Toxicological And Biochemical Basis Of Synergism Between The Entomopathogenic Fungus And Botanical Pesticides Against Megalurothrips Usitatus

Megalurothrips usitatus belongs to Thysanoptera:Thripidae.Because of their small size and difficult control,they have gradually become one of the most important agricultural pests in the world.At present,chemical control is the main way.However,during the control,many problems such as pest resistance,killing natural enemies,pesticide residues and environmental pollution have been caused.Especially,under great importance attached to food safety and environmental safety,biological control has become the leading measure.Entomopathogenic fungus have a certain insecticidal effect,which is long-lasting and environmentally friendly,and are generally considered as the best choice for biological control.However,spore germination is needed during the control,which leads to a longer incubation period and higher environmental requirements.Therefore,in this study,the pathogenicity of ten strains of entomopathogenic fungus in M.usitatus were investigated.The strains with high virulence were screened by bioassay,and subjected to compatibility test with botanical pesticides.The virulence of fungi with high compatibility and botanical pesticides was tested indoor in M.usitatus.The effects of their synergistic effect on the changes in superoxide dismutase(SOD),acetylcholinesterase(AChE),catalase(CAT)and peroxidase(POD)activities of M.usitatus were explored,so as to lay a foundation for the development and utilization of their mixture.1.Screening of highly virulent strains for M.usitatus:The virulence of 10 high-quality strains stored in the laboratory to`M.usitatus was determined indoor with the concentration of 1×10~8 spores/mL.Two highly virulent strains Lecanicillium attenuatum SCAUDCL-53and Beauveria SB010 were screened.The virulence of the two highly virulent strains at 1×10~4,1×10~5,1×10~6,1×10~7 and 1×10~8 spores/mL to M.usitatus was determined,respectively.At 1×10~8 spores/mL,the infected M.usitatus were collected,and the infection situation was observed under a microscope.The results showed that Lecanicillium attenuatum SCAUDCL-53 and Beauveria SB010 had high pathogenicity to M.usitatus,and mycelia appeared on the surface of M.usitatus on the first and third day.The botanical pesticides(matrine,Azadirachtin and rotenone)of different concentrations to the M.usitatus was determined.The results showed that the toxicity of the three botanical pesticides to the thrips was different,and the lethal rate to the test insects was lower than 40%.2.Compatibility of highly virulent strains with botanical pesticides and screening of their combination concentrations:The effects of botanical pesticides including matrine,azadirachtin and rotenone at 0.05,0.125,0.25,0.5 and 1.0mg/mL on the colony growth and spore germination of highly virulent strains were determined,respectively.The results demonstrated that matrine at the five concentrations had high compatibility with L.attenuatum SCAUDCL-53 and Beauveria SB010,and could be used in later experiments.3.Determination of virulence of highly virulent strains,matrine and their combinations to M.usitatus:The fatality of the pairwise combinations of two highly virulent strains at 1×10~4,1×10~5,1×10~6,1×10~7 and 1×10~8 spores/mL with matrine at 0.05,0.125,0.25,0.5 and 1.0mg/mL,respectively,to M.usitatus was detected.The results revealed that the pairwise combinations of SCAUDCL-53 at 1×10~4and 1×10~5spores/mL and SB010 at 1×10~4,1×10~5and 1×10~6spores/mL with matrine at 0.5mg/mL had significant synergistic effects.4.Effects of highly virulent strains,matrine and their combinations on the activity of detoxifying enzymes of M.usitatus:SOD,POD,CAT and AChE activities in M.usitatus treated with highly virulent strains,matrine and their combinations were determined on the3rd and 5thd,respectively.The results presented that the four detoxifying enzymes of the M.usitatus treated with fungicides,drug and their combinations changed in different degrees.Over time,SOD of M.usitatus showed an upward trend in the blank control group,while the activities of SOD under other treatments and other three detoxifying enzymes presented a downward trend.After five day of treatment,the activity of each detoxifying enzyme under fungicides,drug and their combinations was significantly lower than that in the blank control group,suggesting that the activities of the four detoxifying enzymes are inhibited.At the third day of treatment,in the Beauveria combinations,the SOD activity under single agent and mixed agents was all significantly lower than that in the blank control group,indicating that SOD has a detoxification effect on fungicides and drug.In conclusion,two highly virulent strains SCAUDCL-53 and SB010 screened by the virulence test of M.usitatus have good compatibility with Matrine.SCAUDCL-53 with 1×10~5,1×10~4 spores/mL and SB010 with 1×10~4,1×10~5,1×10~6 spores/mL with 0.5mg/mL matrine had a significant synergistic effect on the test insect,and the enzyme activity of each detoxifying enzyme was inhibited after the treatment of the test insect with the fungicide,medicament and their combination.This paper provides a scientific basis for the synergism of pathogenic fungi and plant pesticides,and a new method for the control of M.usitatus.