UV-A radiation reshapes physiological traits and post-stress biocontrol performance of Serratia marcescens CS-1 against Carposina sasakii

Solar ultraviolet-A (UV-A) radiation is an important environmental factor that may limit the field performance of microbial biocontrol agents, but its effects on entomopathogenic bacteria remain insufficiently understood. In this study, we evaluated the effects of gradient UV-A irradiation durations (0–120 min) on the survival, physiological traits, secondary metabolite production, and biocontrol efficacy of Serratia marcescens CS-1 against Carposina sasakii. UV-A exposure markedly reduced CS-1 survival, with a sharp decline observed after 12 min of irradiation, followed by a low-level residual survival phase. Kinetic analysis further supported this non-linear inactivation pattern, with an estimated residual survival level of 9.14% and a half-life of 7.84 min for the UV-A-sensitive fraction. UV-A also reshaped antioxidant enzyme responses: CAT and GSH-Px activities declined rapidly during early irradiation, whereas Prx activity increased under prolonged exposure. During post-stress recovery, prodigiosin production and chitinase activity showed non-linear changes, indicating that UV-A affected not only immediate viability but also subsequent metabolic regulation in survivor-derived populations. Insect bioassays showed that UV-A reduced the immediate insecticidal activity of directly irradiated suspensions, while re-cultured survivor-derived suspensions retained relatively strong larvicidal potential. Overall, these findings demonstrate that UV-A influences CS-1 through coordinated effects on survival, stress physiology, secondary metabolism, and post-stress biocontrol performance. This study provides useful evidence for improving the environmental stability and application strategy of S. marcescens-based biocontrol agents.