Abstract:  Carbon dioxide (CO₂) is an important component of air. It is not only one of the main raw materials for plant photosynthesis, but also directly affects the life activities of insects as a chemical signal. CO₂ plays an important role in the foraging behavior of Diptera, Coleoptera and Lepidoptera. CO₂ can affect the oviposition behavior of flies and moths. CO₂ is an important indicator for social insects to adjust the climatic conditions in the nest. The research on the mechanism of CO₂ perception in insects can help to better understand the chemosensory systems in insects, and may also provide some new strategies for pest monitoring and control. Since the two CO₂ receptor genes GR21a and GR63a co-expressed in Drosophilia were indentified in 2017, CO₂ receptor genes of many insect species have been identified with the development of high-throughput sequencing techniques combined with sequence homology analysis. For this reason, the major breakthrough has been made in the research for the mechanism of CO₂ perception at the peripheral nervous system level in insects. The CO₂ receptor genes of insects are expressed on specific receptor neurons, which have the ability of sensing small fluctuations in the external CO₂ in the environment and further transmit the CO2 signal to the central nervous system of the brain. The transduction of CO₂ signal in the central nervous system can be divided into the processing in the primary brain center-antennal lobe and the processing in the higher brain center in insects. CO₂-projecting neurons form complex dendrites within specific glomerulus in the antennal lobe, and then continue to project toward the lateral horn and upward to the mushroom body of the higher centers in the brain. Homologous genes of CO₂ receptor genes have not been identified in the genomes of some insects, but the responses of these insects to CO₂ have been reported earlier, suggesting that other pathways sensing CO₂ exist in these insects. We summarized the related research progress from four aspects: the importance of CO₂ for the life activities of insects, the mechanism of CO₂ perception at the peripheral level in insects, the mechanism of CO₂ perception at the central nervous system level in insects, and other CO₂ perception pathways in insects. We also emphatically introduced the effects of CO₂ on insects and the identification and functional research of CO₂ receptor genes, providing some useful ideas and methods for the further study on the mechanism of CO₂ perception and the development of green prevention and control.

Key words: CO₂, perception mechanism, gustatory receptor, receptor neuron, functional characterization