Electrical Penetration Graph Recording of Russian Wheat Aphid (Hemiptera: Aphididae) Feeding on Aphid-Resistant Wheat and Barley.

Biotypes of Russian wheat aphid, Diuraphis noxia (Kurdjumov), have nullified D. noxia-resistant 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. noxia-resistant IBRWAGP4-7 barley plants displayed significantly more non-phloem (pathway) phase movements and significantly less sieve element phase (SEP) feeding than on susceptible plants. EPG recordings of D. noxia biotype 2 feeding are the first ever recorded, but no differences between biotype 2-susceptible and -resistant barley plants were found for any EPG parameter in biotype 2 aphids fed barley. No wheat genotype-D. noxia biotype interactions were detected, but when responses were averaged across resistant and susceptible wheat genotypes, biotype 1 displayed a significantly longer pathway phase and significantly more SEP feeding than biotype 2, and biotype 2 engaged in significantly more xylem drinking than biotype 1. IBRWAGP4-7 barley resistance to biotype 1 appears to be controlled by both intercellular factors encountered during the pathway phase and intracellular factors ingested during SEP feeding. The lack of differences in EPG parameters displayed by biotype 2 feeding on barley suggests that biotype 2 resistance in IBRWAGP4-7 barley is based on tolerance to D. noxia feeding instead of altered feeding patterns. Resistance in 'KS94H871' wheat appears to be a function of phloem, non-phloem, and xylem factors that extend the duration of pathway feeding and limit SEP feeding.