Fate of Bacillus thuringiensis strains in different insect larvae

In favorable conditions Bacillus thuringiensis spores germinate and vegetative cells multiply, whereas in unfavorable conditions Bacillus thuringiensis sporulates and produces insecticidal crystal proteins. The development of B. thuringiensis strains was investigated in the larvae of insects belonging to the orders Lepidoptera and Diptera. Bacillus thuringiensis strains able to kill the insects did not always multiply in cadavers. Strains with no specificity to kill the insect sometimes multiplied when the insects were killed mechanically. These results indicate that some insect larvae represent an environment that favors the germination of B. thuringiensis spores and the multiplication of vegetative cells; however, there was no correlation between the toxin specificity and the specificity of the host.