Carbon dioxide (CO₂) released by plants can serve as a cue for regulating insect behaviors. Hyphantria cunea is a widely distributed forestry pest that may use CO₂ as a cue for foraging and oviposition. However, the molecular mechanism underlying its ability to sense CO₂ has not been elucidated. Our initial study showed that CO₂ is significantly attractive to H. cunea adults. Subsequently, 44 H. cunea gustatory receptors (GRs) were identified using transcriptome data, and 3 candidate CO₂ receptors that are specifically expressed in the labial palps were identified. In vivo electrophysiological assays revealed that the labial palp is the primary organ for CO₂ perception in H. cunea, which is similar to findings in other lepidopteran species. By using the Xenopus oocyte expression system, we showed that the HcunGR1 and HcunGR3 co-expressions produced a robust response to CO₂, but HcunGR2 had an inhibitory effect on CO₂ perception. Finally, immunohistochemical staining revealed sexual dimorphism in the CO₂-sensitive labial pit organ glomerulus (LPOG). Taken together, our results clarified the mechanism by which H. cunea sense CO₂, laying the foundation for further investigations into the role of CO₂ in the rapid spread of H. cunea.