APV infection does not alter symbiont-mediated protection
against other mortality agents: We next examined whether the protective
effects of R. insecticola against P. neophidis or H.
defensa against A. ervi were also influenced by virus
co-infection. Results strongly indicated the protective effects ofR. insecticola against P. neophidis were not reduced by
APV infection as measured by much higher aphid survival and lower fungal
sporulation when compared to aphids without R. insecticola (Fig
2A, B, Table S4). However, APV infection of aphids without R.
insecticola, resulted in lower survival and higher fungal sporulation
rates than infection with P. neophidis alone (Fig. 2A-C). The
high-level protective effects of H. defensa /APSE-3 (ND18.H3) and
moderate protective effects of H. defensa /APSE-2 (5D-AB.H2)
against A. ervi were also not lowered by APV infection (Fig.
2D-I; Table S5). For aphid lines without facultative symbionts, aphid
survival was very low, while successful wasp development (mummification)
was high, but these did not generally differ between APV positive and
negative lines (Fig. 2D-I; Fig S1; Table S5). The one exception to this
latter trend was the WI246-8 line, which produced fewer mummies if
infected with APV (W1246-8+APV) but this outcome was also associated
with more aphids dying while also not producing a parasitoid (dual
mortality) rather than an increase in aphid survival (Table S5; Fig.
S1E, F).
Since parasitoid fitness is known to be influenced by host quality, we
also examined whether A. ervi developing in hosts infected by APV
exhibited reduced fitness by estimating the size of emerging female wasp
offspring. We found that smaller female A. ervi were produced
from APV-infected aphids in three of the four assayed aphid lines that
lacked facultative symbionts (Table 4A, B). We did not measure the size
of emerging wasps from aphids hosting H. defensa /APSE-3 because
very few mummies were produced due to the high level of protection this
strain confers. However, we did measure the size of female wasp
offspring that developed in aphids hosting H. defensa /APSE-2.
Interestingly, no differences were detected between the size of wasps
that emerged from aphids with H. defensa/ APSE-2 that were
persistently infected with APV versus aphids that were not virus
infected (Table 4B).