Water Relations of the Desert Blister Beetle Cysteodemus armatus (Leconte) (Coleoptera: Meloidae)

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Abstract
Several parameters of the xeric adaptiveness of the desert blister beetle Cysteodemus armatus were studied in the field and laboratory. Field measurements demonstrated that these beetles were most active during warmer parts of the day with exposure to high air (>35 C) and soil (>55 C) temperatures. Beetles had body temperatures consistently higher than ambient air temperatures but less than substrate temperatures. Rates of water loss (173 mg day⁻¹, including fecal losses), gravimetrically determined in the laboratory at 30 C, were higher than field-determined tritiated water turnover (125 mg day⁻¹). The for water loss were highest (5.4) at 25-30 C and lowest at 30-35 C (1.6). Cysteodemus armatus is subjected to stressful conditions and compensates for water losses with water-rich food (creosote flowers with 85% water content). However, the voracious feeding habits of these beetles are most likely devoted to energy accommodation rather than the water balance. Females ingest a mean of 185 cal day⁻¹, with a fecal output of 41 cal day⁻¹ and a metabolic output of 71 cal day⁻¹, providing about 73 cal day⁻¹ for egg production, with a batch of 100 eggs produced every 3.2 days. Under stress with no food available the beetles have higher rates of water loss than any other desert species studied. The major water saving displayed by stressed animals is through reduction of fecal water output. A total water budget showed a gain of 200 mg day⁻¹ and losses of 184 mg day⁻¹, excluding reproductive losses.