Pathogenicity of a novel Serratia marcescens strain against the rice leaf folder Cnaphalocrocis medinalis and...

Frequent outbreaks of the rice leaf folder Cnaphalocrocis medinalis cause severe yield losses in rice across Asia. Reliance on chemical insecticides has accelerated resistance development, underscoring the urgent need for alternative strategies and deeper insight into underlying biological mechanisms. Entomopathogenic bacteria serve as important models to investigate insect-pathogen interactions and host immune responses, offering perspectives on the mechanisms driving insect mortality.

We report the discovery of a novel pathogenic strain of Serratia marcescens (strain PQJ-1), isolated from naturally diseased C. medinalis larvae, using culture-dependent methods combined with 16S rRNA sequencing. This strain showed remarkably high larvicidal activity, with mortality reaching 86% at 8 × 10⁸ CFU mL^-1 and an LC₅₀ of 0.872 × 10⁶ CFU mL^-1. Notably, early instars showed heightened susceptibility, indicating strong stage-dependent variation in host susceptibility post bacterial infection. Beyond mortality, mechanistic innovation was revealed through transcriptome profiling, which identified 686 differentially expressed genes (DEGs) in infected larvae. Functional analyses uncovered broad disruptions to host metabolic and immune pathways, offering novel insights into host-pathogen interactions. qRT-PCR validation further strengthened the robustness of these findings.

This is the first report of a high-virulence S. marcescens strain against C. medinalis coupled with transcriptomic insights into its pathogenic mode of action. The findings primarily advance the mechanistic understanding of insect-pathogen interactions and facilitate future identification of microbial insecticidal factors. © 2026 Society of Chemical Industry.