The Bird cherry-oat aphid (Rhopalosiphum padi) is an aphid in the superfamily Aphidoidea in the order Hemiptera. It is a true bug and sucks sap from plants. It is often considered as a major pest in cereals in temperate cereal crops, and particularly in some Northern European countries. It is the principal vector of many viruses including the barley yellow dwarf virus (BYDV), the Cereal yellow dwarf virus–RPV, Filaree red leaf virus, Maize leaf fleck virus, and Rice giallume virus, as well as oat yellow leaf disease and the Onion yellow dwarf virus.