Temperature Regulation by Respiratory Evaporation in Grasshoppers

Grasshoppers of the species Schistocerca nitens (Thiinberg), Locusta migratoria (L.) and Tmethis pulchripennis (Bolivar) are able to withstand air temperatures higher than lethal internal temperature (48 °C) for more than an hour, during which time they maintain an internal temperature as much as 8°C below air temperature. Rates of evaporation at high air temperatures are much greater than those observed for cuticular transpiration alone. The rate of evaporation and the ventilation frequency remain relatively constant at temperatures of up to about 45°C, above which they both increase markedly. The depression of internal temperature thus appears to be caused by increased tracheal ventilation for evaporative cooling. This finding contradicts the common assumption that evaporative cooling is of little adaptive advantage for thermoregulation in insects. In L. migratoria, the increase in ventilation appears to be achieved almost entirely by an increase in frequency of ventilation, although other species may alter tidal volume as well.