Culture medium of Bacillus thuringiensis serovar japonensis Buibui enhances the insecticidal activities of .DELTA.-endotoxins from B. thuringiensis serovar kurstaki and aizawai against lepidopterous pest insects.

The effects of the culture medium of Bacillus thuringiensis serovar japonensis Buibui on the insecticidal activities of B. thuringiensis formulations were investigated by a diet incorporation method using four lepidopterous insects, Spodoptera litura, Mamestra brassicae, Plutella xylostella and Adoxophyes honmai. Although the culture medium alone was not lethal to lepidopterous insects, its combination with δ-endotoxins from B. thuringiensis serovar kurstaki and aizawai, which were lethal only to lepidopterans, increased the toxicity higher than those by δ-endotoxins alone. The synergistic levels by the addition of culture medium reached a maximum of 42 fold based on a comparison of LC50, but the rates differed among species of insects tested and the kinds of δ-endotoxins used.