The Adaptation Mechanism Of Spodoptera Exigua To Emamectin Benzoate Stress With Different Sublethal Dose

The beet armyworm,Spodoptera exigua(Hubner)is a worldwide important agricultural pest,belonging to lepidoptera,noctuidae.S.exigua now has developed a high level of resistance to most conventional pesticides,because of the long-term chemical control.As a kind of new biological insecticide with characteristics of high-activity,long-duration and unique-mechanism,emamectin benzoate in field has a good efficacy to Lepidoptera pests,especially to S.exigua.In order to use this insecticide reasonably,prolonging its application periods to control S.exigua and delaying the S.exigua resistance,it is necessary to study further the interaction relationship between emamectin benzoate and S.exigua.Many report results indicated that the sublethal effects of insecticides in fileds not only affect the physiological and biochemical characteristics of target pests,but also result in target pests the evolution of resistance to insecticides.Therefore,the studies of the effects on development,the detoxifying enzyme activities and the expressions of relative genes in S.exigua treated by sublethal dose emamectin benzoate can help us understand the resistance evolution processes of S.exigua to emamectin benzoate,and providing a theoretical foundation and scientific basis for S.exigua integrated control.In this study,different sublethal concentrations of S.exigua to emamectin benzoate were firstly explicated in our lab by the toxicity tests,and S.exigua larvae at 3rd instar were treated by emamectin benzoate with different sublethal doses.And then these larvae development status were studied and building life tables of all treatments.At the same time,combined q-PCR and enzyme activity assay techniques,system analysis the sublethal effects on S.exigua to emamectin benzoate,and the possible molecular mechanism of resistance evolution were clarified.The main results showing as follows:1.After S.exigua larval at 3rd instar treated by emamectin benzoate for 72 h,the toxic regression equation of S.exigua to emamectin benzoate was obtained,that was y=5.8037+1.3285x:,median lethal concentration LC50 was 0.248 mg·L-1 with SE was 0.04,95%confidence interval was 0.18?0.35 mg·L-1 and R value was 0.9971.2.Compared with CK,after S.exigua larval at 3rd instar treated by emamectin benzoate with different sublethal doses(LC5?LC20?LC50)for 72 h,the larval period,pupal period,pre-oviposition period,abnormal rate of pupa and moth of S.exigua were increased significantly(P<0.05),while,the adult longevity,oviposition period,pupation rate,pupal weigh,emergence rate and per female eggs of these S.exigua were decreased significantly(P<0.05),indicating that the sublethal effects of emamectin benzoate to S.exigua growth and reproduction have an inhibition effects in some degrees.3.In the study,the detoxifying enzyme activities and the expressions of relative genes in S.exigua larval treated by emamectin benzoate were tested and analyzed.Results indicated that,after S.exigua larvae at 3rd instar treated by emamectin benzoate with induction dose as LC5?LC20?LC50 for 72 h,respectively,the mixed-function oxidases(MFO)activity and the expressions of SeCYP450 were increased significantly(P<0.01),and their fluctuated trends were all increased at first and then decreased following the increasing doses of emamectin benzoate.The trend of glutathione S-transferase(GST)activity in S.exigua was similar to MFO,while the expression trends of SeGSTs and SeGSTs1 were different from that of GST activity.Compared with the control,the expressions of SeGSTs increased in S.exigua treated by emamectin benzoate with the induction doses increasing significantly(P<0.01),while that of SeGSTs1 decreased.The esterases activities in S.exigua treated by emamectin benzoate with three induction doses were all decreased significantly(P<0.01),which was similar to that of SeCarE.Therefore,MFO,GST and their related genes SeCYP450,SeGSTs and SeGSTs1 may involve in the resistance evolution process of S.exigua larval to emamectin benzoate.4.In the study,the correlation analysis results indicated that there was significant correlation between MFO,EST activities and the expressions of corresponding genes SeCYP450 and SeCarE,respectively(P<0.01).However,only significant correlation between GST activities and SeGSTs expressions were showed(P<0.01),and significant correlation between GST activities and SeGSTs1 expressions were not found(P>0.05).So these results could indicated that 3 detoxification enzymes are super-gene family enzymes,and their activities are determined by several related genes,and some genes may play an important role.However,these mechanisms are not clear now and needing to study in the future futherly.