Abstract: 【Aim】 This study aims to clarify the levels and mechanisms of indoxacarb resistance in different populations of the cotton bollworm， Helicoverpa armigera, so as to scientifically control this insect pest and to effectively avoid the rapid development of resistance to indoxacarb. 【Methods】 The resistance levels and the synergistic effects of PBO, DEF and DEM on indoxacarb in the 3rd instar larvae of different populations of H. armigera, including the susceptible population (CP), the indoxacarb-selected population (TP), Yishui population (YP) from Yishui, Shandong and Handan population (HP) from Handan, Hebei, were determined with leaf-dipping method. The activities of three detoxification enzymes ［mixed function oxidase (MFO), carboxylesterase (CarE) and glutathione S-transferase (GST)］ and acetylcholinesterase (AchE) in these populations were assayed. 【Results】 The CP population of H. armigera was still susceptible to indoxacarb, while the TP, YP and HP populations exhibited decreased sensitivity, low-level resistance and moderate-level resistance to indoxacarb, with the resistance ratios of 4.36-, 8.06- and 15.34-fold, respectively. In the TP population, the toxicity of indoxacarb to the 3rd instar larvae of H. armigera increased when they were fed on the leaves treated by three synergists for 0, 6 and 12 h. The synergistic effects of PBO and DEF to indoxacarb in the 3rd instar larvae were greater than that of DEM. After the 3rd instar larvae of H. armigera were fed on the leaves treated by PBO, DEF and DEM for 12 h, the synergistic ratios were 3.86-, 2.52-, and 4.57-fold in the HP population, while 1.11-, 0.52- and 1.09-fold in the CP population, respectively. The activities of MFO, CarE and GST in the HP population were significantly higher than those in the CP and TP populations. The activities of MFO and CarE in the YP population were significantly higher than those in the CP population, while the CarE activity in the YP population was significantly lower than that in the HP population； however, there was no significant difference in the AchE activities among different populations. 【Conclusion】 The results suggest that when a moderate-level resistance level is reached, the enhancement of MFO, CarE and GST activities confers resistance to indoxacarb in H. armigera, and the resistance to indoxacarb is significantly synergized by the metabolic inhibitors PBO, DEF and DEM.

Key words: Helicoverpa armigera; indoxacarb, insecticide resistance, metabolic inhibitor, synergism, detoxification enzyme