Yeast and yeast products are widely considered alternative sources of protein for baits used in fruit fly suppression. The objective of this study was to develop new protein bait formulations from locally available materials in Mauritius, thereby making baits more affordable and reducing the cost of the fruit fly monitoring and control programs. Locally available waste brewery yeast (WBY) was modified in a digester. The WBY was exposed to different boiling and proteolysis conditions. A two-choice bioassay was conducted and each of the 64 142resulting baits were tested against water in a noncompetitive situation with two fruit fly species of economic importance: the peach fruit fly, Bactrocera zonata (Saunders), and the melon fly, Zeugodacus cucurbitae (Coquillett). Three baits, F1, F2, and F3, showed significantly more fly attraction ranging from 0.7 to 1.1 mean fly catches. These baits were used for further testing for optimal concentrations (7.5, 10, 12.5, and 15% v/v) in field cages. With B. zonata, bait attractiveness increased significantly with increasing bait concentrations for both male and female flies. With Z. cucurbitae, an increase in attraction was observed but attractiveness was not significantly different. Bait concentration (10% v/v) was selected for open field trials using the three preselected baits (F1, F2, and F3). Two cucurbit plantations were chosen to test the baits against commercial protein hydrolysate in Tephri Traps®, targeting Z. cucurbitae. A similar trial was conducted in a fruit orchard to test selected baits in attracting B. zonata. The results of traps baited with modified WBY at 10% v/v were comparable to commercial protein hydrolysate in attracting flies. A 5-year cost-benefit analysis indicated that a net benefit of US$283,558.60 is possible if modified WBY is used instead of imported commercial protein hydrolysate. Thus, modified WBY is a promising cost-effective alternative to the imported costly protein hydrolysate in fruit fly suppression programs for Mauritius.