FATE AND EFFICACY OF ACEPHATE AFTER APPLICATION TO PLANTS AND INSECTS

A single foliar application of 14C-labeled acephate was absorbed rapidly by cotton leaves (>50% in 24 h), and unabsorbed residues were essentially depleted in 48 h. The absorbed acephate was metabolized by the leaves to small amounts (ca. 9% of dose) of the insecticide methamidophos and to lesser amounts (<5% combined) of at least four other products. Two of the latter four products were tentatively identified as 0, 5-dimethyl phosphorothioate and S-methyl acetylphosphoramidothioate. Absorbed acephate and/or its metabolites were rapidly translocated throughout the plant including the fruit. However, with normal application methods, any such translocation of toxicants that might occur is apparently insufficient to kill pests that feed on new growth or fruit. Acephate was considerably more toxic to third-stage tobacco budworms, Heliothis virescens (F.), than to adult boll weevils, Anthonomous granáis Boheman, in tests with topical applications to the insects and with bioassays of treated cotton foliage. Some evidence obtained in studies of the absorption and metabolism of 14C-labeled acephate by the two species suggests that the metabolic conversion of the chemical to methamidophos in tobacco budworms may contribute to the observed differences in susceptibility between species. © 1979, American Chemical Society. All rights reserved.