Categories of resistance (antibiosis, antixenosis, and tolerance) in switchgrass (Panicum virgatum L.) to aphids

Switchgrass, Panicum virgatum L., is a perennial grass native to the North American prairie and has recently been identified as a practical biomass feedstock for energy production. However, the viability of switchgrass as a feedstock will be dependent, at least in part, on effective pest management strategies. To date, little is known about the potential insect pests of switchgrass populations being developed for bioenergy production. Thus, it is important to identify potential insect pests of switchgrass and to describe the plant-insect interactions at multiple ecological levels. In this study, we set out to better understand the interactions between host plants and piercing-sucking insects, using two potential switchgrass pests, Sipha flava (Forbes) (yellow sugarcane aphid) and Schizaphis graminum (Rondani) (greenbug). Two switchgrass populations (Kanlow and K x S) characterized as resistant were evaluated for the categories of resistance (antibiosis, antixenosis, and tolerance) to these aphids using choice and no-choice studies.  Antibiosis studies found Kanlow had significantly lower aphid fecundity than all other switchgrass populations, for both aphids tested, indicating antibiosis is an important factor in resistance.  Plant damage ratings and functional plant loss indices showed that K x S posseses moderate levels of tolerance to S. flava and may also posses tolerance to S. graminum when aphid numbers are taken into account.  Choice studies indicated that no antixenosis was present among the switchgrass tested, however, K x S was preferred by S. graminum after 24 hours.