Psyllid endosymbionts exhibit patterns of co-speciation with hosts and destabilizing substitutions in ribosomal RNA.

Eubacterial 16S rDNAs were sequenced from endosymbionts of seven psyllids (Psylloidea) and one whitefly (Aleyrodoidea), to investigate the evolution of endosymbionts and their hosts. Primary endosymbionts from all psyllids formed a highly supported clade, tentatively placed as the sister to whitefly primary endosymbionts, and showing several points of congruence with the host morphological phylogeny. Almost all host taxa yielded an additional eubacterial sequence, related either to known psyllid secondary endosymbionts or to other insect endosymbionts or parasites. The relationships of some secondary endosymbionts also suggested cospeciation with psyllid hosts, or ancient horizontal transfers. All primary endosymbionts, and some secondary endosymbionts, exhibited molecular genetic effects of a long-term, intracellular existence in their biased nucleotide content and decreased stability of rRNA secondary structure.