington in which conventional alfalfa seed fields were directly adjacent to RR fields.  Pollen and seed were sampled from conventional domiciles at increasing distances from a RR source over the course of the 2013 and 2014 alfalfa pollination season, and tested for the presence of the transgene.  Our results demonstrate measurable impacts of ALCB-facilitated pollen dispersal across an agricultural landscape beyond what has been previously recorded.  These findings will be used to develop a predictive model for gene flow that seed producers can use to minimize cross pollination between genetically engineered and conventional seed fields in alfalfa-producing regions.