The effects of greenbug,Schizaphis graminum(Rondani), feeding on the nonstructural carbohydrate concentrations of field-grown seedling and vegetative sorghum plants,Sorghum bicolorMoench, were measured by high-performance liquid chromatography. Four individual experiments were completed for each of the plant growth stages to compare nonstructural carbohydrate concentrations between greenbug-infested and uninfested plants. Greenbug-infested seedling plants tended to have greater concentrations of nonstructural carbohydrates in the shoots and lower concentrations in the roots when compared with uninfested plants. The concentration of sucrose in the shoots of seedling plants increased and starch in the roots decreased in a linear relationship with increasing greenbug density. In contrast to seedling plants, roots of greenbug-infested vegetative plants had a greater concentration of total nonstructural carbohydrates and shoots had a reduced concentration. The starch concentration in the shoots of infested vegetative plants decreased with increasing greenbug density. These results demonstrate that sorghum plants at these two growth stages respond differently to greenbug feeding in their ability to maintain nonstructural carbohydrate concentrations.