Experiments were conducted on adult females of Ceratitis capitata to determine (1) whether feeding a protein source in adulthood increases egg production (2) whether the females are self-selective with respect to feeding, and (3) whether deprivation of a protein source alters the perception threshold for this nutrient. The results obtained showed: that when a protein source is ingested throughout adult life, egg production is increased; that the females proved to be self-selective with respect to the choice of food, and that deprivation of a protein source alters the perception threshold.