EFFECT OF POOL BOTTOM SUBSTRATE ON RESIDUES AND BIOACTIVITY OF CHLORPYRIFOS, AGAINST LARVAE OF CULEX TARSALIS (DIPTERA: CULICIDAE)

Abstract

AbstractThe bioactivity and disappearance of chlorpyrifos in Dursban® 2.5 G and M formulations was studied in the laboratory and in the field in temporary pools lined with sod, clay, or sand substrate. The activity and presence of chlorpyrifos in the water was determined by bioassay with Culex tarsalis Coquillett larvae and chemical analysis by gas-liquid chromatography.The tests indicated that, at equal rates of application in pools with organic matter or clay substrate, the 2.5 G formulation resulted in lower chlorpyrifos concentrations than the Dursban M, but provided periods of larval mortality equal to or greater than the M formulation except in laboratory sod-lined pools. At a given application, the shortest period of larval mortality and lowest detectable residues occurred in sod-lined pools, whereas in the sand-lined pools, the longest period of larval control and the highest residual concentration of chlorpyrifos in the water was encountered.