Low temperature induced alterations in certain biochemical constituents of 5th instar larvae of Philosamia ricini (Lepidoptera: Satunidae)

Anita Singh, Ratnesh Kr Sharma, Bechan Sharma

Department of Biochemistry, University of Allahabad, Allahabad, UP, India

Abstract: Studies on cold acclimation of insects including silkworms have shown significant variations in the levels of various biomolecules to cope with heat-shock. The present study has been carried out on cold-stressed 5th instar Philosamia ricini Hutt larvae to assess the physiological strategy adopted by this silkworm species for its survival at low temperatures. In this study, various biochemical assays have been performed in hemolymph, silk gland, and fat body of the larvae. The results revealed that exposure to low temperatures (10°C ± 1°C) leads to the accumulation of high levels of glycerol content in hemolymph, silk gland, and fat body of larvae in comparison with control group reared at ambient temperature conditions (25°C ± 3°C). The treatment of P. ricini larvae with low temperatures resulted in decreased trehalose content in all 3 insect tissues tested. The activities of phosphatases (acid and alkaline) were found to be significantly increased. However, the activities of aminotransferases (L-alanine-2-oxoglutarate aminotransferase [GPT, EC: 2.6.1.2] and L-aspartate-2-oxoglutarate aminotransferase [GOT, EC: 2.6.1.1]) were significantly inhibited in the hemolymph. The data indicated that trehalose could function as the major carbohydrate source of energy in acclimated 5th instar P. ricini larvae, whereas glycerol appears to confer cryoprotection.

Keywords: acclimation, aminotransferases, hydrolases, silk gland, hemolymph