Why in news?
Two years after scientists released the parasitic wasp Anagyrus lopezi into tapioca fields of South India, farmers report that the once–devastating cassava mealybug infestation is under control. Yields have recovered and chemical pesticide use has dropped, demonstrating the success of classical biological control.
Background
The cassava (or tapioca) mealybug (Phenacoccus manihoti) is native to South America. It appeared in Kerala in April 2020 and spread rapidly across Tamil Nadu and Kerala, causing tuber yields to plunge to 5–12 tonnes per hectare. To avoid heavy losses, scientists from the ICAR–National Bureau of Agricultural Insect Resources (NBAIR) sought a natural enemy.
With approval from India’s plant quarantine authorities, NBAIR imported the parasitoid wasp Anagyrus lopezi from the International Institute of Tropical Agriculture in Benin, West Africa. After rigorous quarantine tests to ensure that the wasp would not harm non‑target species, researchers developed mass‑rearing techniques and trained extension officers and farmers. On 7 March 2022, the first field release took place at Yethapur in Salem district, Tamil Nadu. Farmers received 3,000 parasitized twigs for gratis distribution, and the programme was later expanded to other affected districts.
How the wasp works
- Host specificity: Anagyrus lopezi targets only the cassava mealybug. Female wasps insert eggs into the soft bodies of the pest.
- Biological control: The developing larvae consume the mealybug from within, killing it. Adult wasps emerge to parasitize new hosts.
- Natural spread: Once released, the parasitoid can disperse 30–40 km beyond the release point, gradually suppressing mealybug populations over a wide area.
Cassava cultivation in India
Cassava (locally called tapioca) is an important horticultural crop in Tamil Nadu, Kerala and the Union Territory of Puducherry. Grown for its starchy tubers, it is processed into flour, sago pearls, laundry starch and alcoholic beverages. The crop thrives in warm, humid climates with annual rainfall above 100 cm and prefers well‑drained red or lateritic loam soils. Cassava can be cultivated up to an elevation of about 1,000 m, but all parts of the plant contain cyanogenic glucosides and must be processed to remove toxins.
Impact of the intervention
Following the release of A. lopezi, mealybug numbers have fallen dramatically. Farmers report that tuber yields are returning to pre‑infestation levels (around 25–35 tonnes per hectare) without the need for insecticides. Training programmes continue to help communities rear and release the wasps themselves, ensuring long‑term management. This case illustrates how classical biological control can offer cost‑effective, environmentally friendly solutions to invasive pests.
Source: ICAR‑NBAIR (Important Information on Anagyrus lopezi) · ICAR – Release of an Exotic Parasitoid Wasp