Modulation of Carbohydrate Metabolism in Asiatic Rhinoceros Beetle (Oryctes rhinoceros [L]) Grubs in Response to Various Stressors

Abstract

Hemolymph of healthy grubs of Oryctes rhinoceros possesses trehalose content of 380 ± 30 mg/dl that is five times higher than the content of glucose. Experimental stressors, either internal or external have resulted in the elevation of glucose through degradation of trehalose mediated by the elevated activity of trehalase; the hyperglycaemia was disproportionate with the decrease of trehalose content. Glycogen phosphorylase (GP), an important enzyme of the skeletal muscle of vertebrates was located in the cell free hemolymph of grubs, at an exponentially elevated level of 320 ± 20 µmols/min/mg protein. Both GP and Hexokinase showed a sharp reduction in activity under exposure to stressors. Accumulation of lactic acid along with an increase in lactate dehydrogenase activity was observed. Inhibition of GP activity by hyperglycaemia together with decline of hexokinase and glyceraldehyde-3-phosphate dehydrogenase, proves that the larvae might have adopted an energy conserving mechanism and thereby channelling glucose for the purpose of defense. Elevation of glucose-6-phosphatase and glucose-6-phosphate dehydrogenase during stress may also help them to synthesis defensive chemicals like glutathione and polyols. Existence of such a wonderful biochemical mechanism helps them to thrive very well in cow dung pits a microenvironment possessing biotic and abiotic stressors, without undergoing diapause.