The symbiotic relationship between microorganisms and arthropods is very common in nature. Some cytoplasmic symbiotic microorganisms alter the normal sex-determining mechanisms in arthropods, causing sex-ratio deviation, killing males and eventually leading to asexual re-production and the possibility of species extinction. In the bio-control of agricultural pests, predatory mites of the Phytoseii-dae family are of great importance. In this study, regarding to the observance of sex-ratio deviation in Ambelyseius swirskii (Acari: Phytoseiidae), the presence of three endosymbiotic bac-terial genera, i.e. Cardinium, Rickettsia and Wolbachia was in-vestigated in adult mites Methods: Firstly, invest
