Wing flexibility enhances load-lifting capacity in bumblebees

Abstract

The effect of wing flexibility on aerodynamic force production has emerged as a central question in insect flight research. However, physical and computational models have yielded conflicting results regarding whether wing deformations enhance or diminish flight forces. By experimentally stiffening the wings of live bumblebees, we demonstrate that wing flexibility affects aerodynamic force production in a natural behavioural context. Bumblebee wings were artificially stiffened in vivo by applying a micro-splint to a single flexible vein joint, and the bees were subjected to load-lifting tests. Bees with stiffened wings showed an 8.6 per cent reduction in maximum vertical aerodynamic force production, which cannot be accounted for by changes in gross wing kinematics, as stroke amplitude and flapping frequency were unchanged. Our results reveal that flexible wing design and the resulting passive deformations enhance vertical force production and load-lifting capacity in bumblebees, locomotory traits with important ecological implications.

Biomechanical strategies for mitigating collision damage in insect wings: structural design versus embedded elastic materials

“…Splinted wasp wings lost more area than both unsplinted wasp wings and bumblebee wings, and accumulated damage at a much faster rate (Mountcastle and Combes, 2013). In contrast to the yellowjacket wing, the bumblebee wing does not have resilin or a flexible joint between the prestigma and stigma, and many of the major veins and vein junctions are located more proximally than in the yellowjacket.…”

“…Several recent studies show that wing flexibility is not merely an inherent liability of lightweight structures subjected to large external forces, but is in fact adaptive for a variety of functional demands, including aerodynamic force production and flight efficiency (Mountcastle and Combes, 2013;Young et al, 2009;Nakata and Liu, 2011). Wing flexibility in some insects is enhanced by mobile vein joints, which often contain embedded resilin, a rubber-like protein with low stiffness and high elastic efficiency (Weis-Fogh, 1961).…”

“…Although relatively few studies have been conducted on the distribution and function of resilin joints in insect wings, these structures have been documented in beetle and earwig hind wings along fold lines that collapse the wing during rest (Haas et al, 2000b;Haas et al, 2000a), and in bumblebee and dragonfly wings along axes where the wings typically flex during flight (Gorb, 1999;Donoughe et al, 2011;Mountcastle and Combes, 2013). A recent study showed that a single resilin vein joint in the bumblebee wing (Bombus impatiens) contributes significantly to overall chordwise wing flexibility, and enhances vertical aerodynamic force capacity (Mountcastle and Combes, 2013).…”

Resonance frequencies of honeybee (Apis mellifera) wings

“…However, resonance can also be detrimental to flight, because driving a system at resonance potentially hinders control, especially the ability to modulate frequency away from the resonance frequency, which insects may need to maneuver. Moreover, the type of wing flexion that is known to have beneficial aerodynamic effects is often perpendicular to the long axis of the wing, in the chordwise direction (Mistick et al, 2016;Mountcastle and Combes, 2013). The alternative stiff element hypothesis is that the resonance frequency of the first longitudinal mode of the wings is far above the wingbeat frequency.…”

Unsteady Aerodynamic Response of a Rapidly Started Flexible Wing

“…Research on a wide range of natural fliers, from insects [1][2][3] to bats [4][5] aims to discover the aerodynamic benefit of membranous wings in the low Reynolds number flight regime. These natural fliers use thin, compliant wings as lifting surfaces, causing their wings to undergo large change in shape during flight [6].…”