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.

To determine how high air temperatures affect thermoregulation, water balance, and force generation during foraging flight, we measured flight muscle temperatures, flight metabolic rates, and water loss rates of honey bees carrying nectar loads at three different air temperatures (20, 30, and 40 °C), and measured wing kinematics with high-speed video at air temperatures of 25 and 40 °C. We then used these data and the prior literature to model heat-limits on honey bee flight.