The effects of different acquisition access periods (AAP) and inoculation access periods (IAP), on the transmission efficiency of Barley yellow dwarf virus (BYDV) by Rhopalosiphum padi (L.) (Homoptera: Aphididae) following feeding on transgenic or non-transformed wheat (Triticum aestivum L.) genotypes, were studied. Three genotypes were tested as virus sources: susceptible cultivar Lambert, and two Lambert-derived transgenic lines expressing the BYDV-PAV coat protein gene (103.1J and 126.02). Lower virus titers were measured in BYDV-infected transgenic plants compared to Lambert. Transmission efficiency increased with an increase in AAP in all genotypes tested. However, aphids were less efficient vectors following feeding on the transgenic genotype 103.1J compared to Lambert. No significant differences in transmission efficiency were detected for R. padi following varying IAPs, regardless of genotype tested.