| The Megalothrips usitatus（Bagrall）belonging order Thysanoptera（Thysanoptera）,family Thripidae（Thripidae）,is an important insect pest of leguminous crops.It can cause serious damages to cowpea affecting the yield,appearance and quality of cowpea consequently causing great losses to cowpea production.At present,the control of M.usitatus mainly relies on chemical measures.Due to the small size of thrips,hidden damage,short development period,strong fecundity,parthenogenetic reproduction,pupation and strong migration ability of adults,the chemicals are not easy to contact thrips.Single application of chemical is not perfect,consequently,high concentration and high frequency insecticide applications are used to control thrips.The injudicious use of chemicals cause high insecticide resistance and risk of excessive pesticide residues.In the pursuit of environmentally friendly control strategies,Beauveria bassiana have become an important means of biological control of pests because of their wide host spectrum,strong pathogenicity,and environmental friendliness.However,the slow mode of action and environmental conditions are the main shortcomings hindering their application.In order to overcome above this paper describes the the pathogenicity of 17 strains of B bassiana against M.usitatus（female adult and pupae）.The highly virulent strains were applied in combination with 9biochemicals.The toxicity of insecticide to M.usitatus is obtained.The compatibility of B bassiana and insecticides were studied.Highly compatible formultions were selected to carry out the research on the mixed application.The invivo toxicity test were used to assess the combined effect of the formulation.The effects of insecticides,B bassiana and formultions on the enzyme activity of M.usitatus were studied separately to provide a theoretical basis for the combined use of B bassiana and insecticides.The main findings are as follows:1.Screening of B bassiana and insecticide against M.usitatus.Conidial suspension of 17 strains of B bassiana,at a concentration of 1×108 spores/m L,was applied to determine the virulence against M.usitatus（female adults and pupae）.The spore suspensions with concentrations of 1×108,1×107,1×106,1×105,and 1×104spores/m L were used for laboratory toxicity determination.The results showed that B.bassiana SB038 and SB063 had high pathogenicity to female adults and pupae of M.usitatus.When the spore suspension concentration was 1×108 spores/m L and the female adults were treated for 7 days after treatment,the adjusted mortality rates of female adults were 91.07%and 83.33%,respectively,and the adjusted mortality rates of pupae were 100%and 81.67%,respectively.The indoor toxicity of 9 insecticide to M.usitatus were determined.The LC50 value shows that spinetoram,emamectin benzoate and acetamiprid have high toxicities to M.usitatus.LC50 values were 4.2935,3.9051 and 77.3271 mg/L,respectively.2.Compatibility of highly virulent strains with insecticide.B.bassiana SB038 and SB063 were combined with spinetoram（10,5,2.5,1.25 and 0.625 mg/L）,emamectin benzoate（10,5,2.5,1.25 and 0.625 mg/L）and acetamiprid（400,200,100,50,25 mg/L）to observe their effects on daily growth and germination of fungi.The results showed that spinetoram has good compatibility with B.bassiana SB038 and SB063 and can be used in subsequent experiments.3.The study clarified the indoor virulence of high-virulence strains and different concentrations of spinetoram on M.usitatus.Five concentrations of spinetoram（10,5,2.5,1.25 and 0.625 mg/L）were mixed with B.bassiana SB038 and B.bassiana SB063（1×108,1×107,1×106,1×105 and 1×104 spores/m L,respectively）to determine their toxicity against M.usitatus.The results showed that when B.bassiana SB038 1×105 spores/m L and spinetoram 2.5 mg/L had the most significant synergistic effect on M.usitatus（χ2 value 32.63>3.841）,the mortality rate was as high as 96.67%.The synergistic effect of SB063 with spinetoram 2.5 mg/L at 1×106spores/m L was also significant（χ2 value 5.32>3.841）,and the mortality rate was78.81%.4.The study has clarified the changes of high virulence strains,spinetoram and their combinations on the activities of protective enzymes and detoxification enzymes in M.usitatus.The adult females of M.usitatus treated with highly virulent strains,spinetoram and their mixture were collected on 3 d and 7 d,respectively,and the enzyme activities of GSH-ST,CAT,ACh E,SOD and POD in vivo were measured.The results showed that the activities of the 5 enzymes in the M.usitatus treated with high virulence strains,spinetoram and their combinations all changed to varying degrees.With the change of time,the SOD,POD,CAT,GSH-ST,and ACh E in M.usitatus decreased first and then increased.After the combined treatment of spinetoram and B.bassiana SB038 and SB063 strains on 7 days,the enzyme activities of ACh E,GSH-ST and CAT in M.usitatus were significantly higher than the control.The enzyme activities were 35.27,62.41（>29.03）mgprot;37.58,37.48（>22.45）mgprot;284.40,317.56（>220.97）mgprot.Except for the combination of spinetoram and strain SB038,the SOD enzyme activity of female adults of M.usitatus was lower than that of the blank control（enzyme activity value 41.16<58.75 mgprot）,and the SOD and POD enzyme activities and blanks of M.usitatus were treated by other combinations of bacteria and drugs.The control difference was not significant,which were 56.45,58.75 mgprot;18.35,17.97,19.16 mgprot,respectively.In summary,two highly virulent strains B.bassiana SB038 and B.bassiana SB063 were screened and their compatibility with spinetoram was determined through the toxicity test and compatibility study of Beauveria bassiana and biochemical insecticide to M.usitatus.Combined toxicity test showed that B.bassiana SB038 concentration of 1×105 spores/m L and B.bassiana SB063 concentration of1×106 spores/m L,mixed with 2.5 mg/L spinetoram,had the most significant synergistic effect on M.usitatus,and each treatment significantly affected the enzyme activity of M.usitatus.The results of this study provide a scientific basis for the synergistic use of insecticide and B.bassiana,and provide a new and effective method for the field control of M.usitatus. |
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