Meeting Abstract
The advent of flight likely facilitated insect dominance of the terrestrial biosphere. In particular, rapid wing oscillations made possible by asynchronous flight muscle allow small insects to hover and maneuver in nearly all habitats on earth. To keep an insect aloft, the flapping wings must produce a sufficiently strong downward draft of air to offset body weight; with this induced flow comes induced power, a major component of aerodynamic power required for flight. Although developments in technology and theory have facilitated rapid advances in our understanding of how insects meet the aerodynamic and energetic demands of flight, the thermal consequences of exposure to a swiftly moving self-generated column of air have received little attention. To better understand the role of induced flow in heat loss for flying insects, we focused on bumblebees, which must maintain high body temperatures to maintain flight necessary for feeding from flowers, and which have relatively high flapping frequencies (and therefore induced flows) to offset their large body size. We measured induced flows and associated wingbeat kinematics for bumblebees of different sizes hovering in free flight in front of artificial flowers. We then measured rates of heat loss from bumblebee models when exposed air streams of the same velocity and basic structure as those measured. As expected, induced flows depended strongly on body mass and wingtip velocity, ranging from 0.2 to nearly 2 m/s. These induced flows resulted in rapid cooling of non-metabolizing bumble bees: a heat balance model suggests that ignoring induced flow underestimates heat loss, leading to erroneous predictions of rapid overheating of hovering bumblebees. These findings likely apply broadly to hovering insects, with the effects of induced flow on heat balance predictably varying with wing kinematics and body size.
