Comparative Transcriptome Analysis of Rhynchophorus ferrugineus (Coleoptera: Curculionidae) Reveals Potential Mechanisms Involved in the Toxication and Detoxification of the External Immune Compound p-Benzoquinone Present in Oral Secretions

p-Benzoquinone (PBQ), a highly toxic compound, is the main active component in larval oral secretions of red palm weevil (RPW), <i>Rhynchophorus ferrugineus</i>, playing critical roles in external immunity and pathogen defense. In this study, we demonstrated that pathogens effectively induce RPW larval external immune responses. On this basis, the toxicity of PBQ to third-instar larvae was determined, with poisoning symptoms observed. The differences in gene expression between larvae before and after treatment with PBQ were analyzed by transcriptome sequencing to potentially involve the mechanisms of PBQ toxicity on larvae and the mechanisms of detoxification in the infected larvae. The results indicated that PBQ exposure was associated with altered expression of chitinase (CHI) and phenoloxidase (PO) genes in RPW larvae, which not only affects the digestion and degradation of the old cuticle but also activates phenoloxidase, further oxidizing tyrosine for its conversion into DOPA and dopamine, resulting in the generation of melanin and different degrees of cuticular melanization. The transcriptional changes further suggest that RPW larvae may employ metabolic processes to counteract the external immune-active compound PBQ toxicity by regulating the expression levels of detoxifying enzyme-encoding genes, such as cytochrome P450 (<i>CYP450</i>), glutathione S-transferase (<i>GST</i>), and ATP-binding cassette transporter (<i>ABC</i>). Our research provides potential novel strategies for pest control by targeting insect metabolic detoxification systems.