A new study published by the researchers of the Shenyang Agricultural University (SAU)  in the journal Current Biology shows that Wolbachia bacteria had manipulated the wasp Encarsia formosa to entirely get rid of its males.

About Wolbachia

• Wolbachia are extremely common bacteria that occur naturally in 50 per cent of insect species, including some mosquitoes, fruit flies, moths, dragonflies and butterflies.
• Researchers from the World Mosquito Program have used mosquitoes infected with Wolbachia bacteria to successfully control dengue 

Discovery of Wolbachia

• Early Research (1920s): Marshall Hertig and Simeon Burt Wolbach discovered bacteria within mosquito cells. 
  • Later studies found similar bacteria in most insects, arthropods including some mosquitoes, fruit flies, moths, dragonflies and butterflies.
  • Naming of the Genus Wolbachia: The genus to which the bacteria belonged was named ‘Wolbachia’.

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Transmission Dynamics of Wolbachia

• Presence in Reproductive Cells: Wolbachia bacteria are present in insect eggs but absent in sperm.
• Transmission by Females: Females can transmit Wolbachia to their offspring, but males cannot. This from the bacteria’s point of view is an evolutionary dead-end.
• Sex Ratio Manipulation: As only Females can transmit Wolbachia to their offsprings, Wolbachia have evolved ways to manipulate their insect hosts to produce more female than male progeny.
• This ensures the bacteria’s continued transmission.

Importance of E. formosa Wasps

• Agricultural Significance: They help control whiteflies, which are major agricultural pests.
  • These wasps were among the world’s first agents of biological pest control. 
  • Whiteflies feed on plant sap, causing productivity losses.
• Biological Control Mechanism
  • The wasp seeks out the nymphs (or larvae) of whiteflies and lays its eggs on them.
  • When the eggs hatch, the larvae that emerge penetrate the nymph, feed on its tissues, grow to adulthood, and in the process kill the nymph.
• Female Wasps are effective hunters: Female wasps act as effective search and destroy weapons against whiteflies.
  • Male wasps are unnecessary for the parasitoid role.

Wolbachia Influence on Sex Ratio

• Natural Occurrence: In the wild, E. formosa wasps rarely produce males.
  • Chromosome Doubling: In the wild, Normal Wolbachia levels induce unfertilized eggs to double chromosome numbers, enabling female development.
  • Mechanism behind this process is currently unknown.
• Laboratory Discovery: Antibiotic treatment (e.g., tetracycline) reduces Wolbachia concentration and as a  result, approximately 70% of progeny are male.

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Wolbachia and Tra Gene 

• Evolutionary Conservation:
  • The tra gene is  evolutionarily conserved in insects and promotes female development.
  • Evolutionarily conserved’ means all insects have it.
  • If this gene is broken (mutated), the default is for males to be born instead of females.
• Discovery by SAU Researchers:
  • Researchers found that in E. formosa wasps, the tra gene was not complete—it was missing important parts.
  • But they discovered that the Wolbachia bacteria living inside these wasps had their own working version of the tra gene.
  • Even though the wasps’ own tra gene was not complete, they used the tra gene from Wolbachia.
  • This allowed the wasps to have female offspring.
• New Discovery:
  • This is the first time scientists have seen bacteria (Wolbachia) give a gene to an insect that helps it make females.
  • Normally, bacteria don’t have this kind of gene, so it’s a big discovery in how insects evolve and reproduce.

Observation by SAU Researchers

• Absence of Mating Behaviour in Treated Males: Males produced by the SAU researchers after antibiotic treatment did not engage in mating behaviour with females.
• Reason: Lack of mating behaviour could be due to prolonged absence from populations or unintended effects of antibiotic treatment.
  • Antibiotic treatment might have unintentionally affected their mating behaviour.
• Significance of Mating: Without males mating with females, the species loses the ability to exchange genetic material and remove harmful mutations.
  • This situation could lead to the potential extinction of the wasp-Wolbachia duo.
• Adaptive Strategies of Wolbachia:
  • The Wolbachia bacteria were shown to be smart enough to double the chromosome number in their host’s unfertilised eggs and to supply them with tra.
  • They also occasionally allow some males to mate, which could be crucial for delaying the extinction of the species.

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