Scale-dependent effects of honeybee abundance on Lima bean pollination and yield

High pollinator abundance can hinder crop productivity due to accumulated reproductive costs associated with repeated visits. We combined observational and experimental approaches across flower, plant, and field scales to evaluate how honeybee ( Apis mellifera ) abundance affects the pollination service, net reproductive benefit, and crop yield in Lima bean ( Phaseolus lunatus ). Natural pollination resulted in lower fruit and seed set than optimal hand cross-pollination, indicating a limitation in the pollination service at the plant level. At the flower scale, net reproductive benefit increased asymptotically with increasing visits, driven primarily by increased fruit set, with no detectable change in seed set. In contrast, crop yield at the field scale declined linearly with increasing honeybee visitation, with each additional 1.2 increase in visits per flower per hour reducing seed production by 21 %. Overall, our results indicate that high honeybee abundance can constrain Lima bean reproduction and yield. Furthermore, these findings underscore the need for pollination studies to use standardized, multi-scale approaches to accurately assess and manage the impact of this superabundant pollinator in agroecosystems.