Biological control programs implemented by IITA and partners on cassava green mite have brought benefits worth more than $1.7 billion to Nigeria, Bénin, and Ghana in the last 18 years.

Diseased plant. Photo by IITA.

Ousmane Coulibaly, IITA Agricultural Economist, describes the figure as “a conservative estimate.”

“The figure represents the amount those countries would have spent over the years on other methods such as chemical control and/or yield losses if they never adopted biological control,” said Coulibaly.

The cassava green mite is a pest that was responsible for a yield loss in cassava in Africa of between 30 and 50% until a natural enemy of the pest helped to contain the devastation. In 1993, scientists from IITA and partners identified Typhlodromalus aripo as one of the most efficient enemies against cassava green mite. The introduction of T. aripo reduced pest populations by as much as 90% in the dry season when pest populations are usually high; in the wet season, pest attacks are not as severe.

T. aripo from Brazil was first released on cassava farms in Bénin and, subsequently, in 11 countries; it is now confirmed as established in all of them, except Zambia. T. aripo has also spread into Togo and Côte d’Ivoire from neighboring countries. It spread to about 12 km in the first year, and as much as 200 km in the second year. Today, the predator of the cassava green mite has been established on more than 400,000 km2 of Africa’s cassava-growing areas.

Scientists say chemical control of the pest was ruled out because of possible adverse effects of chemicals on illiterate farmers and the environment. Also, disease pathogens and pests tend to develop gradual resistance to chemical pesticides over time. Moreover, most chemical pesticides are not selective and might destroy the natural enemies and the pests together.

Coulibaly notes that since the release of T. aripo, benefits in Nigeria have been estimated at $1.367 billion, followed by Ghana $305 million, and Bénin $54 million. Consumed by more than 200 million people in sub-Saharan Africa, cassava is a staple food that is rich in calories, highly drought tolerant, thriving in poor soils, and easy to store in the ground.