First direct quantification of floral handling costs in bees

Floral handling can be energetically costly for bees, yet these costs are rarely measured. We provide the first direct quantification of the metabolic cost of floral buzzing in bumblebees and evaluate its ecological significance. Using flow-through respirometry synchronized with laser vibrometry, we measured carbon dioxide production during floral buzzing by Bombus terrestris and compared it with flight take-off, which is powered by the same thoracic muscles. Floral buzzing required high muscular effort compared with other behaviours, with approximately 0.10 J per event and mass-specific power approximately 293 W/kg. Overall costs were comparable to take-off because floral buzzing bouts are longer despite a lower metabolic rate. Metabolic rate scaled with body mass, whereas intertegular span did not, implying that transient load rather than structural size better explains energetic demand in short, high-intensity behaviours. Metabolic traits were highly repeatable within individuals, but variable between individuals, and colony identity also explained additional variance. Converting costs to nectar equivalents showed that floral buzzing required slightly more nectar than take-off and that requirements rose as nectar sugar concentration declined. We conclude that floral buzzing is a major, previously unquantified component of bee energy budgets that is likely to shape nectar demands, flower visitation patterns and generally plant-pollinator interactions.