Beauveria bassiana invades their host initially through yeast bodies, a obligatory parasitic cycle among most entomopathogenic fungi. virulence of B.bassiana (ATCC 74040) which cultured on SDAY in Yeastlike cycle toward third nymphal stage of Trialeurodes vaporariorum were investigated. The conidia of fungus in this phase developed by budding from germinating conidia after 24h incubation. Average size of cells were 5-10 μm. Colony of fungus were initially circular some later were cover with mycelia. On the basis of isolate type,timing and growth rate of yeast inoculum productin varied. Conidia and yeast-like had similar virulence against Trialeurodes vaporariorum , and average mortality were 65.4 % with 106 cells/ml. and 78.5 % with 10 7 cells/ml.,respectively. The results of bioassay indicated that the Yeast-like bodies are effective inoculum for B. bassiana against insects rather than conidia against some pests. Production of well-defined yeast phase culture may be essential work for using

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