Density of the entomopathogenic fungus, Beauveria bassiana Vuillemin (Deuteromycotina: Hyphomycetes) in forest air and soil

Monthly changes in densities of Beauveria bassiana in the air and soil of forest stands were measured using selective media to investigate the density dynamics of this fungus. In a windbreak forest of Pinus thunbergii along the coast where B. bassiana has been introduced for the experimental control of Monochamus alternatus, fungal density was higher than in a neighboring untreated forest. Wild B. bassiana was also isolated from inland forests of Quercus serrata, and Chamaecyparis obtusa; in particular, the density of B. bassiana in the soil of the Q. serrata forest was extremely high. Utilizing the same selective medium, conidial dispersal from a nonwoven fabric fungus carrier was also investigated. The fungal conidia were dispersed by the air; however, the density of the fungus in the air at more than 50 m from the source did not differ from the natural density of the fungus. This result was compared with the lethal density of the fungus on mulberry leaves for the silkworm, and the risk of infection is thought to be very rare.