Synergistic and additive interactions of Serratia marcescens S-JS1 to the chemical insecticides for controlling Nilaparvata lugens (Hemiptera: Delphacidae)

The combined use of entomopathogens and chemical agents has been suggested as an alternative strategy to control pest insects. However, the effectiveness of combinations of entomopathogenic bacteria and insecticides against rice planthoppers is largely unknown. Here, we evaluated the separate and combined effects of an entomopathogenic bacterium, Serratia marcescens S-JS1, and spirotetramat or thiamethoxam insecticides against third-instar nymphs of Nilaparvata lugens Stål (Hemiptera: Delphacidae) under laboratory and greenhouse conditions. Under laboratory conditions, the combinations caused higher mortality in the third-instar nymphs of N. lugens and produced a synergistic or additive effect compared with the treatments with either bacterial suspension or insecticide alone. Application of S-JS1 (1 × 109 cfu/ml) in combination with 20 mg/liter spirotetramat resulted in 80.5% of N. lugens nymphal mortality, compared with 52.7% in spirotetramat alone treatments, and interactions resulted in a synergistic responses. Other combination treatments of S-JS1 with either insecticide concentration all exhibited additive interactions. In further greenhouse tests, S-JS1 (1 × 109 cfu/ml) + spirotetramat (20 mg/liter) and S-JS1 (1 × 109 cfu/ml) + thiamethoxam (5 mg/liter) showed additive effects against the nymphs, and were found to be most effective relative to their individual treatments on days 5 and 9. Our results indicate that S. marcescens S-JS1 combined with insecticide may provide a promising new strategy for controlling N. lugens.