centre stage

Biting back

Disease-causing insects, especially mosquitoes, are the target of a groundbreaking programme that renders the flying killers infertile

Deep inside the building that houses the Tata Institute for Genetics and Society (TIGS) in Bengaluru, a quiet revolution is brewing. Or buzzing. In the basement is an airtight, highly sanitised insectary with hundreds of thousands of mosquitoes: larvae, nymphs, wrigglers — as the tadpole-like infants are called once they emerge from their pupae — and adults, all kept in sealed tanks and containers.

Of the many species of mosquitoes, these are the kind that are ‘vectors’, ones that spread diseases. “We have three kinds of mosquitoes in the insectary: anopheles, which cause malaria; aedes, which cause dengue and chikungunya; and culex, which cause filaria,” says insectary manager Sunita Swain. “We have built this state-of-the art place to study mosquito behaviour as well as work on finding repellents.”

“Vector-borne diseases are a huge burden for India,” says senior scientist Sonia Sen. “The people affected are disproportionately poorer folk who live in more crowded conditions and have little access to proper sanitation. More recently, because of the spread of the aedes mosquito in densely packed urban areas, dengue and chikungunya are increasingly affecting the better-off as well. That has sparked a growing interest in addressing the issue.”

Protection priority

Scientists look at vector-borne disease from different perspectives. Some focus on destroying the parasites that piggyback on mosquito-driven diseases. Others want to create vaccinations or newer, more effective drugs to protect people.

The TIGS approach is to interfere with the human-mosquito interface by trying, first, to understand mosquito behaviour. What causes mosquitoes — and only the female of the species — to bite humans? Why does the female mosquito switch from having plant-based foods the rest of the time, to seeking out human blood just before laying eggs? And what are the ways in which these patterns can be disrupted?

Mosquito repellents are another piece on the research menu. “The mosquito menace has spread to places like Florida in the United States,” says senior scientist Jay Prakash Shukla of the infectious diseases team at TIGS. “It is the dengue-causing aedes aegypti that is most commonly found there, and till now their approach has been to spray insecticides. But the mosquitoes have developed a resistance to these insecticides, leading to companies investing several million dollars to make new insecticides.”

Given India’s ayurveda heritage, Mr Shukla feels repellents made from natural sources is a better bet. “Mosquitoes avoid certain toxic plants; we should try and make use of these to create natural repellents,” he adds.

Mr Shukla and his team have an olfactometer (an instrument that detects and measures odour) to understand exactly what attracts and repels vector mosquitoes. Extracting essential oils from ayurvedic plants, the scientists run the oils through the olfactometer, which holds a large number of mosquitoes. They then track which odours the insects fly towards or away from. “Once we know for sure which smell drives mosquitoes away, we can create a super repellent,” adds Mr Shukla.

Stemming the spread

Senior scientist Sampath Kumar is working on what is known as an endosymbiont project: trying to attack the bacteria that lives within the mosquito (which is known as the endosymbiont) and suppressing its reproductive traits in an attempt to curtail the spread and transmission of disease.

Paddy plus

Sting in the tale

  • India has an estimated 15 million malaria cases and about 20,000 deaths are caused by the disease every year
  • TIGS’s infectious diseases team is trying to use biological control methods, and create ecofriendly super repellents from natural sources
  • The team is also targeting insect pests that cause economic losses to farmers

Mr Kumar works with the dengue-causing aedes to inject a bacteria known as Wolbachia into the female mosquito. Then, when released into the wild, the mosquito may try to mate but the Wolbachia will render it sterile. That is how a crashing of the population can take place.

The team has started work with fall armyworms, a pest that feeds on 128 kinds of plants, including maize and paddy. This insect, which was discovered in India only in 2018, is found quite extensively in America, where it has developed resistance to various insecticides used to smoke it out.

“We are worried that fall armyworms here will also develop resistance and that would be a nightmare for farmers, especially those who cultivate paddy,” says Mr Kumar. “We’ve selected Karnataka as a focal point to see if the field populations of fall armyworms have started to show any resistance. If we find evidence of this, we will advise policymakers to use a different kind of insecticide to delay the possibility of resistance.”

The other pest on the radar is the coffee stem borer, a hard-to-kill beetle that burrows deep into the coffee plant, covers up its entry hole with excreta and stays there for eight months, laying eggs and eating the plant from the inside. TIGS is looking at applying electric shocks to kill this borer.

The mosquito remains the primary target, though. “Mosquitoes have inhabited this planet way before humans,” says Ms Sen. “We’ve had to live with mosquitoes for all of our existence and we haven’t been able to beat them, which is why we need a multipronged approach.”

If TIGS’s experiments work, the technology can be shared with the rest of the country, or be replicated elsewhere. That sort of a collaboration might be required if India is to be malaria-free by the government’s deadline of 2030.