BIOLOGICAL ACTIVITY OF CHLORPYRIFOS, CHLORPYRIFOS-METHYL, PHORATE, AND COUNTER® IN SOIL

Abstract

AbstractThe potential of chlorpyrifos-methyl and Counter® (S-[tert-butylthio) methyl] O, O-diethyl phosphorodithioate) as soil insecticides was assessed in the laboratory. Two established soil insecticides, chlorpyrifos and phorate, which are similar in chemical structure to chlorpyrifos-methyl and Counter respectively were included for comparative purposes. Spectrum of activity was determined using 24–48 h crickets, Acheta pennsylvanicus (Burmeister), 24–48 h adults, Chaetopsis spp., third stage darksided cutworms, Euxoa messoria (Harris), northern corn rootworm adults, Diabrotica longicornis (Say), and honeybees, Apis mellifera L. Chlorpyrifos-methyl and chlorpyrifos showed the broadest spectrum of activity being toxic to all five species of insects; Counter and phorate were toxic to four of the five. Initial activity in soil was assessed relative to soil type, moisture, and temperature using crickets as the indicator species. Chlorpyrifos-methyl was as effective and more consistent in activity than chlorpyrifos. Counter was more effective and consistent in soil than phorate other than under conditions of low soil moisture. No clear relationship between chemical structure and either direct contact or initial toxicity in soil was apparent. Tests on persistence of biological activity in mineral soil indicated that, as is generally the case with dimethyl and diethyl forms of organophosphorus insecticides, chlorpyrifos-methyl was even less persistent than chlorpyrifos. Counter was slightly more persistent than phorate. Although very active the potential of chlorpyrifos-methyl as a soil insecticide would be restricted by its limited persistence. Counter was considered to have good potential.