21Host-associated gut microbial communities can have large impacts on host ecology and 22 evolution, and are typically shaped by host taxonomy and diet. Different host species often 23 harbor distinct microbial communities, potentially because (1) host dietary specialization 24 determines microbial colonization, (2) host-specific selection acts on diet-acquired microbiota, 25and (3) a combination of both processes. While the first possibility involves passive 26 community structuring, the other two may arise from a functional association and should 27 produce stable microbial communities. However, these alternatives have rarely been tested in 28 wild host populations. We used 16S rRNA amplicon sequencing to characterize the gut 29 bacterial communities of six dragonfly species collected across multiple seasons and 30 locations. We found that variation in bacterial community composition was predominantly 31 explained by sampling season and location, and secondarily by host species. To distinguish 32 the role of host dietary specialization and host-imposed selection, we used insect-specific 33 primers to identify prey in the gut contents of three focal dragonfly species. We found that 34 these dragonflies -considered to be generalist predators -consumed distinct prey, with 35 seasonal diet variation. Together, the patterns of host dietary specialization and spatial and 36 temporal variation suggest a strong role of passive processes in shaping the gut bacterial 37 community. Indeed, the abundance and distribution of ~76% of the bacterial community 38 members were consistent with neutral community assembly. Our results contradict the 39 pervasive expectation that host-imposed selection shapes gut microbial communities, and 40 highlight the importance of joint analyses of variation in host diet and gut microbial 41 communities of natural host populations.