The Energetic Costs of Calling in the Bushcricket Requena Verticalis (orthoptera: Tettigoniidae: Listroscelidinae)

1. The metabolic costs of calling for male Requena verticalis Walker (Tettigoniidae: Listroscelidinae) were measured by direct recordings of oxygen consumption. The acoustic power output was measured by sound pressure levels around the calling bushcricket. 2. The average metabolic cost of calling was 0.143ml g21 h21 but depended on calling rate. The net metabolic cost of calling per unit call, the syllable, was calculated to be 4.3431026±8.331027 ml O2 syllable21 g21 bodymass (S.E.) from the slope of the relationship between total V̇O∑ and rate of syllable production. The resting V̇O∑, calculated as the intercept of the relationship, was 0.248mlO2 g21 bodymass h21. 3. The energetic cost of calling for R. verticalis (average mass 0.37g) was estimated at 31.8531026 J syllable21. 4. Sound pressure levels were measured around calling insects. The surface area of a sphere of uniform sound pressure level [83dB SPL root mean square (RMS) acoustic power] obtained by these measurements was used to calculate acoustic power. This was 0.20mW. 5. The metabolic efficiency of calling, based on total metabolic energy utilisation, was 6.4%. However, we propose that the mechanical efficiency for acoustic transmission is closer to 57%, since only about 10% of muscle metabolic energy is apparently available for sound production. 6. R. verticalis emits chirps formed of several syllables within which are discrete sound pulses. Wing stroke rates, when the insect is calling at its maximal rate, were approximately 583min21. This is slow compared to the rates observed in conehead tettigoniids, the only other group of bushcrickets where metabolic costs have been measured. The thoracic temperatures of males that had been calling for 5min were not significantly different from those of non-calling males. 7. For R. verticalis, calling with relatively slow syllable rates may reduce the total cost of calling, and this may be a compensatory mechanism for their other high energetic cost of mating (a large spermatophylax).