Insecticidal activity of pyrethrum extract and its four insecticidal constituents against house flies. VI—Relative toxicity of pyrethrin I and pyrethrin II against four strains of house flies

Abstract

AbstractFreshly reconstituted samples of pyrethrins I and II were tested against four strains of house flies. Pyrethrin II was 1·21–1·50 times more toxic than pyrethrin I, 24 h. after treatment, and 1·09–1·54 times more toxic, 48 h. after treatment. The strain of flies and the method of immobilising the insects before treatment (CO2 or chilling) had little effect on the relative toxicity of the two esters. Two strains resistant to organophosphorus insecticides were very strongly resistant to knock‐down but not to kill by the pyrethrins. The two esters were stable for 3 months when stored as 5% w/v solutions in darkness at −20°; only pyrethrin II lost some of its insecticidal activity (23%) when left in acetone solution in daylight for 5 days at 15–20°.