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

Abstract

In vivo and in vitro metabolism of [14C]fipronil 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.

Surface contact toxicity and synergism of several insecticides against different stages of the tropical bed bug, Cimex hemipterus (Hemiptera: Cimicidae)

“…Fipronil is biotransformed by microsomal monooxygenases to a number of metabolites, the most important of which is fipronil‐sulfone, but most insects are susceptible to both the fipronil parent and the metabolite. Durham et al 48 showed that, in the European corn borer Ostrinia nubilalis (Hübner), the synergist PBO inhibited the activity of the microsomal monooxygenases and so suppressed the biotransformation process. This had no overall effect on the PBO synergism of fipronil against O. nubilalis , as both the parent and metabolite molecules were highly toxic to that insect, but the authors pointed out that small differences between the activity of the two compounds against other insects could lead to the observed variations in PBO synergism mentioned above.…”

Synergistic and Antagonistic Effects of Piperonyl Butoxide in Fipronil-Susceptible and Resistant Rice Stem Borrers,Chilo suppressalis

“…The microsomal monooxygenase oxidative system is considered to be involved in the degradation of fipronil, as the formation of fipronil-sulfone, the predominant metabolite of fipronil, is dependent on this enzyme system (Brookhart et al 1994; Scharf et al 2000; Durham et al 2002). A synergistic action would indicate the potential for using piperonyl butoxide to decrease the toxicity of fipronil that can be metabolised by P450 oxidative metabolism.…”

“…A synergistic action would indicate the potential for using piperonyl butoxide to decrease the toxicity of fipronil that can be metabolised by P450 oxidative metabolism. It is interesting that the effect of piperonyl butoxide on the action of fipronil was synergistic in house flies ( Musca domestica ) (Scott et al 1997), antagonistic in German cockroach ( Blattella germanica ) and European corn borer ( Ostrinia nubilalis ) (Durham et al 2002; Valles et al 1997), and had no effect in western corn rootworm ( Diabrotica virgifera virgifera ) (Scharfet al 1999). In this paper, the application of PBO had a significant antagonistic effect on the toxicity of fipronil accompanied with decreasing the effects of fipronil on mortality of the susceptible larvae, whereas PBO had an obvious synergistic effect on the toxicity of fipronil to the resistant larvae causing a decreased LD 50 value and an increased mortality compared to fipronil alone.…”

Sulfone Metabolite of Fipronil Blocks γ-Aminobutyric Acid- and Glutamate-Activated Chloride Channels in Mammalian and Insect Neurons

“…with fipronil (Caboni et al, 2003). In European corn borer (Ostrinia nubilalis Hubner), fipronil sulfone was formed through the microsomal cytochrome P450 oxidation system in the midgut in vivo and in vitro (Durham et al, 2002). The biological conversion of fipronil to fipronil sulfone was completely blocked with piperonyl butoxide, a cytochrome P450 monooxygenase inhibitor, in vivo and in vitro (Hainzl et al, 1998;Caboni et al, 2003).…”