Study On The Synergism And Wettable Powder Of Beauveria Bassiana To Bactrocera Dorsalis

Bactrocera dorsalis,as a worldwide quarantine pest,has now spread to most areas of the country,and it is casuing extremely serious harm to agricultural production.Using entomopathogenic fungi to manage B.doraslis has emerged as a novel tactic with the adcancement of research.Insect pathogenic fungi represented by Beauveria bassiana can not only control B.dorsalis,but also cause little environmental harm.However,there are several drawbacks,such as the unstable effect and protracted cycle of pathogenic fungi in insect pests control.Therefore,in this study,B.bassiana strains with high virulence and pathogenicity against B.dorsalis were first screened,and insecticides with good biocompatibility were screened after that.After doing indoor virulence testing and greenhouse testing,a compound a gent with a favorable controlling effect on B.dorsails was discoverd,and the formula of Bb-32 wettable powder was screened out.It has significant practical and scientific value and offers a practical basis for the management of B.dorsalis.The following are the main findings:1.In this experiment,15 strains of B.bassiana were isolated and purified from the strains and commercial products provided by Hubei Academy of Forestry Sciences.Through the virulence test on the adults of B.dorsalis,the strains with high virulence toward B.dorsalis were screened.Through the virulence test to the adults of B.dorsalis,the highly virulent strains of B.dorsalis were screened.Among them,the corrected mortality of B.bassiana Bb-32 and Bb-33 to B.dorsalis was 61.7%and 58.96%respectively,which was significantly higher than that of other strains.The median lethal concentration(LC₅₀)of the two highly virulent strains of B.dorsalis was tested.The results showed that the median lethal concentrations of B.bassiana Bb-32 and Bb-33were 8.9×10⁷,1.67×10⁸ conidia/ml,respectively.2.The median lethal concentration of six insecticides was determined for B.dorsalis.The LC₅₀ of Emamectin benzoate,Spinosad,Avermectin,Thiamethoxam,Beta-cypermethrin synergism and Imidacloprid to B.dorsalis adult were 1.77 mg/L,7.48mg/L,8.86 mg/L,71.09 mg/L,112.95 mg/L and 255.99 mg/L.The biocompatibility of six insecticides with two kinds of B.bassiana was evaluated from three aspects of spore germination,mycelium growth and spore production at lethal concentration,sublethal concentration and sublethal concentration.It was found that the biocompatibility of Emamectin benzoate with Spinosad and B.bassiana Bb-32 and Bb-33 was good,so it could be used to study the compound agent.3.In the laboratory test of the combined toxicity of insecticide and B.bassiana against B.dorsalis,when Emamectin benzoate:Bb-32=4:1,Emamectin benzoate:Bb-33=4:1,Spinosad:Bb-32=4:1,the co-toxicity coefficients were 151.74,123.87and 121.30,and all of which were greater than 100.Under this ratio,the compound had a synergistic effect on the control of B.dorsalis and a certain decreasing effect.Therefore,this ratio is the optimal ratio for the mixture of Emamectin benzoate with Bb-32,Bb-33and Spinosad with Bb-32.4.In the greenhouse experiment,this experiment tested the control effect of the compound on the adults and pupae of B.dorsalis,as well as inhibition of oviposition in fruit by female B.dorsalis.The combination of B.bassiana Bb-32,Emamectin benzoate and Spinosad has a better control effect.The control effect on B.dorsalis adults was23.42%,30.39%,33.29%,36.38%,41.61%and 31.51%,32.88%,32.97%,37.00%and37.88%at the 2nd,4th,6th,8th and 10th days.In the control of B.dorsalis adults,the toxicity of the compound consisting of B.bassiana Bb-32,Emamectin benzoate or Spinosad was not significantly different from that of single insecticide,but was significantly higher than that of B.bassiana.Considering the 20%reduction effect of the compound agent,these two compound agents have certain application value in the actual control of B.dorsalis.5.In the preparation of the wettable powder of Bb-32,by studying the influence of additives on the wetness and dispersability of the powder and the biocompatibility with sporangium powder,it was determined that in the wettable powder,the carrier was attapulgite,the wetting agent was BX,the proportion was 7%,the dispersant was MF,the proportion was 7%,and the sporangium powder content was 25%.