GREENBURG (HOMOPTERA, APHIDIDAE) FEEDING EFFECTS ON NONSTRUCTURAL CARBOHYDRATES IN SORGHUM

The effects of greenbug, Schizaphis graminum (Rondani), feeding on the nonstructural carbohydrate concentrations of field-grown seedling and vegetative sorghum plants, Sorghum bicolor Moench, were measured by h igh-performance liquid chromatography. Four individual experiments wer e completed for each of the plant growth stages to compare nonstructur al carbohydrate concentrations between greenbug-infested and uninfeste d plants. Greenbug-infested seedling plants tended to have greater con centrations of nonstructural carbohydrates in the shoots and lower con centrations in the roots when compared with uninfested plants. The con centration of sucrose in the shoots of seedling plants increased and s tarch in the roots decreased in a linear relationship with increasing greenbug density. In contrast to seedling plants, roots of greenbug-in fested vegetative plants had a greater concentration of total nonstruc tural carbohydrates and shoots had a reduced concentration. The starch concentration in the shoots of infested vegetative plants decreased w ith increasing greenbug density. These results demonstrate that sorghu m plants at these two growth stages respond differently to greenbug fe eding in their ability to maintain nonstructural carbohydrate concentr ations.