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Pure Mysore and two bivoltine breeds NB4D2 and CSR2 were reared at 25°C, 30°C and 35°C and 75-80 RH% from a day before 4th moult till spinning. Larval weight, larval duration, silk gland weight, silk gland - somatic index, silk conversion index, silk productivity, ERR, rate of cocooning, cocoon yield, cocoon weight, shell weight, shell percentage, filament length and fecundity were significantly reduced at 35°C than at 30°C. The economic characters were affected more in bivoltine races than in PM, and in CSR2 than in NB4D2 in the two bivoltine races. Expression of economic characters, when late age worms were held at high temperature, has a functional value in the selection of high temperature tolerant breeds. The physiological basis of temperature compensation in the expression of economic traits in races having different limits of high temperature tolerance is examined. The severity of impairment of economic traits, and the time and the number of larvae and pupae died have a strong racial bias. [ABSTRACT FROM AUTHOR]