To determine if either additive affected the ability of virus to move into gut cells, we used TEM to visualize virion attachment and virus penetration across the gut membrane (Fig. 3) . Aphids were fed on sodium sulfite-or EDTA-treated as well as nontreated virions for a 48-hr AAP. Non-treated (Fig. 3A, B) and EDTA-treated virions (Fig. 3C , D) were observed to attach to apical plasmalemma lining the HG lumen, in coated pits invaginating and budding into the cytoplasm, as well as retained Figure 1 . Negative stained grids, coated with CYDV-RPV coat protein antibody, of purified virus from each virus preparation after purification and virus recovered from membranes fed on by R. padi for a 24 h AAP. Virion morphology was similar within each group and a representative picture for each is shown. Transmissible virions after purification (A) and after membrane feeding (B) look morphologically similar. Non-transmissible virions after purification (C) and after membrane feeding (D) look morphologically similar to each other and are indistinguishable from transmissible virions in shape and size. Scale bars = 100 nm. doi:10.1371/journal.pone.0048177.g001 in vesicles dispersed throughout the cytoplasm. In contrast, sodium sulfite-treated virions were rarely observed to interact with the apical plasmalemma nor were they observed within the cytoplasm of the HG. However, virions were observed in the HG lumen ( Fig. 3E , F). The patterns of virus transmission and virus distribution within the aphid for each purified virus (non-treated, EDTA-or sodium sulfite-treated) were consistent in five aphids fed on the different virus preparations ( Table 2) .