The Control of Water Loss in Desert Tenebrionid Beetles

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Abstract
1. Total water loss in tenebrionid beetles was composed of transpiratory losses from the cuticle and spiracles, water associated with defaecation, and water from the release of defensive quinone droplets or oral fluids. 2. Freshly killed specimens of E. armata, C. muricata and C. verrucosa had higher transpiration rates over long and short exposures than did living animals of the same species. These results may reflect the cessation of active water retention by cuticular and spiracular regulation in dead animals. 3. Cuticular transpiration, although low in absolute rate, was a greater source of water loss than respiratory transpiration in E. armata, C. muricata and C. verrucosa at temperatures from 25 to 42.5 °C and at 0% R.H., suggesting that spiracular control of water loss was of considerable importance in maintaining water balance. 4. A marked increase in respiratory transpiration over previous low rates was observed at 40 °C for E. armata and at 42.5 °C for C. muricata and C. verrucosa, and indicated a temperature-induced breakdown in spiracular water regulation due to increased respiratory activities. In contrast, cuticular transpiration maintained a linear rate of increase over the temperature range investigated. 5. A direct relationship existed between oxygen consumption and estimated respiratory transpiration for E. armata from 25 to 40 °C and at 0% R.H. 6. Evidence for the presence of discontinous respiration and unidirectional tracheal air flow in E. armata was presented. 7. Cuticular transition temperatures were measured for E. armata (40 °C), C. muricata (47.5 °C), and C. verrucosa (50 °C) with results showing that the autumn species (E. armata) possessed a lower cuticular breakdown point than either of the two summer species. 8. Much of the success of tenebrionid beetles in desert habitats is due to the development of highly impermeable cuticles and well regulated spiracular control mechanisms for reducing the loss of body water.

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