title: Comparative acaricide susceptibility and detoxifying enzyme activities in field-collected resistant and susceptible strains of Tetranychus urticae.
abstract: A field-collected strain (MR-VL) of the two-spotted spider mite, Tetranychus urticae Koch, exhibited strong resistance to bifenthrin, dicofol and fenbutatin oxide in comparison with a susceptible laboratory strain (LS-VL). The MR-VL strain was screened for cross-resistance with several currently used acaricides. Cross-resistance was detected with clofentezine (RR = 2631), dimethoate (RR = 250), chlorfenapyr (RR = 154), bromopropylate (RR = 25), amitraz (RR = 17), flucycloxuron (RR = 15) and azocyclotin (RR = 7). Abamectin, acequinocyl, bifenazate, tebufenpyrad and spirodiclofen did not show any signs of cross-resistance. Enhanced detoxification by increased activity of mono-oxygenases (MO) and esterases is at least partially responsible for the observed resistance and cross-resistance. MO assays with 7-ethoxycoumarin (7-EC) were optimised and 7-ethoxy-4-trifluoromethylcoumarin (7-EFC), a new MO-substrate, was evaluated for the first time in T urticae and proved to be a good alternative to 7-EC. Approximately 3- and 4-fold higher MO activity was detected with 7-EFC and 7-EC respectively in the MR-VL strain. Kinetic parameters of general esterase assays with 4-nitrophenyl acetate and 1-naphthyl acetate as substrate indicated that more esterases were present in the MR-VL strain. A first attempt was made to classify the esterases present in T urticae. Acetyl-, aryl- and carboxyl-esterases were detected with the use of inhibitors after separation by native PAGE. Glutathione-S-transferases did not seem to play any role in the observed resistance and no differences were detected when the general oxidative capacities of the two strains were compared.
authors.affiliation: Laboratory of Agrozoology, Department of Crop Protection, Faculty of Agricultural and Applied Biological Science, Ghent University, Coupure links 653, 9000 Ghent, Belgium. Thomas.vanleeuwen@ugent.be
authors.forename: Thomas
authors.initials: T
authors.lastname: Van Leeuwen
authors.forename: Steven
authors.initials: S
authors.lastname: Van Pottelberge
authors.forename: Luc
authors.initials: L
authors.lastname: Tirry
mesh_terms: D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004950:Esterases / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D007305:Insecticide Resistance; D007306:Insecticides / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism; D040102:Tetranychidae / Q000201:enzymology*
chemical_list: D007306:Insecticides; D007527:Isoenzymes; D003577:Cytochrome P-450 Enzyme System; D005982:Glutathione Transferase; D004950:Esterases