Functional characterization of carbon dioxide receptors in the fall armyworm, Spodoptera frugiperda.
BACKGROUND: Carbon dioxide (CO2) is an important chemosensory cue involved in host plant recognition and environmental navigation in moths. In insects, CO2 detection is generally mediated by specific gustatory receptors (GRs). This study aimed to identify and functionally characterize CO2-related GRs in the fall armyworm, Spodoptera frugiperda. RESULTS: Three candidate GR genes, designated SfruGR1, SfruGR2, and SfruGR3, were identified through genomic and transcriptomic analyses. Phylogenetic analysis showed that these receptors clustered with conserved insect CO2 GRs and formed three distinct monophyletic clades. Quantitative real-time PCR revealed that SfruGR3 was expressed at significantly higher levels than SfruGR1 and SfruGR2 across multiple adult tissues and larval stages. Two-electrode voltage clamp recordings in Xenopus oocytes showed that only the co-expression of SfruGR1 + SfruGR3 among seven receptor combinations produced significant responses to bicarbonate ions (HCO₃-), which were used to represent dissolved CO2. Electrolabialpalpography assays demonstrated that FAW labial palps responded to CO2 in a concentration-dependent manner, with 1% CO2 eliciting the strongest electrophysiological response, especially in females. In Y-tube olfactometer assays, males were significantly attracted to 1% CO2, whereas females showed only a weak behavioral response. CONCLUSION: These results indicate that SfruGR1 and SfruGR3 are key components of CO2 perception in FAW. This study provides new insight into the molecular and behavioral mechanisms of CO2 sensing in this destructive agricultural pest. © 2026 Society of Chemical Industry.