Water balance and rectal absorption in the grasshopper Oedipoda

ABSTRACT. The xeric grasshopper Oedipoda germanica pyrenaica (Uvarov, 1936) has a daily cycle of water-gain from feeding during the afternoon and water-loss at night. The afternoon peak of water-gain in laboratory animals is correlated with a short-term rise in the osmotic pressure of the haemolymph in field animals. It is estimated that starved large animals would deplete their water reserves within 8–11 days. Water loss in faeces production is a major component of total water loss only during the late afternoon to early evening; at all other times transpiratory water losses are considerably greater. Overall, 23% of the daily water loss occurs through the faeces. From hindgut cannulation experiments, c. 80% of water entering the rectum is reabsorbed. A comparison of transpiratory water losses of xeric and mesic Orthoptera and some xeric Coleoptera revealed that water losses are some 6–7 times higher in Orthoptera than in similar sized Coleoptera.