Response of Russian Wheat Aphid Resistance in Wheat and Barley to Four Diuraphis (Hemiptera: Aphididae) Species

Three Diuraphis</it> species, Diuraphis frequens</it> (Walker), Diuraphis mexicana</it> (McVicar Baker), and Diuraphis tritici</it> (Gillette), were known to exist in the United States before the 1986 appearance of the Russian wheat aphid, Diuraphis noxia</it> Kurdjumov. The Russian wheat aphid soon became a significant pest of wheat although other endemic Diuraphis</it> species were known to infest wheat. Wheat and barley entries resistant and susceptible to Russian wheat aphid biotype 2 were evaluated against all four Diuraphis</it> species to determine their host interrelationships. Leaf chlorosis, leaf roll, leaf number, plant height, and infestation levels were assessed 21 d after the plants were infested by aphids in a no-choice caged environment. D. mexicana</it> was unable to survive on wheat by 21 d after infestation and effects on the plant damage variables were negligible. D. frequens</it> survived at low levels on resistant and susceptible plant entries and had a low impact on plant damage and growth. Russian wheat aphid biotype 2 and D. tritici</it> were damaged most wheat and barley lines except the Russian wheat aphid biotype 2-resistant wheat lines containing genes from Dn7, STARS 2414-11, and CI2401; and resistant barley containing genes from STARS 9577B and 9301B. Russian wheat aphid biotype 2 and D. tritici</it> reduced the growth of resistant plants by 25–50% and susceptible entries by 65–75%. Reductions at this level are typical under no-choice studies but resistant cultivars do not have these reductions under field conditions. The Russian wheat aphid biotype 2 resistant wheat lines would be effective in managing both wheat pest species.