Distribution of sound pressure around a singing cricket: radiation pattern and asymmetry in the sound field

Male field crickets generate calls to attract distant females through tegminal stridulation: the rubbing together of the overlying right wing which bears a file of cuticular teeth against the underlying left wing which carries a sclerotized scraper. During stridulation, specialized areas of membrane on both wings are set into oscillating vibrations to produce acoustic radiation. The location of females is unknown to the calling males and thus increasing effective signal range in all directions will maximize transmission effectiveness. However, producing an omnidirectional sound field of high sound pressure levels may be problematic due to the mechanical asymmetry found in this sound generation system. Mechanical asymmetry occurs by the right wing coming to partially cover the left wing during the closing stroke phase of stridulation. As such, it is hypothesized that the sound field on the left-wing side of the animal will contain lower sound pressure components than on the right-wing side as a result of this coverage. This hypothesis was tested using a novel method to accurately record a high-resolution, three dimensional mapping of sound pressure levels around restrained Gryllus bimaculatus field crickets singing under pharmacological stimulation. The results indicate that a bilateral asymmetry is present across individuals, with greater amplitude components present in the right-wing side of the animal. Individual variation in sound pressure to either the right- or left-wing side is also observed. However, statistically significant differences in bilateral sound field asymmetry as presented here may not affect signalling in the field.

雄性田野蟋蟀通过覆翅摩擦发声（tegminal stridulation）来吸引远距离雌虫：即带有表皮齿列的上方右翅与带有硬化刮器的下方左翅相互摩擦。在摩擦发声过程中，双翅上的特化膜质区域会产生振荡振动以辐射出声波。鸣唱的雄性无法知晓雌虫的位置，因此向所有方向扩展有效信号范围将最大化传播效能。然而，由于该发声系统存在机械不对称性，产生高声压级的全向声场可能存在困难。机械不对称性源于摩擦发声的闭合冲程阶段，此时右翅会部分覆盖左翅。据此，研究人员提出假说：受此覆盖影响，蟋蟀左翼侧的声场声压分量将低于右翼侧。为验证该假说，本研究采用一种全新方法，对经药物刺激后鸣唱的固定双斑蟋（Gryllus bimaculatus）个体周围的声压级进行高分辨率三维精准测绘。结果显示，个体间存在双侧声学不对称性，右翼侧的振幅分量更高，同时左右两侧的声压也存在个体差异。不过，本研究中观测到的双侧声场不对称性，在统计学上可能并不会对野外的信号传递产生影响。