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, S ecale cereale L.) and nonhost (sorghum, Sorghum bicolor (L.) Moench) p lants was studied using a computerized electronic insect feeding monit or. Most waveforms recorded for Russian wheat aphid feeding on wheat a nd other grass species resembled those previously recorded for other a phids, including three distinctive waveforms for salivation, X-wave, a nd ingestion. The X-waveforms of Russian wheat aphid had more than one voltage peak. Histology of the Russian wheat aphid feeding site confi rmed that when the sequence of waveforms, salivation-X-wave-ingestion, appeared on a strip chart recorder, stylets and salivary sheath alway s 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 a chieve committed phloem ingestion (> 15 min phloem sap ingestion) on s orghum than on wheat. The Potential Phloem Ingestion Index (PPII) on s orghum hybrid NC+ 630-X was estimated to be 24% compared with 97% on ' Payne' wheat. There was no significant (P > 0.05) difference in durati on of phloem ingestion among wheat, rye, and oat cultivars. Russian wh eat 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 genotype s.