Technical Abstract: Potato virus Y (PVY), a Potyvirus, is transmitted by aphids in a non-persistent manner. PVY severely affects potato production worldwide. Single and mixed infections of PVY strains, namely PVYO, PVYNTN, and PVYN:O are a common occurrence in potato systems. However, information available on the ability of aphids to simultaneously transmit multiple PVY strains, specificity associated with simultaneous transmission, and factors affecting the same are limited. Aphid-mediated transmission experiments were conducted to test the ability of individual aphids to transmit multiple strains using a PVY indicator host. Preliminary results revealed that aphids can transmit at least two viral strains simultaneously. Subsequently, aphid mediated transmission of three dual-strain combinations was tested using potato plants. Individual aphids transmitted two viral strains simultaneously for all three dual-strain combinations. In all aphid-mediated dual-strain infections involving PVYNTN, the rate of PVYNTN infection was greater than the infection rates of the second strain and dual-strain combinations, indicating specificity associated with transmission of PVY strains. Results of aphid-mediated transmission experiments were compared with results obtained through mechanical transmission. In general, PVY infection rates from aphid-mediated transmission were lower than the rates obtained through mechanical transmission. Unlike aphid-mediated transmission, component strains in dual-strain inoculations were not eliminated during mechanical transmission. These results suggest that there may also be interference associated with aphid-mediated transmission of closely related PVY strains. Perhaps, the observed specificity and/or interference may explain the increase in the incidence of PVYNTN and other necrotic strains in recent years.