Resistance to three biopesticides and changing populationtrends in the diamondback moth in differentvegetable planting areas of Yunnan, China
Author of the article:YIN Yan-Qiong1** LI Xiang-Yong1 ZHAO Xue-Qing1 CHEN Ai-Dong1***MU Wei-Dong2 ZHENG Li-Ping3
Author's Workplace：1. Agriculture Environment and Resources Institute, Yunnan Academy of Agricultural Sciences, Kunming 650205, China;2. Tonghai County Plant Protection and Quarantine Station, Tonghai 6527003, China;3. Midu County Plant Protection and Quarantine Station, Midu 675600, China
Key Words：diamondback moth, biopesticdes, resistance, change trend
Abstract：
[Objectives] To understand trends in insecticide resistance in the diamondback moth, Plutella xylostella (L.), and the population dynamics of this species, in Tonghai and Midu counties, which are the two main vegetable growing areas of Yunnan province. [Methods] During 2008-2015, resistance levels of these two diamondback moth populations to abamection, spinosad and Bacillus thuringiensis(BT) were assessed by the leaf-dipping method in a laboratory. [Results] In 2008, resistance to abamectin and spinosad were high in both populations. With respect to abamectin, the respective LC50s for Tonghai and Midu were 34.017 and 25.688 mg/L, and the resistance ratios were 1 700.85 and 1 284.40, respectively. For spinosad, LC50s were 13.728 and 19.830 mg/L, respectively, and the resistance ratios were 114.40 and 165.25, respectively. Both populations were highly resistant to spinosad. With respect to Bt, the respective LC50s for each population were 0.530 and 0.538 mg/L, and the resistance ratios were 2.04 and 2.07, respectively, which are relatively low. By 2015, the respective resistance ratios of the two diamondback moth populations to abamectin had dropped to 455.70 and 255.05. Although this decrease was statistically significant, resistance remained high. There was no significant drop in spinosad resistance in either population in 2015, resistance ratios remained a moderate 35.56 and 75.28, respectively, in that year. There was, however, a significant difference in resistance between years; the LC50 increasing from 0.885 to 19.830 mg/L. Both populations remained sensitive to Bt; with resistance ratios in 2015 of 5.41 and 1.73, respectively. [Conclusion] The resistance of the Tonghai and Midu populations of P. xylostella to the three biopesticides were similar from 2008 to 2015. Although resistance to abamectin and spinosad declined over time, it remained relatively high. Both populations currently only display low resistance to Bt and consequently we recommend using Bt in rotation with other insecticides to improve control of the diamondback moth in Yunnan.