Characterization of Carboxylesterase Associated with Malathion Insensitivity in the Field Population of the Oriental Migratory Locust

Carboxylesterases (CarEs) from two field populations of the oriental migratory locust, Locusta migratoria manilensis (Meyen), were examined to try to understand their contribution to malathion insensitivity. The CarEs activities in Wudi population (WD) were 1.75- and 1.50-fold significantly higher than those in Huangliu population (HL) when α-naphthyl acetate (α-NA) and β-naphthyl acetate were used as substrates, respectively. Such elevated CarEs activities presented in the WD could be because of an increased staining intensity of the α-NA-hydrolyzing CarEs as shown on the nondenaturing polyacrylamide gel electrophoresis. Inhibition studies of CarEs using paraoxon and malaoxon indicated that CarE activities in the HL were more strongly inhibited than those in the WD. Furthermore, a 449-bp DNA fragment of CarE was obtained from L. migratoria manilensis. Hemiquantity reverse transcription-polymerase chain reaction analysis showed that CarE gene expression level in the WD was higher than that in the HL. The higher CarE activities and the increased CarE mRNA level in the WD appeared to be associated with decreased susceptibility to malathion in the WD due to the application of organophosphorus insecticides.