Abstract: Studies on mortality and rate of development of Helicoverpa armigera due to feeding of spore- -endotoxin complex of indigenous strain HD-695 (8,500 IU mg-1) and standard strain HD-1-S-1980 (16,000 IU mg-1) of Bacillus thuringiensis var. kurstaki revealed that the differences in potencies did not cause significant differences in retardation. Both the bacterial toxins induced similar biological effects (significant larval mortalities, marked larval retardation, reduction in pupation, emergence and fecundity, as well as inconsistent increase in pre-oviposition period and prolongation of generation period) of the test insect.