Wolbachia Titers Are Relate to Sex Determination of Trichogramma Pretiosum

Once infected with parthenogenesis inducing (PI) Wolbachia, the reproductive mode of Trichogramma pretiosum would change from bisexual to thelytokous parthenogenesis; however, male offspring would also appear after maternal females’ continuous massive oviposition. Whether there was a relationship between Wolbachia titer and sex determination in T. pretiosum was unclear. In this study, we compared the sex ratio of the offspring of parthenogenetic and bisexual restored lines of T. pretiosum, and measured the Wolbachia titer in parthenogenetic line of T. pretiosum before and after oviposition, in different body parts, as well as at different developmental stages. Results indicated that all the offspring produced by parthenogenetic line females on the 1st day of egg-laying were females, and male offspring were gradually appearing with the increase of females’ oviposition age; but the male offspring began to appear on the 1st egg-laying day of bisexual restored line. After oviposition, Wolbachia titer in maternal female of parthenogenetic line was maintained at a lower level compared to those of pre-oviposition females. QRT-PCR results showed that Wolbachia in male offspring was significantly lower than that in female ones; and Wolbachia could be detected in all body parts of female parasitoids, and the titer was highest in abdomen. At different developmental stages, relative Wolbachia titer was higher in eggs and adults than other stages, and the Wolbachia titer in ovaries post-oviposition was significantly lower than that of pre-oviposition. In conclusion, Wolbachia titer is closely related to the sex determination of T. pretiosum.