Decreased Wolbachia titers cause gradual change in masculinization of intersex individuals of thelytokous Trichogramma dendrolimi

Intersex is defined as sexually aberrant individuals composed of a single sexual genotype that simultaneously displays female and male characteristics. The occurrence of intersex individuals in egg parasitoids, Trichogramma spp., is often associated with the symbiotic bacteria, Wolbachia, which induce thelytokous parthenogenesis of Trichogramma. It is still unclear whether intersex was caused by the reduced Wolbachia titer, effects of abiotic factors, or interactions between abiotic factors and Wolbachia. To answer this question, the females of Wolbachia-infected (TDW) and uninfected (TD) Trichogramma dendrolimi were treated using different tetracycline or rifampicin concentrations. The results showed that the proportion of intersexes or males of TDW offspring significantly increased as the concentration of both antibiot- ics increased; however, they did not occur without antibiotics. Occurrence of intersex was not observed in TD offspring. Twelve types of intersex were found and categorized by masculinization levels. The masculinized level of offspring inter sex increased with tetracycline but not with rifampicin. Wolbachia titers of maternal TDW females significantly decreased with higher antibiotics concentrations. Wolbachia titers of intersex offspring were higher than offspring males, lower than offspring females, and negatively correlated with masculinized level of offspring intersex. The results revealed that the frequency and masculinized level of offspring intersex is quantitatively dependent on Wolbachia titer. Our findings provide an insight into the interaction of Wolbachia titers on the sex determination of Trichogramma.

Automated summary

Intersex is a sexually aberrant condition in which individuals display both female and male characteristics. This study investigates the causes of intersex occurrence in Trichogramma spp. egg parasitoids and finds that it is closely related to the symbiotic bacteria, Wolbachia. The study reveals that the frequency and masculinized level of offspring intersex in Trichogramma are quantitatively dependent on the Wolbachia titer.