Phylogenetic position of yeast-like symbiont of Hamiltonaphis styraci (Homoptera, Aphididae) based on 18S rDNA sequence.

Almost all aphids harbor bacterial intracellular symbionts in mycetocytes. However, some Cerataphidini aphids do not harbor them but possess yeast-like extracellular symbionts in the abdominal hemocoel, suggesting that in a lineage of this group replacement of symbiont occurred from an intracellular bacterium to an extracellular fungus. To investigate the origin of the newly-acquired symbiont, the 18S rDNA sequence of the yeast-like symbiont of Hamiltonaphis styraci was determined by PCR direct sequencing. Molecular phylogenetic analyses indicated that the symbiont belongs to the subphylum Ascomycotina, the class Pyrenomycetes. It was also suggested that the yeast-like symbiont of H. styraci and that of planthoppers are phylogenetically very closely related to each other.