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Thermoregulation of elevated thorax temperatures is necessary for bees to achieve the high rates of power production required for flight, and is a key factor allowing them to occupy widely varying thermal environments. However, the mechanisms by which bees thermoregulate during Eight are poorly understood. Thermoregulation is accomplished by balancing heat gain and heat loss via the following routes: convection, evaporation, and metabolic heat production. There appears to be a diversity of thermoregulatory mechanisms employed during Eight among bee species. Some species, particularly Bombus spp,, actively increase the distribution of thoracic heat to the abdomen during flight as air temperature (T-a) rises, and apparently thermoregulate by varying convective heat loss. However, thermal variation in convection has not been directly measured for any free-flying bee. Above 33 degrees C, Eying Apis mellifera greatly increase evaporative heat loss with T-a, and many other species "tongue-lash" during Eight at high T(a)s or when artificially heated, Thus, evaporation seems to be important for preventing overheating during flight at very high T(a)s. Flying A. mellifera and Centris pallida strongly decrease metabolic rate as T-a increases, suggesting that they are varying metabolic heat production for thermoregulation and not aerodynamic requirements. Variation in metabolic heat production appears to be mediated by changes in wingbeat kinematics, since wingbeat frequency decreases with T-a for A. mellifera and Centris spp, It is unknown if the decrease in Eight metabolic rate at higher T(a)s occurs secondarily as a consequence of greater efficiency or if it is truly an active response.