Fitness cost and molecular basis of imidacloprid resistance in brown planthopper, Nilaparvata lugens (Stål) in India.

This study aims to assess the fitness cost associated with imidacloprid resistance and expression of cytochrome P450 genes in brown planthopper, Nilaparvata lugens (Stål). After continuous selection with imidacloprid exposure over 10 generations in a glass house, N. lugens developed a 12.84-fold resistance. The demographic and life history parameters of imidacloprid resistant (IMI-R) and susceptible (IMI-S) strains of N. lugens were compared by age-stage, two-sex life table approach. The duration of egg, third instar, fifth instar, pre-adult and total pre-oviposition period were significantly prolonged in IMI-R strain. However, the fecundity of IMI-R strain (194.59) was significantly lower as compared to IMI-S strain (224.05). There was no significant effect on the duration of other nymphal instars and adult longevity. Whereas the intrinsic rate of increase and doubling time differed significantly in the IMI-R and IMI-S strains, the relative fitness of IMI-R strain was 0.74, clearly indicating a trade-off between imidacloprid resistance and fitness in N. lugens. In IMI-R strain, two P450 genes CYP6ER1 and CYP6AY1 were significantly upregulated by 5.85 and 3.35-fold, respectively compared to the IMI-S strain. Our results conclude that imidacloprid resistance in N. lugens has significant fitness cost due to prolonged developmental stages, reduced fecundity, altered demographic parameters and upregulation of P450 genes. Lower fitness of imidacloprid resistant strains has direct implication in management of N. lugens in rice ecosystems, as any withdrawal of exposure could potentially recover susceptibility.