Transcriptomic responses of red palm weevil (Coleoptera: Curculionidae) larvae to low-temperature exposure

The red palm weevil, Rhynchophorus ferrugineus (Olivier), is one of the most destructive palm pests worldwide. Despite its tropical origin, this species tolerates moderately low temperatures and has an expansion potential that may be enhanced by global warming. However, the molecular mechanisms underlying cold stress remain poorly understood. This study provides a transcriptomic analysis of its larval response to cold stress. Using RNA-Seq on larvae exposed for 7 d to a sublethal low (5 °C) or control (23 °C) temperature, we identified 701 differentially expressed unigenes (580 protein-coding genes, 81 long noncoding RNAs [lncRNAs], and 40 with transposable elements [TEs]), of which 448 were upregulated and 253 downregulated under cold exposure. Functional enrichment revealed strong repression of cell cycle, along with the induction of stress-responsive pathways, including small heat shock proteins, detoxification enzymes (CYPs, UDP-glucuronosyltransferase), immune effectors (antimicrobial peptides, lectins, peptidoglycan-recognition proteins), and genes involved in cuticle remodeling. A subset of differentially expressed lncRNAs and TE-linked genes was associated with immune and chaperone responses, suggesting multilayered transcriptional regulation. These results indicate that R. ferrugineus larvae respond to low temperature by downregulating non-essential, energy-intensive programs while activating molecular chaperones, detoxification and immune defenses, and reinforcing structural barriers. This pattern, probably underestimated by the stronger starvation stress of controls, is consistent with an integrated strategy involving metabolic depression and enhanced cryoprotection. Our results represent a fundamental step that will guide data-driven studies to determine whether the cold-response mechanisms identified here are fully deployed in R. ferrugineus, as well as for future research on novel pest control strategies.