Clones of greenbug,Schizaphis graminum(Rondani), biotypes J and E were investigated for numerical increase and damage to eight small grains. The small grain cultivars were: ‘Triumph 64’ and ‘Dickinson 28A’ wheat; ‘Wintermalt’ and ‘Post’ barley; ‘Elbon’ and ‘Insave F. A.’ rye; and ‘Nora’ and CI 1580 oat. On the 18th d after infestation at 17:15°C and a photoperiod of 15:9 (L:D) h., J differed from E by a greater density per plant on ‘Post’, ‘Wintermalt’, and CI 1580 but had a lower density per plant on ‘Nora’, ‘Dickinson 28A’, ‘Triumph 64’, ‘Insave F. A.’, and ‘Elhon’. The plant damage ratings after 21 d demonstrated clear differences between the greenbug clones. Differences among cultivar responses to clones remained the same at four different temperature and photoperiod regimes. ‘Dickinson 28A’ and ‘Post’ were the most consistent in distinguishing greenbug clones E and J. Damage ratings were correlated with the numbers of aphids per plant on specific cultivars. Clone J from the barley growing region of Idaho had greater densities and caused more damage than clone E on the barley cultivars, but clone J had fewer progeny and caused less damage than clone E on the wheat and rye cultivars.