Host genotype-endosymbiont associations and their relationship with aphid parasitism at the field level.
The relationship between endosymbionts and insects represent complex eco-evolutionary interactions. Vertically transmitted endosymbionts can be a source of evolutionary novelty by conferring ecologically important traits to their insect hosts, such as protection against natural enemies. Host-endosymbiont associations could constitute an adaptive complex (holobiont) on which selective pressures present in the environment can act, being transferred to the next generation. Although several laboratory-based studies have confirmed host genotype × symbiont interactions, few studies have been directed at those associations in the natural populations and their ability to protect themselves from parasitism pressure at the field level. A field-based approach to study the aphid genotype-endosymbiont associations and its relationship with the total parasitism in the grain aphid Sitobion avenae was conducted. From the field study, experiments were carried out to study the defensive effect of the two most common facultative endosymbionts (Regiella insecticola and Hamiltonella defensa) present in S. avenae against one of the most important parasitoid species, Aphidius ervi. Evidence is presented here of a high specificity of the aphid clone-endosymbiont associations in the field; however, the field and experimental results here do not support a relationship between the aphid clone-endosymbiont associations and a proxy of total parasitism in S. avenae. These findings highlight the importance of particular host clone-endosymbiont couplings as a key factor in gaining an understanding of the coevolutionary dynamics of endosymbionts in nature and their effect on the invasive potential of pest insects.