Bioassay Control Of Several Species Of Important Noctuida Pests By MabrNpv And Synergism Research

In this paper,we conducted bioassay to several varieties of important noctuidae pests by using Mamestra brassicae Nuclear Polyhedrosis Virus,and selected noctuidae pests controlled better,and then mixed MabrNPV with pesticide and 4 kinds of chemicals respectively,and the mixture was used to select the chemical reagent which had synergistic effect on MabrNPV.Finally,we used mixture of MabrNPV and beauveria brongniartii to determine wheather beauveria brongniartii have synergy effects on MabrNPV.The main research results of this paper is as follows:（1）Primary screen of several varieties of important noctuidae through MabrNPV We detected the toxicity of MabrNPV to five varieties of important noctuidae pests on agricultural production through bioassay method.The results showed that the MabrNPV were pathogenic to Spodoptera litura,Spodoptera exigua,Helicoverpa armigera,Mythimna Separata,Agrotis ypsilon,and there were differences in pathogenicity,and for 2nd instar larvae,LC₅₀ to the pests was 1.19×10⁵ PIB/ml,2.02×10⁵ PIB/ml,4.30×10⁵ PIB/ml,2.15×10⁶ PIB/ml and 1.29×10¹⁶ PIB/ml,the pathogenicity of MabrNPV to Spodoptera litura and Spodoptera exigua was the highest and to Mythimna Separata was the lowest.The pathogenicity of MabrNPV to Spodoptera litura and Spodoptera exigua was significant different from that to other three varieties of noctuidae pests.（2）The detection of toxicity of MabrNPV to Spodoptera litura and Spodoptera exigua at different age and LT₅₀The LC₅₀ and LC₉₀ of MabrNPV to 1st-instar,2nd-instar and 3rd-instar larvae of Spodoptera litura were 3.58×10⁴ and 2.10×10⁸ PIB/ml,1.00×10⁵ and 3.85×10⁸ PIB/ml,1.53×10⁶ and 1.50×10¹¹PIB/ml respectively;the LC₅₀ and LC₉₀ of MabrNPV to 1st-instar,2nd-instar and 3rd-instar larvae of Spodoptera exigua were 6.08×10⁴ and 5.79×10⁸ PIB/ml,1.85×10⁵ and 1.21×10⁹ PIB/ml,4.91×10⁶ and 1.02×10¹² PIB/ml respectively.The toxicity of MabrNPV to Spodoptera litura and Spodoptera exigua decreased with the increase of the instar,and larval susceptibility of viruses decreased with the increase of the instar.LC₅₀ and LC₉₀ of MabrNPV to Spodoptera exigua at every instar were larger than that of Spodoptera litura,which indicated that the toxicity of MabrNPV to Spodoptera litura was higher than that of Spodoptera exigua.LT₅₀ of 108 PIB/ml MabrNPV against 1st-instar,2nd-instar and 3rd-instar larvae of Spodoptera litura and Spodoptera exigua was 1.86 d and 2.14 d,1.90 d and2.26 d,3.18 d and 3.83 d respectively;LT₅₀ of 1×10⁶ PIB/ml MabrNPV against 1st-instar,2nd-instar and 3rd-instar larvae of Spodoptera litura and Spodoptera exigua was 3.71 d and 4.49 d,3.91 d and 4.53 d,5.92 d and 6.22 d respectively.Under the sameconcentration,Fifty percent lethal time of MabrNPV against the larvae of Spodoptera litura and Spodoptera exigua increased with the increase of the instar;at the same instar,lethal time of MabrNPV reduced with the increase of its concentration.（3）Research on synergy effects of the mixture of MabrNPV with pesticidesCumulative correction mortality of MabrNPV mixed with five kinds of pesticide respectively against 2nd-instar of Spodoptera litura: rotenone mixture > chlorantraniliprole mixture >chlorpyrifos mixture > lambda-cyhalothrin mixture > acetamiprid mixture;co-toxicity coefficient:rotenone mixture > chlorpyrifos mixture > chlorantraniliprole mixture >lambda-cyhalothrin mixtur > acetamiprid mixture;both cumulative corrected mortality and co-toxicity coefficient of rotenone mixture against 2nd-instar of Spodoptera litura were the highest,so synergia effect of the mixture of rotenone and MabrNPV was obviously,while both cumulative corrected mortality and co-toxicity coefficient of