RNA interference revealed the roles of two carboxylesterase genes in insecticide detoxification in Locusta migratoria.

Carboxylesterases (CarEs) play key roles in metabolism of specific hormones and detoxification of dietary and environmental xenobiotics in insects. We sequenced and characterized CarE cDNAs putatively derived from two different genes named LmCesA1 and LmCesA2 from the migratory locust, Locusta migratoria, one of the most important agricultural pests in the world. The full-length cDNAs of LmCesA1 (1892 bp) and LmCesA2 (1643 bp) encode 543 and 501 amino acid residues, respectively. The two deduced CarEs share a characteristic α/β-hydrolase structure, including a catalytic triad composed of Ser-Glu (Asp)-His and a consensus sequence GQSAG, which suggests that both CarEs are biologically active. Phylogenetic analysis grouped both LmCesA1 and LmCesA2 into clade A which has been suggested to be involved in dietary detoxification. Both transcripts were highly expressed in all the nymphal and adult stages, but only slightly expressed in eggs. Analyses of tissue-dependent expression and in situ hybridization revealed that both transcripts were primarily expressed in gastric caeca. RNA interference (RNAi) of LmCesA1 and LmCesA2 followed by a topical application of carbaryl or deltamethrin did not lead to a significantly increased mortality with either insecticide. However, RNAi of LmCesA1 and LmCesA2 increased insect mortalities by 20.9% and 14.5%, respectively, when chlorpyrifos was applied. These results suggest that these genes might not play a significant role in detoxification of carbaryl and deltamethrin but are most likely to be involved in detoxification of chlorpyrifos in L. migratoria.