| Effects of three insecticides on soil insect pests and nontarget carabids were evaluated in a series of laboratory, microplot and field plot studies. In the field studies, granular formulations of chlorpyrifos and tefluthrin were applied as a planting treatment (APT), and permethrin was applied with broadcasting as post-emergence treatment (PET). APT prevented stand losses by black cutworm, Agrotis ipsilon (Hufnagel), and root injury by rootworms, Diabrotica spp., which occurred in plots receiving PET and untreated control (UC). As a result, yields of APT were significantly greater than that of PET or UC, especially when population of insect pests were at economic levels.;Laboratory bioassays using topical and soil contact exposure techniques demonstrated that the insecticides used were toxic to carabids. The toxic effects were also demonstrated in microplot studies, where adult carabids of Scarites substriatus Haldeman were subjected to insecticide treatments in a contained environment.;The behavior of carabids in field plots treated and untreated were monitored using pitfall traps throughout the year of treatment and the year following treatment. Five carabid species, Harpalus pensylvanicus Say, Pterostichus chalcites Say, S. substriatus Haldeman, P. stygicus (Say), and Anisodactylus sanctaecrucis F., were the dominant species, representing ;Besides the direct and indirect effects of insecticides, variations of field habitats and weather conditions among years were considered other factors affecting carabid activity. Seasonal abundance of carabids exhibited species characteristics. H. pensylvanicus and P. stygicus appeared to be the later season species, while P. chalcites, S. substriatus, and A. sanctaecrucis were the early season species. Seasonal abundance of these species suggests their role in the fluctuation of soil insect pests in corn field. However, activities of carabids varied in response to the heterogeneity of habitats. |
