Penetrance during Wolbachia‐mediated parthenogenesis of Trichogramma wasps is reduced by continuous oviposition, associated with exhaustion of Wolbachia titers in ovary and offspring eggs

Abstract

BACKGROUND: Thelytokous Wolbachia-infected Trichogramma wasps are superior to bisexual uninfected wasps regarding biological control programs. However, continuous oviposition weakens the parthenogenesis-inducing (PI) strength of Wolbachia. Whether this reduced PI strength relates to decreases in the titer of Wolbachia in the ovary and offspring eggs of Trichogramma remains unclear. Here, using fluorescence in situ hybridization (FISH) and reverse transcription quantitative polymerase chain reaction (RT-qPCR) methods, we investigated how the penetrance of Wolbachia-mediated parthenogenesis, Wolbachia density, and distributions of two Wolbachia-infected Trichogramma species, T. pretiosum (TP) and T. dendrolimi (TD), were influenced by different host access treatments [newly-emerged virgin females (NE), 7-day-old females without access to host eggs (NAH), and 7-day-old virgin females with access to host eggs (AH)].RESULTS: Continuous oviposition decreased Wolbachia PI strength and titers in TP and TD. Continuous oviposition in AH decreased Wolbachia titers in abdomen and offspring eggs of TP and TD females, compared with NAH and NE; NAH had a lower thorax Wolbachia titer than NE. The numbers of parasitized host eggs and offspring wasps, and emergence rates of offspring deposited by AH were lower than those of NE and NAH, for either species.CONCLUSION: Weakened PI strength, driven by continuous oviposition in Trichogramma wasps, is associated with Wolbachia titer exhaustion in ovary and offspring eggs. Wolbachia density is dependent on PI strength in Trichogramma wasps, highlighting the side effects of continuous oviposition regarding thelytokous Wolbachia-infected Trichogramma in biological control programs.

Wolbachia -Driven Memory Loss in a Parasitic Wasp Increases Superparasitism to Enhance Horizontal Transmission

“…It is worth noting that Wolbachia signals in adult heads were weak. Similarly, our previous study also found that Wolbachia density was low in the heads of Trichogramma pretiosum and T. dendrolimi based on qPCR and Fish detection ( 39 ). Though Wolbachia signals were weak in adult heads, we still detected a significant downregulation of memory-related gene expression in infected adults compared with their uninfected counterparts.…”

Posterior concentration of Wolbachia during the early embryogenesis of the host dynamically shapes the tissue tropism of Wolbachia in host Trichogramma wasps

“…However, no Wolbachia signals were detected in the heads of pupal or adult T. dendrolimi and T. pretiosum . Our previous study revealed that Wolbachia infection caused memory loss, increased the incidence of superparasitism, and attenuated the host discrimination mechanism in T. dendrolimi ( Zhou et al., 2022a ). Though the Wolbachia titers in the heads of Trichogramma adults were low, the endosymbiont nonetheless caused behavioral changes in the wasps.…”

“…The PI strength in Trichogramma wasps is strongly influenced by Wolbachia density in the germ line and eggs. Previous studies showed that weak PI strength is often associated with biotic (e.g., continuous oviposition) or abiotic (e.g., high temperature) factors that can affect the transmission rate of Wolbachia ( Zhou et al., 2022a ; Guo et al., 2023 ). The unstable PI strength of Wolbachia -infected Trichogramma can impact the quality of Trichogramma offspring and their efficacy in pest control.…”

“…FISH was conducted to detect Wolbachia signals in the early embryo (30, 50, 60, 70, 90, and 120 min) and at various developmental stages (24 h (late embryo), 48 h (larva), 72 h (larva), 120 h (pre-pupa), 168 h (pupa), and 240 h (adult)) of T. dendrolimi and T. pretiosum according to previously described procedures ( Zhou et al., 2022a ; Zhou et al., 2023 ). An egg card containing ~300 host eggs was introduced into a Durham’s tube (30 mm in length × 6 mm in diameter) and could be parasitized by ~500 T. dendrolimi or T. pretiosum females within 5 min.…”

“…Wolbachia can induce thelytokous parthenogenesis in certain parasitoid wasps, such as Trichogramma spp. ( Huigens et al., 2000 ; Zhou et al., 2022a ; Zhou et al., 2023 ). Thelytokous parthenogenesis, also known as female-producing parthenogenesis, is defined as the production of female offspring without genetic contribution from paternal males ( Ma and Schwander, 2017 ).…”