Bumble bees show an induced preference for flowers when primed with caffeinated nectar and a target floral odor

Abstract

Caffeine is a widely occurring plant defense chemical^1,2 that occurs in the nectar of some plants, e.g., Coffea or Citrus spp., where it may influence pollinator behavior to enhance pollination.^3,4 Honey bees fed caffeine form longer lasting olfactory memory associations,⁵ which could give plants with caffeinated nectar an adaptive advantage by inducing more visits to flowers. Caffeinated free-flying bees show enhanced learning performance⁶ and are more likely to revisit a caffeinated target feeder or artificial flower,^7-9 although it is not clear whether improved memory of the target cues or the perception of caffeine as a reward is the cause. Here, we show that inexperienced bumble bees (Bombus terrestris) locate new food sources emitting a learned floral odor more consistently if they have been fed caffeine. In laboratory arena tests, we fed bees a caffeinated food alongside a floral odor blend (priming) and then used robotic experimental flowers¹⁰ to disentangle the effects of caffeine improving memory for learned food-associated cues versus caffeine as a reward. Inexperienced bees primed with caffeine made more initial visits to target robotic flowers emitting the target odor compared to control bees or those primed with odor alone. Caffeine-primed bees tended to improve their floral handling time faster. Although the effects of caffeine were short lived, we show that food-locating behaviors in free-flying bumble bees can be enhanced by caffeine provided in the nest. Consequently, there is potential to redesign commercial colonies to enhance bees' forage focus or even bias bees to forage on a specific crop.

Keywords: Bombus terrestris; alkaloids; associative learning; bumble bees; flower constancy; pollination; strawberry flowers.