UPSC Prelims 2023 Q67: Wolbachia Method — Explained

'Wolbachia method' is sometimes talked about with reference to which one of the following?

  1. Controlling the viral diseases spread by mosquitoes
  2. Converting crop residues into packing material
  3. Producing biodegradable plastics
  4. Producing biochar from thermo-chemical conversion of biomass

Answer: (a) Controlling the viral diseases spread by mosquitoes

Statement-wise explanation

  • a: correct — Wolbachia is a bacterium that lives inside insect cells. WHO says it occurs naturally in about 60% of common insects. In the Wolbachia method, scientists put the bacterium into Aedes aegypti mosquitoes and release them. Wolbachia makes it harder for the mosquito to pass on dengue, chikungunya and Zika viruses. In a 2017 trial in Yogyakarta, Indonesia (published in the New England Journal of Medicine, 2021), dengue cases fell by 77% and dengue hospitalisations by 86% where these mosquitoes were released.
  • b: incorrect — Crop residue such as paddy straw can be turned into moulded packaging, boards or pellets by mechanical and thermal processing. None of these processes is called the Wolbachia method. Wolbachia is an insect bacterium and has no role in processing crop residue.
  • c: incorrect — Biodegradable plastics such as PLA (polylactic acid) and PHA (polyhydroxyalkanoates) are made by fermenting sugars or starch with microbes, or by bacteria storing polymer inside their cells. Wolbachia cannot be used for this. It can only live inside host cells and cannot be grown in industrial fermenters.
  • d: incorrect — Biochar is made by pyrolysis: biomass is heated to roughly 300–700 °C with little or no oxygen. This is a thermo-chemical process and uses no living organism. A bacterial 'method' such as Wolbachia has nothing to do with it.

How to eliminate

Three of the options are about the same theme: turning biomass or waste into a product (packing material, plastic, biochar). Only one option is about disease control. That makes it the odd one out, and UPSC often places the answer there. The name 'Wolbachia' looks like a Latin genus name, which points to a living organism. That helps a little against biochar (pure thermo-chemistry) but not against bioplastics, which also use microbes. In the end you need the fact itself. Remember: Wolbachia is a bacterium put into Aedes aegypti mosquitoes to cut transmission of dengue, Zika and chikungunya. India's ICMR-Vector Control Research Centre in Puducherry has developed local Wolbachia mosquito lines with Monash University, Australia.

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How the Wolbachia method works

Wolbachia is an intracellular bacterium. WHO says it occurs naturally in about 60% of common insect species. The main dengue mosquito, Aedes aegypti, does not usually carry it. Scientists put it into mosquito eggs in the lab. Two things then help it spread through wild mosquitoes:

  • Maternal inheritance: an infected female passes Wolbachia to all her eggs.
  • Cytoplasmic incompatibility: when an infected male mates with an uninfected female, her eggs do not hatch. Infected females therefore leave more offspring, and the bacterium takes over the population.

Wolbachia also competes with viruses inside the mosquito. Dengue, Zika and chikungunya then replicate poorly, so the mosquito transmits them less.

Two strategies

Strategy Who is released Result
Population replacement (e.g. World Mosquito Program, wMel strain) Males and females Mosquitoes remain, but they transmit viruses poorly; the effect lasts on its own
Population suppression (incompatible insect technique) Males only Eggs do not hatch and mosquito numbers fall; releases must continue

How it differs from other vector-control tools

Tool Basis Genetic modification?
Wolbachia Natural bacterium No; the mosquito's DNA is unchanged
Sterile Insect Technique Males sterilised by radiation No
Self-limiting GM mosquitoes (e.g. Oxitec) Gene that kills offspring Yes
Insecticides, larvicides Chemicals Not applicable

Status: WHO's Vector Control Advisory Group concluded in 2020 that the replacement method had shown public-health impact. WHO set up a Guideline Development Group; it expects to issue formal recommendations in late 2027. In India, ICMR-VCRC Puducherry backcrossed Australian wMel and wAlbB Wolbachia mosquitoes with local Puducherry Ae. aegypti to create local lines. Wolbachia does not replace dengue vaccines. It cuts transmission, while vaccines reduce how severe the disease is.

In the news

In June 2021, a large randomised trial in Indonesia was published showing that Wolbachia mosquitoes cut dengue by 77%. In July 2022, ICMR-VCRC Puducherry announced Wolbachia-carrying Aedes aegypti lines adapted to Indian conditions for controlling dengue and chikungunya. Both stories kept the method in the news before the 2023 exam.

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