THERMAL-PROPERTIES FOR DIGESTIVE ENZYMES OF A SUB-ANTARCTIC BEETLE, HYDROMEDION-SPARSUTUM (COLEOPTERA, PERIMYLOPIDAE) COMPARED TO THOSE IN 2 THERMOPHILIC INSECTS

1. Proteolytic, lipolytic, amylolytic and cellulolytic activities were studied in adults of the phytophagous beetle, Hydromedion sparsutum, indigenous to the sub-Antarctic island of South Georgia. 2. Gastric enzyme activities were measured at experimental temperatures of 5-40-degrees-C and results were compared with those obtained from two thermophilic insects, Gryllus bimaculatus and Tenebrio molitor. 3. Protease and lipase activities in Hydromedion were 10-15 times lower than in Gryllus and Tenebrio. 4. In the temperature range of 5-15-degrees-C, alpha-amylase activity from Hydromedion was only slightly lower than that from Gryllus. 5. Hydromedion gut homogenates exhibited a distinct cellulolytic activity, even at a low temperature of 5-degrees-C. 6. Cellulolytic activity in the digestive tract of Hydromedion was confirmed by the evolution of (CO2)-C-14 after consumption of labelled cellulose. 7. The thermal properties of digestive enzymes agree well with the role of Hydromedion as primary decomposer in its ecosystem.