Bacterial endosymbionts of the pine bark adelgid,
(Insecta: Hemiptera: Adelgidae), were investigated using transmission electron microscopy, 16S and 23S rRNA-based phylogeny, and fluorescence
hybridization. Two morphologically different symbionts affiliated with the
were present in distinct bacteriocytes. One of them (“
Annandia pinicola”) is most closely related to an endosymbiont of
, suggesting that they originate from a lineage already present in ancient adelgids before the hosts diversified into the two major clades,
. The other
Hartigia pinicola”) represents a novel symbiont lineage in members of the Adelgidae. Our findings lend further support for a complex evolutionary history of the association of adelgids with a phylogenetically diverse set of bacterial symbionts.