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

Authors: CASTRILLO, LOUELA - CORNELL UNIVERSITY; UGINE, TODD - CORNELL UNIVERSITY; FILOTAS, MELANIE - ONTARIO MINISTRY OF AGRI; SANDERSON, JOHN - CORNELL UNIVERSITY; Vandenberg, John; Wraight, Stephen

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2007
Publication Date: 4/1/2008
Citation: Castrillo, L.A., Ugine, T.A., Filotas, M.J., Sanderson, J.P., Vandenberg, J.D., Wraight, S.P. 2008. Molecular characterization and comparative virulence of Beauveria bassiana isolates (Ascomycota: Hypocreales) associated with the greenhouse shore fly, Scatella tenuicosta (Diptera: Ephydridae). Biological Control. 45:154-162.

Interpretive Summary: The shore fly Scatella tenuicosta is an important nuisance pest in greenhouses. Both the larvae and adults feed on algae that grow on wet greenhouse surfaces. Because these insects do not directly damage plants, their control by means other than broad-spectrum chemical insecticides has not been extensively investigated. Recent studies have indicated, however, that these insects are potentially important mechanical (contact) vectors of many plant pathogens, and there is increasing demand for additional control methods. Objectives of the current research included 1) identification and characterization of insect pathogenic fungi found at epizootic levels in caged shore fly populations and 2) assessment of the microbial biological control potential of these fungi, including comparisons to commercially available fungal pathogens. Molecular investigations resulted in discovery of three genetically distinct, novel strains of Beauveria bassiana. Laboratory bioassays showed that shore fly larvae and pupae were highly resistant to infection by these pathogens; however, two strains exhibited exceptionally high virulence against adult shore flies: direct applications of low dosages of spores killed > 90 percent of adult flies, and approximately 50 percent of adults acquired lethal doses of fungal spores either during the act of emergence from pupae previously sprayed with B. bassiana or through contact with treated pupae. Both of these strains were substantially more virulent than two commercial strains of B. bassiana. These results indicate strong potential for development of these or other strains of B. bassiana for biological control of shore flies.

Technical 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. Direct spray application on adults resulted in 91 and 94% mortality from B. bassiana strains ST1 and ST2, respectively. Secondary pick up of inocula by adults from sprayed pupae also resulted in 52–55% mortality, suggesting these fungi have considerable potential as biological control agents against shore flies.