Laboratory Tests of Allethrin for Stability, Residual Action and Toxicity1,2

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Abstract
Against Aedes aegypti larvae, allethrin was 1/2-1/3 as toxic as pyrethrins, but when exposed to u.-v. light, or heat in the laboratory, allethrin appears less subject to breakdown. Against house flies in an oil sprey, allethrin was as toxic as pyrethrins when fresh and retained its effectiveness better than pyrethrins after subjection to light or storage in glass under room conditions. From acetone or water emulsions, allethrin residues on plywood or glass panels at 144 mg./sq. ft. persisted for several months against house flies. The flies recovered from similar residues of pyrethrins when tested 1 week after application. When allethrin was combined with a synergist, the amt. of residue could be reduced to 28 mg. sq. ft. The residual action of the pyrethrins was also markedly improved. Allethrin emulsions applied to some types of painted surfaces were not as durable as those on painted wood. The emulsifier used may influence effectiveness. Up to 30 hours of exposure to u.-v. light was necessary to affect allethrin residues of 144 and 72 mg. per sq. ft. In a settling mist test against female American roaches 4-6 times the dose of allethrin is needed to give the same mortality as pyrethrins, whereas against German roaches allethrin was 0.7-0.9 as effective as pyrethrins.

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