Western cherry fruit fly, Rhagoletis indifferens Curran (Diptera: Tephritidae), is a major pest of sweet cherry, Prunus avium (L.) L., in the Pacific Northwest of the United States, Spinosad bait is applied weekly to kill flies before they develop eggs, but its effects on oviposition by reproductively mature flies are unknown. In this study, the main objective was to identify insecticide bait treatments that can prevent oviposition after being ingested by reproductively mature R. indifferens. First, flies were fed liquid bait. Of flies fed spinosad bait, 20% oviposited and all died within 1 d. Of flies fed acetamiprid sucrose, 72% oviposited after 1 wk, and all recovered from paralysis within 1 d. Of flies fed spinosad bait acetamiprid, 7% oviposited and most died within 1 d. None of the flies fed spinosad bait thiamethoxam oviposited and all died within 1 d. Of flies fed thiamethoxam sucrose, 2% oviposited and most died within 1 d. None of the flies fed spinosad thiamethoxam sucrose oviposited and all died within 1 d. Of flies fed spinosad sucrose, 11% oviposited and almost all died within 1 d. Next, flies were fed 2-d-old dried baits. No flies fed dried spinosad thiamethoxam sucrose and thiamethoxam sucrose oviposited. On the basis of absolute numbers of eggs laid by flies fed liquid and dried treatments, spinosad thiamethoxam sucrose may be the most effective of the seven insecticide baits tested for preventing oviposition by reproductively mature R. indifferens.