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Many insects harbour facultative endosymbiotic bacteria, often more than one type at a time. These symbionts can have major effects on their hosts' biology, which may be modulated by the presence of other symbiont species and by the host's genetic background. We investigated these effects by transferring two sets of facultative endosymbionts (one Hamiltonella and Rickettsia, the other Hamiltonella and Spiroplasma) from naturally double-infected pea aphid hosts into five novel host genotypes of two aphid species. The symbionts were transferred either together or separately. We then measured aphid fecundity and susceptibility to an entomopathogenic fungus. The pathogen-protective phenotype conferred by the symbionts Rickettsia and Spiroplasma varied among host genotypes, but was not influenced by co-infection with Hamiltonella. Fecundity varied across single and double infections and between symbiont types, aphid genotypes and species. Some host genotypes benefit from harbouring more than one symbiont type.

Original publication




Journal article


J Evol Biol

Publication Date





2654 - 2661


Acyrthosiphon pisum, Pandora neoaphidis, Sitobion avenae, endosymbiosis, inclusive fitness, resistance, secondary symbiont, Animals, Aphids, Fungi, Genotype, Host-Pathogen Interactions, Rickettsia, Spiroplasma, Symbiosis