Tobacco hornworm, Manduca sexta L., larval feeding studies were conducted on field-grown immature green or ripening yellow-green leaves of ‘K 326’ flue-cured tobacco, Nicotiana tabacum L., in 1994. The effects of leaf maturity on hornworm survival rate, days to complete each larval stage, pupal weight, and total consumed leaf area were measured. Tobacco hornworms fed yellow-green tobacco leaves required significantly more days to complete development to pupation and adult emergence (23.1 q and 39.3 d, respectively) than corresponding larvae reared on green leaves (19.8 d and 36.1 d). Larval survival and pupal weights were similar for individuals reared on both leaf types. The hornworm larvae reared on yellow-green leaves consumed significantly more total leaf area (1877 cm² vs. 1586 cm²) than did larvae reared on green leaves. Results indicate that hornworms are capable of causing late-season economic losses to flue-cured tobacco. Thus, this pest must be monitored throughout the entire production season and control measures applied when necessary until harvesting is completed.