Abstract: Two bivoltine races viz. NB4D2 and CSR2 acclimatized to temperate climates, and one multivoltine race viz., Pure Mysore (PM) acclimatized to tropical climates were exposed to two selected high temperatures of 32℃ and 36℃ during 5th instar larval and pupal stages. The tropical multivoltine PM showed less larval and pupal mortality than temperature tolerant bivoltine NB4D2 and temperature sensitive bivoltine CSR2. Haemolymph trehalose levels were relatively higher, and glucose level and trehalase activity lower during moult. At 32℃ and 36℃, haemolymph sugar level and trehalase activity showed only a marginal increase during larval moult. Moulted larvae showed a significant drop in haemolymph trehalose level and increase in trehalase activity and glucose levels. Also, the moulted larvae showed a further decrease in trehalose levels and increase in glucose level and trehalase activity when exposed to higher temperature. Feeding larvae showed a significant drop in glucose level and increase in trehalose level in haemolymph at 25±1℃. At 32℃ and 36℃, haemolymph glucose and trehalose levels and trehalase activity increased in feeding larvae in PM and NB4D2 but decreased in CSR2. Spinning larvae showed a significant decrease in haemolymph glucose level and trehalase activity and marginal decrease in trehalose level. At higher temperatures, an increase in blood sugar level and trehalase activity was observed in spinning larvae in temperature tolerant PM and NB4D2 and decrease in temperature sensitive CSR2. Haemolymph sugar level and trehalase activity increased during pupal development in all the three races. At the two higher temperatures, the haemolymph sugar  level and trehalase activity increased in PM. But, in NB4D2 the   increases in haemolymph sugar level and trehalase activity in pupae at 36℃ were less than those at 32℃. In CSR2, an increase in haemolymph glucose level was observed at 32℃ but haemolymph glucose decreased to the level lower than the control when the ambient temperature of the pupae was raised to 36℃. But, haemolymph trehalose level and activity decreased when the pupae of CSR2 were held at higher temperatures, the decrease being more at 36℃ than at 32℃. Acclimation to high temperature in the mulberry silkworm, Bombyx mori thus depended upon the race and developmental stage in the life cycle and was manifested by the changes in haemolymph sugar level and trehalase activity.

Key words: Bombyx mori, haemolymph, glucose, trehalose, trehalase, temperature tolerance, acclimation