Biotypes of Russian wheat aphid, Diuraphis noxia (Kurdjumov), have nullified D. noxiaresistant wheat. In this study, feeding of North American D. noxia was measured in aphids fed resistant and susceptible wheat and barley using electrical penetration graph (EPG) recordings. Interactions between barley genotypes and D. noxia biotypes were significant. EPG recordings of biotype 1 aphids fed on D.…