Bioassay of Field-Treated Soils to Determine Bioactivity and Movement of Insecticides1

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Abstract
Granular aldrin, diazinon, heptachlor, parathion (Niran®) and phorate were applied at 1, 2, and 4 lb actual toxicant/acre as a 7-in. band treatment at planting time. Soil samples taken at various depths both in the treated row and adjacent to the row were bioassayed with house crickets, Acheta domesticus (L.), to determine bioactivity as well as vertical and lateral movement of insecticides. Bioactivity in the field varied with soil type and moisture. Aldrin and heptachlor performed similarly and more consistently than did diazinon, parathion and phorate. Based on the bioassay of all 1 lb per acre treatments from all field plots, diazinon, parathion and phorate bioactivity ranged from 10-70% mortality 4 weeks following treatment to less than 20% after 6 weeks; aldrin and heptachlor produced 80-100% mortality at 8 weeks. Horizontal and vertical movement of insecticides varied with the soil type and moisture. Organophosphorus insecticides exhibited less movement than aldrin and heptachlor. Analysis of variance indicated a 4-factor interaction with significance at the 5% level of probability. The response of an insecticide in the soil is a complex one varying with soil type, insecticide, pounds of actual toxicant per acre, and posttreatment data or interval of sampling. All of these factors are interdependent upon one another.