No evidence for an effect of Wolbachia on mtDNA variation and evolution in natural populations of Sesamia inferens(Lepidoptera: Noctuidae)

Wolbachia are widespread maternally-inherited endosymbiotic bacteria that infect numerous arthropods. This study represents a thorough survey of the Wolbachia infection patterns in the pink stem borer, Sesamia inferens (Walker), an important rice pest in China, based on nucleotide comparisons for the surface protein (wsp) and cell division protein (ftsZ) genes. The effects of Wolbachia on mtDNA variation and evolution of S. inferens were also investigated. Although we identified six genetically diverse strains, we found infections to be infrequent, with only 7.8% of hosts infected, and identified geographical differences in infection rates between southern and northern populations. Nucleotide indexes (haplotype diversity (Hd), nucleotide diversity (Π) and number of variable sites (S) of mtDNA in infected populations were not significantly lower or higher than that in the uninfected populations. Furthermore, there was no association between Wolbachia infection status and phylogeny of mtDNA haplotypes. Analysis of molecular variance (AMOVA) showed that significant differentiation mainly existed within groups rather than among the groups. Additionally, using Tajima's D and Fu's F values, the mtDNA genes did not deviate significantly from neutral evolution. Taken together these results indicate that currently there were no effects of Wolbachia infection on host mtDNA variation and evolution in S. inferens.