IntroductionThe bacterial endosymbiont,Wolbachiaspp. induce thelytokous parthenogenesis in certain parasitoid wasps, such as the egg parasitoid waspsTrichogrammaspp. To complete the cycle of vertical transmission,Wolbachiadisplays efficient transovarial transmission by targeting the reproductive tissues and often exhibits strong tissue-specific tropism in their host.MethodThe present study aimed to describe the basicWolbachiadistribution patterns that occur during the development ofWolbachia-infected, thelytokousTrichogramma dendrolimi, andT. pretiosum. We used fluorescencein situhybridization (FISH) to investigateWolbachiasignal dynamics during early embryogenesis (from 30 to 120 min).Wolbachiatiters and distributions from the embryo to adult stages ofTrichogrammaafter early embryogenesis were detected by absolute quantitative polymerase chain reaction (AQ-PCR) and FISH. The symmetry ratios (SR) of theWolbachiasignals were calculated using the SR odds ratios in the anterior and posterior parts of the host. The SR was determined to describeWolbachiatropism during early embryogenesis and various developmental stages ofTrichogramma.ResultsWolbachiawas concentrated in the posterior part of the embryo during early embryogenesis and the various developmental stages of bothT. dendrolimiandT. pretiosum.Wolbachiadensity increased with the number of nuclei and the initial mitotic division frequency during early embryogenesis. The totalWolbachiatiter increased with postembryogenesis development in bothT. dendrolimiandT. pretiosum. However, theWolbachiadensities relative to body size were significantly lower at the adult and pupal stages than they were at the embryonic stage.DiscussionThe present work revealed that posteriorWolbachiaconcentration during early host embryogenesis determinedWolbachialocalization in adult wasps. By this mechanism,Wolbachiaexhibits efficient vertical transmission across generations by depositing only femaleWolbachia-infected offspring. The results of this study describe the dynamics ofWolbachiaduring the development of theirTrichogrammahost. The findings of this investigation helped clarifyWolbachiatropism inTrichogrammawasps.