Effects of cadmium stress on the biological fitness and insecticide susceptibility of the rice pest brown planthopper, Nilaparvata lugens (Stål)

BACKGROUND The brown planthopper (BPH) is one of the most destructive migratory pests of rice. In paddy ecosystems, cadmium (Cd) contamination and pesticide exposure are major environmental stressors. However, studies simulating BPH immigration into and emigration from Cd‐contaminated areas, and evaluating the effects of Cd on BPH development, reproduction, and insecticide susceptibility remain scarce. RESULTS Continuous Cd stress over three generations significantly reduced parental female longevity and fecundity, and decreased offspring egg hatchability. Compared to the control, the relative fitness values of the offspring population produced by 0.1, 0.5, and 2.5 mg/L Cd‐treated parents decreased to 0.78, 0.72, and 0.51, respectively. Furthermore, Cd exposure markedly increased BPH susceptibility to chlorpyrifos (median lethal concentration (LC 50 ) from 27.91 to 19.55 mg/L), imidacloprid (from 481.94 to 226.89 mg/L), nitenpyram (from 14.03 to 9.60 mg/L), and sulfoxaflor (from 19.69 to 12.14 mg/L). This increased susceptibility was further demonstrated to be associated with the down‐regulation of five detoxification genes – CYP417A2 , UGT386G2 , UGT386N1 , ABCH1 , and CarE2 . Transcriptomic analysis revealed that differentially expressed genes were significantly enriched in cuticle‐related pathways. Moreover, transmission electron microscopy showed reduced cuticle thickness under Cd stress. In addition, microbiomic analyses revealed a marked increase in the symbiont Arsenophonus , which is known to correlate with higher insecticide susceptibility. CONCLUSION These results show Cd stress impairs BPH fitness and increases susceptibility to multiple insecticides. These changes may be caused by the down‐regulation of detoxification genes, reduced cuticular barrier function, and shifts in symbiotic bacteria. These findings provide a mechanistic basis for adaptive pest management strategies in Cd‐contaminated rice agroecosystems, thereby supporting more sustainable and effective control practices.