Locked Pollen, Unchanged Buzzes: Bumblebee Foraging Behavior Persists Despite Pollen Restriction in a Poricidal Legume

In plants that offer pollen as their sole floral reward, this resource is finite and nonreplenishable, making such plants useful systems for studying how resource availability across flowers shapes pollinator behavior. Because tropical ecosystems of the Global South harbor exceptionally diverse plant–pollinator interactions, understanding pollinator behavior in these systems is important for understanding the evolution of plant–pollinator relationships. Using the legume Chamaecrista latistipula , which offer only pollen as a floral reward, we assessed how pollen availability affects the foraging behavior of its most frequent pollinator, the bumblebee Bombus morio . We hypothesized that bees would reduce handling time and increase their vibrational effort as pollen availability decreased. By partially or completely sealing the pores of poricidal anthers, we created a gradient of pollen availability (0%, 36%, 64%, and 100%, with the latter representing an unmanipulated control). We used video and audio recordings to quantify handling time, buzzing time, grooming time, number of vibrational pulses, and vibration amplitude and fundamental frequency during bee visits. We also recorded the number of flowers visited by each bee after it left the focal flower. Contrary to our hypothesis, pollen restriction did not affect the number of vibrational pulses, buzzing time, fundamental frequency, or vibration amplitude. The only detectable response to the floral resource manipulation was a reduction in handling time, which decreased in the 0% pollen treatment, in which bees omitted grooming because no pollen was accessible. Our results indicate that bees follow a stereotyped vibrational routine when foraging on pollen‐offering flowers and that this behavior persists even when the immediate reward is reduced or absent. This limited behavioral adjustment may reflect the absence from our experiment of secondary cues left by previous visitors or constraints imposed by fixed behavioral routine required to exploit poricidal anthers.