Host Associations of <I>Diuraphis noxia</I> (Homoptera: Aphididae) Biotypes in South Africa

Abstract

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. No RWASA1 samples were collected from oats, but RWASA2 seemed 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.

Evaluation of Russian wheat resistance sources with the spectrum of South African Diuraphis noxia biotypes

“…Some of the accessions used in this study were collected from Afghanistan and Iran. These countries are the major sources and contributors of most resistance genes used in most breeding programs (Du Toit, 1989; Harvey & Martin, 1990; Jankielsohn, 2014; Liu et al., 2001; Saidi & Quick, 1996). PI 634770 is a SA breeding line carrying Dn9 that confers resistance to RWASA1 and is ineffective against other biotypes (Jankielsohn, 2014; Liu et al., 2001).…”

“…Currently, five different RWA biotypes, designated according to virulence profiles against D. noxia resistance genes, are known to occur in SA; that is, RWASA1 (Walters et al., 1980), RWASA2 (Tolmay et al., 2007), RWASA3 (Jankielsohn, 2011), RWASA4 (Jankielsohn, 2014), and RWASA5 (Jankielsohn, 2019). Russian wheat aphid biotypes are resistance‐breaking pest populations that significantly damage plants containing specific resistance gene(s) rendering them susceptible (S) although they were previously resistant (R) (Jankielsohn, 2014). They vary from one another through virulence profiles against different wheat cultivars with different R genes (Jankielsohn, 2011; Jankielsohn et al., 2016).…”

“…The pool of known genes that are still suitable for deployment in R cultivars is, however, limited and needs to be expanded. The Dn7 , Dn2401 , and Dn2414 are three RWA resistance genes R to most known RWA biotypes globally (Jankielsohn, 2014; Puterka et al., 2014). However, both Dn7 and Dn2414 have been introgressed from rye ( Secale L.) via the 1RS translocation and 1RS is associated with bad bread‐making quality traits (Graybosch et al., 1990), thus making them unsuitable for use in SA and global breeding programs.…”

Russian Wheat Aphid Distribution in Wheat Production Areas: Consequences of Management Practices

“…Furthermore, approximately 20 species in the Aphididae have evolved resistance to insecticides [21] that can be associated with detectable changes in reproductive rates [22]. In South Africa RWA showed considerable biotypic adaptation and change in reproductive rate to resistant wheat [25,27,38], resulting in five RWA biotypes occurring in wheat production areas where RWA resistant wheat were deployed in the Eastern Free State. This may be an indication that RWA in South Africa have the adaptive ability to develop resistance to active ingredients of insecticides used to control them in the Western Cape.…”

“…Chlorpyrifos selection seen in wheat production may result in large scale changes in susceptibility and control failures. Russian wheat aphid variation in virulence to small grains occurs [24,25] as well as variation in fecundity [26,27]. There is a possibility that RWA can also evolve virulence to active ingredients in chemicals.…”