Artificial augmentation of soybean leaves with reduced glutathione (GSH) elicited all of the same responses from Mexican bean beetle (MBB),Epilachna varivestisMulsant, as did fumigation with the air pollutant sulfur dioxide. Larval growth, rate of development, and survivorship as well as adult fecundity and longevity were all significantly greater on excised leaves that had been allowed to imbibe a solution of the tripeptide. In addition, adults showed a strong preference for feeding on the treated leaves over nontreated leaves. Increased fecundity after feeding on treated leaves was a consequence of the earlier and longer period of egg laying rather than a change in the rate of egg production. The effects of GSH treatment were even more distinct than those produced by exposure of plants to the pollutant. These results establish the very close correlation between changes in foliar glutathione and alteration of MBB success on this plant in response to air pollution.