Feeding behavior of Schizaphis graminum (Rondani) on resistant and susceptible populations of switchgrass, Panicum virgatum L.

Switchgrass, Panicum virgatum, is a perennial grass native to the North American prairie and has recently been identified as a practical biomass feedstock for energy production. To date, little is known about the potential insect pests of switchgrass populations being developed for bioenergy production; however, recent studies have demonstrated differential resistance among those switchgrass populations to several key insect crop pests. Previous work has indicated that both antibiosis and tolerance are important categories of resistance in switchgrass; however, limited information is available on the mechanisms of this resistance. The greenbug, Schizaphis graminum, an important pest of many cereal crops, has a host range of more than 70 graminaceous species worldwide and is one potential key pest in switchgrass. In this study, our goal was to better understand the potential mechanisms involved in insect resistance in switchgrasses by characterizing S. graminum feeding behavior on susceptible (KxS) and resistant (Kanlow and Summer) switchgrass populations using electrical penetration graphs. Studies of feeding behavior found no differences for the time to first probe or time to first sieve element phase among the three switchgrass populations. However, duration of sieve element phases for S. graminum was significantly less on Kanlow compared to KxS and Summer. Schizaphis graminum also had a significantly lower potential phloem ingestion index and fewer aphids showing sustained phloem ingestion on Kanlow than both KxS and Summer. These results suggest that resistance factors in Kanlow are located in the phloem tissue.