R. insecticola reduces fitness costs associated with APV infection while H. defensa increases costs: Across all five aphid genotypes, lifetime fecundity assays showed that APV-infected aphids without facultative symbionts produce fewer progeny than non-infected aphids (Table 3). APV infection also reduced aphid longevity in all genotypes except WI576N-27 (Table 3B). Since R. insecticola and H. defensa confer protection against specialized fungi and parasitoids (Scarborough et al. 2005, Parker et al. 2013), we next asked if either affected the fitness costs associated with APV infection. We found that aphids hosting R. insecticola(genotype LSR1) produced far more offspring and lived longer than control lines without R. insecticola when infected by APV (Table 3C). The cumulative fecundity of the R. insecticola subline with a persistent APV infection was nearly identical to that of the R. insecticola subline without APV. In the absence of APV, we did not observe significant reductions in fecundity or longevity in aphids of harboring R. insecticola compared to symbiont-free controls (Table 3C).
In contrast to R. insecticola , aphids hosting H. defensa /APSE-3 (ND18.H3) or H. defensa /APSE-2 (5D-AB.H2) exhibited even larger reductions in fecundity and longevity relative to those with only APV infection (Table 3D, E). Thus, R. insecticolareduced the fitness costs of APV infection while H. defensaincreased them. In the absence of APV, both H. defensa lines exhibited reductions in fecundity and longevity when compared to controls without facultative symbionts (Table 3D, E).