Thomas Van Leeuwen1, Steven Van Pottelberge, Ralf Nauen, Luc Tirry. 1. Laboratory of Agrozoology, Department of Crop Protection, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, Ghent, Belgium. thomas.vanleeuwen@ugent.be
Abstract
BACKGROUND: Bifenazate is a carbazate acaricide known for its potency, particularly against tetranychid mite species such as the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). It was recently shown that the compound needs to be activated by an S,S,S-tributyl-phosphorotrithioate (DEF)-sensitive mechanism in spider mites to display full acaricidal efficacy. The ability of well-known organophosphates and carbamates to inhibit the activation of bifenazate and thus compromise its acaricidal potential was tested. RESULTS: Esterase activity determined in vivo after pre-exposure of mites with organophosphates and carbamates revealed--depending on the compound--varying esterase inhibition nicely correlated with the ability of the individual compound to antagonise bifenazate action on mites. CONCLUSIONS: The findings illustrate that organophosphates and carbamates interfere with bifenazate efficacy, most probably by inhibiting carboxylesterases responsible for the activation of the pro-drug. As a result of the strong antagonism, mixtures of bifenazate with carbamates or organophosphates should not be used under field conditions. Moreover, there exists a real threat in repeatedly applying organophosphates and bifenazate. The present study again illustrates how important mode of action information is for the proper planning of resistance management strategies. Copyright (c) 2007 Society of Chemical Industry.
BACKGROUND:Bifenazate is a carbazate acaricide known for its potency, particularly against tetranychid mite species such as the two-spotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae). It was recently shown that the compound needs to be activated by an S,S,S-tributyl-phosphorotrithioate (DEF)-sensitive mechanism in spider mites to display full acaricidal efficacy. The ability of well-known organophosphates and carbamates to inhibit the activation of bifenazate and thus compromise its acaricidal potential was tested. RESULTS:Esterase activity determined in vivo after pre-exposure of mites with organophosphates and carbamates revealed--depending on the compound--varying esterase inhibition nicely correlated with the ability of the individual compound to antagonise bifenazate action on mites. CONCLUSIONS: The findings illustrate that organophosphates and carbamates interfere with bifenazate efficacy, most probably by inhibiting carboxylesterases responsible for the activation of the pro-drug. As a result of the strong antagonism, mixtures of bifenazate with carbamates or organophosphates should not be used under field conditions. Moreover, there exists a real threat in repeatedly applying organophosphates and bifenazate. The present study again illustrates how important mode of action information is for the proper planning of resistance management strategies. Copyright (c) 2007 Society of Chemical Industry.