Biocontrol potential of Serratia marcescens isolates from Cydalima perspectalis: high larvicidal activity and chitinase gene diversity

Abstract Cydalima perspectalis (boxwood moth) is an invasive and harmful butterfly species that damages the leaves and branches of boxwood ( Buxus spp.) species. The need for alternative and environmentally friendly biological control strategies against chemical control methods necessitates the effective management of this pest. In this study, five bacterial isolates were obtained in pure form from C. perspectalis (boxwood moth) larvae. The isolates were identified as Serratia marcescens (CP1, CP3, CP4, CP5) and Pantoea dispersa (CP2) based on 16S rRNA gene sequencing, with similarity values ranging from 97 to 100%. To the best of our knowledge, this study provides the first report of Serratia marcescens isolated from C. perspectalis in Türkiye within a biological control context. Scanning electron microscopy (SEM) was used to visualize the bacterial morphology. The isolates were characterized for their growth at varying pH levels and NaCl concentrations, indicating a tolerance range of pH 6–9 and up to 5% NaCl for most isolates. PCR analysis of chitinase genes revealed diversity among S. marcescens strains: CP1 harbored all four chitinase genes (A, B, C, D), whereas CP3 and CP5 contained genes B and C, and CP4 had genes A and B. Bioassays conducted under controlled laboratory conditions demonstrated varying insecticidal activity of the bacterial isolates against C. perspectalis larvae. CP1 showed the highest larval mortality rate (86.6%) within 10 days, while CP2 exhibited significantly lower activity (p < 0.05). These findings suggest that S. marcescens , particularly the CP1 isolate, holds promise as a potential biocontrol agent against C. perspectalis .