The nutritional interaction between niacin (nicotinic acid) and a group of nine other B vitamins in the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), larval diet was evaluated. Four doses of niacin (0, 0.2, 2.0, and 20 ppm) and four doses of a mixture of nine other B vitamins (0, 7.07, 70.7, and 707 ppm) in the diet were cross-tested. The other B vitamins consisted of thiamin, riboflavin, pantothenic acid, pyridoxine, folic acid, biotin, inositol, choline chloride, and p-amino benzoic acid. Diets with high doses (≥70.7 ppm) of the other B vitamins and low doses (≤0.2 ppm) of niacin resulted in no pupal recovery. However, a delayed larval duration and reduced pupal recovery resulted when no niacin and 7.07 ppm or lower of the other B vitamins were compared with those from a complete diet that contained 20 ppm niacin and 707 ppm of the other B vitamins. With omission of the other B vitamins, larval duration was delayed but was not dose dependent on niacin. Pupal recovery was not affected if niacin levels were maintained at or >0.2 ppm and the other B vitamins were absent. With 20 ppm of niacin in the diet, the larval duration and pupal recovery were dependent on the dose of the other B vitamins. Larval durations were shortened with elevated doses of the other B vitamins, whereas pupal recoveries increased with elevated dose of the other B vitamins. Therefore, the other vitamins reduced the larval duration when niacin was maintained at ≥2 ppm. When the niacin levels decreased to ≤0.2 ppm, doses of the other vitamins has to be reduced <7.07 ppm to maintain normal larval development.