Wolbachia-density variation in weevils of the tribe Naupactini (Coleoptera, Curculionidae)

The intracellular bacteria Wolbachia pipientis infects arthropods and filarial nematodes and is able to manipulate host reproduction. It has been reported an association between parthenogenesis and Wolbachia infection in weevils from the tribe Naupactini. A curing experiment suggested that a threshold density of Wolbachia is required for parthenogenetic reproduction to occur. The aim of this study was to analyze Wolbachia infection status and density in two sexually reproducing species from the tribe Naupactini, Naupactus xanthographus and Naupactus dissimulator. Wolbachia infection was detected in individuals from both species in several geographic locations, not being fixed. Quantification through real time PCR confirmed that Wolbachia loads in sexual species were significantly lower than in parthenogenetic ones; these results support the hypothesis of a threshold level for parthenogenetic reproduction to occur in Naupactini weevils. Strain typing showed that both sexual species carry wNau1, the most frequent strain in parthenogenetic Naupactini weevils. In addition, the presence of the WO phage, which might be an important factor regulating infection density in some hosts, was detected in this strain. Finally, Wolbachia wNau1 was located throughout the whole insect body, which is in agreement with the idea of a recent acquisition by horizontal transfer of wNau1 across the tribe Naupactini.