| The beet armyworm (Spodoptera exigua (Hümber)), is a worldwide distributed and polyphagous pest, which has developed resistance to many insecticides. In recent years the damage by the Spodoptera exigua to crops increased dramatically in China. Diamide insecticide chlorantraniliprole and flubendiamide, with novel mode of action have higher control effect on S. exigua. In order to make good use of the two insecticides and implement effective resistance management strategy, we surveyed resistance of filed population of S. exigua from Shandong, Henan, Liaoning provinces in China to ten insecticides. Further more, the susceptibilities of eggs, 2nd, 3rd, 4th instar larvae, adults and antifeedant effect of Spodoptera exigua to chlorantraniliprole and flubendiamide were investigated through the bioassay. The results were summarized as follows:1 Resistance monitoring in Spodoptera exiguaSpodoptera exigua (Hübner) collected from seven regions from Shandong, Henan and Liaoning, China and a Lab colony of Wuhan (WHLC) were evaluated for their susceptibilities to ten insecticides (emamectin benzoate, chlorfenapyr, indoxacarb, spinosyn, tebufenozide, methoxyfenozide, chlorfluazuron, beta-cypermethrin, chlorpyrifos and methomyl) in 2008, 2009 and 2010 using a leaf-dip bioassay method.The results indicate that field populations of S. exigua exhibit different resistance levels to different insecticides, in which the resistance to methoxyfenozide, chlorfluazuron, beta-cypermethrin and chlorpyrifos were moderate to high. The resistance ratios of S. exigua to chlorfluazuron were the highest and increased from 31.49~88.19 in 2008 to 609.72~2324.80 in 2009, 1184.39~25697.92 in 2010, the resistance developed rapidly and can not control the pest effectively in 2010; for methoxyfenozide, the resistance ratios ranging from 72.63~191.91 in 2008 to 84.94~952.77 in 2009 and 139.70~495.28 in2010; the resistance ratio to beta-cypermethrin were 95.31~437.97-fold in 2008, 51.23~1304.40-fold in 2009 and 27.27~1095.31-fold in 2010, in which the resistance of S. exigua in Taian, Anqiu, Tengzhou increased rapidly from 2009 to 2010; the resistance to chlorpyrifos were 25.05~40.64-fold in 2008, 10.80~1183.35-fold in 2009, and 19.12~267.98-fold in 2010, in which the resistance ratio in Luoyang decreased rapidly from 2009 to 2010. The field populations of S. exigua showed moderate resistance to spinosyn and tebufenozide, in which the resistance to spinosyn ranging from 1.98~5.13-fold in 2008 to 17.09~71.70-fold in 2009 and 14.31~64.20-fold in 2010, the resistance ratio increased obviously except the Luoyang population; for the tebufenozide, the resistance ratio were moderate in most regions and resistance ratio were 12.58~30.11-fold in 2008, 0.89~80.80-fold in 2009, 14.93~90.09-fold in 2010.The resistance of indoxacarb ranging from 12.25~17.12-fold in 2008 to 2.27~18.00-fold in 2009 and 3.40~23.43-fold in 2010, the resistance regularity isn't obvious. The resistances to emamectin benzoate were low level with the resistance ratios below 10-fold in all the three years except for the population of Binzhou in 2009 and 2010 and Luoyang in 2009; S. exigua showed low resistance to methomyl, and the resistance ratio ranging from 1.29~6.75-fold in all three years.The seven field populations of S. exigua to chlorfenapyr remained at susceptive stage, and the resistance ratio were ranging from 0.23-fold to 1.98-fold.There are several reasons accounting for varying degrees of resistance, including selection pressure, cropping structure and migration, in which the migration of S. exigua maybe play an important role.2 Study on the mode of action of diamide insecticides to different developmental stages of Spodoptera exiguaThe susceptibilities of eggs, 2nd, 3rd, 4th instar larvae and adults of Spodoptera exigua to chlorantraniliprole and flubendiamide were investigated using egg-dip method, leaf-dip method, topical application, stomach poison test, residual film and fed poison nutrient solution method. The results indicate that there were no ovicidal activities in the two insecticides, but the survival rates of neonate larvae of eggs were decreased with the concentration of the two insecticides increased; The toxicity of chlorantraniliprole and flubendiamide to 2nd instar larvae were the highest, which were 1.50-, 6.17-fold than the 3rd instar larvae and 22.25-, 44.95-fold than 4th instar larvae. The chlorantraniliprole and flubendiamide had good oral toxicity to 4th instar larvae of S. exigua, and were 14.10, 8.44-fold than the contact toxicity, respectively. The activities of adults indicated that the chlorantraniliprole were higher than flubendiamide with the toxicity ratios were 25.53 to 34.19-fold. The results of antifeedant test showed obvious antifeedant effect to larvae of S. exigua after treatment with the two insecticides. After 48h, antifeedant ratio reached the maximum, and the ratios were 82.73%, 84.15%. The larvae showed feeding cessation, lethargy and muscle paralysis after treated with chlorantraniliprole and flubendiamide.
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