Zimmerman-Gries, S., Virus Research Laboratory, Volcani Institute of Agricultural Research, Bet Dagan, Rehovot, Israel, Department of Entomology, Hebrew University, Faculty of Agriculture, Rehovot, Israel
Harpaz, I., Virus Research Laboratory, Volcani Institute of Agricultural Research, Bet Dagan, Rehovot, Israel, Department of Entomology, Hebrew University, Faculty of Agriculture, Rehovot, Israel

Sampling of aphids in the Galilee mountains indicated a remarkable ebb in the numbers of alate Myzus persicae individuals during the hottest summer months of June-September. This apparen seasonal lack of vectors was reflected in the results of a preliminary field trial carried out there in the summer of 1966, whereby hardly any aphid transmission of potato virus Y (PVY) could be noticed. In 1967 virus-tested Up-to-Date seed potatoes were planted there next to virus-infected seed. Virus incidence among tubers lifted from these initially virus-free plants was as follows: potato virus X (PVX) 0%, PVY 3.9%, alfalfa mosaic virus (AMV) 0.3% and potato leaf-roll virus (PLRV) 0.3%. A similar trial was repeated in 1968, but the planting date was some 4 weeks later than in 1967. Incidence of virus among the progeny, was as follows: PVX 0%, PVY 1.2%, PLRV 0.4%, AMV 6.0% and stolbur disease 6.4%. © 1970 Kluwer Academic Publishers.