Insecticidal activity of pyrethrum extract and its four insecticidal constituents against house flies. IV.—Knock‐down activities of the four constituents

Abstract

The knock‐down activities of pyrethrins I and II and cinerins I and II were studied on house flies (Musca domestica L.) by a measured drop technique. Unanaesthetised flies held by suction during dosage were inspected at frequent intervals for 5 h. The tests were done at 20† with the materials tested dissolved in n‐dodecane.The relative toxicities of the materials, measured at ED₅₀ differed at different times after treatment; 4 min. and 2 h. after treatment they were, respectively : pyrethrum extract, 1.0, 1.0; pyrethrin II, 1.98, 1.58; cinerin II, 0.69, 0.51; pyrethrin I, 0.60, 1.07; cinerin I, 0.50, 0.64. The KD₅₀ end‐points were : pyrethrin II, 10 min.; cinerin II, 11 min.; pyrethrum extract, 13 min.; pyrethrin I, 17 min.; cinerin I, 20 min. At KD₅₀ end‐point the relative toxicities and the relative speeds of knock‐down (given in brackets) were: pyrethrum extract, 1.0 (1.0); pyrethrin II, 2.16 (1.30); pyrethrin I, 0.72 (0.76); cinerin II, 0.66 (1.18); cinerin I, 0.55 (0.65). The relative toxicities of pyrethrin II and cinerin II decreased with the passage of time after treatment because flies recovered sooner from them than from pyrethrin I and cinerin I.Possible reasons are discussed for the differences in the order of the relative toxicities of the constituents when determined by different methods.