Transmission of CYDV-RPV is dependent upon the virus circulating through the aphid. The interaction between the virions from each purification treatment and the aphid was evaluated, particularly to identify possible barriers to transmission. To determine if aphids ingested and acquired virus, aphids were collected following a 24-h AAP on membranes containing each type of purified virus: buffer only, EDTA-treated, or sodium-sulfite treated. Total RNA was extracted from half of the aphids from each treatment and the remaining aphids were transferred to healthy oat seedlings for a 3-day inoculation access period (IAP). Total RNA was also extracted from those aphids immediately following the 3-day IAP. Viral RNA (vRNA) was detected within aphids after a 24-h AAP for each virus treatment preparation (Fig. 2) using RT-PCR and CP-specific primers. After 24-h, vRNA can be detected in all three groups of aphids. At 24-h, virus could be in the gut lumen, and/or in the HG cells and possibly in the hemolymph. This indicates aphids were ingesting, and possibly acquiring, the virus under all conditions. For aphids collected after a 3-day IAP, vRNA was detected for the buffer only treatment (Fig. 2) indicating uptake of the virus into the hemolymph, which was supported by high level of transmission (92% transmission, Table 2 ). No vRNA was detected after 3 day IAP (Fig. 2) for EDTA-or sodium sulfite-treated virions in the aphids. EDTAtreated virions were still transmitted by aphids to oat seedlings (92% transmission efficiency, Table 2 ), suggesting there was virus uptake and persistence occurred within the aphid, albeit at levels not sensitive enough to detect using RT-PCR. However, the sodium sulfite treatment reduced the rate of virus transmission into oat seedlings (Tables 1 and 2) . Taken together with the RT-PCR results, these data suggest that sodium sulfite-treated virions may not be acquired. If the virus is not acquired, any virus remaining in the lumen after 24-h may flow out of the aphid in the honeydew [25] .