Curing Parthenogenesis-Inducing (PI) Wolbachia-Induced Reproductive Disorders in the Egg Parasitoid Telenomus remus

TL;DR

Scientists cured a parasitic wasp of a bacteria that alters its reproduction and found that cured wasps can reproduce normally but face breeding barriers with uninfected wasps.

Contribution

The study demonstrates reproductive incompatibility between cured and uninfected wasp populations, which has implications for biological pest control.

Findings

Cured wasps retained normal sexual reproduction but showed strong male-biased offspring when crossed with uninfected wasps.

Second-generation hybrids showed partially recovered sex ratios, suggesting genetic divergence rather than permanent damage.

The findings highlight the importance of evaluating reproductive barriers before using cured wasp populations in pest control.

Abstract

Certain bacteria live inside insects and can dramatically alter how they reproduce. One such bacterium, called Wolbachia, infects a tiny parasitic wasp (Telenomus remus) that naturally controls fall armyworm, a destructive crop pest. This bacterium causes infected female wasps to produce only female offspring without mating, which could be advantageous for pest control programs that rely on female wasps to attack pest eggs. However, previous studies on related wasp species suggested that long-term infection may permanently damage the wasps’ ability to reproduce normally. We removed the bacterium using antibiotics and tested whether cured wasps could still mate and produce offspring normally. While cured wasps reproduced normally among themselves, crosses between cured and naturally uninfected wasps produced almost exclusively male offspring, indicating a breeding barrier between these two populations. Importantly, this barrier partially disappeared in the next generation, suggesting it results from genetic differences accumulated during their separate evolutionary histories rather than permanent reproductive damage. These findings are valuable for agricultural pest management because they reveal that mixing wasp populations with different infection histories may cause unexpected breeding problems, potentially undermining biological control efforts against crop pests.

Wolbachia is an endosymbiotic bacterium widespread in invertebrates that causes various reproductive effects, including cytoplasmic incompatibility, feminization, male killing, and the induction of parthenogenesis (PI). PI-Wolbachia wRem converts Telenomus remus, an egg parasitoid of Spodoptera frugiperda, from arrhenotokous reproduction (male-producing) to thelytokous reproduction (female-producing). Long-term symbiosis between egg parasitoids and Wolbachia has been shown to lead to reproductive barriers and “female functional virginity,” causing progressive and potentially irreversible sex ratio imbalances. However, whether such reproductive barriers occur in T. remus remains unknown, which has important implications for biological control programs utilizing this parasitoid. To address this question, we cured wRem using tetracycline and conducted crossing experiments with naturally uninfected strains (W-). The results indicated that the cured strain (Wcure) retained normal sexual reproductive capability, with self-crossing fertilization rates comparable to those of W- strains. However, first-generation hybridization between Wcure and W- strains produced strongly male-biased offspring (male proportion: 94.3% and 85.8% for W-♂ × Wcure♀ and Wcure♂ × W-♀, respectively), indicating substantial reproductive incompatibility. Notably, an asymmetric pattern was observed between reciprocal crosses. In second-generation hybridization experiments, hybrid females (W-/Wcure) mated with W- or Wcure males showed markedly recovered sex ratios (male proportion: 14.3% and 15.6%, respectively), although total offspring numbers remained lower than in self-crossing groups. These results suggest that the reproductive incompatibility in T. remus differs from female functional virginity and is more consistent with mitonuclear incompatibility arising from population divergence. The partial recovery in second-generation hybrids indicates that surviving F1 hybrid females likely represent individuals selected for compatibility, rather than exhibiting progressive deterioration of sexual function. These findings offer insights into Wolbachia’s impact on parasitoid reproduction and highlight key considerations for biological control applications, underscoring the importance of evaluating reproductive barriers before deploying cured strains and preventing symbiont loss within populations.

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