The melon fly, Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae), is the most damaging pest of cucurbits in Reunion Island. The influence of adding borax and modifying pH on the effectiveness of different food attractants for both sexes of the melon fly is analyzed by a release-recapture method in field cages. Adding borax to protein hydrolysates Nulure and Buminal strongly reduced their attractiveness for B. cucurbitae. Acidification of 5% Buminal solution (from pH 6 to pH 3) doubled its attractiveness for melon fly. Conversely, Torula yeast at pH 10.5 was significantly more attractive than the standard Torula yeast at pH 9 (28% of captured flies compared with 17%). However, a further pH increase of the yeast solution does not improve its attractiveness. The results are discussed in relation to other studies on pH modification of various baits for Tephritidae.