Abstract: Carboxylesterase plays an important role in insect detoxification and metabolism processes of insecticides. This research aims at analyzing the expression levels of carboxylesterase gene in Sitobion avenae（Fabricius）under imidacloprid stress. Homologous cloning strategy was used to clone carboxylesterase gene cDNA fragment，and its expression variations under different dose of imidacloprid were analyzed with qRT-PCR. A carboxylesterase gene cDNA fragment of 392 bp，named SaEST 3（GenBank accession number is KY 441614），was amplified from S. avenae（Fabricius）using homologous cloning strategy. The gene sequence coded a polypeptide of 130 amino acid residues，the calculated molecular mass was 14 kD and the theoretical isoelectric point（pI）was 4.93. Homology alignment and bioinformatics analysis suggested that the amino acid sequence of SaEST3 was highly identical to that of carboxylesterase gene from Acyrthosiphon pisum（94%），Diuraphis noxia（85%），Aphis nerii（80%），and Myzus persicae（80%）. The results of qRT-PCR showed that the relative expression of SaEST 3 mRNA was up-regulated under different dose of imidacloprid. In a summary，the cloned sequence was carboxylesterase gene of S. avenae（Fabricius），and imidacloprid stress may affect the expression of SaEST 3 gene in S. avenae（Fabricius）.

Key words: carboxylesterase, Sitobion avenae（Fabricius）, imidacloprid, clone, gene expression