Soil-insecticide bioassays and seed treatments for soil-insect control in Central Queensland, Australia

Abstract

Twelve insecticides were tested as seed treatments or as banded applications in laboratory soil bioassays against striate false wireworm larvae ( Pterohelaeus alternatus Pascoe). The systemic carbamate insecticides carbofuran and furathiocarb, when applied as seed treatments, protected sorghum from damage at rates ⩾0.7 kg a.i./100 kg seed. These chemicals did not kill a high proportion of larvae, and feeding deterrence as the mode of action was indicated. The soil-active synthetic pyrethroids tefluthrin and bifenthrin, applied as banded sprays, protected seedlings and killed larvae at rates as low as 0.05 kg a.i. ha −1. The most effective organophosphate was ebufos, which protected seedlings at rates > 1.0 kg a.i. ha −1. In field trials on the Central Highlands of Queensland, seed treatments of carbofuran and furathiocarb significantly increased establishment of cotton and sorghum, but not that of sunflower, when false wireworm adults and wingless cockroaches ( Calolampra elegans Roth and Princis) were present. The carbamates were superior to pyrethroids in protection of emerging seedlings. Systemic insecticides did not prevent lethal damage to emerging sunflower seedlings when surface-active insect densities were similar to the numbers of seedlings (45 000 ha −1). Thiodicarb seed treatment in cotton (at 0.7 kg a.i./100 kg seed) significantly reduced numbers of black field earwig ( Nala lividipes Dufour).