Multilocus Sequence Typing Of Wolbachia Endosymbionts In The Rice Water Weevil, Lissorhoptrus Oryzophilus Kusche And Their Effects On Host Reproduction

Wolbachia endosymbionts are obligate intracellular bacteria of arthropods and filarial nematodes, which can cause a number of reproductive modifications in their hosts, such as cytoplasmic incompatibility, parthenogenesis, feminization and male killing. The rice water weevil (RWW), Lissorhoptrus oryzophilus Kuschel (Coleoptera, Curculionidae) is an alien insect species in China. This weevil reproduces bisexually in native regions, but parthenogenetically in all of invaded regions. Previous studies revealed that this weevil was infected with supergroup-B Wolbachia, based upon the detection and phylogenetic analysis using a single wsp or 16S rRNA gene. However, it is not clear whether there exist superinfections in this weevil. In this study, Wolbachia in different L. oryzophilus populations was detected, and characterized by multilocus sequence typing (MLST) which is a more reliable approach for phylogenetic analysis compared to the method based on a single gene. Moreover, effects of Wolbachia on the reproduction of parthenogenetic L. oryzophilus were examined by subjecting weevils to antibiotic treatments. The results were summarized as follows:We detected a total of 103 adult rice water weevils from seven invasive parthenogenetic populations in China and one native bisexual population in Beaumont, Texas, USA for the Wolbachia infection. All of the weevil samples were found to be positive based on the PCR amplification by using wsp gene-specific primers, indicating that each weevil population was infected by Wolbachia at a frequency of 100%. Each population was infected by a singe Wolbachia strain. All of the Wolbachia isolates from the weevils of China had the absolutely same MLST genes, but they were evidently divergent from the isolate from weevils of native population. It implies that the Wolbachia in native and invasive L. oryzophilus may have different origins.We reared parthenogenetic weevils on the young rice plants provided with antibiotic solutions, which were supposed to be absorbed by roots and transported to leave blades and then taken by weevils feeding. Tetracycline treatment (able to delete Wolbachia) strongly reduced number of deposited eggs, and no egg could hatch in this treatment. In comparison, fecundity and egg viability were similar between the gentamicin (has the same action mode as tetracycline against bacteria but has no effect on Wolbachia) and water treatments, with the egg hatchability reached nearly 80% in both treatments. It can be concluded that Wolbachia have some critical functions in the reproduction of parthenogenetic rice water weevils.