A desert bee thermoregulates with an abdominal convector during flight

Flying endothermic insects thermoregulate, likely to improve flight performance. Males of the Sonoran Desert bee, Centris caesalpiniae Cockerell, seek females at aggregations beginning at sunrise and cease flight near midday when air temperature peaks. To identify the thermoregulatory mechanisms for C. caesalpiniae males, we measured tagma temperatures, wingbeat frequency, water loss rates, metabolic rates, and tagma masses of flying bees across shaded air temperatures of 19 to 38°C. Surface area, wet mass, and dry mass declined with air temperature, suggesting that individual bees do not persist for the entire morning. The largest bees may be associated with cool, early mornings because they are best able to warm themselves and/or because they run the risk of overheating in the hot afternoons. Thorax temperatures were high (38 to 45°C) and were moderately well-regulated, while head and abdomen temperatures were cooler and less controlled. Abdomen temperatures converged on thorax temperatures as air temperature rose, indicating active heat transfer from the pubescent thorax to the relatively bare abdomen with warming. The mass-specific metabolic rate increased with time, air, and thorax temperatures, but wingbeat frequency did not vary. Mass-specific water loss rate increased with air temperature. Using a heat budget model, we showed that whole-body convective conductance increased through the morning, and that the primary mechanism of regulating thorax temperature during flight for these bees is increased use of the abdomen as a convector at higher air temperatures.