It is common for animals, plants and fungi to participate in a wide range of associations with microorganisms, and symbioses have been demonstrated to play a crucial role in the evolution of complexity and adaptation for various organisms. Being the most diverse animal class on earth, particularly insects are associated with an extraordinary variety of symbiotic microorganisms. In many insects the symbionts patronize the host´s metabolic potential by producing essential dietary supplements, thereby promoting the survival of their host. However, recent studies yielded evidence that symbiotic microorganisms can play an essential role for the protection of the insect host, its nutritional resources and it´s offspring against pathogenic bacteria and fungi. This thesis investigates the unique symbiotic association of beewolf wasps with antibiotic producing Streptomyces bacteria. Solitary digger wasps of the genera Philanthus, Philanthinus and Trachypus, engage in a unique and highly specific symbiosis with bacteria of the genus Streptomyces that provide protection to the wasp´s progeny. Female wasps cultivate the symbionts in specialized antennal gland reservoirs and secrete them into the subterranean brood cells as a white substance prior to oviposition. Subsequently, they are taken up by the beewolf larva and are incorporated into the silken walls of the cocoon. On the cocoon surface the symbiotic bacteria provide an antimicrobial defense against pathogen infestation by producing a cocktail of different antibiotic substances, thereby significantly enhancing the survival probability of the wasp offspring during their long and vulnerable phase of hibernation.