Diversity and ecology of bacteriocyte-associated symbionts in adelgids (Hemiptera: Adelgidae)
Symbioses between bacteria and insects are widespread in nature. Estimated ten percent of all insects harbour bacteriocyte-associated symbionts in their body cavity. These heritable symbionts provide essential nutrients, which are absent in the hosts' diet; therefore, they are often essential for their host insect. Adelgids (Insecta: Hemiptera: Adelgidae), members of a relatively small insect family (~ 65 described species), contain species that represent severe pests for the forest ecosystem.
... he adelgids are a sister group of the phloem-feeding aphids, which often harbour one single obligate symbionts called Buchnera aphidicola. Knowledge about adelgids bacteriocyte-associated symbionts is still scarce and thus the adelgid/symbiont association was examined in this thesis. Adelgids harbour various vertically transmitted bacteriocyte-associated symbionts that belong either to Gammaproteobacteria or Betaproteobacteria. Interestingly, none of the newly found symbionts is directly related to B. aphidicola or other symbionts of insects. Based on phylogenetic and genome analyses, these relationships represent relatively recent symbiotic associations. Co-evolution between symbiont and host, and symbiont replacements were identified that define this symbiosis. Hence, adelgids acquired their own symbionts during evolution after the separation from their aphid sister group. Future studies of adelgid symbionts diversity and their genomes will bring a deeper understanding of this symbiosis. The insect family Adelgidae could serve as a case study for symbiont replacement and multiple acquisition events.