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March 31, 2010

IITA to study natural enemies of white fly in cassava

The International Institute of Tropical Agriculture (IITA) is intensifying its efforts to find a sustainable solution to controlling populations of the whitefly, Bemisa tabaci. These tiny insects transmit the viruses that cause the Cassava Mosaic Disease and the Cassava Brown Streak Disease that are wreaking havoc on Africa’s cassava production.

Together, the two diseases cause an estimated damage of more than 1 billion USD to Africa’s cassava every year and threatening the food security and livelihoods of millions dependent on the crop.

IITA will invest in a two-year project that will identify the most effective natural enemies of the whitefly that can be deployed to reduce its population. It will also explore cassava varieties, including wild relatives, with resistance to the pest.

Dr James Legg, IITA entomologist who has been working on cassava diseases for over 10 years, says in areas where the pandemic is present the vector population is up to a hundred times greater than in areas not yet affected.

Therefore, he says, in addition to transmitting the viruses, ‘super-abundant’ Bemisia whitefly also cause physical damage to the cassava plants. Studies conducted in Uganda showed that yield losses from whitefly damage alone can be as much as 50%.

“We have been studying the biological characteristics and genetics of this ‘super-abundant’ Bemisia whitefly and assessing its local natural enemies,” he says. “With the new project, we will intensify our efforts to search for and test the effectiveness of these natural enemies as part of an integrated disease management strategy.”

The whitefly has several parasitoids – parasitic wasps that develop within young whitefly larvae, eventually killing them in the process. Although local parasitoids already ‘take out’ up to half of all whitefly young, the new project aims to make this control even stronger by introducing exotic parasitoids.

The research will identify which of these parasitoids are most suitable for the climatic conditions in Tanzania and Cameroon using computer software such as CLIMEX. The most suitable species will be selected to test their efficacy under quarantine conditions before field testing.

Dr Legg said the research will also explore cassava varieties that are resistant to whitefly. “So far our efforts have concentrated on breeding varieties with resistance to the viruses. This new dimension offers great promise for strengthening overall control of the cassava virus and virus vector system,” he says.

The project will be carried out in collaboration with International Centre for Tropical Agriculture and the University of Tel Aviv in Israel. It will target Nigeria, Cameroon, and Tanzania.

IITA has in the past successfully implemented classical biocontrol programmes that restricted the spread of the cassava green mite and cassava mealybug in sub-Saharan Africa. With this new project, IITA and its partners hope that by combining biocontrol in novel ways with host plant resistance, great strides can be made in tackling one of Africa’s most destructive pests.


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