Synergy between zwittermicin A and Bacillus thuringiensis subsp kurstaki against gypsy moth (Lepidoptera : Lymantriidae)

Bacillus cereus French & French increased the mortality of 3rd-instar gypsy moths, Lymantria dispar (L.), caused by Bacillus thuringiensis subsp. kurs taki Berliner. B. cereus did not cause mortality of L. dispar when applied alone. The activity of various B. cereus strains was correlated positively with their accumulation of zwittermicin A, an aminopolyol antibiotic, in cu lture. When a constant dose of B, thuringiensis subsp. kurstaki and increas ing concentrations of purified zwittermicin A were applied to artificial di et, mortality of larvae was directly proportional to the dose of zwittermic in A. Zwittermicin A by itself caused no mortality at the concentrations te sted. Addition of zwittermicin A to a culture of a mutant strain of B, cere us that does not accumulate zwittermicin A restored. synergistic activity. These results indicate synergy between B. thuringiensis subsp. kurstaki and zwittermicin A. The potential for enhancing efficacy of B. thuringiensis a nd delaying development of insect resistance are discussed.