In vivo and in vitro metabolism of fi pronil by larvae of the European corn borer Ostrinia nubilalis

Authors

Eric W. Durham, University of Nebraska-Lincoln
Blair D. Siegfried, University of Nebraska-LincolnFollow
Michael E. Scharf, Purdue University

Document Type

Article

Date of this Version

July 2002

Comments

Published in Pest Management Science 58:8 (2002), pp. 799–804. Copyright © 2002 Society of Chemical Industry; published by John Wiley & Sons. Used by permission.

Abstract

In vivo and in vitro metabolism of [₁₄C]fi pronil was examined in a susceptible European corn borer (Ostrinia nubilalis, Hübner) laboratory strain. [₁₄C]Fipronil penetrated the larval integument slowly, with 71.5% of the applied radioactivity recovered from surface rinses 24 h after topical application. Despite this slow penetration, radioactivity was detected in both the excrement and internal organo-soluble fractions. Radioactivity in the internal aqueous fraction and tissue pellet accounted for less than 0.8% of total radioactivity. The in vivo studies suggest that fipronil oxidation to its sulfone metabolite is the major route of metabolic conversion. In vitro studies were performed using subcellular microsomal fractions isolated from European corn borer larval midguts. Cytochrome P450-dependent monooxygenase activity (methoxyresorufin O-demethylase) was consistently observed in midgut preparations, and formation and detection of the sulfone metabolite in the same midgut preparations was also NADPH-dependent and inhibited by piperonyl butoxide. In vitro metabolism results indicate microsomal monooxygenases are responsible for the conversion of fipronil to its sulfone form in the European corn borer.