Insecticidal Activity and Persistence of Terbufos, Terbufos Sulfoxide and Terbufos Sulfone in Soil2

Abstract

Terbufos, t. sulfoxide, and t. sulfone were toxic, broad spectrum contact insecticides which were ca. 1/12, 1/3, and 1/5, respectively, as toxic as carbofuran to 24–48 h field crickets, Acheta pennsylvanicus (Burmeister). In moist Plainfield sand, terbufos was nearly lOX more toxic to crickets than was carbofuran, while the sulfoxide and sulfone were ca. 3/4 and 1/4 as toxic, respectively. The insecticidal activity was influenced by soil type, moisture, and temperature. Terbufos was sufficiently volatile to cause fumigant toxicity to crickets placed above treated soil whereas the sulfoxide and sulfone were not. In laboratory tests, chemical analysis showed that t. sulfone and t. sulfoxide were ca. equally persistent in soil; terbufos was less persistent. Oxidative processes were observed to be important in the disappearance of both terbufos and t. sulfoxide and to proceed more rapidly in muck than in sand. Bioassay studies indicated that, in sand, the biological activity arising from the application of terbufos was due, primarily, to the persistence and high insecticidal Cati city of the parent material. In a field study in which granular formulations of terbufos and phorate were incorporated into soil, both insecticides were more persistent, and the amounts of the parent compounds oxidized to their respective sulfoxides and sulfones were greater, in muck than in sand. Residues in carrots and radishes grown on treated soil were slightly higher, and the persistence of residues in these soils was slightly greater for terbufos than for phorate.