- Carbon dioxide (CO2) as a greenhouse gas has been increasing in recent decades. Because an elevated atmospheric CO2 influences insect physiology and behaviour, we hypothesize that pheromone-mediated communication in the moth is affected by an increased CO2 level. We test the behavioural responses of male Helicoverpa armigera to sex pheromone in a wind tunnel, demonstrating a significant reduction of approaching behaviour to the odour source at a high CO2 level (1000ppm). Electroantennogram (EAG) responses of male to the pheromone component are also significantly suppressed in high CO2 environments (600 and 1000ppm), indicating that a high CO2 level inhibits both behavioural and electrophysiological responses of male to the sex pheromone. Interestingly, the EAG response of the whole head preparation of males is influenced more by the elevated CO2 level than that of the antenna-cut preparation. A sequential increase of CO2 levels from an ambient CO2 level also decreases the EAG response of the whole head but not of the labial palp-removed head, implying a potential mediation of labial palp in the head where the CO2 receptor is located. By contrast, sex pheromone production in females reared under or shifted to an elevated CO2 condition is increased, and the putative underlying mechanism for this is discussed. The present study provides an insight into the adaptive strategy of moth pheromone communication in a changing environment.