The relationships that exist between plecopteran (stoneflies) and microbial communities in freshwater systems are, as yet, only poorly understood. However, it is generally accepted that early instars of many plecopteran species graze on microbial biofilms in riverine sediments. In this study, we investigated the possibility that plecopteran nymphs act as a storage reservoir and/or vector for transmission of the fish pathogen A. salmonicida to its fish hosts. Molecular analysis of hindgut microbial communities of plecopterans from the Nyack flood plain in northwest Montana indicated the presence of Aeromonas salmonicida, a known fish pathogen. Feeding assays were developed in which stonefly nymphs were presented with a suite of different bacterial isolates from the Nyack site, as well as the type strain of A. salmonicida. In these feeding assays, the nymphs showed a preference for A. salmonicida over all of the other isolates tested. In subsequent experiments, plecopteran nymphs were maintained solely on a diet of A. salmonicida, which clearly sustained their survival over control nymphs with no bacteria present. Viable A. salmonicida was recovered directly from nymph hindgut contents indicating that plecopteran nymphs could serve as a reservoir and vector for transmission of A. salmonicida to fish feeding on these insects. Current studies are aimed at determining whether nymph frass might also represent a mode of transmission to susceptible fish hosts.