Potato virus Y (PVY) (Potyvirus: Potyviridae) is the most economically important virus affecting the seed-potato production in the United States. PVY is vectored by several potato colonizing and non colonizing aphid species in a non persistent manner and has a wide host range. Myzus persicae and Macrosiphum euphorbiae (Aphidae: Hemiptera) are among the most efficient colonizing aphid vectors. Rhopalosiphum padi (Aphidae: Hemiptera), a cereal aphid that migrates in large numbers through potato fields at the middle of the potato growing season, is also capable of transmitting PVY. Hairy nightshade, Solanum sarrachoides (Sendtner), a prevalent and difficult to control annual solanaceous weed in the Pacific Northwest, has been reported to be an alternate host for several potato viruses including PVY and a preferred host for M. persicae and M. euphorbiae. Hence, hairy nightshade plants might play an important role as potential inoculum source for the virus in the field. We studied the transmission of two PVY strains present in the Pacific Northwest (PVY^O and PVY^NTN) by the three above mentioned aphid vectors from hairy nightshade and potato plants and determined how the transmission of the two PVY strains was affected by the source of virus inoculum and by the vectors.