SummaryPopulations of cereal aphids were sampled from 1985–1988 and assayed for transmission of barley yellow dwarf virus (BYDV),Rhopalosiphum padi, Rho‐palosiphum maidis, Sitobion avenae, Metopolophium dirhodum, Schizaphis graminumandMacrosiphum euphorbiaecollected from host plants transmitted BYDV in bioassays. Of the 1028Diuraphis noxiacollected from plants, one may have transmitted BYDV. The isolate involved resembled SGV in serological and biological characteristics, but since it was not recoverable by any of more than 800D. noxiasubsequently tested, we suspect it may have been a contaminant.Among those aphids collected during the autumn from a suction trap adapted for live collection,R. paditransmitted BYDV most frequently. Other trapped species which transmitted BYDV included:R. maidis, Rhopalosiphum insertum, Macrosiphum euphorbiae, Metopolophium dirhodumandCeruraphis eriophori.An adapted Infectivity Index indicated thatR. padiis by far the most important vector of BYDV during the autumn sowing season in southwestern Idaho. MaleR. padiconsistently transmitted BYDV more frequently than did females collected during the same per