Abstract
Heritable bacterial endosymbionts are found in a large fraction of insects. Most of them can manipulate the reproduction of their hosts towards infected females to promote their spread in insect populations. Common phenotypes are cytoplasmic incompatibility, feminization, male killing, and parthenogenesis. Pityogenes chalcographus revealed partial unidirectional incompatibilities between Northeastern and Central European populations. Mitochondrial analyses found differences between these regions, however, genetic structure on the nuclear level seems to be less pronounced; a possible effect of an endosymbiont infection. Although low-titer infections with Wolbachia were found no relation between this endosymbiont and incompatible populations was observed. Certain populations of Ips acuminatus are strongly female-biased due to parthenogenesis. Previous studies focused on karyogamic effects causing this reproductive mode but endosymbionts have not been studied in detail so far. Here, we present a study on the pre lence of the endosymbionts Wolbachia, Spiroplasma, Arsenophonus, Cardinium, and Rickettsia in the two bark beetle species. PCR screening with taxon-specific primers showed no evidence for the presence of those bacteria and thus does not indicate endosymbionts to be the causal factors of incompatibilities in P. chalcographus and parthenogenesis in I. acuminatus. The influence of low-titer endosymbiont infections and other potential aspects will be discussed.