Abstract
Fate of Bacillus thuringiensis orally introduced into the last instar larvae of the silkworm, Bombyx mori, and the fall webworm, Hyphantria cunea, was studied. In the larvae which survived the inoculation of B. thuringiensis, the bacteria were rapidly discharged from the alimentary canal. In contrast, in the cadavers of the larvae which died as a result of the inoculation of B. thuringiensis, the number of viable cells of this bacterium increased 15 to 66 times and the sporulation was evident. However, in the cadavers of the silkworm larvae in the late autumn and in the fall webworm larvae of the third generation, the growth and sporulation of B. thuringiensis were suppressed by coexisting enteric bacteria. These results suggest that the recycling of B. thuringiensis in nature takes place in insect cadavers under the low density of competitive microorganisms.
