Flying, nectar-loaded honey bees conserve water and improve heat tolerance by reducing wingbeat frequency and metabolic heat production

Heat waves are becoming increasingly common due to climate change, making
it crucial to identify and understand the capacities for insect
pollinators, such as honey bees, to avoid overheating. We examined the
effects of hot, dry air temperatures on the physiological and behavioral
mechanisms that honey bees use to fly when carrying nectar loads, to
assess how foraging is limited by overheating or desiccation. We found
that flight muscle temperatures increased linearly with load mass at air
temperatures of 20 or 30°C, but, remarkably, there was no change with
increasing nectar loads at an air temperature of 40°C. Flying,
nectar-loaded bees were able to avoid overheating at 40°C by reducing
their flight metabolic rates and increasing evaporative cooling. At high
body temperatures, bees apparently increase flight efficiency by lowering
their wingbeat frequency and increasing stroke amplitude to compensate,
reducing the need for evaporative cooling. However, even with reductions
in metabolic heat production, desiccation likely limits foraging at
temperatures well below bees’ critical thermal maxima in hot, dry
conditions.