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The level of susceptibility of the two-spotted spider mite, Tetranychus urticae Koch, populations collected from greenhouses in Antalya and Isparta regions of Turkey against chlorpyrifos was determined by a petri dish bioassay method. This study consisted of two stages. In the first stage, using a diagnostic dosage (0.026 ml chlorpyrifos in 100 ml distilled water) it was determined whether these populations are resistant or susceptible to chlorpyrifos. Then, different dosages of chlorpyrifos were applied to resistant populations to determine LC 50 and LC 90 values. Resistant ratios of populations were calculated by dividing the LC 50 values of resistant populations by that of a susceptible population of T. urticae strain GSS. The resistance ratio of T. urticae populations collected from greenhouses ranged from 8.00 to 1,774.00. Results show that while three of the populations gathered from the Isparta region, where greenhouse vegetable growing has been increasing since 2000, are susceptible, two of them are only partially resistant to chlorpyrifos. On the other hand, all the twospotted spider mite populations collected from the Antalya region, the centre of greenhouse vegetable production for many years, were found to be highly resistant to chlorpyrifos.

Changes in insecticide susceptibilities and detoxifying enzyme activities were measured in a strain of Tetranychus urticae Koch following repeated exposure to the organophosphate insecticide, chlorpyrifos. Twelve consecutive selection at the LC 60 of the parental strain increased resistance from 8.58 to 91.45 fold. The interaction of some synergists [piperonyl butoxide, triphenyl phosphate and S-benzyl-O,O-diisopropyl phosphorothioate (IBP)] with chlorpyrifos was analyzed in the selected strain. Solely IBP showed a low synergistic effect with chlorpyrifos. The selected strain also demonstrated resistance against abamectin, propargite, clofentezine and fenpyroximate. The mode of resistance inheritance to chlorpyrifos was found to be incompletely dominant, and not sex-linked. Non-specific esterase enzyme activity was raised from 19.35 to 33.59 mOD/min/mg proteins during the selection period and it was observed that esterase band intensities visualized by polyacrylamide gel electrophoresis increased. This study has investigated the selection of resistance to chlorpyrifos and documented resistance to abamectin, propargite, clofentezine and fenpyroximate in Turkish T. urticae. Esterase enzymes may be playing a role in chlorpyrifos resistance while glutathione S-transferase (GST) and P450 enzymes do not appear to have any significant involvement.

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Selection for spiromesifen under laboratory conditions resulted in the development of spiromesifen resistance in the predatory mite N. californicus. Predatory mites that are resistant to pesticides are considered valuable for use in resistance management programmes within integrated pest control strategies.