The sugarcane aphid, Melanaphis sacchari (Zehntner), is spreading throughout the Louisiana sugarcane growing regions and is the main vector of sugarcane yellow leaf virus. We identified possible sources of plant resistance to this aphid species in commercial germplasm of sugarcane, and also explored biochemical bases of this resistance. Five sugarcane cultivars (LCP 85-384, HoCP 91-555, Ho 95-988, HoCP 96-540, and L 97-128) were screened in the greenhouse as well as under field conditions. Based on r_m (intrinsic rate of aphid increase) values, substantial differences among cultivars were recorded in the greenhouse tests. It is estimated that L 97-128 can produce almost three times more numbers of sugarcane aphids as compared to the resistant cultivar i.e. HoCP 91-555. Population monitoring studies at the field level showed that HoCP 91-555 sustains its resistance under field conditions. The preliminary HPLC analysis of phloem sap samples collected from both varieties did not detect arginine, threonine, and histidine, three of the nine essential amino acids, in HoCP 91-555. The analysis of honeydew collected on these varieties indicated that four amino acids, tyrosine, isoleucine, lysine, and proline were only detected in the honeydew from aphids feeding on the susceptible variety L 97-128. Water potential and total phenolics readings from these varieties did not show any significant differences. Obtained results suggest that the absences of essential amino acids in the phloem sap and aphid inability to synthesize particular amino acids on the resistant variety are possible reasons for resistance in sugarcane to the sugarcane aphid.