β-Glucosidase is validated as an elicitor for early immune responses in plants and it was detected in the salivary glands of Frankliniella occidentalis in previous research. Seven differentially expressed genes encoding β-Glucosidase were obtained by comparing the transcriptomes of F. occidentalis adults grown under two different CO ₂ concentrations (800 ppm vs. 400 ppm), which might be associated with the differences in the interaction between F. occidentalis adults and its host plant, Phaseolus vulgaris under different CO ₂ levels. To verify this speculation, changes in defense responses based on the production and elimination of reactive oxygen species (ROS) in P. vulgaris leaves treated with three levels of β-Glucosidase activity under ambient CO ₂ (aCO ₂) and elevated CO ₂ (eCO ₂) were measured in this study. The results showed that both leaves infested with thrips and those sprayed with the pure β-Glucosidase solution showed significant increases in ROS levels under aCO ₂ and eCO ₂, and the activities of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were increased correspondingly, while in leaves infested with FoβGlu-1-silenced thrips, the ROS levels and activities of these enzymes did not change significantly during the first 12 hours of injury regardless of CO ₂ level. Besides, significantly higher levels of ROS and lower activities of SOD, POD and CAT in injured leaves under eCO ₂ compared to aCO ₂ were noticed, which would negatively affect P. vulgaris leaves and facilitate thrips damage.