How do "mute" cicadas produce their calling songs?

Changqing Luo,Cong Wei,Christian Nansen,Ricardo Bomfim Machado

doi:10.1371/journal.pone.0118554

Changqing Luo, Cong Wei + Show 2 more

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https://doi.org/10.1371/journal.pone.0118554

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Abstract

Insects have evolved a variety of structures and mechanisms to produce sounds, which are used for communication both within and between species. Among acoustic insects, cicada males are particularly known for their loud and diverse sounds which function importantly in communication. The main method of sound production in cicadas is the tymbal mechanism, and a relative small number of cicada species possess both tymbal and stridulatory organs. However, cicadas of the genus Karenia do not have any specialized sound-producing structures, so they are referred to as “mute”. This denomination is quite misleading, as they indeed produce sounds. Here, we investigate the sound-producing mechanism and acoustic communication of the “mute” cicada, Karenia caelatata, and discover a new sound-production mechanism for cicadas: i.e., K. caelatata produces impact sounds by banging the forewing costa against the operculum. The temporal, frequency and amplitude characteristics of the impact sounds are described. Morphological studies and reflectance-based analyses reveal that the structures involved in sound production of K. caelatata (i.e., forewing, operculum, cruciform elevation, and wing-holding groove on scutellum) are all morphologically modified. Acoustic playback experiments and behavioral observations suggest that the impact sounds of K. caelatata are used in intraspecific communication and function as calling songs. The new sound-production mechanism expands our knowledge on the diversity of acoustic signaling behavior in cicadas and further underscores the need for more bioacoustic studies on cicadas which lack tymbal mechanism.

Highlights

The use of sounds in communication, both within and between species, occurs widely among vertebrates and arthropods
When the K. caelatata males were at rest, the forewings were held roof-like over the body; the basal inner margin of the forewing was locked in the wing-holding groove which was located much closer to the lateral margin of the V-shaped cruciform elevation than that in other cicadas (Fig. 3d), and the forewing costa was supported over the upward-curved lateral part of the operculum (Fig. 3e)
When the forewings returned to their resting position, the highly sclerotized costa of forewing struck the upward-curved lateral part of the operculum, which resulted in the production of the impact sound (S1 Video)

Summary

Introduction

The use of sounds in communication, both within and between species, occurs widely among vertebrates and arthropods. The most common structure used by cicadas to produce sounds is the tymbal organ which is essentially composed of a ribbed membrane at the base of the abdomen and an attached muscle. Different types of stridulatory organs have been described in a relatively small number of cicada species [13]. The stridulatory organ found in these cicada species, similar to that observed in crickets, katydids and grasshoppers, consists of a scraper (usually a part of one of the tegminal veins) and a file (a specialized part of either the mesonotum, or the pronotum, or the hind wing) [14,15]

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