Abstract: 【Aim】 The South American tomato pinworm, Tuta absoluta, is a newly invaded devastating pest in China, causing severe damage to tomatoes. However, the current status of insecticide resistance in newly invaded T. absoluta populations in China has not been reported. The objective of this study is to clarify the susceptibility of the field populations of T. absoluta from Xinjiang and Yunnan to six commonly used insecticides and its relationship with the activities of detoxification enzymes. 【Methods】 Laboratory toxicities of six frequently used pesticides to the 2nd instar larvae of Xinjiang and Yunnan populations of T. absoluta were tested by using leaf-dip method. The synergistic effects of three synergistic agents including the  CYP450 inhibitor piperonyl butoxide (PBO), the esterase inhibitor triphenyl phosphate (TPP) and the GST inhibitor diethyl maleate (DEM) on chlorantraniliprole were determined in the bioassay against the 2nd instar larvae of T. absoluta, and the activities of detoxification enzymes including cytochrome P450-dependent monooxygenase (CYP450), glutathione S-transferase (GST) and carboxylesterase (CarE) in the 2nd instar larvae of the laboratory susceptible population and resistant field population (Xinjiang population) of T. absoluta were determined by enzyme activity assay, to ascertain the relationship of insecticide resistance with detoxification enzyme activities. 【Results】 The susceptibility of Yunnan population of T. absoluta to the six insecticides from high to low was emamectin benzoate, chlorfenapyr, spinosad, indoxacarb, chlorantraniliprole, and beta-cypermethrin, while that of Xinjiang population to the six insecticides from high to low was emamectin benzoate, chlorfenapyr, chlorantraniliprole, spinosad, indoxacarb, and beta-cypermethrin. Compared with the laboratory susceptible population, both Yunnan and Xinjiang populations showed the highest level of resistance to chlorantraniliprole, with the resistance ratios of 212.7 and 169.3, respectively. The bioassay results revealed that the three synergistic agents PBO, TPP and DEM showed no obvious synergistic effect on chlorantraniliprole. The enzyme activity assays showed that the activities of CYP450, GST and CarE in the 2nd instar larvae between the laboratory susceptible population and resistant field population of T. absoluta were not 
significantly different. 【Conclusion】 Both Xinjiang and Yunnan populations of T. absoluta show different levels of resistance to the tested six pesticides, with the highest resistance level to chlorantraniliprole, and the insecticide resistance of T. absoluta is unrelated to the activities of detoxification enzymes. The results of this study provide valuable information for the field control and insecticide resistance management of T. absoluta.

Key words: Tuta absoluta, invasive species, Xinjiang population, Yunnan population; insecticides, toxicity test, detoxification enzyme