Relation of the Rate of Penetration and Metabolism to the Toxicity of Sevin to Three Insect Species1

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Abstract
Sevin® (1-naphthyl N-methylcarbamate) labelled with C14 has been used on three insect species by topical application in acetone. Sevin is absorbed rapidly into house flies (Musca dumestica L.), 75% of a dose penetrating within 4 hours. It is rapidly metabolized and excreted, so final toxicity is low as shown by the LD50 = 2.0 μg./ ♀ Resistant house flies differ from susceptible ones only in greater metabolism and consequent lower mortality. If metabolism is prevented by addition of a synergist such as sesamex, the toxicity of Sevin is increased up to fifty-fold, and much of the absorbed Sevin remains in the body unchanged. The critical step is the hydrolysis of Sevin to 1-naphthol and methyl amine, which is controlled by a carbamate esterase enzyme. When this is inhibited, e. g., by sesamex, the toxicity is high. Sevin penetrates more slowly into the large milkweed bug (Oncopeltus fasciatus (Dall.)), e. g., 40% of an applied dose enters in 8 hours. It is metabolized and excreted very slowly so that LD50 is low, i. e., 0.5 μg./insect. The German cockroach (Blattella germanica (L.)) absorbs Sevin slowly and metabolizes it rapidly. This results in low toxicity, LD50=20 μg./♂. The metabolic products are different in the three species and are formed by different reactions.