D3281: Floral traits predict native bee visitation length in sunflower crops

Bee pollination is essential for food production and ecosystem sustainability. Multiple studies have shown that agricultural intensification negatively impacts wild bee abundance and diversity, but less is known regarding effects on bee behavior that could impact pollination services. We assessed the influence of landscape contexts and floral metrics on bee visitation across sunflower farms. We visited 13 sunflower farms twice during summer 2019, assessing wild bee visitation to individual sunflower heads. For predictors, we measured floral metrics such as corolla diameter and presence of pollen (since some sunflowers are pollen-sterile), along with landscape composition around the farms at 0.5-, 1-, and 2.5-kilometer radii. Larger corollas and the presence of pollen resulted in longer visits overall. Later blooming flower heads also received longer visits. However, visit duration also differed with bee species; bees in the genus Halictus spend more time per visit than Bombus or Melissodes. Higher proportions of agricultural fields surrounding the farms resulted in bees spending less time on a flower across 1 and 2.5 kilometer radii. This could be because agricultural intensification can result in agrochemical use and limited floral diversity. Overall, we found that agricultural landscapes and floral characteristics of individual sunflowers influence visitation dynamics. Our results are relevant given that time spent on a flower is a proxy for pollination services, impacting food production and ecosystem sustainability.