Empty flowers have no impact on foraging choice in bumble bees (Bombus impatiens) in a social foraging context

Plants offer rewards such as nectar and pollen to entice flower-visiting insects. Flowers containing nectar may occasionally become empty due to climatic conditions, the time of day, or previous floral visitations. When flowers become empty, flower visitors must decide whether to abandon the flower or the patch. If the forager decides to remain in the patch, it must decide which flowers to visit next. Previously, Apis cerana and Bombus terrestris have shown evidence of similarity effects, where the bees were more likely to visit flowers more similar in colour, temperature, or nectar quality to the empty flower. Here, we examine the response of bumble bees, B. impatiens, when they encounter previously high-quality, now empty artificial flowers. We predicted that the presence of an empty, but previously rewarding flower changes bumble bee preferences for neighbouring flowers in the same patch. Furthermore, since bumble bees are social foragers, we also counted the nestmates present on flowers whenever a bee landed on a flower to feed. We found that for the most part, empty flowers did not affect bumble bees' preference relationships between the remaining flowers in a patch. Rather, their floral choice was influenced predominantly by social information, bumble bees were more likely to forage on a flower where other bumble bees were physically present. We conclude that while high-quality, yet unavailable options can affect the foraging preferences of individual bees, information from conspecifics is a more important driver of decisions in bumble bees.