Molecular characterization of the amplified carboxylesterase gene associated with organophosphorus insecticide resistance in the brown planthopper, Nilaparvata lugens

Widespread resistance to organophosphorus insecticides (OPs) in Nilaparvata lugens is associated with elevation of carboxylesterase activity. A cDNA e ncoding a carboxylesterase, NI-EST1, has been isolated from an OP-resistant Sri Lankan strain of N. lugens, The full-length cDNA codes for a 547-amino acid protein with high homology to other esterases/lipases. NI-EST1 has an N-terminal hydrophobic signal peptide sequence of 24 amino acids which sug gests that the mature protein is secreted from celss expressing it,The nucl eotide sequence of the homologue of NI-EST1 in an OP-susceptible, low ester ase Sri Lankan strain of IV. lugens is identical to NI-EST1. Southern analy sis of genomic DNA from the Sri Lankan OP-resistant and susceptible strains suggests that NI-EST1 is amplified in the resistant strain. Therefore, res istance to OPs in the Sri Lankan strain is through amplification of a gene identical to that found in the susceptible strain.