The Leuven groep has a twofold contribution to this EU-project: (A) use PCR-based molecular biological methods to determine the identity and abundance of endosymbiotic micro-organisms associa- ted with attine ants. Methods include Small Subunit Ribosomal RNA-encoding sequences and oligonucleotide DNA probes directly applied to microscopic sections of ant tissue. (B) light and electron microscopy for research projects in the EU-network. This particularly concerns a structural study of exocrine glands and functional morphology of the reproductive system of social insects.