These data support the hypothesis that transmission of CYDV-RPV requires the formation of a critical disulfide bond pairing either intramolecular, within the CP or RTP, or intermolecular with a specific host protein, and that treatment with sodium sulfite promotes a random process of thiol-disulfide exchange that creates structures that interfere with normal virus transmission. Sodium sulfite-treated virions did not enter into the HG or into the ASG and thus, a partial overlap in the biochemical mechanisms for virus entry may exist in these two aphid tissues. Previous work using infectious mutants of other luteovirids supports the role of cysteine residues within the capsid as contributing to virus-host specificity and even aphid transmission. PLRV mutants with cysteine deletions or modification of residues flanking cysteines residues show phenotypes in a host-dependent manner Two mutants D-P-K (which alters two cysteine-flanking residues) and H-C-K (which deletes the cysteine residue) showed defects in systemic infection in the host Physalis floridana, but not in Solanum tuberosom, Nicotiana benthamiana, or Nicotiana clevelandii [11] . Aphid transmission of the D-P-K mutant was severely impaired when acquired from or inoculated into P. floridana [11] .