Abstract: In order to clarify the molecular mechanisms of deltamethrin resistance in Spodoptera litura (Fab.), the esterase gene of S. litura was cloned by using the RT-PCR with degenerate primers and rapid amplification of cDNA ends (RACE) strategies, and designated as Slest2. Sequence analysis demonstrated that the fragment was 1 796 bp in full-length with a 63 bp 5′ UTR and 119 bp 3′UTR (GenBank accession no. DQ445461), the open reading frame encoded a 537-amino-acid protein. Homology analysis indicated that the deduced amino acid residues of Slest2 had very high similarity with those from other species, and contained several conserved domains in all esterase proteins. The relative expression level of Slest2 was compared between the resistant strain and the susceptible strain using real-time quantitative PCR technique. The transcription level of Slest2 tested with cDNA as template in the resistant strain was 46.85-fold as high as that in the susceptible strain. However, the test with gDNA as template indicated that the resistant strain and the susceptible strain had similar gene copies of Slest2 (the former was 1.16-fold as high as the latter). The results suggest that the higher transcription level of Slest2 contributes to insecticide resistance in S. litura.

Key words: Spodoptera litura; carboxylesterase, insecticide resistance, resistant strain, susceptible strain, sequence analysis, real-time quantitative PCR