Acetic acid production in larval diets for the Mediterranean fruit fly, Ceratitis Capitata (Wiedemann), was suppressed to levels below OSHA permissible exposure limits using a combined treatment of pasteurization and antibiotics (oxytetracycline and streptomycin). Acetobacter spp., Gluconobacter oxydans , and Zymomonas mobilis strains were identified as the major bacteria responsible for acetic acid production in the diet. The treated diets had 50% less titratable acid than the untreated diets, resulting in atmospheric acetic acid levels of 5.0 over the first 6 d of larval development whereas untreated diets fell from pH 5.8-6.2 to pH 3.7-4.0 during the same period. As a result, treated diets improved pupal yields by 36-58% without any apparent adverse affects on insect quality.