Dynamic changes of resistance to conventional insecticides in the brown planthopper, Nilaparvata lugens(Hemiptera: Delphacidae) in the main rice growing regions in Guizhou Province, southwestern China

[Aim] The objective of this research is to assess the resistance of the brown planthopper, Nilaparvata lugens(Stal) to conventional insecticides in Guizhou, southwestern China. [Methods] The resistance to six insecticides (imidacloprid, thiamethoxam, isoprocorb, clothianidin, acetamiprid and ethofenprox) in field populations of N. lugens collected from three rice growing regions (Huangping, Tongzi, and Kaiyang) in Guizhou Province during 2013-2015 was assayed by rice dipping method. [Results] Substantial variations of the resistance level to different insecticides existed in N. lugens populations from Guizhou. Compared with the susceptible population of N. lugens, the three field populations have developed moderate-level resistance to imidacloprid, thiamethoxam, isoprocorb and clothianidin during 2013-2015, with the resistance ratios of 21.88-95.38, 10.91-69.36, 13.00-57.23 and 23.11-39.54-fold, respectively, while these field populations were still sensitive to acetamiprid and ethofenprox, with the resistanc