DESICCATION RESISTANCE AND WATER-BALANCE IN SOUTHERN AFRICAN KERATIN BEETLES (COLEOPTERA, TROGIDAE) - THE INFLUENCE OF BODY-SIZE AND HABITAT

Desiccation resistance and water balance nj ere examined in the adults of seven trogid species, which differed both in body size and in the habitats from which they were collected. Body water contents (51-58% f resh mass) and desiccation rates at 27 degrees C (0.00026-0.00093 g h( -1)) in these species were very similar to those of unrelated, similar -sized beetles from arid habitats. The keratin beetles differed marked ly from many other adult Coleoptera by virtue of their very high haemo lymph osmolality and inability to regulate haemolymph osmolality, and to catabolise lipids for water production, during desiccation. Like mo st other insects, the xeric trogid species had lower rates of water lo ss and longer survival times than trogids from mesic areas, This was d ue both to lower rates of water loss and to the larger body size of sp ecies from the more arid areas. Because absolute body water content wa s higher in large beetles than in small ones, larger body size conferr ed higher desiccation resistance on the very large Kalahari desert spe cies. This suggests that there may be strong selection for large body size in such insects from arid areas. Most ecological and ecophysiolog ical investigations of geographical variation in body size, and the sp ecies-body size distribution, have focused on temperature and metaboli c rate as explanatory variables. This study suggests that attention sh ould also be given to desiccation resistance.