Raccah, B., Department of Virology, The Volcani Center, ARO, Bet Dagan, Israel
Pirone, T.P., Department of Plant Pathology, University of Kentucky, Lexington, KY, United States
Madden, L.V., Department of Plant Pathology, Ohio State University, Wooster, OH, United States

Several monitoring procedures were used in an attempt to determine the aphid species primarily responsible for spread of two non-persistent viruses in tobacco. Myzus persicae (Sulz.), Rhopalosiphum maidis (Fitch), and the combined species of Aphis spp. (L.), comprised more than 70% of the 1149 trapped alive by suction, in 1982; none of the live trapped aphids was viruliferous. These 3 species comprised more than 90% of those collected on plants and between 62.3-94% of those trapped in green tiles in all 4 years from 1982 to 1985. Stepwise regression procedures were used to determine which species were significantly correlated with the increase of two tobacco viruses in the fiedl. Myzus persicae was included in the regressional model in all 4 years for aphids collected from tobacco leaves and in 3 out of 4 years for aphids collected in green tiles. Rhopalosiphum maidis was found to be significant on plants only in 1982, while in the green-tile catch it was included in 1983 and 1984. Species which belong to Aphis spp. were only included in 1983 and 1984 for green-tile trapped aphids. Other aphid species collected from plants, as a composite predictor, were also included in the model. However, they had a limited contribution to the total disease incidence owing to their low proportion in the population. The significance of colonizing species and incoming alates in the inoculation of these viruses is discussed. © 1988.