Aerodynamic Sound Production from Flying Beetles

Abstract

The flapping wings of insects generate sounds during their flight. Recent interdisciplinary studies have extensively investigated the lift and thrust mechanisms produced from flapping flight; however, the associated sounds produced are less understood. Most studies have examined the amplitude and frequency with respect to wing beat reporting on the associated harmonic structure. The directionality and phase relationships have been examined in more detail in a few recent studies for flies and mosquitoes. In this study, we examine the sound generation mechanism from two invasive beetle species to Hawaii which are the Oriental Flower Beetle and the Coconut Rhinoceros Beetle. The wing beat, amplitude, and phase relationships are measured and determined with an eight element spherical microphone array. The mechanism of second harmonic generation for the different species is investigated with adaptive signal processing (Empirical Mode Decomposition) and complementary high speed optical video. The rotational motion of wing has a significant role in the second harmonic for the Coconut Rhinoceros Beetle. The different location and phase oscillation of the elytron for the two species results in different vortex generation during the down stroke.