A BSTRACT In Sterile Insect Technique (SIT) programs, mass-reared males of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), are maintained on a sugar-agar diet before their release into the environment. Several studies suggest that nitrogenous dietary supplements improve the mating competitiveness of the sterile males, thus increasing the cost effectiveness of SIT. Other research, however, has not supported this notion. Here, we further investigate the potential usefulness of

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... n-containing diet additives by examining the effect of 4 different nitrogenous materials-yeast hydrolysate, urea, whey protein, and honey-on the mating success of sterile C. capitata males. These materials were mixed directly with the sugar-agar diet in varying concentrations (1, 5, or 10%). Trials conducted in outdoor field-cages generated 2 consistent results across all diets: (1) neither the type nor concentration of nitrogenous material used elevated the mating success of sterile males above that observed for the standard sugar-agar diet, and (2) wild males invariably had a significant mating advantage over sterile males, accounting for an average of 81% of the total matings per replicate. In addition, a field comparison of short-term dispersal from a central release point revealed no significant difference between sterile males fed (i) the sugar-agar diet or (ii) the sugar-agar diet supplemented with yeast hydrolysate (10%) in either the number or spatial distribution of recaptured individuals. Our results do not support the proposal that pre-release nitrogenous dietary supplements improve the field performance of sterile C. capitata males in SIT programs.