Effects of antibiotics on biological activity of Cry1Ac in Bt-susceptible and Bt-resistant Helicoverpa armigera strains

Abstract In this study, the results showed that the population of midgut bacteria and larval mortality due to Cry1Ac are significantly reduced in antibiotic-treated larvae from Bt-susceptible, -resistant and field-collected strains (96S, BtR, FS respectively) of Helicoverpa armigera . The percentage reduction of larval mortality with increasing concentrations of antibiotics was significantly different among strains with the smallest effect observed in FS. It has been suggested that antibiotics could influence the toxicity of Cry1Ac, possibly by eliminating gut bacteria, hence gut bacteria might be playing essential roles in Bt-induced killing of H. armigera . But elimination of midgut microflora with antibiotics had no effect on resistance level.