First direct quantification of floral handling costs in bees

Abstract

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 synchronised with laser vibrometry, we measured carbon dioxide production during buzzing by Bombus terrestris and compared it with flight take-off, which is powered by the same thoracic muscles. Buzzing required high muscular effort, with [~]0.10 J per event and mass-specific power [~]293 W kg-{superscript 1}, and overall costs comparable to take-off because buzzing bouts are longer even though the metabolic rate is lower. Absolute metabolic rate increased 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 repeatable within individuals, and colony identity explained additional variance, consistent with genetic or shared environmental effects. Converting costs to nectar equivalents showed that 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 supplementation, flower sequencing, and plant-pollinator interaction strength.