Many bacteria associated with arthropods play important roles in host functional traits, and the structure of these bacteria can be influenced by intracellular symbionts. In this study, a survey of bacterial endosymbionts present in natural populations of the two-spotted spider mite, Tetranychus urticae, was conducted in North, Razavi, and South Khorasan Provinces. A total of 1440 spider mites collected from three localities associated with eight host plants were screened for endosymbionts. Among the three detected facultative endosymbionts, Wolbachia, Cardinium, and Rikettsia, different infection frequencies (91.6%, 9.72%, and 9.72%, respect-ively) were observed. None of the individuals carried Arsenophonus or Spiroplasma. In the majority of the studied populations, multiple infections by endosymbiont were detected and the prevalence of individuals with the Wolbachia-Rikettsia coinfection (9.72%) was higher than the frequency of the individual coinfection rates with other symbionts. The findings of the current study suggest that the frequencies of endosymbiont infections may be affected by collection site characteristics, including geographic location (latitude, longitude), altitude, and collection date, as well as host plant species. Wolbachia infection rates were higher in mites collected from Razavi Khorasan Province compared to those from other localities. The highest frequencies of Cardinium and Rickettsia were observed in North and South Khorasan Provinces. Host plants also significantly influenced the prevalence of endosymbionts in the present study. The results of vertical transmission experiments indicated that temperature influences vertical transmission in symbiotic bacteria.

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