Evaluation of Resistance to Abamectin in the Populations of Tuta absoluta (Lepidoptera: Gelechiidae), Collected from Isfahan Province, Iran

The tomato leafminer (Tuta absoluta Meyrick) (Lepidoptera: Gelechiidae) is one of the most important pests of tomato worldwide. In this study, resistance of different populations of the tomato leaf miner from Isfahan Province was evaluated against abamectin. The median Lethal Concentrations (LC50) of different populations were estimated by bioassays using a leaf-dip method. The LC50 value of abamectin in the reference population of Isfahan University of Technology (IUT) was estimated as 5.67 mg ai L-1, while the population of Shahre-e-Abrisham 1 showed the highest (25-fold) resistance, with an LC50 value of 143.18 mg ai L-1. Pre-treatment of different populations with diethyl maleate (DEM) synergist, an inhibitor of glutathione-S-transferases (GSTs), increased significantly abamectin toxicity. GST activity was also found significantly different between resistant and reference populations. Triphenyl phosphate (TPP), an inhibitor of esterases (ESTs), reduced the LC50 value of abamctin in the populations as much as 1.73- to 3.73-fold. The activity of ESTs in these populations was also significantly different. Furthermore, inhibition of cytochrome P450 monooxygenases (CYP450s) by piperonyl butoxide (PBO) increased abamectin toxicity between 1.3- to 2.9-fold in tested populations. The highest ratios of synergism for DEM (5.86), TPP (3.73-fold), and PBO (2.91-fold) were observed in Shahre-e-Abrisham 1. It seems that GSTs and ESTs play a more important role in the resistance development against abamectin in the studied populations. High levels of resistance to abamectin in the collected populations from Isfahan Province shows the importance of insecticide resistance management based on the early detection of resistance and alternative use of insecticides.