Differential free amino acids impacting feeding behavior and performance of the sugarcane aphid on sugarcane

The sugarcane aphid,Melanaphis sacchari, is the main vector of sugarcane yellow leaf virus disease and is distributed throughout Louisiana’s sugarcane growing regions. Five commercial sugarcane varieties produced in Louisiana (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 for resistance to the sugarcane aphid. In both greenhouse and field experiments, L 97-128 was found to be the most susceptible and HoCP 91-555 the most resistant variety. The differences in susceptibility were additionally confirmed by studying the feeding behavior of the sugarcane aphid on LCP 85-384, L 97-128, and HoCP 91-555 using the electrical penetration graph (EPG) technique. Differences among varieties were not detected in the time for aphids to initiate sieve element feeding, and in the frequency of cell punctures (potential drops) prior to sieve element feeding. However, the mean duration of the sieve element phase was significantly more on L 97-128 as compared to that of HoCP 91-555. Phloem sap extracts of L 97-128 and HoCP 91-555 indicated that two essential FAAs (histidine and arginine) were absent in the phloem sap of HoCP 91-555. Analyses of honeydew collected from aphids feeding on both varieties indicated that two essential (leucine and isoleucine) and two non-essential (tyrosine and proline) FAAs were present only in the honeydew of aphids on L 97-128. These studies indicate that amino acids significantly affect behavior as well as performance of the sugarcane aphid on resistant and susceptible varieties.