Molecular Identification of Carboxylesterase Genes And Their Potential Roles in the Detoxification Metabolism of Three Insecticides in Grapholita Molesta

The oriental fruit moth, Grapholita molesta (Busck), is one of the most damaging pests worldwide in stone and pome fruits. Application of chemical pesticides is still the main method to control this pest, and results in resistance of G. molesta to several types of insecticides. Carboxylesterase (CarE) is one kind of the important enzyme involved in the detoxificationmetabolism of xenobiotics and insecticides. However, the function ofCarEs in detoxification metabolism process of G. molesta is still unclear. In the present study, we found thatthe enzyme activity of CarEs and mRNA expression of 6 CarE genes were consistently elevated after 5th instar larvae treated with 3 insecticides (emamectin benzoate, lambda-cyhalothrin, andchlorantraniliprole). The multiple alignments of amino acid sequences, phylogenetic trees, and spatio-temporal expression profiles were analyzed to identify the molecular characteristic of these 6 CarE genes. We further investigated the function of these 6 CarE genes in detoxification metabolism using RNAi and found that the susceptibility of G. molesta to all these 3 insecticides were obviouslyraised afterGmCarE9, GmCarE14, GmCarE16, and GmCarE22 knockdown, respectively. We also determined the effect of these 4 CarE genes on mRNA expression and enzymatic activity of 3 antioxidant genes. The results showed that the enzyme activity of SOD, CAT, and POD were significantly increased after these 3 insecticides treatment, but the enzymatic activities and gene expression ofSOD, CAT, and POD were obviously reduced after knockdown of GmCarE9, GmCarE14, GmCarE16, and GmCarE22,separately. Overall, these results demonstrated that GmCarE9, GmCarE14, GmCarE16, and GmCarE22 play an important role in the detoxificationmetabolism and antioxidant protection ofG. molesta to emamectin benzoate, lambda-cyhalothrin, and chlorantraniliprole treatment. This study not only expands our understanding of CarEs in insecticide detoxification metabolism, and also provides a theoretical basis for better resistance management of G. molesta.