RUSSIAN WHEAT APHID (HOMOPTERA, APHIDIDAE) FEEDING-BEHAVIOR ON HOST AND NONHOST PLANTS

Feeding behavior of Russian wheat aphid, Diuraphis noxia (Mordvilko), on host (wheat, Triticum aestivum L.; oat, Avena sativa L.; and rye, Secale cereale L.) and nonhost (sorghum, Sorghum bicolor (L.) Moench) plants was studied using a computerized electronic insect feeding monitor. Most waveforms recorded for Russian wheat aphid feeding on wheat and other grass species resembled those previously recorded for other aphids, including three distinctive waveforms for salivation, X-wave, and ingestion. The X-waveforms of Russian wheat aphid had more than one voltage peak. Histology of the Russian wheat aphid feeding site confirmed that when the sequence of waveforms, salivation-X-wave-ingestion, appeared on a strip chart recorder, stylets and salivary sheath always terminated in phloem tissue. Russian wheat aphid salivated more and ingested less while feeding on sorghum than on the other cultivars. It took Russian wheat aphid four times longer to locate the phloem and achieve committed phloem ingestion (> 15 min phloem sap ingestion) on sorghum than on wheat. The Potential Phloem Ingestion Index (PPII) on sorghum hybrid NC+ 630-X was estimated to be 24% compared with 97% on 'Payne' wheat. There was no significant (P > 0.05) difference in duration of phloem ingestion among wheat, rye, and oat cultivars. Russian wheat aphid feeding on susceptible hosts and unacceptable nonhost plants could be used as a basis of comparison among genotypes in identifying sources of resistance to Russian wheat aphid. Also, this method could be used as a quick and nondestructive method to locate and understand the type and mechanisms of resistance exhibited by resistant genotypes.