Metschnikowia cf. typographi and other pathogens from the bark beetle Ips sexdentatus – Prevalence, histological and ultrastructural evidence, and molecular characterization

Ips sexdentatus (six-spined engraver beetle) from Austria and Poland were dissected and examined for the presence of pathogens. Specimens collected in Austria were found to contain the ascomycetous fungus Metschnikowia cf. typographi. Infection rates ranged from 3.6% to 26.8% at different collection sites. M. cf. typographi infected midguts were investigated by histological, ultrastructural and molecular techniques. Extraordinary ultrastructural details are shown, such as ascospores with bilateral flattened flanks resembling alar rims at both sides of their attenuating tube-like ends. These have not yet been described in other yeast species. Molecular investigations showed a close phylogenetic relationship to the fungi Metschnikowia agaves and Candida wancherniae. Presence of the entomopathogenic fungus Beauveria bassiana found in Austria was confirmed both morphologically and molecularly. The eugregarine Gregarina typographi was diagnosed most frequently. Infection rates of all I. sexdentatus specimens ranged from 21.4% to 71.9% in Austria and 54.1% to 68.8% in Poland. Other entomopathogenic protists, bacteria, or viruses were not detected.