Isolation and characterization of an entomopathogenic Serratia strain against rice delphacid planthoppers.

BACKGROUND: Delphacid planthoppers (Hemiptera: Delphacidae), including the brown planthopper (Nilaparvata lugens), pose a significant threat to global rice production, highlighting the urgent need for sustainable and effective biological control agents. Here, we isolated a virulent strain of Serratia nematodiphila named BPH1 from diseased N. lugens and characterized its insecticidal activity, genomic features, and virulence-associated phenotypes. RESULTS: S. nematodiphila BPH1 exhibited median lethal concentrations (LC50) of 5.5 × 104 and 2.4 × 108 CFU/mL for N. lugens adults and nymphs, respectively. At a concentration of 108 CFU/mL, the median lethal time (LT50) was approximately 15 h for adults and 45 h for nymphs. Whole-genome sequencing revealed a 5.15 Mb draft genome assembly containing a complete prodigiosin biosynthetic gene cluster and multiple serralysin metalloprotease genes, representing candidate virulence-associated genomic features. The strain exhibited extracellular protease activity and swimming and swarming motility in vitro, which are commonly associated with bacterial entomopathogenicity. In insecticidal-spectrum assays, the strain caused mortality in two additional delphacid planthoppers, Laodelphax striatellus and Sogatella furcifera, and in the mosquito Aedes albopictus, whereas it showed no pathogenicity toward the green peach aphid Myzus persicae under the tested conditions. CONCLUSION: These results reveal a virulent Serratia strain with strong insecticidal activity against rice planthoppers, and highlight genomic and phenotypic features potentially associated with pathogenicity. © 2026 Society of Chemical Industry.