| The rapid development of intensivism and scale for alfalfa farming in Xinjiang, which leads to frequent outbreaks of pests and increasing mono-culture crops of planting structure, makes the pet damage one of the main obstacles for alfalfa production. In this thesis, the method to obtain the high virulent Beauveria strains by screened and mutated was used, the biological characteristics of Beauveria strains and its compatibility with chemical insecticides were researched, and how to improve the the insecticidal effect of Beauveria strains and applicable condition in the field were studied. Those works provided the theoretical basis for production application of Beauveria bassiana and biological control of alfalfa insects.The main results of this thesis are as follows:1. Testing was conducted to assesss virulence of10Beauveria strains to the3rd instar larvae of Hypera postica, and two strains, Bb01and Bb04, were selected with high pathogenicity. Then, these strains were further evaluated in pathogenity in concentrations of×105、×106、×107、×108、×109spores/mL, by which LC50was obtained for the two strains by3.19×106spores/mL and8.3×106spores/mL, respectively in15days after treatment.2. The two stains. BbOl and Bb04, were identified both as Beaureria bassianas using the BLAST intercomparison of sequences obtained from their ribosomes of DNA-ITS-PCR via landing ncbi.3.Starting from per-selected Beauveria bassiana BbOl. the two highest chitinase strains selected were Bb-10-12and Bb-30-14strains, which were obtained by UV mutagenesis method, and diluted to a certain concentration gradients of×105、×106、×107、×108、×109spores/mL. There existed a significant difference in the virulence of three Beauveria bassiana stains by lab testing of their effects on the virulence to L3H. postica. The results showed that9days after treatment, the Bb-10-12. Bb-30-14strains, and the corrected mortality of wild-type L3were100.00%.77.78%. and62.97%. respectively. Finally, Bb-10-12was selected for the highest pathogenicity.It had been found from BbOl and Bb-10-12biological characteristics of trials, on the PSA medium was more suitable for the growth and sporulation of the strains: the most suitable temperature for the highest rate of spore germination was25℃: and relative humidity above75%is conducive to spore germination, but UV inhibited germination of the spores. The results provided the basis for the field application.4. The Bb-10-12strain of Beauveria bassiana, which was virulent to the2nd and4th instar larvae of H. postica. and adult, was tested using concentration of1.65×108spores/mL. and LT50was obtained for as7.73days.9.10days, and27.48days. The strain’s virulence was influenced by temperature and humidity. When temperature was25℃. the pathogenicity of the adult Hypera postica in the condition that the relative humidity is above95%is significantly higher than that of below85%.5. Field trial of Bb-10-12strain for controlling the pest showed a less than50%in efficiency. It is found that in the compatibility test with five chemical insecticides, the growth inhibition rate is the lowest for colonies with one drip, are6.49%and7.41%for the colonies of BbOl and Bb-10-12with the highest concentration of1.0×. The chemical insecticide with lowest germination inhibition rate for the spores of mutation strains Bb-10-12is lambda-cyhalothrin, and the highest with the highest concentration of1.0×is16.94%. The chemical insecticide with lowest germination inhibition rate for the spores of wild strains Bb0l is cyhalothrin. and the highest germination inhibition rate with the highest concentration of1.0×is22.04%.6. Tests of pathogenicity to Sitona lineatus and Tychius Medicaginis adult indicated that the strain Bb-10-12had higher pathogenicity for S. lineatus, LC50was4.4536×104spores/mL after12days of treatment. It has a certain pathogenicity of Tychius Medicaginis to Beauveria bassiana. The corrected mortality is74.36%when the concentration is1.65×109spores/mL, and LC50of1.7011×108spores/mL after20days of treatment. |
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