Biocontrol is a more cost-effective and sustainable intervention than pesticides. Over three years, it saved India’s papaya crop and thousands of farmers.


One morning in November 2010, Radha Doraisamy had a test tube in her hand and doubts on her mind. Three years earlier, she had given up on papaya farming after her grove of six acres was destroyed by a pest. The bug had overrun her farm in no time. In two months, the biennial crop of papaya fruits were shrouded in a white, fluffy cotton mass, making the harvest useless.

In her forties, Radha, whose two children work in Chennai, spends most of her day on the farm. In a region where absentee landlordism is much prevalent, Radha bucks the trend and lives in a two-storey house in the middle of her 20-acre farm.

Every day she wakes at five a.m. and does the rounds, often talking to the plants. She farms papaya, coconut, cassava and sugarcane, crops suited to the black cotton soil of the Deccan region.

Radha’s decision to stay put at her farm in a landlocked village—increasingly under threat by forces of urbanisation from Mettupalayam in the north and Coimbatore in the south—seemed to have paid off. Her crops sold well, till the papayas started turning white.

The destroyer of crops—a Mexican traveller that left a trail of destruction and economic gloom in its path—was a yellow insect smaller than the eye of a needle, called the papaya mealybug. Or Paracoccus marginatus, as the scientists identified it.

Within a year, the mealybug had spread all across south India, and papaya production had fallen by as much as 80 per cent. Indian farmers were losing an estimated Rs.1,500 crore annually as the bug continued its flight of conquest. Radha suffered a loss of Rs.30 lakh that year: she had spent Rs.5 lakh on planting papaya, and Rs.25 lakh as loss of income on account of the damaged fruit.

It was eight months before Radha could make a fresh start. This time, she was told, there was a solution at hand. A way had been found to get rid of the pest that had destroyed papaya crops in four states and was spreading northward.

The solution seemed absurdly simple. All Radha had to do was to take a test tube provided by the government, unseal it, and amble down the papaya grove, tilting it towards the black soil. The test tube contained close to a hundred wasps—so small that they were barely discernible—that act as a parasite on the pest. The wasps would lay eggs inside the pest and, once hatched, the larvae would consume the internal organs of the host and kill it.

Like Radha, more than 20,000 farmers across Tamil Nadu were provided with these tubes and asked to unseal them and walk around their farms.

Radha’s discomfort was understandable. The test tube and the power accorded to it were in stark contrast to traditional pest management techniques she was familiar with. Typically, once a pest attack occurs, the farmer buys a bottle of pesticide from the local agricultural store, dilutes it with water, loads it in a mechanical sprayer, and sprinkles the pesticide through a nozzle on to each and every plant in the field. Each spraying would cost close to Rs.9,000 per acre. And this had to be repeated a few times until the harvest.

In contrast, the proposed solution was a one-time intervention. In fact, after the introduction of wasps, the mealybug incidence was controlled not only in fields where they were released, but also in neighbouring grounds. This is because subsequent generations of the wasp moved out in search of the mealybug.

Radha’s unsealed and tilted test tube contained the hope that farmers who had lost much to the bug sorely needed.

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