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Levels of insecticide resistance, carboxylesterase activity, and carboxylesterase expression were investigated in both omethoate-selected resistant and susceptible strains of cotton aphids, Aphis gossypii (Glover). The resistant strain exhibited 21.72-fold resistance to omethoate based on comparison LC 50 values with the susceptible strain in cotton aphids. Five substrates, α-naphthyl acetate (α-NA), β-naphthyl acetate (β-NA), α-naphthyl butyrate (α-NB), α-Naphthyl propionate (α-NPr), and α-naphthyl phosphate (α-NP) were used to determine carboxylesterase activity in both resistant and susceptible strains of cotton aphids. Carboxylesterase activity was significantly higher in resistant strain than in susceptible strain, 11-fold for α-NA and β-NA, 12-fold for α-NB and 10-fold for α-NPr and α-NP. The levels of gene expression for carboxylesterase of both resistant and susceptible strains were determined by real-time quantitative PCRs. Compared with the susceptible strain, the relative transcription levels and gene copy numbers of the carboxylesterase were 4.54- and 0.97-fold in the resistant strain, respectively. These results indicated that the increased expression of the carboxylesterase resulted from the increased transcription levels of carboxylesterase mRNA was related to omethoate resistance in cotton aphids. |
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