Synergistic Effects of Supernatants from Serratia marcescens Culture on Larvicidal Activity of Bacillus thuringiensis Cry1C Toxin against Common Cutworm, Spodoptera litura

The supernatants of Serratia marcescens culture was shown to possess an enhancing effect on the larvicidal activity of Bacillus thuringiensis delta-endotoxin (Cry1C) against the common cutworm, Spodoptera litura. The synergistic effect was observed in both larval mortality and growth inhibition. The synergistic activity increased in proportion to the increment either of the supernatant or CrylC concentration. The addition of supernatants of S. marcescens culture to Cry1C was able to enhance the insecticidal activity of delta-endotoxin over 8 fold compared with that of toxin alone. The synergism was very high to the insecticidal activity against S. litura but not in other three lepidopterous insects tested, i.e., Mamestra brassicae, Plutella xylostella and Adoxophyes honmai. Therefore the synergistic activity of the supernatants of S. marcescens culture seemed to be specific to insect species.