RESUMO
BACKGROUND: We report on the status of imidacloprid and ethiprole resistance in Nilaparvata lugens Stål collected from across South and East Asia over the period 2005-2012. RESULTS: A resistance survey found that field populations had developed up to 220-fold resistance to imidacloprid and 223-fold resistance to ethiprole, and that many of the strains collected showed high levels of resistance to both insecticides. We also found that the cytochrome P450 CYP6ER1 was significantly overexpressed in 12 imidacloprid-resistant populations tested when compared with a laboratory susceptible strain, with fold changes ranging from ten- to 90-fold. In contrast, another cytochrome P450 CYP6AY1, also implicated in imidacloprid resistance, was underexpressed in ten of the populations and only significantly overexpressed (3.5-fold) in a single population from India compared with the same susceptible strain. Further selection of two of the imidacloprid-resistant field strains correlated with an approximate threefold increase in expression of CYP6ER1. CONCLUSIONS: We conclude that overexpression of CYP6ER1 is associated with field-evolved resistance to imidacloprid in brown planthopper populations in five countries in South and East Asia.