Sources of protection against a parasitoid wasp: Are symbiont-based and aphid encoded resistance additive?

There are several Hamiltonella defensa-APSE (Bacteria-bacteriophage) strains which are known to confer varying levels of protection to the pea aphid (Acyrthosiphon pisum) against parasitism by the aphidiine braconid (Aphidius ervi). The only two APSE variants found in North America are APSE2 and APSE3. Based on previous research, APSE2s confer moderate levels of protection and APSE3s confer high levels of protection. However, I have recently found that multiple pea aphid clonal lines are resistant to parasitism in the absence of secondary symbionts, nevertheless, these resistant genotypes may also maintain infection with H. defensa. The goal of this study, is to examine the interaction between aphid-based and H. defensa-conferred resistance, which could be additive or redundant and thus provide either additional benefits or possible added costs with no extra benefits. I recently reported a second APSE-2 type that conferred no protection beyond that of a moderately resistant aphid background, suggesting redundancy. This study will examine the effects of multiple H. defensa-APSE strains in multiple aphid backgrounds (known to be resistant or susceptible) and determine the resistance phenotypes associated with both types of protection.