Biochemical markers linked to abamectin resistance in Tetranychus urticae (Acari: Tetranychidae)

Abamectin resistance monitoring with the two-spotted spider mite, Tetranychus urticae Koch, using a diagnostic dose revealed resistant strains from the Netherlands (NL-00), Colombia (COL-00), and Brazil (BR3-00). Resistance to abamectin in these strains was associated with significantly enhanced O-deethylation of 7-ethoxycoumarin mediated by cytochrome P450-dependent monooxygenases (MFO). The abamectin-resistant strains NL-00 and COL-00 showed severalfold higher MFO activity than the susceptible strain GSS. Furthermore a higher glutathione S-transferase (GST) activity was detected toward 1-chloro-2,4-dinitrobenzene (CDNB) and monochlorobimane, a new substrate leading to a fluorescent product upon conjugation with glutathione. The measured 1.6- and 2.0-fold increases in GST activity toward CDNB in strains COL-00 and NL-00 were almost proportional to the resistance factors of 26 and 54. respectively. Frequency distribution of GST activity measured by the microfluorometric assay using monochlorobimane in homogenates of individual spider mites showed totally separated activity patterns for the susceptible strain GSS and the abamectin-resistant strain NL-00. In contrast to strain NL-00, abamectin resistance in the Brazilian strain was not stable in the laboratory over 6 months and the loss of resistance coincided with decreased GST and MFO activity. The involvement of GST and MFO in abamectin resistance in T. urticae was confirmed by synergism studies with the MFO inhibitor piperonyl butoxide and the GST inhibitor diethyl maleate. This paper is the first attempt to biochemically describe abamectin resistance in T urticae. (C) 2002 Elsevier Science (USA).