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Wolbachia Bacteria: Manipulators of Sex and Survival in Insects
Context: Researchers from Shenyang Agricultural University found that Wolbachia bacteria caused the wasp Encarsia formosa to completely eliminate males, as reported in Current Biology.
Key Highlights
- A century ago, American researchers discovered bacteria within mosquitoes‘ cells, later identified in most insects and many other arthropods.
- These bacteria were classified under the genus Wolbachia.
- The bacteria reside in insect eggs but not in sperm, allowing females to transmit them to offspring, while males cannot.
- This bias manipulates their hosts, favouring the production of more female progeny to ensure their transmission and survival.
- The tra gene is universally present in insects promoting female development by producing the Tra protein. Mutations in tra prevent the production of functional Tra protein, leading to default male development in progeny.
- They discovered that the Wolbachia bacteria within the wasp’s genome possessed a functional tra gene, acquired through horizontal gene transfer from beetles (order Coleoptera).
The Wasp and Its Bacterial Partner
- Encarsia formosa, commonly known as the “farmer-friendly Amazon,” is a parasitoid wasp belonging to the order Hymenoptera. It plays a crucial role in biological pest control.
- These wasps efficiently target whiteflies, which feed on plant sap and cause significant agricultural losses.
- The female wasp lays her eggs on whitefly nymphs (larvae), and her progeny emerges from the nymph’s carcass after feeding on its tissues.
Mechanism of Manipulation: The exact method by which Wolbachia doubles the chromosome number in unfertilised eggs is still unclear.
- Hymenopteran Sex Determination: In wasps, bees, and ants, males develop from unfertilised eggs (haploid) while females develop from fertilised eggs (diploid).
- Wolbachia’s Role: This bacteria is responsible for doubling the chromosome number in unfertilised eggs of the Encarsia formosa wasp, causing them to develop into females.
- Antibiotic Experiment: Treatment with antibiotics such as tetracycline reduces Wolbachia levels, resulting in the production of male offspring.
Implications
- Males produced after antibiotic treatment by SAU researchers did not mate or inseminate females.
- This suggests they may have lost mating ability due to long absence in Encarsia formosa populations or as an unintended effect of antibiotics.
- If no sexual exchange is possible, Encarsia formosa may lose its ability to eliminate harmful mutations from its genome, potentially resulting in the early extinction of the species due to genetic stasis facilitated by Wolbachia.
About Wolbachia Bacteria
- It is a common bacteria in insects, harmless to humans and animals (for example, fish, birds, pets).
- Approximately 6 in 10 of all insects, including butterflies, bees, and beetles, around the world have Wolbachia.
- Aedes aegypti mosquitoes, carriers of dengue, Zika, and chikungunya, do not naturally have Wolbachia.
- Scientists introduce Wolbachia into Aedes aegypti mosquitoes to reduce their population.
- Effectiveness: Communities in Texas and California, as well as countries like Singapore, Thailand, Mexico, and Australia, have successfully reduced populations of Aedes aegypti mosquitoes.
- Targeted Control: Specifically target Aedes aegypti mosquitoes and do not affect other mosquito species.
- The United States, by the Environmental Protection Agency (EPA) regulates the use of mosquitoes with Wolbachia.