Using molecular biological tools (group-specific SSU rDNA PCR, cloning, RFLP, sequencing), the diversity of Eubacterial, Archaebacterial and Eucaryotic microparasites will be determined in leafcutter ants (Acromyrmex sp.). Next, the prevalence of the identified parasites (parasite-specific PCR) in ant colonies will be determined and correlated to the measured genetic diversity in the colonies (microsatellite DNA data). In a last step, we will determine the parasite load in individual ants and deter- mine the infected tissues using fluorescent in situ hybridisa- tion.