ABSTRACT
Bacterial endosymbionts of the pine bark adelgid,
Pineus strobi
(Insecta: Hemiptera: Adelgidae), were investigated using transmission electron microscopy, 16S and 23S rRNA-based phylogeny, and fluorescence
in situ
hybridization. Two morphologically different symbionts affiliated with the
Gammaproteobacteria
were present in distinct bacteriocytes. One of them (“
Candidatus
Annandia pinicola”) is most closely related to an endosymbiont of
Adelges tsugae
, suggesting that they originate from a lineage already present in ancient adelgids before the hosts diversified into the two major clades,
Adelges
and
Pineus
. The other
P. strobi
symbiont (“
Candidatus
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.