Mass scaling of kinematics and power during normal and maximal hovering flight performance in the bee Xylocopa varipuncta

The understanding of insect flight has been hampered by the absence of data for insects hovering at maximal capacity. Hovering flight performance of Xylocopa varipuncta (Anthophoridae) was increased by decreasing air density via the graded substitution of N₂ with He in normoxic air; this manipulation necessitated increased power requirements up to the point of aerodynamic failure. Smaller bees were able hover in lower gas densities than larger bees. Aerodynamic analysis revealed that X. varipuncta possess considerable power reserves, with muscle mass specific power at maximal performance 20% higher than in normodense hovering. The increase in power output between normal and maximal hovering flight performance was driven by significant increases in wing stroke amplitude, but not wingbeat frequency. In contrast to allometric studies of gas exchange during flight, the muscle mass specific power output during normal and maximal hovering flight increased significantly with body mass. Unlike previous studies of flight kinematics allometry, there was no significant relationship between wingbeat frequency and body mass. Wingstroke amplitude significantly increased with body mass during normal hovering flight and maximal hovering flight performance, although the mass effect was less pronounced during maximal performance. These results are the first to describe the kinematics and power requirements of maximal hovering flight performance in an insect, and question the applicability of interspecific allometric relationships to a single species.