Effects of different concentrations of GF-120 NF Naturalyte Fruit Fly Bait on attraction and feeding responses, mortality, and control of the western cherry fruit fly, Rhagoletis indifferens Curran, were determined. In the laboratory, flies that had been exposed to sugar and yeast extract and then deprived of all food for 16–20 h were attracted to 40.0% GF-120, but not to 0.6 and 4.8% GF-120 (vol:vol). Nonstarved flies were not attracted to any concentration. Flies in the field were not attracted to 55.6% GF-120 on cherry leaves, and few flies fed on the bait. In the laboratory, males fed for shorter durations on and ingested lower amounts of 0.6% than 4.8 or 40.0% GF-120, but females fed equally on all concentrations. Spinosad in GF-120 was highly toxic to flies. Lethal concentrations₅₀ (LC₅₀ values) of spinosad for starved flies at 1–4 d were 1.5–0.7 ppm. When gravid flies were exposed to cherries treated with 0.6, 4.8, and 40.0% GF-120, mortality was greater at each higher concentration, but none prevented oviposition. Field spray tests comparing 0.6, 4.8, and 40.0% GF-120 in 225 ml of spray per cherry tree resulted in 79–94% lower larval infestations than in controls, but no differences were seen among the concentrations. Evidence from this study indicates that fresh 40.0% GF-120 was attractive in the laboratory but that flies were not attracted to fresh GF-120 from far distances within trees, suggesting that suppression of populations is caused in large part by flies finding the bait through normal movement over large areas.