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The Russian wheat aphid (RWA), <i>Diuraphis noxia</i> (Kurdjumov), is one of the main pests of small-grain cereal crops, including bread wheat, <i>Triticum aestivum</i> (Poaceae). In a series of glasshouse experiments, we evaluated the systemic effect of endophytic <i>Beauveria bassiana</i> strain PPRI 7598 on <i>D. noxia</i> biotype RWASA1 using three South African wheat cultivars, Gariep, Molopo, and Kariega. The objectives of the study were: (a) to determine the effect of endophytism on RWA reproduction and population growth, and (b) to assess the effect of the endophyte on aphid biomass and <i>T. aestivum</i> response to <i>D. noxia</i> herbivory using a damage rating index. Plant endophytic colonisation was confirmed before each trial using a <i>B. bassiana</i>-selective medium. Three independent trials were performed 10 days apart under glasshouse conditions. The effect of the endophyte-treated versus non-treated plants varied significantly in terms of net reproductive rate (R0) and the intrinsic rate of increase (rm) of the <i>D. noxia</i> population. Overall, the endophyte significantly reduced <i>D. noxia</i> R0 by approximately 14 nymphs/female and decreased the aphid mass by 13% in treated plants, whereas the mean aphid mass increased by 17% in control plants in all pooled cultivars. These findings demonstrated the endophytic potential of <i>B. bassiana</i> strain PPRI 7598 for suppression of <i>D. noxia</i> populations in RWASA1-susceptible cultivars. The integration of <i>B. bassiana</i> endophytism with host plant resistance may counteract biotype development and support a more sustainable approach towards RWA control in integrated pest management programmes.