Inert reusable substrates as potential replacements for wheat bran in larval diets for Mediterranean fruit fly, Ceratitis capitata (Wied.) (Dipt., Tephritidae)

Abstract

Two small-scale experiments were undertaken to evaluate the substitution of various inert substrates for wheat bran in the bulk larval diets of Mediterranean fruit fly. In the first experiment, the bran component was removed from the standard Seibersdorf diet and the remaining ingredients added to either diced high-density (HD) sponge, sheet HD sponge, diced low-density (LD) foam, sheet LD foam, moquette (synthetic) or woollen carpet. When the performance criteria for these treatments were compared against those for the standard Seibersdorf bran diet the pupal recovery levels were halved, the larval duration was extended by more than 2 days and the mean pupal size was reduced by ≥10%. Adult emergence and flight ability were unaffected. In the second experiment, yeast (YS) or bran-based (BS) starter diets were applied to finisher diets that contained various inert substrates instead of wheat bran. Pupal recoveries were similar for the YS applied to diced HD sponge (50.1%), BS applied to either diced HD sponge, sheet HD sponge and woollen carpet (60.6, 55.6 and 54.5%, respectively) and the standard Seibersdorf diet (59.7%). For all the other substrate treatments (sheet HD sponge, diced LD foam, fine synthetic grass, coarse synthetic grass and woollen carpet) to which yeast starters were applied pupal recovery levels were inferior (P < 0.05) to that of the standard diet. Mean larval duration was comparable (P > 0.05) in the BS treatments (as above) (7.03, 7.58 and 7.46 days) and standard Seibersdorf diet (6.87 days), but was significantly longer for the YS applied to diced HD sponge (8.40 days) and for all the other treatments. The mean pupal size of flies produced from any treatment with an inert substrate was less (P < 0.05) than that of flies from the Seiberdorf standard diet, but generally remained within an acceptable size range for medfly. It is suggested that the inclusion of torula yeast and wheat germ in the yeast-based starter diet should enhance the performance of diced HD sponge as a bulking agent substitute, and that this needs further investigation at mass-rearing levels.