Toxicity Of Malathion And Deltamethrin Mixture To Locusta Migratoria And Their Toxicological Mechanisms

Locusta migratoria(Orthoptera: Oedipodidae)is a major pest of gramineous crops,such as wheat and corn.In recent years,L.migratoria has developed insecticides resistance including malathion and chlorpyrifos because these insecticides were widely used.The mixtures of pesticides are the most effective method to overcome the resistance and are used in controlling other pests.In this thesis,we have assayed the toxicity of mixture of malathion with deltamethrin and studied the toxicological mechanisms by determining enzyme activity and enzyme genes expression.The contents of this thesis include the following parts:(1)Toxicity of malathion and deltamethrin mixture to the 3th-instar locustsWe first studied individually the toxicity of malathion and deltamethrin to the 3rd-instar nymph through the bioassay method.The toxicity regression equation for malathion was y=4.5004x-0.5289.The value of LD50 and its95% confidence interval was 7.05(6.63-7.88)?g/g(insect weight).The toxicity regression equation for deltamethrin was y=3.7524x+1.2384.The value of LD50 and its 95% confidence interval was 41.45(37.72-46.01)ng/g(insect weight).Then,0.5 ?g/ml deltamethrin was selected to mix individually with 0.06,0.12,and 0.18 mg/ml malathion and the mixtures were used to treat the 3th-instar locusts.The results showed that the corrected toxicity ratios(CTR)of the three mixtures were 1.59,6.98,and 2.51,respectively.The results suggested that the three mixtures have synergistic effects on the controlling L.migratoria based on the synergism evaluation.The mixture has the best synergistic effect when 0.5 ?g/ml deltamethrin was mixed with 0.12 mg/ml malathion.(2)Study on the toxicity mechanism of malathion-deltamethrin mixture to the 3th-instar locustsWe assayed AChE and detoxification enzyme activities after the locusts treated with malathion and deltamethrin individually or mixtures.The resultsshowed that AChE activities after malathion treatments were lower than the control and had no significant difference(P>0.05).Compared with the control,ACh E activity was increased after deltamethrin treatment.AChE activities were decreased with the malathion concentration increasing in the malathion and deltamethrin mixture while there were no significant differences with the control(P>0.05).Malathion reduced P450 activities and no significant differences were observed compared with the control(P>0.05).CYP450 activity was significantly inhibited by deltamethrin(P<0.05)and was 0.57 times of the control.CYP450 activity showed the increase trend with the malathion concentration increasing in the malathion and deltamthrin mixture and there were no significant differences among the treatments(P>0.05).CYP450 activity was significantly inhibited by the mixture of 0.06mg/ml malathion with 0.5 ?g/ml deltamethrin(V:V=1:1)(P<0.05)and was0.56 times of the control.Esterase activities were inhibited by malathion and showed a decline tendency with malathion concentration increase.After treated with 0.18 mg/ml malathion,esterase activity has reduced 26.43%compare with the control.Malathion with deltamethrin mixture decreased esterase activities in nymph while no significant differences with the control were found(P>0.05).Malathion and deltamethrin induce individally GST activities of locusts.GST activities of locusts treated with 0.12 mg/ml and0.18 mg/ml malathion and 0.5 ?g/ml deltamethrin were 1.97,2.22,and 2.08 times of the control,respectively.GST activities were significantly increased by malathion-deltamethrin mixture(P<0.05)and were 2.65,2.59 and 2.29 times of the control,respectively.These findings suggested that there might have three reasons for the synergism of malathion-deltamethrin mixture: first,malathion and deltamethrin inhibited their target,respectively.Second,malathion inhibited esterase and CYP450 activity and reduced the malathion and deltamethrin detoxification.Third,deltamethrin induced the oxidative desulfurization of CYP450 and increased the toxicity of malathion.(3)Effects of malathion-deltamethrin mixture on the genes expression of detoxification enzymeRT-qPCR technique has been used to analyze the expression of CarE genes and CYP450 genes of locusts treated with malathion and deltamethrin individually or mixture.The expressions of LmCesA1 and LmCesA2 were similar to the tendency of esterase activities.After malathion-deltamethrin mixture treatments,the inhibition of LmCesA1 and LmCesA2 expression has been enhanced with malathion concentration increase.The difference was not statistically significant among different mixture groups.The variation trends of LmCYP6FG1,LmCYP6FD2,LmCYP9AQ1,LmCYP9AQ2,and LmCYP409A1 expression were consistent with the variation trend of CYP450 activity.The expression of these genes were increased with malathion concentration increase in malathion-deltamethrin mixture and were the highest when the locusts were treated with the mixture of 0.5 ?g/ml deltamethrin and 0.18 mg/ml malathion and were 2.74,3.04,3.91,1.47,and1.55 times of those of locusts treated with the mixture of 0.5 ?g/ml deltamethrin and 0.06 mg/ml malathion.Deltamethrin induced the expressions of LmCYP6FD1 and LmCYP6FE1.These results suggested that the decreased expressions of LmCesA1,LmCesA2,LmCYP6FG1,LmCYP6FD2,LmCYP9AQ1,LmCYP9Q2,and LmCYP409A1 were the main factors leading to the synergism effects of malathion-deltamethrin mixture to L.migratoria.The induction of LmCYP6FD1 and LmCYP6FE1 expressions by deltamethrin might be another reason for the synergism effects of malathion-deltamethrin mixture to L.migratoria.In summary,these results enriched the studies about the effects of malathion with deltamethrin mixture on the enzyme activity and the genes expression in L.migratoria.Furthermore,these results would provide reference information and theoretical basis for improvement of controlling pests using mixed pesticides and provide novel strategies for controlling locusts.