Thermoregulation and evaporative cooling in the cicada Okanagodes gracilis (Homoptera: Cicadidae).

1. Okanagodes gracilis uses a combination of physiological and behavioral mechanisms to regulate body temperature (Tb) to a prescribed range. 2. High thermal tolerances (48.6 degrees C Tb) and evaporative cooling permit the species to remain active during the hottest parts of the day. 3. The regression of Tb on ambient temperature (Ta) (Y = 0.142X + 34.63) intersects the isothermal line at 40.4 degrees C, below the shade-seeking value of 41.2 degrees C. 4. In the laboratory, weight (water) loss is faster at higher (46 degrees C) than at lower (43 degrees C) temperatures; the cicadas were able to survive mass losses of 25% in the laboratory. 5. Pores in the dorsal thorax and abdomen are the probable sites of water loss. 6. O. gracilis is the first cicada reported that is able to continue activity while simultaneously feeding and evaporatively cooling. 7. Behavioral mechanisms of thermoregulation and the possible thermoregulatory value of the species' coloration are discussed.