Dynamics of CYP6ER1 expression in the brown planthopper, Nilaparvata lugens Stål under exposure to imidacloprid

Importance of the work:The brown planthopper Nilaparvata lugens Stl causes severe damage to rice crops in Indonesia.CYP6ER1 contributes to N. lugens resistance against imidacloprid.Objectives: To investigate the relative roles of the cytochrome P450 monooxygenase, CYP6ER1, in determining their resistance phenotype to imidacloprid. Material and Methods:This study investigated the relative expression of CYP6ER1 in N. lugens at various developmental stages, imidacloprid concentrations, and exposure times using Real-time quantitative polymerase chain reaction (RT-qPCR).The N. lugens population from Pringsewu Province, Lampung, was exposed to imidacloprid for two generations (Psw2) and six generations (Psw6).The relative gene expression of CYP6ER1 in the laboratory, Psw2, and Psw6 populations were determined at first and fifth instars, in male and female adults. Result:The resistant ratios of Psw2 and Psw6 were 3.7 and 5.4-fold, respectively, higher than that of the laboratory population.The CYP6ER1 expression of Psw2 was up-regulated in all developmental stages, but in Psw6, it was up-regulated only in the early stages.In Psw6, CYP6ER1 was up-regulated after the population was exposed to 350 and 1050 ppm imidacloprid with exposure times of 24, 72, and 96 hr after treatment using the third instars, relative to the before exposure levels.Main finding: Up-regulation of CYP6ER1 occurred only in the first instars of Psw6 and in other stages of Psw2.In Psw6, CYP6ER1 was rapidly up-regulated starting from the first 24 hr and increased with time until 96 hr after treatment.These findings showed the involvement of CYP6ER1 in imidacloprid detoxification.These CYP6ER1 expression patterns may be used to develop rapid diagnosis for resistance management purposes.Neonicotinoids, neuroactive insecticides, have been widely used to manage N. lugens for more than 20 years due to their persistent residual effect and high selectivity (Gorman et al., 2008).In Indonesia, imidacloprid, a neonicotinoid, has been used to manage N. lugens since 1992 (Ditjen PSP, 2017).Imidacloprid resistance has been detected across various N. lugens populations in Indonesia.Low levels of resistance were reported in Juwiring populations (RR = 7-fold), moderate levels of resistance were reported in Sukamandi populations (RR = 12.7fold), and high levels of resistance were reported in the Karawang populations (RR = 108.1fold)(Baehaki et al., 2016;Surahmat et al., 2016).Additionally, populations in Banyumas and Cilacap were moderately resistant to imidacloprid with resistance ratios (RR) of 46.20 and 29.37-fold, respectively (Londingkene et al., 2016;Diptaningsari et al., 2020).N. lugens resistance to imidacloprid has also been reported in several countries in Asia, such as China,