For each purified virus preparation (buffer only; buffer including EDTA and sodium sulfite; buffer including EDTA only; buffer including sodium sulfite only), healthy R. padi aphids were allowed a 24-48 h AAP on stretched ParafilmH membranes made by standard protocol by stretching in two directions until very thin. Approximately 75 ml of the virus preparation, at 20-60 mg/ml concentration containing 15% sucrose was used in each membrane. After 24 h, aphids were allowed a 3-4 day IAP on 7 day old oat seedlings (Coast black), 5 aphids per plant, 12-16 plants per treatment. Plants were fumigated with Orthene to kill the aphids. The fumigated plants were placed in the greenhouse and observed for symptom expression 3-4 weeks later. Infected plants were evaluated by obvious yellowing and reddening of the leaves, and dwarfing of the plant. In addition, a randomly selected subset of the leaves (symptomatic and asymptomatic) was tested by double-antibody sandwich enzyme linked immunosorbent assay (DAS-ELISA) using anti-CYDV-RPV antibodies. Each type of virus preparation was tested 2-4 times.