Isolation And Identification Of Aspergillus Nomius Strain And Study On Its Pathogenicity To Two Insects

At present,the control of Helicoverpa armigera and Bemisia tabaci is mainly based on chemical control,but the environmental and health problems caused by chemical pesticides are becoming more and more prominent.The use of entomopathogenic fungi to control agricultural and forestry pests conforms to the concept of green development,and has become one of the hot topics of biological control.The main work of biological control is to exploit the native pathogenic microorganism.In this study,three strains were isolated and cultured from parts of Helicoverpa armigera that died in the rearing process.The classification status and culture characteristics of these three strains were studied by morphological identification and molecular identification methods,and a highly pathogenic strain was screened out by laboratory virulence test and pot experiment,aiming to provide theoretical support for the local biological control.（1）The results of isolation,identification and culture characteristics of the three strain showed that:The three strains MLC1,MLC2 and MLC3 were isolated from the diseased Helicoverpa armigera corpses,were identified as aspergillus nomius by means of morphological and molecular identification.The three strains grew fast on PDA and the order of growth rate from fast to slow MLC2>MLC3>MLC1.The colony diameters of strains MLC1,MLC2and MLC3 reached 77.10±0.34 mm,84.97±0.18 mm,79.90±0.21 mm,after 15 days of culture,respectively.The conidial yield of three strains were higher than 9×10⁶ spores/cm²,after 15 days of culture,and the conidial yield of strain MLC2 was the highest,with the value of 1.4×10⁷spores/cm²,and that of strain MLC3 was the lowest,with the value of 9.95×10⁷ spores/cm².After 24h of culture,60%of spores germinated,and the spores of strain MLC2 germinated the highest,with a germination rate of 93%.The germination rate of spores of strain MLC3 was 61%.（2）The screening of highly virulent strains and the pathogenic determination of Helicoverpa armigera and Bemisia tabaci showed that:At the same concentration of 1×10⁷ spores/m L,the cumulative corrected mortality rate of the three strains against the third instar larvae of Helicoverpa armigera was in the order from high to low MLC2>MLC1>MLC3,and Strain MLC2 has the best virulence effect,with a corrected mortality of 63.79%and LT₅₀ of 6.50 d.Strain MLC3 showed the lowest virulence to the third instar larvae,with a corrected mortality of 29.31%and LT₅₀ of 10.25 d.The pathogenicity of the strain MLC2 to the third instar larvae of Helicoverpa armigera and the nymph of Bemisia tabaci under different spore suspension concentrations was studied.The strain MLC2 showed strong virulence to the third instar larvae of Helicoverpa armigera.At the concentration of 1×10⁸spores/m L,the cumulative mortality and LC₅₀and LT₅₀reached 81.94%and 8.9×10⁵spores/m Land 6.46 d after 11 days of treatment,respectively.At the same time,the strain had certain pathoenicity to the nymphs of Bemisia tabaci.After treated with 1×10⁸spores/m L for 10 days,the calibrated mortality and LC₅₀ and LT₅₀ of the nymphs of Bemisia tabaci reached98%and 1.2×10⁵spores/m L and 2.9 d,respectively.（3）The results of.highly virulent strains against Bemisia tabaci in pot test showed that:At the concentration of 1×10⁸spores/m L,the strain of MLC2 showed high control efficiency for Bemisia tabaci adults in the pot trial,with the control effect of 70.77%and 62.95%after3 days and 7 days,respectively.At the concentration of 2×10⁸spores/m L,the greenhouse control efficiency of Beauveria bassiana was the lowest,with the control effect of 38.90%and 31.32%after3 days and 7 days,respectively.