Temperature regulation by evaporative cooling in a desert grasshopper

Conventional wisdom held that heat-stressed insects could not use evaporative cooling (EC) to keep body temperature (Tb) lower than ambient (T,) because their relatively large body surface area to volume ratios (s:v) would necessitate evaporating more water than they could afford To the contrary, it has been shown that species of cicada, grasshopper and beetle use EC and maintain Tb<T, for extended periods of time We examined EC in the desert-dwelling grasshopper, Calliptamus barbants. Male Calliptamus are significantly smaller than females (0.37 vs. 1.72 g), and we hypothesised that males would be less able to thermoregulate at high T, than females. We measured evaporative water loss in 12 male and 15 female Calliplamus at T.=23-50°C. Below 46°, Tk in both sexes remained close to T, however the relative rate of evaporation in males was 3 times greater than in females (2.82± 1.16 vs. 0.88±0 54 % body mass/h), which can be partially accounted for by scaling effects. When T,>46°C, both used EC to keep Tb<T, Mean maximum relative water loss rate was the same for males and females, i.e., 7.4 % body mass/hour and maximum Tb-T, was 2°C at T,=50°C The results do not support our hypothesis, namely within the range of T, examined, male Calliptamus maintained Tb as well as did the larger females.