From devastation to recovery: How a parasitic wasp saved South India’s tapioca crops

Two years after scientists from the National Bureau of Agricultural Insect Resources (NBAIR), under the Indian Council of Agricultural Research (ICAR), released a tiny parasitic wasp into South India’s tapioca fields, the crop that once faced near devastation from an invasive pest is now thriving again. Farmers in Tamil Nadu, Kerala, and Puducherry report that their tapioca harvests have returned to pre-outbreak levels. This marks a rare success in controlling a major agricultural pest without chemicals. 

Cassava, better known as tapioca, is grown on about 1.73 lakh hectares in India, with Tamil Nadu and Kerala together contributing more than 90% of total production. Before the outbreak, yields averaged 35 tonnes per hectare, far above the global average of 10.76 tonnes, and India exported value-added tapioca products worth nearly ₹200 million annually, according to NBAIR officials. 

However, the mealybug’s arrival in Thrissur, Kerala, in April 2020 changed this landscape. By 2021, nearly 1.43 lakh hectares were infested, and some areas of Tamil Nadu saw yields collapse to 5–12 tonnes per hectare. The pest fed on the plant sap, causing leaf curling, stunted growth, and poor tuber formation. With no effective local predators, the infestation escalated quickly and posed a serious economic threat to farmers, they said. 

Chemical sprays were considered, but repeated pesticide use was costly, harmful to the environment, and unsustainable for small farmers. ICAR–NBAIR scientists instead turned to classical biological control, a strategy that introduces a natural enemy from the pest’s native region to restore ecological balance. 

“In nature, every species has natural enemies that keep its population in check. Scientists identified a tiny parasitic wasp, Anagyrus lopezi, that specifically targets the cassava mealybug. The wasp lays its eggs inside the pest, and the developing larvae consume it from within, naturally reducing mealybug numbers without harming other crops,” S. N. Sushil, Director, ICAR-NBAIR said.  

After identifying the parasitoid Anagyrus lopezi as a suitable natural enemy, the institute imported a shipment from the International Institute of Tropical Agriculture (IITA), Benin, West Africa, as part of its mandate to introduce live biological control agents for pest management. Rigorous quarantine studies at NBAIR’s facilities confirmed the wasp’s host specificity and biosafety, ensuring it would target only the cassava mealybug without affecting other crops or beneficial insects. 

The first field release of A. lopezi was then conducted in March 2022 at Yethapur, Salem district, with around 300 farmers. This was followed by large-scale releases across Tamil Nadu, Kerala, and Puducherry, covering more than 500 farmer fields. To support adoption, ICAR–NBAIR set up three satellite mass-production centres, distributed over 200,000 parasitoids, and conducted 25 awareness programmes and multiple training sessions. The parasitoids spread naturally beyond the release points, up to 30–40 km, gradually bringing the mealybug population under control. 

By 2023–24, the programme had achieved remarkable results. Yields in the hardest-hit districts, including Salem, Namakkal, Dharmapuri, rebounded to 35 tonnes per hectare, restoring farmers’ income and livelihoods. Across the previously infested 1.43 lakh hectares, the mealybug is now under natural control and has eliminated the need for chemical sprays. 

The team behind the initiative includes Sampathkumar M., M. Mohan, A. N. Shylesha, Sunil Joshi, Ankita Gupta, and Mr. Sushil, who are still monitoring the parasitoid’s spread.