acetamiprid mixture against 2nd-instar of Spodoptera litura were the lowest.Cumulative correction mortality of MabrNPV mixed with five kinds of pesticide respectively against 2nd-instar of Spodoptera exigua: rotenone mixture > chlorantraniliprole mixture > chlorpyrifos mixture > lambda-cyhalothrin mixture > acetamiprid mixture;their co-toxicity coefficient: rotenone mixture > chlorantraniliprole mixture > chlorpyrifos mixture >lambda-cyhalothrin mixture > acetamiprid mixture;both cumulative corrected mortality and co-toxicity coefficient of rotenone mixture against 2nd-instar of Spodoptera exigua were the highest as well,while both cumulative corrected mortality and co-toxicity coefficient of acetamiprid mixture against 2nd-instar of Spodoptera exigua were the lowest.As a whole,mixing rotenone with MabrNPV shortened the insecticidal time of MabrNPV with obvious synergia effect,the mixture of those two was the best formula.（4）The synergia effect of the mixture of MabrNPV and beauveria brongniartiiThe regression equation of the toxicity of beauveria brongniartii against 2nd-instar of Spodoptera litura was Y=1.0893+0.5519X（r=0.9937）,and the cumulative mortality of the moth larvae increased with the increase of concentration of beauveria brongniartii,within16.95%-74.58%,with positive correlation.MabrNPV was mixed with beauveria brongniartii,and the correction mortality rates of all treatments after 7 days were all above 50%,especially the correction mortality rate of β×C was the highest with 98.31%,and that of β×B and β×A both were above 80%,which showed that high concentration of beauveria brongniartii mixed with MabrNPV had better control effect on 2nd-instar of Spodoptera litura.By calculating co-toxicity coefficient,co-toxicity coefficient of those mixtures were from 27.12 to 69.5,of which co-toxicity coefficient of the mixture of beauveria brongniartii with LC₇₀ or LC₅₀ and MabrNPV with LC₇₀ was the highest,which was the best formula.（5）The synergia effect of the mixture of MabrNPV and 4 kinds of chemicalsThe pathogenicity of MabrNPV mixed with two additives-organic silicon or tea saponin to2nd-instar of Spodoptera litura was obvious,and LC₅₀ was 1640.5 and 4628.1PIB/ml respectively,less than 1.00×10⁵ PIB/ml,and the corresponding synergic ratios were 60.69 and 20.61 more than1,with obvious synergic effect.When MabrNPV was mixed with two additives-brown sugar or K₂CO₃,LC₅₀ was 2.1876×10⁶ and 1.7696×10⁵ PIB/ml respectively,more than 1.00×10⁵ PIB/ml,and the corresponding synergic ratios were 0.0457 and 0.5651,less than 1,with no synergia effect.Synergic effects of four kinds of chemicals from large to small were as follows: Organic silicon,tea saponin,K2CO3 and brown sugar.The control effects of MabrNPV mixed with 500×,1000×,2000× or 5000× organic silicon additives on 2nd-instar of Spodoptera litura were obvious,and LC₅₀ of 500×,1000×,2000× and 5000× organic silicon additives was 1.1636×10³ PIB/ml,1.8017×10³ PIB/ml,2.2252×10³ PIB/ml and 7.4132×10⁴ PIB/ml respectively,and the corresponding synergic ratios were 85.94,55.50,44.94 and 1.348 respectively,and the control effects: 500× > 1000× > 2000× > 5000×,so the control effects of MabrNPV mixed with500×,silicone additives against 2nd-instar of Spodoptera litura to the best.The insecticidal activity of MabrNPV mixed with 500×,1000×,2000× or 5000× tea saponin additives against 2nd-instar of Spodoptera litura was good,LC₅₀ of MabrNPV mixed with 500×,1000×,2000 × and 5000 × tea saponin additives respectively were 3.0771×10³ PIB/ml,5.1281×10³ PIB/ml,8.6327×10³ PIB/ml and 1.33×10⁵ PIB/ml,and the corresponding synergic ratios were 32.50,19.50,11.58 and 0.75,so the control effects of MabrNPV mixed with 1000×,silicone additives against 2nd-instar of Spodoptera litura to the best.