| The Aleurodicus dispersus Russell,was a destructive invasive pest in Hainan, it brings great Josess of the forestry crops. Biological characteristics of the Verticillium lecanii of Entomopathogenic fungi by separated from diseasing body of A.disperses, screening and optimization of the fermentation substrates for solid and liquid, the pathogenicity and mechanism of conidiophore and crude toxin to the larvae of A.disperses were studied in this paper, which provided the basis for the best control A.disperses, achieved " bacteria to treat bug ".The main results were as follows:(1) V. lecanii strains could grow and produce conidiophore between15～35℃. With the rising of temperature,the speed of hyphae growth and the quantity of conidiophore producing were increased, the optimum temperature for hyphae growth and producing conidiophore was30℃.The hyphaes were radial growth,wavy edge and surface density of the colonies.The suitable temperature for spore germination was between20～30℃. In saturated humidity, spore germination was fast and tidy.With the reduction of humidity, the time of spore germination was extended, the germination rate was gradually reduced.After screening and optimization for this strains to selective medium, the optimal formula was0.5%maltose,1%peptone,25μg·mL-1dipotassium hydrogen phosphate,10μg·mL-1nicotinic acid, pH:7, this formula was moremore beneficial to hyphal growth and sporulation.(2) The strains were cultivated on a large scale by using the liquid-solid two-phase fermentation. The liquid fermentation culture medium for the strains were screened and optimizated. In the condition of4%granulated sugar,2%peptone,25μg·mL-1dipotassium hydrogen phosphate, and10μg·mL-1lactoflavin selecting as the fermentation substrates, and with5%inoculum concentration, the biomass of hyphae were the most after cultivating6days.Cheaper farm and sideline products were used for soil fermentation,and large-scale production of fermentation substrates were screened.In the final peanut cake, millet, phosphate, and rice husk were chosen as the best component fermentation substrates, and the mass ratio of peanut cake and millet was1:2.The optimum temperature for soil fermentation was30℃and the quantity of conidiophore producing were the highest after cultivated14days. It could promote the sporulation of V. lecaniiwere by prolonged daily photoperiod.(3) The results of indoor and outdoor pathogenic experimental showed thatV. lecanii have good pathogenicity for the2-4instar nymphae of A.disperses,while the pathogenicity was the worst for the1instar nymphae.The characteristics of A.disperses infection by V. lecaniiwere were researched by using the method of paraffin sections,The results showed that the strin invaded through the skin. The spores of V. lecaniiwere were germinated on the surface of A.disperses after18hours, and penetrated skin and infected insect internal organization after28hours. The internal organization diseased between42hours and72hours, and hyphae penetrated the skin again. The internal organization of polypide were decomposed between96hours and168hours, and hyphae accumulated on the surface of A.disperses and produced conidium.(4) The insecticidal activity material to A.disperses were extracted from hyphae and zymotic fluid by using the method of liquid formation. It found that crude toxin inside the cell which extracted from hyphae all had insecticidal activity for A.disperses after cultivating different time.The results showed that its insecticidal activity achieved significant difference, when the concentration of lOd was5mg·ml-1, the insecticidal activity could reach92.57%after cultivatinging72hours, the liquid fermentation which was removed hyphae (exocellular crude toxin) also had insecticidal activity for A.disperse. When the concentration of fermented liquid was10mg·ml-1, the insecticidal activity could reach60.78%after cultivatinging72hours. |
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