Molecular characterization and comparative virulence of Beauveria bassiana isolates (Ascomycota: Hypocreales) associated with the greenhouse shore fly, Scatella tenuicosta (Diptera: Ephydridae)

Abstract

Reports of natural infections of the insect pathogenic fungus Beauveria bassiana (Bals.) Vuill. (Ascomycota: Hypocreales) in greenhouses and laboratory colonies of Scatella tenuicosta Collin (Diptera: Ephydridae), a nuisance pest and vector of plant pathogens, suggest the potential for using B. bassiana for microbial control of this pest. In this study we assessed the diversity of B. bassiana isolates found associated with a colony of shore flies and compared these isolates to two commercial B. bassiana strains. Microsatellite markers were used to assess genetic variation among fungal isolates from adults and pupae of S. tenuicosta, adults of Hexacola neoscatellae Beardsley (Hymenoptera: Figitidae), a hymenopteran parasitoid of S. tenuicosta, and algal food source in greenhouses. Twenty-seven single spore isolates were resolved into three distinct haplotypes using eight microsatellite markers. Two haplotypes were most common, comprising several strains collected from infected shore flies and parasitoids. The third haplotype was observed in only one strain from a shore fly pupa. Bioassays of a representative strain of each haplotype against third-instar larvae, pupae and adults of shore flies showed that adults were more susceptible to the fungus than the other two stages. Secondary pick up of inocula from sprayed pupae by adults resulted in 52% and 55% mortality from B. bassiana strains ST1 and ST2, respectively. Direct spray application on adults resulted in 91 and 94% mortality from these two strains, suggesting their potential as biological control agents against shore flies.