Big in the tropics-Are there thermal advantages of large body size for carpenter bees in hot climates?

Large body size is a major advantage for flying insects living in cold climates. Size-related metabolic heat production allows them to maintain their body temperature high enough for flight even at low ambient temperatures. Due to an elevated risk of overheating, however, large body size should be a disadvantage in hot climates. The present study asked whether large body size may provide a thermal benefit for bees even in tropical environments. To answer this question, we observed the foraging behaviour of two different-sized carpenter bee species at flowers of Allamanda sp. in the hot semi-arid region of Brazil. The larger species (Xylocopa frontalis) visited flowers preferentially earlier in the morning and at lower ambient temperatures than the smaller species (X. cearensis). Prior to the foraging peak of X. cearensis, nectar was more abundant in the flowers, which certainly increased the foraging success by X. frontalis. Under cool conditions, moreover, the large species harvested nectar more rapidly than the small species. A thermographic survey revealed that individuals of X. frontalis had higher thoracic temperatures than X. cearensis at the same ambient temperature, and that flower handling became faster with increasing thoracic temperature. These results clearly demonstrate that high thoracic temperatures associated with large body size are an advantage for big bees in hot environments, particularly early in the morning, since they allow an early foraging onset and lead to an increased nectar-collecting efficiency.