Overexpression of carboxylesterase-1 and mutation (F439H) of acetylcholinesterase-1 are associated with chlorpyrifos resistance in Laodelphax striatellus

Previous studies investigating a chlorpyrifos-resistant (YN-CPF) strain indicated chlorpyrifos resistance was a result of Laodelphax striatellus carboxylesterase-1 (Ls.CarE1)-mediated detoxification and acetylcholinesterase (AChE) insensitivity. In this study, we found via immunoblotting that the protein level of Ls.CarE1 was significantly overexpressed in the YN-CPF strain compared with that observed in the chlorpyrifos-susceptible (YN) strain. Moreover, the full-length gene encoding acetylcholinesterase-1, designated Ls.AChE1, was cloned from the YN-CPF and YN strains. A sequence analysis found an amino acid mutation (Phe439His) in Ls.AChE1 (corresponding to F331 in the standard matured AChE sequence of Torpedo californica) and the mutation frequencies of Phe439His were 91%, 54% and 0% in the YN-CPF, the chlorpyrifos relaxed selection (YN-RSF) and the YN strains, respectively. The results offer new evidence that support the involvement of both AChE insensitivity and CarE metabolism in the resistance to chlorpyrifos in the YN-CPF strain.