RESUMEN
The bird cherry-oat aphid, Rhopalosiphum padi (L.) (Heteroptera: Aphididae), causes heavy losses to wheat crops worldwide by direct damage and virus transmission. This study was conducted to identify putative resistance mechanisms in four wheat varieties (Bobtail, Ladd, Stephens, and Skiles) and one advanced line (YS434)where R. padi was subjected to choice and no-choice tests. Antixenosis, antibiosis and tolerance studies were conducted in controlled environmental conditions at temperature of 20±5°C, 5065% RH, and a photoperiod of 14:10 (L:D) h. Based on the antixenosis test, the variety Skiles was found susceptible to R. padi, while the line YS434 showed a significant level of resistance; the varieties Bobtail, Ladd, and Stephens showed intermediate response. In the antibiosis experiment, R. padi produced less progeny on the variety Skiles as compared with other varieties, but the developmental time for nymphs was also significantly shorter on Skiles and recorded higher intrinsic rate of natural increase (r(m)) values as compared with the varieties YS434, Bobtail, and Ladd. In the tolerance tests, the variety Ladd showed significantly lower tolerance index value than YS434, followed by Skiles, Bobtail, and Stephens. The plant resistance index value was greater for the variety Ladd, followed by Stephens, YS434, and Bobtail. In conclusion, this study provides baseline information that will contribute to the identification of putative resistance factors for a future breeding program against this aphid.