Occurrence of pathogens in associated living bark beetles (Col., Scolytidae) from different spruce stands in Austria

Pathogen occurrence was studied in 16 099 adult specimens of 10 different bark beetle species, which live associated on Norway spruce (Picea abies (L.) Karst.). Beetles (mainly Ips typographus L. and Pityogenes chalcographus L.) were collected from 6 different localities in Austria (4 secondary spruce stands and 2 natural forest type stands, 9 sampling plots in total) in elevations between 400 m and 1600 m. Various viral, protozoan, and fungal pathogens could be diagnosed with a light microscope in the examined beetles. Numerous pathogen species were known from former studies, some pathogens were totally new or could be found in a new host species beside their type host. The most dominant pathogen species were Protozoa, Gregarina cf. typographi, Malamoeba cf. scolyti, and Chytridiopsis cf. typographi. Over the whole investigation period, the highest pathogen diversity with eight pathogen species was found in I. typographus. Differences were observed in the pathogen complex of each beetle species from the different collection sites and in different years of investigation. Several species showed an overlapping in their host range and infected various bark beetle species. Furthermore, pathogen occurrence and prevalence differed in bark beetles from 4 different sampling plots in an area (one locality) within a distance of a few kilometres.