Abstract
M.Sc. (Botany)
Wheat is the second most important grain crop produced in South Africa. It is mostly used for
human consumption (e.g. biscuits, rusks, breakfast cereals, and bread) with the remainder being
used as seed and animal feed. Wheat is also used for production of alcohol for ethanol, absorbing
agents for adhesives, disposable diapers and industrial uses as starch on coatings (Department of
Agriculture, Forestry and Fisheries, 2011). The leading wheat producing areas in South Africa
since 1994 are the Western Cape (38 %), Free State (26 %) and Northern Cape (17 %)
(Department of Agriculture, Forestry and Fisheries, 2011). There are two main classes of
cultivated wheat, these are durum wheat (Triticum durum) that contributes 5 % and common or
bread wheat (Triticum aestivum L.), which contribute 95 % of the world wheat production
(Kiplagat, 2005). One of the major threats to wheat production in South Africa and other
countries is the Russian wheat aphid (RWA), (Kurdjumov), (Diuraphis noxia, Hemiptera:
Aphididae) (Brooks et al., 1994).
In South Africa, the Russian wheat aphid was reported as a pest of wheat in 1978 in the Eastern
Free State (Walters, 1980). In the beginning of the 1979 season, it was detected only in the
Eastern Free State, but quickly spread to the Western Free State and parts of Lesotho.
Infestations were also isolated in some areas of KwaZulu-Natal, North West and Gauteng
Province (Walters et al., 1980).
Aphids are soft bodied insects and are the most economically important phloem feeders
impacting on plants (Dixon, 1985; Klingler et al., 2009). Aphids damage plants in four ways.
Firstly, they ingest vital plant metabolites including large volumes of translocated sugars from
the phloem sap, diverting energy from the plant and reducing yield. Secondly, they secrete saliva
into the plant tissues while probing the layers of leaf to find the phloem, in some instances the
secreted saliva is thought to be phytotoxic (Dedryver et al., 2010). The physical damage done to
the leaf along with the toxic attributes of the saliva leads to localized necrosis in some aphid
plant interactions (Klingler et al., 2009). Thirdly, aphids act as virus vectors and they can be
transmitted in a non-circulative or circulative manner (Chen et al., 2012).