Water Profligacy as an Adaptation to Hot Deserts: Water Loss Rates and Evaporative Cooling in the Sonoran Desert Cicada, Diceroprocta apache (Homoptera: Cicadidae)

Thoracic and abdominal temperatures (Tth and Tabd) of Diceroprocta apache were monitored during exposure to an ambient temperature (Ta) of 45.5 C in dry air. Mass-specific heating constants averaged 0.36 ± 0.036 min g⁻¹ below body temperature (Tb) of 39-40 C, but above that temperature range heating constants decreased to 0.012 ± 0.002 min g⁻¹ as a result of evaporative cooling. After 1 h exposure to 45.5 C, Tb's were still ≥2.9 degrees C below Ta. Tb's maintained by cicadas in these experiments were similar to those obtained from D. apache in the field by Heath and Wilkins. Evaporative cooling in D. apache is facilitated by a comnbination of an inherently high cuticular permeability and activation of an energy-dependent process that facilitates transcuticular water flux (TWF). In contrast with the usual situation when xeric and mesic species are compared, estimated cuticular permeabilities of D. apache are significantly greater (by 40% at 30 C) than those of the more mesic cicada species, Tibicen dealbatus. When the TWF-facilitating process is activated, D. apache loses ~30%-35% of its body water within the first hour. Such high water losses would be fatal for most terrestrial arthropods, but D. apache tolerates such losses with no obvious detriment. These findings suggest the testable hypothesis that adaptation to hot deserts by arthropods with ready access to water may be enhanced by high cuticular permeabilities and consequent rapid rates of evaporative water loss.