Insecticidal activity of pyrethrum extract and its four insecticidal constituents against house flies. II.—Synergistic activity of piperonyl butoxide with the four constituents

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Abstract
The toxicity to female house flies, 5‐6 days old, of the four insecticidal constituents of pyrethrum, combined with piperonyl butoxide at six ratios (from 10 : 1 to 1 : 20 w/w), was determined by a measured drop technique. The order and magnitude of the toxicities of the synergised constituents (relative to synergised pyrethrum extract) vary with the amount of synergist present. At 1 : 8 (pyrethroid/piperonyl butoxide) the relative toxicities of the four constituents were: pyrethrum extract, 1.0 (1.0); pyrethrin I, 1.31 (0.85); cinerin I, 1.28 (0.53); pyrethrin II, 0.90 (1.37); cinerin II, 0.58 (0.49). (The relative toxicities of the constituents alone are given in brackets.) At this ratio, the synergistic factors of the four constituents were: pyrethrin I, 18; cinerin I, 27; pyrethrin II, 6; cinerin II, 14; pyrethrum extract, 10. The possible explanations for differences of the extent to which the constituents are synergised are discussed.