VC-013

DDT, γ-BHC, and dialdrin are inactivated as insecticides by dry clay soils, and are reactivated at high relative humidity.Insecticides are also inactivated in soils which are high in organic matter.In this study, 24-48-hr.-old 1st-instar nymphs of Gryllus pennsylvanicus were used on Plainfield sand and a muck containing 0.52 and 64.6% organic matter, resp.All of the insecticides were more active in moist sand than in dry sand.Heptachlor was 7.8, DDT 9.9, parathion 24.4, Diazinon 132.1, and VC-13 188.6 fold more toxic in moist sand than dry sand.While heptachlor and DDT were, resp., 1.3 and 1.5 fold less toxic in dry muck as in moist muck, Diazinon, VC-13 and parathion were 1.5, 1.7 and 2.5 fold more toxic, resp.At field moisture capacity DDT is 38.5, heptachlor 61.6, Diazinon 65.7, VC-13 73.3 and parathion 92.0 fold less toxic in the muck as compared with the sand.In moist soils, inactivation is proportional to the organic content, while in dry soils it is related to the adsorptive capacity of the mineral fraction.