Giant reed, Arundo donax (L.), is known for its potential as a bioenergy crop. To evaluate the effect of the aphid Melanaphis donacis (Passerini) on plants growing in the Metropolitan Region of Chile, three treatments with six plots each were compared: imidacloprid, the agricultural detergent TS2035, and an untreated control. Aphid density levels in the untreated control plants averaged 136.27 aphids leaf-1 along the growing season, while TS2035 and imidacloprid averaged 8.26 and 0.98 aphids leaf1 , respectively. The greatest yield of A. donax (95.1 t dry matter (DM) ha-1) was obtained with the TS2035 detergent, followed by imidacloprid and the untreated control, with values of 88.8 and 84.1 t DM ha-1, respectively. However, there were no significant differences (p ? 0.05) in DM yields of A. donax between treatments. Thus, control of M. donacis with insecticides would be unnecessary in bioenergy crops of A. donax in this region.