Spirodiclofen resistance risk assessment in Tetranychus urticae (Acari: Tetranychidae): a biochemical approach
2002
Rauch, Natascha | Nauen, Ralf
Spirodiclofen belongs to a novel class of acaricides active against all developmental stages and female adults of tetranychid mite species such as the two-spotted spider mite Tetranychus urticae. Spirodiclofen showed no cross-resistance to organophosphates, METI’s (mitochondrial electron transport inhibitors), hexythiazox and abamectin in well-characterised strains with high resistance to at least one of these established acaricides. A monitoring with spirodiclofen at a diagnostic concentration of 4 mg litre−1 revealed full susceptibility of multi-resistant T. urticae strains from Colombian roses. Artificial laboratory selection of a T. urticae field strain from Italy resulted in a slow increase of resistance over 21 months and 37 selection cycles with spirodiclofen. The selected strain exhibited a 13-fold resistance and investigations of detoxifying enzymes in vitro revealed that the constant selection with spirodiclofen led to an increase in the activity of metabolic enzymes. Compared to the non-selected parental generation the selected strain showed a 1.2-fold significantly increased carboxylesterase activity detected with a purpose-designed spirodiclofen-specific substrate, 1-naphthyl 2,2-dimethylbutyrate. Glutathione S-transferase activity with CDNB as substrate was also increased 1.2-fold, but monooxygenase activity measured by 7-ethoxycoumarin O-deethylation was even 2.1-fold increased. Synergism and metabolism studies in T. urticae in vivo supported the results of the biochemical assays, i.e., ester cleavage and oxidative detoxification seemed to be the major degradation pathway of View the MathML sourcespirodiclofen in T. urticae. The degradation is significantly increased in the spirodiclofen selected strain.
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