Synergism Of Insect Growth Regulators To Beauveria Bassiana For Biocontrol Of Myzus Persicae And Mixture Formulation

Green peach aphid?Myzus persicae?is a worldwide pest.The biological control of peach aphids has become a hot topic in the current study due to the environmental pollution caused by traditional chemical prevention and the increased resistance of peach aphids.The entomopathogenic fungi Beauveria bassiana is an important biological pesticide,has the advantages of high efficiency,low toxicity,pollution-free,environmental friendly.However,there are some disadvantages such as slow insecticidal speed and unstable control effect.The development of complex preparation preparation is one of the effective methods to solve this problem.In this paper,firstly,the highly virulent Beauveria bassian was screened by the biological determination of the greenhouse peach aphid;Secondly,we screened out the insect growth regulators with strong compatibility through the compatibility test of insect growth regulator and B.bassiana;Thirdly,the selected insect growth regulators and B.bassiana were mixed at different concentrations.The compound was used to determine the indoor virulence of Myzus persicae,then,the combination of synergistic effects is selected by the calculation of the of the CO toxicity coefficient.Then,The optimal complex-match mode is calculated by the mathematical model.Finally,the control effect of the optimal combination mode was determined through greenhouse control experiment.The main results are as follows:1.Screening of high virulent strains.The toxicity of 10 strains of B.bassiana strains against Myzus persicae is determined with insect dipping method.There are 5strains with strong virulence to Myzus persicae,virulence order:Bb2032>Bb2078>Bb98>Bb2004>Bb19,corrected mortality are 97.53%?93.83%?90.12%?85.19%?80.25%,LT₅₀ are:5.168d?5.338d?5.755 d?6.037d?6.200d;The order of LC₅₀:Bb2032<Bb2078<Bb98<Bb2004<Bb19,Therefore,Bb2032 on Myzus persicae have higher pathogenicity,It can be used in the development of further compound preparation.2.Compatibility of Beauveria bassiana and insect growth regulator:5 kinds of insect growth regulators have different degree inhibition on the spore germination of Bb2032 under the high concentration,mideum concentration and low concentration.The inhibition rate of Azadirachtin 0.3%EC on spore germination of B.bassiana is the smallest,under mideum concentration and low concentration,which are 47.23%and 37.31%;5 kinds of insect growth regulators have only a slight inhibitory effect on mycelial growth of Bb2032.The inhibitory effect of Flufenoxuron 25%SC on the mycelial growth of B.bassiana is the least,and that of Azadirachtin;The inhibition rate of Azadirachtin 0.3%EC on spore production of B.bassiana is the smallest,under mideum concentration and low concentration,which are 7.79%and 4.60%.Therefore,Azadirachtin 0.3%EC and Flufenoxuron 25%SC shows good compatibility with Bb2032.3.Co-toxicity and Preliminary screening of synergistic combinations:The LC₅₀of Azadirachtin 0.3%EC single agent to the Myzus persicae is 11.99mg/L,the LC₅₀of Flufenoxuron 25%SC single agent to the Myzus persicae is 88.30mg/L.The compound Bb2032 and Azadirachtin 0.3%EC in the volume ratio of the CO toxicity coefficient is greater than 100,there are varying degrees of synergism on the biological control of Myzus persicae;The compound Bb2032 and Flufenoxuron 25%SC in the volume ratio of the CO toxicity coefficient is 21.13¹17.82.Therefore,the compound Bb2032 and Azadirachtin 0.3%EC shows a better synergy.4.The calculation of the theoretical optimum proportion:Mass fraction?K?of effective components of Bb2032 in compound,X is obtained by inverse sine transformation,Y represents the co toxicity coefficient.The results show that after mathematical fitting:The theoretical optimum ratio of 1.8×10⁵ spores/ml of Bb2032strain and 12mg/L of Azadirachtin 0.3%EC is 1:1.0090.At the same time,the co toxicity coefficient is the highest,reaching 219.02.5.Greenhouse control effect of the theoretical optimal compound agents on Myzus persicae:The Bb2032 single agent?1.84×10⁵spores/ml?,the Azadirachtin0.3%EC single agent?11.99mg/L?and the theoretically optimal compounding agent of Myzus persicae have high pathogenicity,The highest control effect of three treatments on greenhouse Myzus persicae at 10d after application in the order of80.83%,82.50%,92.50%.Therefore,the order of greenhouse effect on Myzus persicae:the theoretically optimal compounding agent>the azadirachtin 0.3%EC single agent>the Bb2032 single agent.Therefore,synergistic effect of the theoretically optimal compounding agent on the prevention and control of greenhouse aphids can be further determined.