Host Associations of Diuraphis noxia (Homoptera: Aphididae) Biotypes in South Africa

The incidence and host associations of Russian wheat aphid were investigated in the wheat-growing areas of South Africa from 2009 to 2011. Most Russian wheat aphid samples were collected on dryland wheat, while few samples were collected on irrigation wheat. Volunteer wheat and rescue grass were the preferred alternative host plants to cultivated wheat for all three biotypes. NoRWASA1samples were collected from oats, butRWASA2seemed to be able to survive successfully on oats, with 12.26% of the total RWASA2 samples collected on oats and 2.83% RWASA2 samples on wild oats. The intrinsic rate of population increase (rm) has often been used as an index of herbivore performance, and alternative host suitability can be quantified using growth rate parameters, such as the intrinsic rate of increase. The rm was determined for the three South African biotypes—RWASA1, RWASA2, and RWASA3—on seven different host plants. Russian wheat aphid biotypes showed a positive intrinsic rate of increase on all host plants tested, indicating that these host plants were all suitable hosts to support populations of all three biotypes. The rm on TugelaDn, which is resistant to RWASA1 but susceptible to RWASA2 and RWASA3, was significantly higher for RWASA3 and lowest for RWASA1. The rm for RWASA2 and RWASA3 was significantly lower on TugelaDn5, which is resistant to these two biotypes. The rm for RWASA2 and RWASA3 was significantly higher than for RWASA1 on both oats and wild oats. Aphid infestation of winter wheat in the spring may be directly influenced by their success and abundance in noncultivated host plants between harvest and emergence of the cultivated wheat. Therefore, it is important to consider the success of different Russian wheat aphid biotypes on host plant alternatives to cultivated cereals when planning a management strategy for Russian wheat aphid in an area.