Phylogenetic relationships of the endosymbionts of mealybugs (Homoptera: Pseudococcidae) based on 16S rDNA sequences. 
A portion of the gene coding for the 16S ribosomal RNA from the endosymbionts of three species of mealybugs [Pseudococcus longispinus (Targioni-Tozzetti), Pseudococcus maritimus (Ehrhorn), and Dysmicoccus neobrevipes (Beardsley)] was cloned, sequenced, and compared to a homologous fragment from bacteria representative of aphid endosymbionts as well as major subdivisions of the Proteobacteria.  Parsimony analysis of the sequences indicated that the mealybug endosymbionts are related and belong to the beta-subdivision; in contrast, previous studies showed that aphid endosymbionts are part of the gamma-subdivision.  These findings suggest that the endosymbiosis of mealybugs is a consequence of a single bacterial infection and indicate that this ancestor was different from the ancestor involved in aphid endosymbiosis.