Abstract Apple is one of the most important and commercial products in Iran and around the world. Two Tetranychus spider mite species, T. turkestni Ugarov and T. urticae Koch, are amongst the most important pests of apple trees in Iran and the world. To control spider mites, farmers often use a variety of acaricides, such as hexythiazox, etoxazole, propargite and abamectin, which are common amongst apple farmers. Repeated and indiscriminate use of acaricides causes rapid development of acaricide resistance. Resistance consequences include the use of acaricides in doses higher than the recommended dose, increasing the frequency of spraying, higher risks of pesticide residue and eliminating natural enemies. The aim of this study was to eva‎luate the resistance of different populations of T. turkestni collected from Semirom apple orchards (Padena1, Padena2, Padena3, Padena4, Semirom1, Semirom2) and one T. urticae population (Pirbakran) from Isfahan to hexythiazox and etoxazole acaricides. In this study, for morphological identification, adult males from all populations were mounted on microscopic preparations. In addition, molecular identification was performed using sequencing partial, cytochrome oxidase I which confirmed species assignment. In order to determine the toxicity of acaricides, bioassays were performed by spraying leaf discs that carried larva or adult mites using a Potter spray tower. The LC50 value of hexythiazox acaricide was estimated as 4.40 mg active ingredient per liter (mg a.i. L-1) for the susceptible population of Padena1. Compared to the susceptible population, Padena4 population with an LC50 value of 38.86 mg a.i. L-1 showed a resistance ratio of 8.82 fold and Pirbakran population with an LC50 value of 1058.108 mg a.i. L-1 showed a resistance ratio of about 240.41 fold. Other populations were found 2 to 8 fold resistant to the hexythiazox. Pretreatment with PBO synergist decreased LC50 value of hexythiazox about 3.17, 12.96, 8.75 and 11.55 fold in Padena1, Padena3, Padena4 and Semirom2 populations, respectively. Between detoxification enzymes, a significant difference was only found in monooxygenases activity between Padena2, Semirom1, Semirom2 and Pirbakran populations with ratio of 1.58, 0.86, 1.37 and 0.73-fold, respectively. Padena1 population was the most sensitive population to etoxazole acaricide while Padena2, Padena4, Semirom2 and Pirbakran populations were the most resistant with LC50 values of 1.01, 1.03, 1.08 and 2239 mg a.i. L-1, respectively. Synergism assays showed that pretreatment with PBO decreased LC50 value of etoxazole 1.83, 2.22 and 1.93-fold in Padena1, Semirom2 and Pirbakran populations, respectively, pretreatment with VER also decreased LC50 value of etoxazole 1.16, 2.26 and 2.54-fold and SUL decreased this value 1.27, 2.17 and 3.30-fold, respectively. Padena1 population with an LC50 value of 19.6 mg a.i. L-1 was the most sensitive population to abamectin and Padena2 and Pirbakran with an LC50 values of 58.9 and 413.3 mg a.i. L-1 were the most resistant populations. The LC50 values of susceptible population of Padena1 and Semirom1 were 55.66 and 60.24 mg a.i. L-1 against propargite. The fifth domain of chitin synthase1 (CHS1) gene was sequenced and based on the sequence chromatographs no amino acid substitution was detected at position 1017. In general, the mechanisms involved in T. turkestani resistance to the hexythiazox and etoxazole are most likely conferred by enhanced activity of detoxifying enzymes and the most important of which are cytochrome P450-dependent monooxygenases. The obtained results could be a great help in early detection and management of resistance to the tested acaricides in T. turkestani populations and to. delay the onset of wide spread acaricide resistance.

جهانگير خواجه علي

نفيسه پورجواد

لادن طلائي، مرتضي زاهدي