LAUSR

Abstract Arthropods are responsible for pollinating the majority of food and fuel crops worldwide. However, global declines in bee populations threaten the delivery of pollination services in both managed and natural ecosystems. Alternative pollinators such as flies, butterflies, beetles, and wasps may provide a buffer that protects agriculture from bee population declines. Flower-visiting flies are abundant in both rural and urban agricultural settings, and in some cases may pollinate plants avoided by bees. Here we explored the structure of plant-pollinator networks for both bee and non-bee pollinator communities across rural and urban farms in western Washington State, USA. We identified several broad groups of pollinators comprising 13 morphogroups of insects and arthropods. While bees were the pollinators observed on reproductive parts of flowers most frequently, syrphid flies contributed to a high number of arthropod-flower visits. We also found that syrphid flies visited four plant types not visited by bees, and that urban and rural farm settings were characterized by different syrphid fly communities. When comparing the networks of plant-arthropod interactions, urban farm settings had more diverse networks overall, with a greater richness of plant-arthropod interactions for both bee and non-bee pollinators. These findings underscore the need for greater focus on alternative pollinators as contributors to pollination services, particularly in urban settings where pollination services may be more impacted by bee declines and habitat loss. Our work will inform specific pollinator conservation efforts in the Pacific Northwest region and more broadly across the United States.