Comparative Transcriptomics Reveals Insecticide-Specific Responses of Diaphorina citri to Chlorpyrifos and Thiamethoxam
The Asian citrus psyllid, Diaphorina citri, is the primary vector of Huanglongbing (HLB), the most devastating citrus disease worldwide. While chemical control using organophosphates (chlorpyrifos) and neonicotinoids (thiamethoxam) remains the primary management strategy, the emergence of insecticide resistance necessitates a deeper understanding of vector molecular responses. In this study, we conducted a comparative RNA-seq transcriptomic analysis of adult D. citri exposed to median lethal concentrations of chlorpyrifos (DSP) and thiamethoxam (SCQ). Toxicity bioassays revealed thiamethoxam to be significantly more toxic than chlorpyrifos. Transcriptomic profiling identified 557 and 896 differentially expressed genes (DEGs) in the DSP and SCQ treatments, respectively, with profound transcriptional downregulation dominating both responses. Functional enrichment analysis demonstrated a shared systemic suppression of chitin-based cuticle development, indicating an overarching structural defense mechanism. However, distinct metabolic reprogramming emerged between the two chemical classes. Chlorpyrifos specifically upregulated lipid and amino acid metabolism to fuel energy-intensive detoxification, whereas thiamethoxam triggered endocytosis pathways, disrupted hormone biosynthesis, and induced a markedly stronger cytochrome P450 response. Notably, classic target-site genes remained transcriptionally stable across treatments. Furthermore, Weighted Gene Co-expression Network Analysis (WGCNA) identified distinct co-expression modules and core hub genes, including sulfotransferases and chitin-binding proteins, driving these divergent stress responses. These findings elucidate the dual architecture of D. citri defense, a shared cuticular response superimposed with class-specific metabolic detoxification, providing crucial molecular targets for resistance management and RNAi-based control strategies.