Alleviation of acetic acid production during mass rearing of the Mediterranean fruit fly (Diptera: Tephritidae)

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 < 1.2 ppm. Atmospheric acetic acid levels from untreated diets at times exceeded 18 ppm, which is nearly double the OSHA limits of 10 ppm. An unexpected result of this study was the ability to control dietary pH levels over the most critical period of larval development (0-6 d). Treated diets maintained pH 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 effects on insect quality.