Barley yellow dwarf virus infectivity of alate aphid vectors in west Wales

Live trapping at 0.9 m of alate aphid vectors of barley yellow dwarf virus (BYDV) at Aberystwyth from 1970 to 1979 showed that ten species transmitted the virus to oat test plants. Conversion of percentage infective at 0.9 m to numbers infective based on continuous trapping at 1.2 m showed Rhopalosiphum padi and R. insertum to be the main vector species in most years, whilst Metopolophium dirhodum and Sitobion auenae were normally of minor importance. The data obtained suggest that epiphytotics of BYDV in autumn-sown cereals were caused by numerous infective vectors flying late in the year and transmitting severe strains of the virus. Evidence is presented that gynoparae and males of R. padi are involved in the autumn spread of BYDV and that three further aphid species, Anoecia corni, Metopolophium albidum and M. frisicum are BYDV vectors. The use of live and continuous trapping techniques in forecasting BYDV epiphytotics is discussed.