TRANSMISSION OF BARLEY YELLOW DWARF VIRUS BY FIELD COLLECTED APHIDS (HOMOPTERA, APHIDIDAE) AND THEIR RELATIVE IMPORTANCE IN BARLEY YELLOW DWARF EPIDEMIOLOGY IN SOUTHWESTERN IDAHO

Populations of cereal aphids were sampled from 1985-1988 and assayed for transmission of barley yellow dwarf virus (BYDV). Rhopalosiphum padi, Rhopalosiphum maidis, Sitobion avenae, Metopolophium dirhodum, Schizaphis graminum and Macrosiphum euphorbiae collected from host plants transmitted BYDV in bioassays. Of the 1028 Diuraphis noxia collected 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 800 D. noxia subsequently 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. padi transmitted BYDV most frequently. Other trapped species which transmitted BYDV included: R. maidis, Rhopalosiphum insertum, Macrosiphum euphorbiae, Metopolophium dirhodum and Ceruraphis eriophori. An adapted Infectivity Index indicated that R. padi is by far the most important vector of BYDV during the autumn sowing season in southwestern Idaho. Male R. padi consistently transmitted BYDV more frequently than did females collected during the same period.