Functional characterization of carbon dioxide receptors in the fall armyworm, Spodoptera frugiperda

Abstract BACKGROUND Carbon dioxide (CO 2 ) is an important chemosensory cue involved in host plant recognition and environmental navigation in moths. In insects, CO 2 detection is generally mediated by specific gustatory receptors (GRs). This study aimed to identify and functionally characterize CO 2 ‐related GRs in the fall armyworm, Spodoptera frugiperda . RESULTS Three candidate GR genes, designated Sfru GR1, Sfru GR2, and Sfru GR3, were identified through genomic and transcriptomic analyses. Phylogenetic analysis showed that these receptors clustered with conserved insect CO 2 GRs and formed three distinct monophyletic clades. Quantitative real‐time PCR revealed that Sfru GR3 was expressed at significantly higher levels than Sfru GR1 and Sfru GR2 across multiple adult tissues and larval stages. Two‐electrode voltage clamp recordings in Xenopus oocytes showed that only the co‐expression of Sfru GR1 + Sfru GR3 among seven receptor combinations produced significant responses to bicarbonate ions (HCO₃ − ), which were used to represent dissolved CO 2 . Electrolabialpalpography assays demonstrated that FAW labial palps responded to CO 2 in a concentration‐dependent manner, with 1% CO 2 eliciting the strongest electrophysiological response, especially in females. In Y‐tube olfactometer assays, males were significantly attracted to 1% CO 2 , whereas females showed only a weak behavioral response. CONCLUSION These results indicate that Sfru GR1 and Sfru GR3 are key components of CO 2 perception in FAW. This study provides new insight into the molecular and behavioral mechanisms of CO 2 sensing in this destructive agricultural pest. © 2026 Society of Chemical Industry.