Russian olive (Elaeagnus angustifolia L.) is an invasive tree in riparian areas throughout much of the western United States. It produces copious numbers of yellow flowers that are often visited by bees and other insects. Little research has examined the pollination ecology of Russian olive and how pollinator interactions contribute to variation in seed production. We conducted a field experiment in which flower clusters were bagged to exclude insect visitation. Seed production was compared between bagged flowers and unbagged flowers (open pollinated) from the same tree that were allowed insect visitors. Flower insect visitation surveys were used to determine the most likely pollinators. Additionally, we assessed viability of seeds produced from unbagged and bagged flowers using germination trials and tetrazolium tests. Overall, unbagged flowers produced ~7x the number of seeds compared to bagged flowers, exemplifying the role insects play in the production of Russian olive seeds. Although numerous insects were found visiting Russian olive flowers, honey bees (Apis mellifera L.) accounted for nearly 70% of flower visits by insects. Seed viability was similar between bagged and unbagged branches, but varied across locations, suggesting site-level differences likely limit the outcomes of plant-pollinator interactions. Currently, biocontrol agents that target reproductive structures are being evaluated for use to limit the spread of Russian olive. Our data suggests that biocontrol agents that feed on flowers may be a viable option for reducing Russian olive propagule pressure.
