Characterization of Greenbug Feeding Behavior and Aphid (Hemiptera: Aphididae) Host Preference in Relation to Resistant and Susceptible Tetraploid Switchgrass Populations

Two choice studies were performed to evaluate greenbug, Schizaphis graminum (Rondani), and yellow sugarcane aphid, Sipha flava (Forbes), preference for two tetraploid switchgrass populations, Summer and Kanlow, and one experimental hybrid, K×S, derived by crossing Kanlow (male)×Summer (female) plants. Additionally, an assessment of S. graminum feeding behavior was performed on the same switchgrass populations, by using the electrical penetration graph (EPG) technique. Choice studies for S. flava indicated a lack of antixenosis, with no preference by aphids among any of the switchgrass populations at any time point. However, choice studies with S. graminum indicated a preference for the K×S plants at 24 h after aphid introduction. No obvious differences were observed for the leaf surfaces between the three populations. Feeding behavior studies for S. graminum on switchgrasses indicated no differences for the time to first probe or time to first sieve element phase among switchgrass populations. However, duration of sieve element phases for S. graminum was significantly less on Kanlow compared to K×S and Summer. S. graminum also had a significantly lower potential phloem ingestion index (PPII) and few aphids showing sustained phloem ingestion on Kanlow as compared to K×S and Summer plants. These results suggest that resistance factors (chemical or mechanical) in Kanlow are located in the phloem tissue. At the whole leaf level, some differences were observed for a subset of polar metabolites, although Kanlow plants were significantly enriched for oxalic acid