Biochemical analysis of a chlorfenapyr‐selected resistant strain of Tetranychus urticae Koch

Abstract

Tetranychus urticae Koch has recently developed resistance to chlorfenapyr in Australia and Japan, but no attempt has yet been made to describe the biochemical mechanisms involved in chlorfenapyr resistance. In this study a laboratory-selected chlorfenapyr-resistant strain was investigated. Resistance to chlorfenapyr was associated with a strong increase in esterase activity and P450 mono-oxygenase (MO) activity but a decrease in 3,3',5,5'-tetramethylbenzidine (TMBZ) peroxidation activity. Differences in esterase activities between susceptible and resistant strains increased with increasing carbon number of the aliphatic side-chain of the nitrophenol substrate. A 4.4-fold increase in the O-deethylation of 7-ethoxy-4-trifluoromethyl coumarin (7-EFC) mediated by P450 MOs was detected. Remarkably, the resistant strain showed only half of the total TMBZ peroxidation activity found in the susceptible strain. The activity of these enzymes was further determined on different crosses and back-crosses of both strains. Results indicated that activities correlated with chlorfenapyr susceptibility and could be considered as biochemical markers. Esterase isozymes of both strains and their crosses were separated with isoelectric focusing (IEF) and visualised after activity staining. It was clear that two distinct zones of enhanced esterase activity were present in the chlorfenapyr-resistant strain (EST 11, pI = 4.88 and EST 16, pI = 4.71). EST 11 was identified with inhibitors as a carboxylesterase. The relative presence and intensity of these esterase zones changed in the different crosses and could be seen as a marker for chlorfenapyr resistance. Glutathione-S-transferase and glucose-6-phosphate dehydrogenase activities were not significantly different between strains. A twofold decrease in TMBZ peroxidase activity in the resistant strain could reflect decreased activation of chlorfenapyr. On the basis of these results the involvement of P450 MOs and esterases in the activation and detoxification of chlorfenapyr in T. urticae is challenged and discussed.

Synergistic toxicity and physiological impact of imidacloprid alone and binary mixtures with seven representative pesticides on honey bee (Apis mellifera)

“…The optical density (OD) was continuously measured at 340 nm every 15 sec for a total of 10 min on Synergy HTX plate reader. The specific GST activity was calculated to nmol CDNB conjugation/min/mg protein using experimentally derived “extinction coefficients” of 5.3 mM -1 cm -1 [37]. …”

Complete maternal inheritance of bifenazate resistance in Tetranychus urticae Koch (Acari: Tetranychidae) and its implications in mode of action considerations

“…However, although high resistance (41000-fold) to some of these acaricides has been documented (Goka, 1998;Devine et al, 2001;Stumpf and Nauen, 2001;Van Leeuwen et al, 2004), no maternal inherited resistance has been found. This probably indicates that either the target protein of these acaricides is encoded by the nucleus or resistance was due to metabolic degradation as demonstrated for pyridaben and chlorfenapyr by employing synergists known to inhibit detoxification enzymes, such as mono-oxygenases and esterases Van Leeuwen et al, 2006). When synergists known to inhibit oxidative and hydrolytic detoxification enzymes were applied to females of strain BR-VL prior to bifenazate treatment, no increase in susceptibility was detected.…”

Acaricidal and quantitative structure activity relationship of monoterpenes against the two-spotted spider mite, Tetranychus urticae

“…As for mechanisms of resistance to acaricides with new modes of action (e.g. abamectin, fenpyroximate, chlorphenapyr, METI-acaricides, spirodiclofen) enhanced detoxification in T. urticae strains has been reported (Devine et al 2001;Nauen 2001, 2002;Kim et al 2004a, b;Van Leeuwen et al 2006;Van Pottelberge et al 2008. Other detoxification or target enzymes such as esterase, cytochrome P450-monooxygenase and glutathione S-transferase may also play a role in metabolizing certain acaricides in T. urticae (Yang et al 2001).…”