Figure 1 : A) MAFFT Whole genome alignment of APV isolates. B) Maximum likelihood phylogeny of APV isolates.
APV is both vertically and horizontally transmitted: We first assessed the efficacy of vertical transmission by determining the proportion of offspring infected females produce that are also infected. Using APV+ aphids (ND18 genotype), we observed that 30-40% of offspring each female produced carried the virus with no significant differences detected between aphids with or without H. defensa (Table 2A). This finding clearly indicated that maternal transmission occurs at moderate rates, but also showed most progeny are not infected. We thus examined two mechanisms for horizontal transmission. We first tested transmission from +APV aphids to -APV aphids feeding on the same host plant using aphid lines that differed in color, including recipient lines with H. defensa or R. insecticola . Half or more of the -APV aphids were infected after 1 week while nearly all were infected after 3 weeks (Table 2B). The presence of H. defensa orR. insecticola did not prevent aphid acquisition of APV. The second assay tested whether A. ervi could horizontally transmit APV by first ovipositing into +APV aphids without facultative symbionts and then being allowed to oviposit into three -APV aphids with or without H. defensa .
Only 3 of the 48 (6%) recipient aphids were infected: two ND18 aphids that had no facultative symbionts and one ND18.H3 aphid hosting H. defensa/ APSE3 (Table S3). We also noted the order of attack (1-3) in recipient aphids which showed that each of the aphids that were infected by a wasp were first in the order of attack.