Effectiveness and Residual Activity of New Compounds in Soil Against the Eye Gnat, Hippelates collusor1

Abstract

The initial biological activity of 39 new insecticides in soil (Coachella fine sand containing 0.15% organic matter) was determined in the laboratory against the eye gnat, Hippelates collusor (Townsend). Of these, 2 compounds produced 90% reduction in eye gnat emergence at rates of less than 0.1 lb of the toxicant per 6-acre in of the soil. Fourteen materials produced 90% reduction in gnat emergence at the rates of 0.2-1.0 lb of the toxicant per 6-acre in of the soil. The remaining materials had LD₉₀ levels of 1.0—48.0 lb of the toxicant per 6-acre in of the soil. Loss of biological activity of these compounds against the eye gnat in soil at 3 rates was studied at intervals of 2, 4, and 8 months. Of the materials evaluated, only 7 showed residual activity of any significance. Bayer 29492 [O, O-diethyl O- [4- (methylthio) -m-tolyl]phosphorothioate] was the most stable compound studied. Four compounds showed low to moderate degrees of residual activity, while the remaining materials showed none. The residual activity of a compound depends both on the initial activity and the stability of the material.