Diapausing bumble bee queens avoid drowning by using underwater respiration, anaerobic metabolism and profound metabolic depression

Overwintering bumble bee queens enter a state of diapause, remaining buried underground until spring. Remarkably, queens of the common eastern bumble bee (Bombus impatiens) can survive complete submersion for at least one week. We investigated the physiological mechanisms enabling this tolerance, testing the hypothesis that submerged diapausing queens rely on both underwater respiration and anaerobic metabolism for survival. Using respirometry, we detected low but consistent CO2 production during submersion, persisting through 4 and 8 days under water. Underwater gas exchange, measured from CO2 levels in the headspace of a respirometry chamber, was supported by a decline in dissolved oxygen in the water. Submerged bees also accumulated lactate as an anaerobic end-product during submersion, which decreased to pre-submersion levels after a week of recovery. Recovery was characterized by an immediate increase in metabolic rate, followed by a gradual decline to pre-submersion levels over one week, accompanied by changes in respiratory patterns. This study reveals that diapausing bumble bee queens survive and recover from prolonged flooding through a combination of underwater respiration and anaerobic metabolism in a state of profound metabolic depression. Such physiological capacity underpins their resilience to environmental extremes and provides insights into how terrestrial insects may persist in flood-prone habitats.