Occurrence of Chytridiopsis typographi (Microspora, Chytridiopsida) in Ips typographus L (Col, Scolytidae) field populations and in a laboratory stock

The prevalence of Chytridiopsis typographi was examined in Ips typographus field populations from 13 localities in Austria and two from the Czech Republic (1992, 1993, 1994). Ch. typographi could be found in the beetles from 13 sites in various frequency. No regular sex-specific differences in infection rates could be observed. Infection rates depending on beetles flight period (monthly amounts) were highest in June collecting beetles from phermone traps (at one site only). Furthermore the frequency of CI?. typographi in an I. typographus laboratory stock was observed during six generations. Starting at 3.2% Ch. typographi-infection in the beetles of the parental generation it increased up to 52.5% in the F2-generation, and 49.6% in the F3-generation. Afterwards a decline of infection rates could be observed in the F4-generation (27.9%) going down to 10.6% in the FS-generation and increasing again in the F6-generation to 67.5%. Those beetles emerging normally from the trunks had always higher infection rats than beetles cut out of the bark without maturation frass. Ch. typographi spores could be found spread in the cells of the whole midgut epithelium of I. typographus in about 70% of these infected beetles, that emerged from their breeding logs.