Facultative 'secondary' bacterial symbionts and the nutrition of the pea aphid, Acyrthosiphon pisum

Abstract.  Facultative 'secondary' bacterial symbionts influence various traits of aphids, including plant utilization patterns and resistance to parasitoids. The present study is designed to test the hypothesis that these multiple effects are underlain by symbiont-mediated changes to the aphid requirement for the dominant dietary nutrients, sucrose and amino acids. The performance of pea aphids ( Acyrthosiphon pisum ) on chemically defined diets of systematically altered sucrose and amino acid content varies among eight parthenogenetic clones, with a pattern that does not match the aphid complements of secondary symbionts, Hamiltonella defensa , Regiella insecticola and Serratia symbiotica . Aphid performance is reduced, increased and unaffected by elimination of S. symbiotica , R. insecticola and H. defensa , respectively, but with no significant effect on the range of diets on which aphids performed well. It is concluded that the impact of secondary symbionts on aphid traits is most unlikely to have a purely nutritional basis.