Using genetic information to identify aphid species has the potential to quickly and accurately differentiate among often confusing species and to identify immature life stages. In this study, mitochondrial cytochrome oxidase I (COI) sequences were used to identify migrant alate aphids landing in legume crops. Preliminary tests indicated sufficient DNA stability for barcoding following 5-days incubations of aphids in 20% propylene glycol in traps. The time and expense needed to identify aphids by COI barcoding was compared with the traditional morphological identification of slide mounted aphids. COI barcoding allowed identification of nymphs present on plants in the field that would otherwise be impossible to identify with most taxonomic keys. This new identification technique will increase the number of specimens, and range of species and life stages, that can be correctly identified for ecological studies; and can be used to verify identity of species difficult to identify with traditional morphological keys.