Development and fecundity were investigated in an invasive alien thrips species, Frankliniella occidentalis (Pergande), and a related native species, Frankliniella intonsa (Trybom), under high CO₂ concentration. Results show that the two thrips species reacted differently toward elevated CO₂ concentration. Developmental duration decreased significantly (11.93%) in F. occidentalis at the CO₂ concentration of 800 μl/liter; survival rate of all stages also significantly increased (e.g., survival rate of first instar increased 17.80%), adult longevity of both female and male extended (e.g., female increased 2.02 d on average), and both fecundity and daily eggs laid per female were higher at a CO₂ concentration of 800 μl/liter than at 400 μl/liter. Developmental duration of F. intonsa decreased, insignificantly, at a CO₂ concentration of 800 μl/liter. Unlike F. occidentalis, survival rate of F. intonsa declined considerably at higher CO₂ concentration level (e.g., survival rate of first instar decreased 19.70%), adult longevity of both female and male curtailed (e.g., female reduced 3.82 d on average), and both fecundity and daily eggs laid per female were reduced to 24.86 and 0.83, respectively, indicating that there exist significant differences between the two CO₂ levels. Results suggest that the population fitness of invasive thrips species might be enhanced with increase in CO₂ concentration, and accordingly change the local thrips population composition with their invasion.