Meeting Abstract
The thorax (or thorax-wing assembly) of flying insects is widely believed to behave as a resonant mechanical oscillator. Thorax resonance is likely critical to the function of asynchronous muscles and may reduce the energetic costs of flight. Some orders of insects, such as Diptera or Hymenoptera, modulate their wingbeat frequencies during flight to affect aerodynamic force production. This implies that, if the thorax indeed behaves as a resonant oscillator, it must behave nonlinearly – linear oscillators have fixed resonant properties. To address potential nonlinearity, we performed a series of experiments on freshly sacrificed Honeybee Apis mellifera thoraxes. First, we conducted static force-displacement tests on the thorax about its ventral axis. Over the approximate range of in-vivo displacements, we found the thorax behaved approximately as a nonlinear hardening spring that became stiffer as it was compressed. Next, we mounted the thorax on a custom vibration shaker system in order to identify the thorax’s linear resonant frequency as a function of compression. From zero to maximum compression, the thorax resonant frequency increased by as much as 100 Hz. This is consistent with the static force-displacement testing, since the thorax linear natural frequency is theoretically proportional to its stiffness. Our results suggest that insects may adjust the equilibrium state of their thorax in order to modulate wingbeat frequency.
