WARK, B.J.*; SANE, S.P.; HOROWITZ, J.; DANIEL, T.; Univ. of Washington, Seattle; Univ. of Washington, Seattle; Univ. of Washington, Seattle; Univ. of Washington, Seattle: Dynamics of hawkmoth antennae: finite element analysis of antennal mechanics.

All moving systems require sensors that encode their motions. Sensing body rotation is particularly important in flight control and both visual and exteroceptive (e.g. halteres) systems have be implicated as key modalities regulating flight paths, at least in Diptera species. While halteres are heralded as outstanding sensors in this regard, far less is know about rotational sensors in non-Dipteran insects. We have suggested that the antennae can serve this role in Lepidoptera. To explore this issue we used the hawkmoth Manduca sexta as a model system. We measured the vibrational motions of antennae during free hovering flight to determine the magnitude of tip motions. We then measured the mechanical properties of antennae (their flexural stiffness) and used these data to estimate the forces required to produce observed tip motions. Armed with mechanical and morphological properties, we developed a dynamic finite element model of an antenna subject to a combination of vibrations with varying levels of rotational precession about an orthogonal axis. Our results show that (a) the predicted motions match those we have observed and (b) the observed vibrational motions generate a rotating pattern of strain at the antennal base. We further explored how the flexural stiffness of antennae affect the patterns of strain at the antennal base by varying flexural stiffness over several orders of magnitude. Simulation results show that for a particular driving frequency, there is a unique value for stiffness that leads to peak strain in the antennal response to rotation. This suggests that filtering of vibrations can be tuned by the flexural stiffness of antennae.