Several vectoring insects, such as aphids and white fly, harbour secondary bacterial endosymbionts. When an insect vectors a persistently transmitted plant virus, this virus should pass through the insect gut into the haemolymph. The secondary bacteria, however, may affect the movement, persistence and replication of the viruses, thereby influencing the vectoring efficacy or specificity of the insect in respect to these plant viruses. This issue, however, has not yet been fully investigated. Hence, the aim of this primary study is to investigate the effect of secondary bacterial endosymbionts of Sitobion avenae clones in respect of the vector specificity and transmission efficiency of barley yellow dwarf virus, as well as to highlight in general the role of secondary bacteria in virus transmission. The experiments were performed according to standard protocols using one virus strain, BYDV-PAV, and four S. avenae clones harbouring different bacterial and genetic profiles. We found that all tested clones were able to transmit the tested virus strain. Therefore, it can be concluded that the secondary bacterial endosymbionts may affect transmission efficiency of S. avenae but not their vectoring specificity. That said, the clones did not significantly differ in their efficiency of virus transmission. However, this study is initial evidence of the effect of secondary bacteria endosymbionts of aphids on virus transmission and further investigation is, therefore, still required.