Abstract: Temperature tolerance of 5th instar larvae and pupae of three races of the silkworm, Bombyx mori at 35, 38 and 40℃ was studied. LT50 values and feducial limits were determined in each case by Probit analysis.  The multivoltine Pure Mysore showed better survival to high temperature treatment than the two bivoltine races. NB4D2 showed better temperature tolerance than CSR2 in the two bivoltine races.  The 90, 70 and 29 kDa heat shock protein bands appeared in the haemolymph after exposure of the larvae to 38℃ for 6 h and to 40℃ for 3 h. The 29 kDa protein band could not be detected in the haemolymph of bivoltine larvae during recovery.  But, expression of the 29 kDa protein was sustained during recovery in the larvae of Pure Mysore. When pupae were held at high temperature, the 90 and 70 kDa proteins were expressed, while the 29 kDa protein was not detected in the haemolymph. These results suggest that heat shock protein expression is associated with the occurrence of thermotolerance among tropical silkworm breeds, and growth stages within a breed.

Key words: Bombyx mori, race, haemolymph, heat shock proteins, thermotolerance