Two kinds of sex ratio distorters in a moth, Ostrinia scapulalis.

We surveyed female-biased sex ratio traits (SR traits) in a moth, Ostrinia scapulalis (Lepidoptera: Crambidae) from six geographic locations in Japan. A small proportion (8.3%) of females showed the SR trait. About half of them were associated with a Wolbachia infection (SRw+), whereas the remaining ones were not (SRw-). No significant differences in frequencies were detected among locations and years for either SRw+ or SRw- females. In SRw+ matrilines, the SR trait was inherited. Curing the Wolbachia infection by tetracycline at the larval stages resulted in all-male broods in the next generation. These characteristics were identical to the Wolbachia-induced SR trait observed previously in the related species Ostrinia furnacalis. The Wolbachia strain in O. scapulalis was indistinguishable from that in O. furnacalis in terms of the wsp and ftsZ gene sequences, suggesting either that infection originated from a common ancestor of the two hosts or that Wolbachia was transmitted horizontally between the host species. In SRw- matrilines, on the other hand, the SR trait was not due to bacterial infection but some other maternally inherited element, since antibiotic treatment had no effect and bacterial PCR did not give the characteristic product. In these matrilines, the SR trait occasionally failed to show, suggesting the presence of nuclear factor(s) suppressing the SR trait.