Susceptibility of cool-season grasses to greenbug biotypes

The development of host plant resistant cereals has been used to limit the damage by greenbugs, Schizaphis graminum Rondani. The success of this strategy has been challenged by the occurrence of resistance-breaking biotypes. The dominant theory suggests that biotype development in this aphid may be driven by the planting of resistant cultivars of cereal grains. However, there are only a few reports examining the interaction of greenbug with native grasses despite the potentially important role they may have in driving the development, and in the harboring of as yet unknown biotypes of greenbugs. Therefore, we investigated the host suitability of eight species of range grasses to determine if any of them may have played a role in the development of greenbug biotypes. These species of grasses are grown on rangeland, pasture, roadsides, and some of them are used in reclamation projects in the Plains states. All entries supported populations of greenbug biotypes and sustained plant damage after a 7 d confinement period. Although wheat, Triticum aestivum L., supported higher greenbug numbers compared with the grasses for most biotypes, some of the grasses suffered equal or more plant damage than wheat. One of the most significant differences among the biotypes occurred with Canada bluegrass, Poa compressa L. Greenbug biotype F adults cultured on Canada bluegrass produced significantly more nymphs than the other biotypes and inflicted a significantly higher damage rating. This damage, which was ultimately lethal, was also observed in all of the species of wheatgrass and mountain brome when challenged with any greenbug biotype. These results suggest that the development of greenbug biotype F is driven by native grasses. While this study did not reveal other grass species that were diagnostic for the other biotypes, these results suggest that a more detailed survey of other cool and warm season grass species would reveal similar results.