Effects Of Three Insecticides On The Main Natural Enemies Of Aphis Gossypii Treated With Sublethal Concentration

At present,Xinjiang has become the country’s largest high-quality cotton production base.In recent years,the dominant structure of pest species and population fluctuation have changed obviously in cotton field in southern Xinjiang.Aphis gossypii is becoming more and more serious.Chemical pesticides and biological natural enemies are the two main measures to control A.gossypii.The application of chemical agents to control A.gossypii could not only kill most of the aphid,but also produce sublethal effect with the passage of time and the change of environmental conditions.At the same time,the combination effect based on the ascending effect of the trophic level of the food chain is bound to have an impact on the natural enemies of the next trophic level.As the dominant natural enemies of A.gossypii in the cotton fields of southern Xinjiang,there is no systematic research about effects of sublethal concentration on the A.gossypii fed by Coccinella undecimpunctata,Chrysopa pallens and Lysiphlebia japonica.It is of great significance to study the effects of three insecticides on the natural enemies of A.gossypii,to improve the level of chemical control of A.gossypii and to cooperate with biological control and prevention.Based on the content of this paper,the research results are as follows:1.Effects of sublethal concentration of three insecticides on A.gossypii and its main natural enemies in the fieldThe virulence of three insecticides to A.gossypii was determined.The results showed that pymetrozine had the highest toxicity to A.gossypii with LC₂₅and LC₅₀values of 0.16 and 0.46 mg/L.The toxicity of Imidacloprid to A.gossypii was the lowest with LC₂₅value of 8.60 mg/L and LC₅₀value of 22.31 mg/L.The results showed that the virulence of the three insecticides to A.gossypii was as follows:pymetrozine>flonicamid>imidacloprid.The three insecticides had different effects on the main natural enemies（Coccinellidae,Chrysopidae and Aphidiidae）at different sublethal concentrations in the field.The effect of imidacloprid on A.gossypii and natural enemies was greater with the increase of imidacloprid concentration in the field.Compared with imidacloprid LC₂₅,the populations of Coccinellidae,Chrysopidae and Aphidiidae decreased significantly after imidacloprid LC₅₀was applied in the field.After the application of pymetrozine LC₂₅and LC₅₀in the field,the populations of natural enemies of pymetrozine LC₂₅and LC₅₀showed a trend of decreasing first and then increasing.After LC₂₅and LC₅₀treatment,the populations of natural enemies in cotton field decreased first and then leveled off,but did not increase at last.2.Effects on the growth and reproduction of the main natural enemies of A.gossypii by treatment with sublethal concentration of three insecticidesThe growth,development and reproduction of C.undecimpunctata,C.pallens and L.japonica were all affected by feeding on three pesticides with sublethal concentrate A.gossypii.The larva development duration of C.undecimpunctata treated with imidacloprid LC₂₅and LC₅₀was 3.01 d and 4.57 d longer than that of the control,respectively.The development duration of the first and second instar larvae of P.macrophylla fed on imidacloprid LC₅₀had the greatest effect,which was extended by 0.91 d and 0.88 d compared with the control,respectively.There were significant differences in the larval development duration of L.japonica parasitize with imidacloprid LC₂₅,imidacloprid LC₅₀and flonicamid LC₅₀treat with A.gossypii,which were 0.96 d,2.64 d and 2.39 d longer than the control,respectively.The ovipositionperiod was shortened by 2.56 d and 3.46 d compared with the control,respectively.The amount of oviposition per female decreased by 22.40%and 32.45%,and the hatching rate decreased by 9.57%and17.02%compared with the control,respectively.C.pallens feeding imidacloprid LC₂₅,imidacloprid LC₅₀,fluorine organism worm amide LC₅₀processed A.gossypii the spawning period,spawning,male/female adult weight and hatching rate have a significant impact,including feeding imidacloprid LC₅₀after processing of A.gossypii to its most affected,compared to the spawning period shortened 5.54 d,reduced104.2 grain of spawning/female;The number of eggs laid and the hatching rate of eggs were not significantly decreased by feeding on A.gossypii treated with sublethal dose of pymetrozine.3.Effects of three insecticides treated with sublethal concentration on the control function of main natural enemies of A.gossypiiThe A.gossypii fed with imidacloprid and flonicamide LC₅₀had the greatest effect on the maximum theoretical daily predation of the 1st and 4th instar larvae of C.undecimpunctata,which decreased by 3.7,2.33,13.25 and 7.01 larvae,respectively.The A.gossypii fed with imidacloprid LC₅₀had the greatest effect on the parameters related to the predation response function of the 3rd instar larvae.Compared with the control group,the instantaneous attack rate of aphid decreased by 0.1192,the treatment time of one A.gossypii was extended from 0.0085 d to 0.0099 d,and the maximum theoretical daily predation was reduced by 16.64 aphid.Feeding imidacloprid LC₅₀of A.gossypii and fluorine organism worm amide LC₅₀of C.pallens 1 instar larvae feed on the reaction function of relevant parameters,compared to the instantaneous attack rate decreased 0.1070,0.1459,respectively,used time respectively from process 1head of A.gossypii increased to 0.1102 d,0.0841 d,0.0360 d,the largest theory feeding amount decreased by 18.71 and 15.89,respectively.Imidacloprid LC₂₅and LC₅₀had the greatest effect on the treatment time of 1 A.gossypii and the maximum theoretical daily predation amount for the 2nd instar larvae of C.pallens.When the A.gossypii treated with imidacloprid LC₅₀,pymetrozine LC₅₀and flonicamid LC₅₀,the transient attack rate of L.japonica decreased by 0.3191,0.1920 and 0.2448,respectively,compared with the control group.The treatment time of one A.gossypii increased from 0.0057 d to 0.0075 d,0.0066 d and 0.0070 d,respectively.The maximum theoretical parasitic population decreased by 42.11,23.92 and 32.58.4.Effects of three insecticides treated with sublethal concentration on detoxification enzyme activity of A.gossypiiA.gossypii treated with imidacloprid and flonicamid LC₅₀was used as food showed significant inhibitory effect on the activity of Car E in natural predators,and the A.gossypii fed/parasified with flonicamide LC₂₅treated A.gossypii showed significant induction effect on the activity of Car E in vivo.The activity of CYP450 in A.gossypii fed on/parasitized with imidacloprid LC₂₅and pymetrozine LC₂₅was significantly promoted by C.undecimpunctata,C.pallens and L.japonica,while the activity of CYP450 in A.gossypii fed/parasitized with imidacloprid LC₅₀and flonicamid LC₂₅and LC₅₀had no significant effect.Three kinds of natural enemies fed on/parasitized A.gossypii treated with high sublethal concentrations of imidacloprid and flonicamid inhibited the activity of GSTs in A.gossypii.