Comparison of esterase gene amplification, gene expression and esterase activity in insecticide susceptible and resistant strains of the brown planthopper, Nilaparvata lugens (Stal)

Organophosphorus and carbamate insecticide resistance in Nilaparvata lugens is based on amplification of a carboxylesterase gene, NI-EST1. An identica l gene occurs in susceptible insects. Quantitative real-time PCR was used t o demonstrate that NI-EST1 is amplified 3-7-fold in the genome of resistant compared to susceptible planthoppers. Expression levels were similar to am plification levels, with 1-15-fold more NI-EST1 mRNA in individual insects and 5-11-fold more NI-EST1 mRNA in mass whole body homogenates of resistant females compared to susceptibles,These values corresponded to an 8-10-fold increase in esterase activity in the head and thorax of individual resista nt insects. Although amplification, expression and activity levels of NI-ES T1 in resistant N. lugens were similar, the correlation between esterase ac tivity and NI-EST1 mRNA levels in resistant individuals was not linear.