Pathogenicity of intrathoracically administrated Bacillus thuringiensis spores in Blatta orientalis

The ability of Bacillus thuringiensis to produce septicaemia in Periplaneta americana and Blatta orientalis has been investigated. Spores and crystals from several wild-type strains as well as spores of a B. thuringiensis crystal-deficient mutant, were first orally administrated at high doses, and no significant mortality was recorded. Intrathoracic injection of spore suspensions in P. americana revealed that this species is not very susceptible to B. thuringiensis spores. B. orientalis, by contrast, was found to be very susceptible to B. thuringiensis, with a LD(50) of about 35,000 spores, that is similar to that reported on Lepidoptera challenged with parenterally injected B. thuringiensis.