The number of glyphosate resistant seeds produced by each of three bee species as they visit alfalfa flowers in sequence during a foraging bout

Since the release of genetically engineered (GE) crops, there has been
increased concern about the introduction of GE genes into non-GE fields of
a crop and their spread to feral or wild cross-compatible relatives. More
recently, attention has been given to the differential impact of distinct
pollinators on gene flow, with the goal of developing isolation distances
associated with specific managed pollinators. To examine the differential
impact of bee species on gene movement, we quantified the relationship
between the probability of getting a GE seed in a pod, and the order in
which a flower was visited, or the cumulative distance traveled by a bee
in a foraging bout. We refer to these relationships as ‘seed curves’ and
compare these seeds curves among three bee species. The experiments used
Medicago sativa L. plants carrying three copies of the glyphosate
resistance (GR) allele as pollen donors (M. sativa is a tetraploid), such
that each pollen grain carried the GR allele, and conventional plants as
pollen recipients. Different foraging metrics, including the number of GR
seeds produced over a foraging bout, were also quantified and contrasted
among bee species. The lowest number of GR seeds set per foraging bout,
and the GR seeds set at the shortest distances, were produced following
leafcutting bee visits. In contrast, GR seeds were found at the longest
distances following bumble bee visits. Values for honey bees were
intermediate. The ranking of bee species based on seed curves correlated
well with field-based gene flow estimates. Thus, differential seed curves
of bee species, which describe patterns of seed production within foraging
bouts, translated into distinct abilities of bee species to move genes at
a landscape level. Bee behavior at a local scale (foraging bout) helps
predict gene flow and the spread of GE genes at the landscape scale.