The feeding toxicity of the natural insecticide spinosad in Provesta protein bait was evaluated for three economically important fruit fly species, the Mediterranean fruit fly, Ceratitis capitata (Wiedemann); the melon fly, Bactrocera cucurbitae Coquillett; and the oriental fruit fly, Bactrocera dorsalis Hendel. Both females and males were evaluated. Spinosad was remarkably similar in toxicity to all three fruit fly species. Male C. capitata (24 h LC50,, values and 95% fiducial limits = 2.8 (2.60-3.0) mg/liter spinosad) were significantly, although only slightly more susceptible to spinosad than females (4.2 (3.8-4.6) mg/liter). Male (5.5 (4.7-6.6) mg/liter) and female (4.3 (3.7-4.9) mg/liter) B. cucurbitae were equally susceptible to spinosad. Female (3.3 (3.1-3.6) mg/liter) and male (3.1 (2.9-3.3) mg/liter) B. dorsalis also were equally susceptible to spinosad. Provesta bait containing spinosad also was evaluated against two parasitoids of tephritid fruit flies, Fopius arisanus (Sonan) and Psyttalia fletcheri (Silvestri). These parasitoids did not feed on the bait, so a contact toxicity test was conducted. Significant amounts of mortality were found only after exposure of parasitoids to spinosad-coated glass vials with concentrations >= 500 mg/liter spinosad. Parasitoids were less susceptible than fruit flies to such a degree that use of spinosad in bait spray should be compatible with these parasitoid species. Because the fruit flies tested in this study were so susceptible to spinosad, this product seems to be promising as a bait spray additive and a replacement for malathion for control of these species. Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Abiotic factors; Chemical factors Bactrocera cucurbitae; Bactrocera dorsalis; Ceratitis capitata (Tephritidae ); Hymenopteran parasites; Fopius arisanus & Psyttalia fletcheri; Non target toxicity of insecticidal bait to parasitoid species, laboratory study Fopius arisanus; Psyttalia fletcheri (Braconidae ); Dipteran hosts; Ceratitis capitata & Bactrocera; Non target toxicity of insecticidal bait to parasitoid species, laboratory study; Fertilizers and pesticides; Spinosad none