Preliminary investigation into the bioacoustics of Cicindela spp. (Coleoptera: Cicindelidae)

Abstract

Initial investigations into bioacoustics of Cicindela spp. (Cicindelidae: Coleoptera) were designed to establish the systematic usefulness of acoustic variables, the possibility of auditory communication, and lay foundations for future studies of acoustic behaviour of the family. Groups were statistically compared using variables derived from photomicrographs of plectra as well as oscillograms and frequency spectrograms of recorded stridulations. The noise-like character of tiger beetle stridulations necessitated a new method of comparing stridulation frequency spectra averages: discrete frequencies from the peak-pick procedure of a Nicolet lOOn mini-analyzer were compared. The plectrum consists of a field of posteriorly oriented spines located ventrally at the elytral apex. Plectra characters show trends towards sexual dimorphism and are related to body size and habitat. Among plectra/elytra characters, plectrum field size and shape show the most promise as taxonomic characters. Stridulations, produced by a two-stroke cycle, consist of 1 to 9 low intensity buzzes (modes), signal mean 49.0 dB at 3 cm (audio range), with an average duration of 0.65 seconds. Cicindelids emit signals of broadband frequency, between approximately 20 Hz and 50 kHz, with significant energy in both audio and ultrasonic ranges. Although stridulations, for the most part, showed no sexual differentiation, species differences were quite apparent. Signal timing and amplitude parameters were based on body size, plectrum structure, phylogeny, and habitat. Stridulation frequency was based on phylogeny and may be related to specific stridulatory behaviour and structure of the pars stridens. Acoustic characters appear to show limited promise as useful taxonomic characters. Temperature at stridulation does not appear to affect stridulatory rates. Evidence suggests that stridulatatory behavior is linked to specific optimal temperatures. Tiger beetles stridulate spontaneously or when subjected to heated, lighted, or crowded conditions. In contrast to most coleopterans, tiger beetles do not stridulate in response to mechanical stimulation, a behavior associated with a disturbance function. This togther with a relatively ordered stridulatory structure, and initial behavioral observations suggest a territorial and/or calling function of cicindelid stridulations.