Gut microflora of Helioverpa armigera influences the biological activity of the delta-endotoxins of the bacterium, Bacillus thuringiensis

Studies were carried out to understand the role of gut microbes in biological activity of the bacterium, Bacillus thuringiensis (Bt) toxin proteins towards cotton bollworm, Helicoverpa armigera. The artificial diet amended with a range of concentrations of antibiotic compounds were used to eliminate the gut microbes of H.  armigera. Mortality of insects fed on diets with Bt and toxin proteins (Cry1Ab and Cry1Ac) was inversely proportional to the concentration of antibiotics in the artificial diet. Nearly 30% reduction in larval mortality was observed from F₁ to F₃ generations when the larvae were reared on diets without antibiotics (with gut microbes) and fed on 0.15% Bt or 12 µg Cry1Ab/Cry1Ac ml^-1 diet, indicating development of resistance to Bt. However, there were no significant differences in larval mortality due to Bt, Cry1Ab or Cry1Ac across generations in insects reared on diets with 250 µg of each antibiotic ml^-1 diet (without gut microflora). The results suggested that gut microflora influenced biological activity of Bt towards H. armigera, and any variation in diversity and abundance of gut microflora will have a major bearing on development of resistance in H. armigera to Bt transgenic crops.