| Beet armyworm, Spodoptera exigua (Hubner) (Lepidoptera:Noctuidae) are major pests of numerous cultivated crops. Frequent use of chemical insecticides controlling S. exigua had led to the development of insecticide resistance. Metaflumizone is a sodium channel inhibitor (SCI) insecticide from semicarbazone class and has exceptional insecticidal activity on lepidopteran pests, coleopteranpests and some sanitation pests.In this paper, the resistance of S. exiguafrom Huizhou to twelve insecticides, resistance risk in S, exigua to metaflumizone, whether cross-resistance exists between metaflumizone and other conventional insecticides of S. exigua and detoxifying enzyme activities were studied. The main results are as follows:1 Monitoring resistance of S. exigua to twelve insecticides in Huizhou, Guangdong ProvinceThis study monitoring the resistance of S. exigua to twelve insecticides with an approach of leaf-dip bioassay method in 2011 and 2012. The results are as follows:Beet armyworm, Spodoptera exigua (Hiibner), strains, originating from field-collected populations in Huizhou resistant to many insecticides. S. exigua exhibits high or extremely high resistance to lambda-cyhalothrin, chlorfluazuron, chlorpyrifos, spinosad, tebufenozide and emamectin benzoate, shows low to moderate resistance to chlorantraniliprole, pyridalyl, indoxacarb, spinosad, endosulfan and methomyl in both two years. The results indicate that the resistance ratios of S. exigua to newer insecticides such as metaflumizone and emamectin benzoate havea obvious change in 2012. The resistance ratio of chlorantraniliprole increased a little in 2012. S. exigua showed high resistance to insect growth regulators such as tebufenozide and chlorfluazuron in 2011 and 2012, in which resistance to chlorfluazuron was decreased in 2012 and resistance to tebufenozide has almost no change. S. exigua exhibits extremely high resistance to chlorpyrifos and lambda-cyhalothrin in both two years as compared with WHLC.2. Assessment of resistance risk in S. exigua to metaflumizone and the mechanisms for resistance to multiple insecticidesA field-population of S. exiguacollected from Huizhou in 2012 was selected after repeated exposure to metaflumizone to determine the risk of resistance evolution. After 12 generations of selection, there was a 3.4-fold increase in LC50. The realized heritability (h2) of resistance was estimated as 0.0858 by using threshold trait analysis. The projected rate of resistance evolution indicated that if h2= 0.0858 and 70%-90% of the population was killed at each generation, and then a 10-fold increase in LC50 would be expected in 15.0-22.7 generations for metaflumizone. These results show that the risk of resistance development exists in S. exigua to metaflumizone after continuous application.Selection (G1-G10) significantly increased resistance ratio for metaflumizone to 6.1-fold compared the original population and 370.4-fold compared with Lab-Sus. The resistance of ambda-cyhalothrin, chlorfluazuron, tebufenozide and chlorantraniliproledecreased a little compared with HZ12-G1. The selection did not affect significantly on indoxacarb, spinosad, methomyl, endosulfan, pyridalyl, chlorpyrifosand emamectin benzoate.Without exposuring to any insecticide, the resistance levelsof lambda-cyhalothrin, emamectin benzoate, chlorfluazuron, tebufenozideand chlorantraniliprole decreased a little compared with HZ12-G1. The resistance of indoxacarb, spinosad, methomyl, endosulfan, pyridalyl, metaflumizone, chlorpyrifoshas almost no change compared with HZ12-G1.This study did not find any cross-resistance between metaflumizone and indoxacarb or lambda-cyhalothrin, and no cross-resistance between metaflumizone and other conventional insecticides.This study used leaf-dip method to measure the synergism to insecticides.DEF showed significant synergism to metaflumizone on HZ11 and HZ12 strain with synergism ration 5.7-fold and 3.4-fold respectively, and little synergism was observed in the susceptible strain (Lab-Sus, SR=1.5-fold).It was surprising that methimazolc also showed obvious synergism on HZ11 and HZ12 strain with synergism ration 3.1-fold and 1.9-fold respectively, and no synergism was observed in the susceptible strain (Lab-Sus, SR=0.7-flod). PBO showed some synergism on HZ11 and HZ12 strain with synergism ration 2.1-fold and 1.7-fold respectively, and no synergism was observed in the susceptible strain (Lab-Sus, SR=0.9-fold). DEM showed little synergism on HZ11 and HZ12 strain with synergism ration 2.1-fold and 1.2-fold respectively, and no synergism was observed in the susceptible strain (Lab-Sus, SR= 1.0-fold). PBO showed significant synergism to lambda-cyhalothrin on HZ12 strain with synergism ration 12.9-fold, and no synergism was observed in the susceptible strain (Lab-Sus, SR=0.9-fold). DEF showed marked synergism on HZ12 strain with synergism ration 4.3-fold, and no synergism was observed in the susceptible strain (Lab-Sus, SR=0.9-fold). DEM and methimazole showed some synergism on HZ12 strain with synergism ration 2.6-fold and 2.3-fold respectively, and no synergism was observed in the susceptible strain (Lab-Sus, SR=1.0-fold and 0.9-fold respectively). PBO, DEM, DEF and methimazole showed little synergism to emamectin benzoate on HZ12 strain with synergism ration 1.0-fold,1.3-fold, 1.0-fold and 1.2-fold respectively, and no no synergism was observed in the susceptible strain (Lab-Sus, SR=0.9-fold,1.2-fold, 1.2-fold and 1.1-fold respectively). Drop method:This study used another four synergists for research including imazalil, clotrimazole, ketoconazole and diphenyl-Ethanedione. Clotrimazole, ketoconazole and diphenyl-Ethanedione has little synergism on metaflumizone except imazalil. DEF and PBO showed significant synergism on metaflumizone with synergism ratio 4.6-fold and 4.7-fold, respectively. Methimazole also showed some synergism with synergism ration 1.7-fold.In conclusion, metaflumizone resistance of S. exiguais main metabolic and mediated by esterases or cytochrome-P450 monooxygenases or both, and FMO was also involved in the metabolic detoxification of metaflumizone. Oxidative detoxification seems to be a major mechanism of resistance to cyhalothrin in the HZ 12 strain, and esterases also have significant role,while FMO and GST have no considerable role. |
PDF Full Text Request