Are competitive interactions between aphid clones mediated by facultative endosymbionts?

Bacterial endosymbionts are key components of aphid biology, as they modify several traits of their insect hosts. Here we studied how bacterial facultative endosymbionts affect the competitive interactions between aphid clones. To address this, we studied intraclonal and interclonal interactions between the two most common clones (G1 and G2) of the cereal aphid Sitobion avenae (Fabricius), including the role of the facultative endosymbiont Regiella insecticola in the outcome of these interactions in a shared host (wheat). The results of this study reveal significant variability in the population growth rates of aphid clones under competitive and non-competitive environments. That trade-off in competitive interactions among aphid clones can influence the dynamics of aphid populations and impact on plant growth and structure. While facultative endosymbionts like R. insecticola do not play a significant role in directly mediating the competitive interactions of aphid clones or affecting specific plant traits, their presence does enhance aphid performance. Aphids harbouring R. insecticola showed higher growth rates in various coexistence scenarios and across different clones with a concurrently reduced capacity to damage host plants, which suggests that R. insecticola produces ecologically relevant consequences for aphids in cereal fields.