Endophytic Effect of the South African Beauveria bassiana Strain PPRI 7598 on the Population Growth and Development of the Russian Wheat Aphid, Diuraphis noxia

The Russian wheat aphid (RWA), Diuraphis noxia (Kurdjumov), is one of the main pests of small-grain cereal crops, including bread wheat, Triticum aestivum (Poaceae). In a series of glasshouse experiments, we evaluated the systemic effect of endophytic Beauveria bassiana strain PPRI 7598 on D. noxia 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 T. aestivum response to D. noxia herbivory using a damage rating index. Plant endophytic colonisation was confirmed before each trial using a B. bassiana-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 D. noxia population. Overall, the endophyte significantly reduced D. noxia 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 B. bassiana strain PPRI 7598 for suppression of D. noxia populations in RWASA1-susceptible cultivars. The integration of B. bassiana endophytism with host plant resistance may counteract biotype development and support a more sustainable approach towards RWA control in integrated pest management programmes.