Carboxylesterase Biochemical And Molecule Mechanisms Of Resistant Aphis Glycines To Lambda-cyhalothrin

Soybean aphid (Aphis glycines Matsumura) is one of the most important sapsucking pests on soybean, which has become a major source of economic loss insoybean production. Long-term and heavy use of insecticides lead to the emergenceof insecticide-resistance for soybean aphid on varity of pyrethroid, which go againstto agricultural production and ecological environment. Carboxylesterase-mediateddetoxification is a major mechanism accounting for the pyrethroids resistance inaphids. So we carried out the study of biochemical and molecular mechanisms forcarboxylesterase in lambda-cyhalothrin resistant strain of soybean aphid, mainlyincludes four parts as follow:1. Selection of lambda-cyhalothrin resistant strain of soybean aphid. As theeffect of continuous selection with lambda-cyhalothrin for26generations, the valueof median lethal concentration （LC50） was increased from0.006ugmL-1to3.844ugmL-1, and resistance ratio reached640-fold. The result demonstrated that weestablished a stable soybean aphid resistant strain.2. Cross-resistance of lambda-cyhalothrin resistant strain with otherinsecticides. We chose15species insecticides belonging to7classes to study thecross-resistance. The result revealed that the resistant strain showed a highcross-resistance with cypermethrin and cis-fenvalerate,56.31-fold,16.96-foldrespectively, a lower cross-resistance with chlorpyrifos and carbofuran,10.49-fold,16.96-fold respectively, scarely cross-resistance with insecticides frompyrrole(pyrazole), chloride nicotinanilide, benzoyl phenylurea and macrolide.3. Biochemistry characteristics of carboxylesterase in susceptible and resistantstrains. The study of activity and eneyme kinetic parameter of carboxylesterasebased on two substrates, α-naphthyl acetate(α-NA) and β-naphthyl acetate(β-NA).The results indicated that activities and maximal velocities (Vmax) ofcarboxylesterases were significantly greater in the resistant strain than that in thesusceptible strain (P <0.05) when two naphthyl-substituted chemicals were used assubstrates. The ratio of the carboxylesterase activity was2.19for α-NA,1.53for β-NA compared with the susceptible strain, respectively, and the ratio of maximalvelocities was1.98for α-NA,3.83for β-NA. However, there were no significantdifferences in the Michaelis constants (Km) for all tested substrates between theresistant and susceptible strains. The above results suggested that the enhancedcarboxylesterase activity played an important role in the lambda-cyhalothrinresistance of soybean aphid, but carboxylesterases in these two strains werequantitatively different but qualitatively similar.4. Molecular mechanisms of carboxylesterase in susceptible and resistantstrains. We study the relative expression levels and gene copy numbers ofcarboxylesterase and E4in susceptible and resistant strains with Real-timequantitative PCR technique. Compared to the susceptible strain, the relativeexpression levels of carboxylesterase and E4mRNA were5.88-fold and4.91-foldrespectively, and gene copy numbers of carboxylesterase and E4were2.93-fold and3.86-fold respectively, for the resistant strain, and the differences were significant(P <0.05). The above results indicated that the enhanced carboxylesterase activitiesmainly relied on gene up-regulation and gene amplification.The result all above indicated that carboxylesterase plays an important role inlambda-cyhalothrin resistance of soybean aphid. The enhanced carboxylesteraseactivities due to gene up-regulation and gene amplification has a close relationshipwith resistance to lambda-cyhalothrin. Meanwhile, the enhanced carboxylesteraseactivities may lead to the cross-resisrance with cypermethrin, cis-fenvalerate,chlorpyrifos, carbofuran.