PHARMACOKINETICS OF CYFLUTHRIN IN SPODOPTERA-LITTORALIS (BOISD) .2. EFFECTS OF LINDANE PRETREATMENT ON THE TOXICITY AND IN-VIVO METABOLISM OF CYFLUTHRIN IN SUSCEPTIBLE LARVAE

In previous studies, we showed that a treatment with a nonlethal dose of lindane induced detoxication enzymes (cytochrome P450 monooxygenase s and glutathione S-transferases) in susceptible Spodoptera littoralis larvae. A subsequent decrease in the toxicity of pyrethroid insectici des, including cyfluthrin, was observed. This study investigates wheth er the decreased efficiency of cyfluthrin in lindane-pretreated S. lit toralis larvae is due to enhanced metabolism of this pyrethroid by the lindane-induced detoxication enzymes. [C-14]Cyfluthrin (2.5 ng/larva) was topically applied to fourth instar S. littoralis larvae 24 hr aft er treatment with a nonlethal dose of lindane (0.2 mu g/larva). The di stribution of C-14 radioactivity in the different body compartments wi thin the 32 hr following treatment with [C-14]cyfluthrin was studied. Penetration, internal recovery, and elimination of radiolabeled materi al were investigated by rinsing the cuticle surface of the larvae and catalytic combustion of the rinsed insects and their feces. The data w ere fitted to a three-compartment model of insecticide pharmacokinetic s. Comparison of the rates of penetration, in vivo distribution, and e limination of [C-14]cyfluthrin showed that lindane pretreatment did no t affect the penetration kinetics of the pyrethroid, nor the internal distribution and elimination of labeled material. High-performance thi n-layer chromatographic analysis of radiolabeled compounds recovered i n aqueous and organic fractions from larval and fecal extracts demonst rated that similar amounts of identical organosoluble metabolites were excreted by control and lindane-pretreated larvae. We therefore concl ude that the decrease in the toxicity of cyfluthrin in lindane-pretrea ted S. littoralis larvae was not due to enhanced metabolism, but was m ore likely related to events within the nervous system. (C) 1994 Acade mic Press, Inc.