EFFECT OF HIGH TEMPERATURE ON PROTEIN AND FREE AMINO ACID LEVELS IN THREE SELECTED SILKWORM RACES

Two bivoltine races viz. KA and CSR acclimated to temperate climates, and one multivoltine race viz. C.Nichi acclimated to tropical climates were exposed to two selected high temperatures of 31°C and 36°C during 5" instar larval growth period from 4" moult to spinning covering viz., moult, post moult and feeding stages. The levels of total protein in the haemolymph, increased during feeding period from first day of 5" instartill sixth day. From seventh day till spinning, the protein levels decreased in all the three races. The levels of free amino acids, which are high during 4" moult, declined through the 5" age of larval development till spinning. C.Nichi showed a relatively higher free amino acid level in haemolymph followed by KA and CSR. Racial differences in the changes in the levels of protein and free amino acids in the haemolymph were observed in the larvae when subjected to two high temperature regimes of 31°C and 36°C. The results showed that high temperature induces specific changes in the metabolism (reversible thermal stress) that have different adaptive value in different races of the silkworm. Relatively higher increase in the free amino acid levels in the haemolymph of C.Nichi presumably provides protective cover to tissues against high temperature by an increase in osmolarity and reduction in evaporative water loss. The absence of such a mechanism may be responsible for temperature susceptibility of the bivoltine races like KA and CSR.