Abstract: 【Aim】 The western flower thrips , Frankliniella occidentalis (Thysanoptera: Thripidae), is a kind of invasive pest which damages greenhouse vegetables seriously in China. Our study aimed to evaluate the insecticide resistance level and offer the theoretical basis for controlling this pest. 【Methods】 Insecticide resistance in field populations of five localities (Beijing, BJ; Shouguang, Shandong, SG; Qingdao, Shandong, QD; Jinning, Yunnan, JN; Chenggong, Yunnan, CG) of F. occidentalis to 9 insecticides (spinosad, chlorpyrifos, abamectin, emamectin benzoate, cyhalothrin, chlorfenapyr, methomyl, imidacloprid and acetamiprid) from China were determined by Munger cell bioassays. The synergisms of mixed-functional oxidase inhibitor piperonyl butoxide (PBO), glutathione S-transferase inhibitor diethyl maleate (DEM) and carboxylesterase inhibitor S,S,S-tributyl phosphorotrithioate (DEF) with spinosad, imidacloprid and emamectin benzoate were determined by the same bioassay method with these field populations. 【Results】 The bioassay results showed that there was a significant high-level resistance to spinosad in BJ, JN and CG populations of F. occidentalis (34.45, 47.45, and 64.45 times, respectively).The JN population revealed a medium-level resistance to methomyl and emamectin benzoate (16.58 and 11.03 times, respectively). The CG population also had a medium-level resistance to most insecticides including emamectin benzoate, acetamiprid, imidacloprid, abamectin, and chlorfenapyr (24.17, 21.69, 20.05, 16.45, and 10.31 times, respectively). Similarly, a medium-level resistance to acetamiprid and imidacloprid was found in the QD population (17.70 and 12.49 times, respectively). However, the SG population had no resistance to any of the insecticides. The results of synergism bioassay showed that significant synergisms of PBO with imidacloprid and emamectin benzoate were found in all field populations. There were synergism of DEM with imidacloprid in CG, SG and QD populations and with emamectin benzoate in BJ, CG and SG populations. Furthermore, we found synergism of DEF with imidacloprid in CG, JN and QD populations and with emamectin benzoate in BJ, CG and JN populations. However, PBO, DEM and DEF showed no significant synergism with spinosad in the all field populations. 【Conclusion】 These results suggest that spinosad and other insecticides should be used alternately to exterminate field populations of F. occidentalis, and adding enzyme inhibitors to emamectin benzoate and imidacloprid can enhance the effect on controlling this pest.

Key words: Franleliniella occidentalis, insecticide resistance, synergist, spinosad, emamectin benzoate, imidacloprid