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.