Components of Evaporative Water Loss in the Desert Tenebrionid Beetles Eleodes armata and Cryptoglossa verrucosa

Water loss in Eleodes armata and Cryptoglossa verrucosa increased with increasing temperature and decreasing vapor activity (av). Rates of evaporative water loss were always about four times greater in E. armata than in C. verrucosa at the different temperatures and 0.0 av, while as av increased the ratio of E. armata loss to C. verrucosa decreased from four at 0.0 av to about two at 0.94 av. A method for determining mesothoracic spiracular, subelytral abdominal, and cuticular water-loss rates was described and validated for living E. armata. Subelytral abdominal water loss through the caudal opening was 8.0 mg H₂O (g·day)⁻¹, mesothoracic spiracular water loss was approximately 7.9 mg H₂ (g·day)⁻¹, and cuticular loss was 26.2 mg H₂O (g·day)⁻¹ at 30 C and 0.0 av. Evaporative water loss was shown to have two unidirectional components, efflux and influx, for both beetles with the use of tritiated water (H3HO). Efflux was independent of av, while influx increased linearly with av, with both components having lower rates in C. verrucosa compared with E. armata.