Submitted to: Journal of Agricultural and Urban Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 18, 1999
Publication Date: N/A
Interpretive Summary: A popular strategy for reducing damage to cereals caused by the greenbug, an important pest of cereal grains, is planting greenbug-resistant varieties. However, resistance-breaking forms of the greenbug have developed over time. One dominant theory is that development of these new forms, called biotypes, is actually caused by the use of the resistant varieties. An alternate theory that we investigated is that common native grasses planted in rangeland, pastures, roadsides, and reclamation projects near cultivated cereal crop plantings may in fact be involved. These grasses have been shown to harbor greenbugs during periods when the cereal crops are unavailable for infestation. It is possible that the interaction with these native grasses has exerted selection pressure on the greenbug, thus driving the formation of a new biotype; or, some of the harbored greenbugs may have been as-yet unobserved biotypes. We investigated the interaction of different biotypes of the greenbug with 8 native grasses an one cultivar of wheat. While all grass entries supported populations of greenbug biotypes, our observations indicated that at the least, the development of one greenbug biotype (biotype F) is driven by native grasses. Although this study did not reveal other grasses diagnostic for other greenbug biotypes, a more detailed study of other cool- and warm-season grasses may reveal similar trends that greenbug biotypes are developing on native grasses. By isolating the causes of the development of resistance- breaking forms of the greenbug, Integrated Pest Management strategies could be developed to reduce their chances of development.
Development of resistant cereals has been used to limit the damage by greenbugs. The success of this strategy has been challenged by the occurrence of resistance-breaking biotypes. The predominant theory suggests that this biotype development may be driven by the planting of greenbug- resistant cultivars of cereal grains. However, only a few reports examine the interaction of greenbug with native grasses, despite the potentially important role they may have in driving the development and harboring of as-yet unknown greenbug biotypes. We investigated the host suitability of 8 species of range grasses to determine if any may have played a role in the development of greenbug biotypes. These grass species are grown on rangeland, pasture, and roadsides, and some are used in reclamation projects in the Plains states. All entries supported greenbug populations and sustained plant damage after a 7-d aphid confinement period. Although wheat supported higher aphid numbers compared with the grasses for most biotypes, some grasses suffered equal or more plant damage than wheat. One of the most significant differences among the biotypes occurred with Canada bluegrass, where biotype F adults produced significantly more nymphs that the other biotypes and inflicted significantly more damage. This damage which was ultimately lethal was also observed in all of the species of wheatgrass and mountain brome when challenged with any of the greenbug biotypes. These results indicate that at the minimum, 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, we feel these results suggest that a more detailed survey of other cool- and warm-season grass species would reveal similar results.