Individual pyrethrins, separated by column chromatography of natural pyrethrums, were tested topically against female and male house flies (Musca domestica L.). Pyrethrin II, cinerin I and cinerin II were, respectively, about 58%, 23% and 25% as toxic as pyrethrin I. However, in combination with sesamex, the toxicity was increased 60-fold with cinerin I, 17-fold with pyrethrin in I, 13 to 22-fold with cinerin II and only 8-fold with pyrethrin II. An unique device of a micro-applicator was described.