Characterization of Wolbachia infecting Pentalonia aphids

Wolbachia (alpha-Proteobacteria) is an obligate intracellular symbiont known to infect more than 65% of insect species. In this study, we examined the prevalence and evolution of Wolbachia infecting aphids in the genus Pentalonia across the Hawaiian islands. A total of 260 colonies of Pentalonia nigronevosa and P. caladii aphids were collected on various host plants (Banana, Heliconia, Taro, Ginger) across the islands of Kauai, Oahu, Maui, Molokai, and Hawaii. Samples of Pentalonia aphids from India and Australia were also obtained through collaborative efforts. Diagnostic PCR was performed using Wolbachia specific primers for 16S, ftsZ and gatB genes to determine the infection frequencies for Wolbachia. Multilocus Sequence Typing system (MLST) was used to identify and characterize the Wolbachia strains. Infection rates among the field-collected colonies of P. nigronevosa and P. caladii were similar and averaged at 85% and 81%, respectively. Wolbachia was also detected in P. nigronevosa samples from Australia and India, demonstrating that infections are not restricted to Hawaii. MLST analyses revealed that a single strain of Wolbachia (wPe) globally colonize Pentalonia aphids. Phylogenetic analyses of the 16S rRNA and MLST gene sequences shows wPe being highly diverged from lineages that infect nematodes and several other arthropods. The large divergence with the extant lineages suggests that wPe may be part of a novel supergroup. Wolbachia is generally regarded as a reproductive manipulator inducing parthenogenesis, feminization, male killing and, cytoplasmic incompatibility. However, since aphids in subtropical and tropical regions tend to reproduce exclusively partenogenetically, it is concivable that Wolbachia spread into these hosts by providing them with net fitness benefits.