Persistence of two pyrethroids insecticides in a mud-sandy-clay soil under field conditions

Abstract

The persistence of two pyrethroid insecticides, cypermethrin and deltamethrin was verified in a mud-sandy-clay soil under field conditions in relation to carbofuran and aldrin insecticides. The evaluation was done with the add of termite workers Cornitermes cumulans Kollar, 1832 as bioindicators. The soil was treated with a dosage five times higher than the LC₅₀ values obtained for the insects in the laboratory. The evaluations were done every seven days, taking soil samples on the field and adjusting it in relation to moisture and weight to receive the bioindicators. The evaluations were done on soil without plants and on the ones cultivated. Wheat plant presence reduced the efficiency of the insecticide cypermethrin. Only after the 38th day the termites began to dig their tunnels in the soil treated with pyrethroids, while for the treatments with aldrin and carbofuran it happened on the 17th and 24th day, respectively. The pyrethroid insecticides had the highest lost of their residual on the first three weeks, however, during the period, they were more stable and were detected by the method during 150 days.