Diuraphis noxia is an insect pest on barley and wheat in Ethiopia. Yield losses of barley can reach up to 79%. Control is through use of resistant barley cultivars. Biotypes can render control with resistance uncertain. In this book it was indicated that no biotypic variation exist in RWA clones on barley in Ethiopia. Susceptibility of one resistant wheat line (Dn4) to the Ethiopian RWA clones indicated biotypic differences between American and Ethiopian RWA clones. Anholocyclic life cycle of RWA in Ethiopia, dependence on land races and fact that barley land races show tolerance to RWA support the finding of no biotypic variation in the Ethiopian RWA clones. It was also indicated in the same book that molecular markers like mtDNA, two microsatellite loci and dnaN and ptrpE genes of the bacterial endosymbiont Buchnera did not reveal genetic variation among worldwide collections of RWA. Only a single substitution was found in the pseudogene (ptrpE) in the Turkish populations. Amercian populations did not reveal a different genetic pattern compared to Ethiopian ones. The absence of genetic variation could be due to the recent and fast spread 0f the insect from its origin.