[Show abstract][Hide abstract] ABSTRACT: Βacteria of the genus Wolbachia are intracellular, maternally inherited bacteria, which infect a wide range of hosts. In order to favour their vertical transmission, the bacteria cause a number of reproductive alterations to their hosts. The best studied action of Wolbachia is the induction of cytoplasmic incompatibility (CI). The different Wolbachia strains are categorised into stains that induce the phenotype and those that don't. In order to study the effect of the host in the induction of cytoplasmic incompatibility, we used isogenic lines of Drosophila melanogaster, which are infected with the same Wolbachia strain. Our results suggest that depending on host genotype, there is great variation in the expression of cytoplasmic incompatibility induced by the same Wolbachia strain. In other words there are host strains, which are more permissive to the expression of the phenotype than others. We haven't been able to correlate the levels of cytoplasmic incompatibility to the localisation of the bacteria in adult testes, which has been suggested to play an important role in the expression of the phenotype.