Like most pathogens, the subspecies of Bacillus thuringiensis (Bt) exhibit host specificity, which in this species is determined primarily by endotoxin proteins in combination with other virulence factors produced during vegetative growth. Recently, it has been proposed that naturally occurring midgut bacteria are the principal cause of death in insects intoxicated by Bt endotoxins, and that this species is not capable of reproduction in the hemolymph or cadavers of dead hosts. In the present study, using B. t. susp. kurstaki and B. t. subsp. aizawai, this general hypothesis is invalidated by showing that in natural hosts, as well as certain atypical hosts, Bt kills, colonizes and sporulates extensively in larval cadavers.