Abstract
Propaphos was metabolized by the green rice leafhopper, Nephotettix cincticeps Uhler and the common cutworm, Spodoptera litura Fabricius to form propaphos sulfoxide, propaphos sulfone, 4-methylsulfinylphenol, 4-methylsulfonylphenol, and unidentified aqueous metabolites. Most of the solvent-soluble metabolites consisted of propaphos, propaphos sulfoxide and propaphos sulfone in the green rice leafhopper. In a case with the common cutworm, formation of hydrolyzed metabolites of propaphos and aqueous metabolites was dominant. Inhibitory activity of propaphos sulfoxide and sulfone to the acetylcholinesterase (AChE) of the green rice leafhopper and the common cutworm larvae homogenates were large enough to exhibit insecticidal effects. However, AChE of the common cutworm topically applied with propaphos was as active as that of untreated insects whereas in a case with the green rice leafhopper, activity of AChE of treated insects decreased compared with that of untreated ones. Thus, insecticidal selectivity of propaphos between two insect species resides in the metabolic difference: Propaphos degraded to non-insecticidal substances in a case with the common cutworm, while the formation of oxidative metabolites which were AChE inhibitors was dominant in the green rice leafhopper.
