Rose bengal and erythrosin B were shown to cause toxicity in the face fly,Musca autumnalis. When larvae were exposed to dye-treated manure, toxicity was observed in the larval, pupal, and adult life stages, depending on the concentration and the dye. Face flies, emerging as adults after treatment with low concentrations of erythrosin B, exhibited signs of decreased ability to complete eclosion from the puparium. Similar results were obtained when erythrosin B was incorporated into the manure by introducing dye-filled gelatin capsules into cattle. Toxicity was dose-related to dye levels in the feed of the cattle.