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Project News 06.2004

A new whitefly species emerges as
a pest of cereals in Central America

Projects :: Whiteflies as pests in tropical highlands
:: Whiteflies as virus vectors in mixed cropping systems
:: Whiteflies as vectors and pests in cassava

Whiteflies as vectors of viruses in cassava and sweetpotato in Sub-saharan Africa

Geographical focus :: Ghana, Benin, Nigeria, Cameroon, Uganda, Kenya, Tanzania, Malawi, Zambia, Madagasgar Start date :: January 1, 1997
Completion date :: December 31, 2000
Project Name :: Sustainable Integrated Management of Whiteflies as Pests and Vectors of Plant Viruses in the Tropics
Project Leader :: Dr. Pamela Anderson
Subproject Name :: Whiteflies as vectors of viruses in cassava and sweetpotato in Sub-saharan Africa
Subproject Description :: Pesticides are not currently used on cassava in Africa. The problem of whiteflies as pests and vectors on cassava is an issue of food security.

Cassava is the third largest source of carbohydrates for human food in the world, with an estimated annual yield of 136 million tons, and Africa is the largest center of production; 57 million tones of cassava were grown on 7.5 million hectares in Africa in 1985 (Fauquet & Fargette, 1990). If one uses the definition that a staple food is one that accounts for more than 200 calories per day in the diet of an individual, then cassava is the second most important staple food, after maize, in sub-Saharan Africa. Nearly 200 million people, or 40% of the Sub-Saharan Africa population relies on cassava. And, in some countries people derive approximately 1000 calories a day, or 50% of daily food intake) from cassava (IITA, 1988).

Although Africa is the greatest producer of cassava, yields are low: 7.4 tones per hectare in 1989 (FAO), compared with a potential of between 30 and 50 tones per hectare. There have been major research successes in combating exotic pests which have devastated cassava in Africa following their introduction from South America. Most prominent amongst these has been the biological control of the cassava mealybug. The effective continent-wide management of this pest resulted in incalculable benefits to cassava farmers in Africa. The indigenous African cassava mosaic disease (ACMD), however, is arguably responsible for even greater reductions in the continent's cassava yield than were attributed to cassava mealybug.

Responses to an international questionnaire sent to all cassava-producing African countries (Fauquet & Fargette 1987) showed that ACMD is present wherever cassava is grown (Figure 4). A survey of 20 farms in Ghana revealed an average 96% of plants infected. Similarly, ACMD incidence exceeded 80% in some districts of Kenya, and nearly 100% in Ivory Coast. Subsequently, the ESCaPP Project has identified ACMD as a key problem in Ghana, Benin, Nigeria and Cameroon, with overall incidence of infection of 72, 55, 82 and 66%, respectively.

Presence and relative importance of African cassava mosaic disease (ACMD) as estimated by agronomic services of different African countries that produce cassava (Fauquet & Fargette, 1990).
Yield losses with individual cultivars have been reported from different countries to range from 20 to 95% (Table 5; Fauquet & Fargette, 1990). Yield losses depend upon the mode and time of infection. In Kenya, ACMD causes a loss of about 70% in tuber yield of plants derived from infected cuttings (Bock, 1982). On the basis of available data, the total reduction of cassava yield in Africa in plants derived from diseased cuttings is at least 50%, or 50 million metric tones, per year and may be equivalent to $2 billion ($US) (Fauquet & Fargette, 1990).

In 1988, reports were received of serious damage to cassava in northern Uganda. Plants were severely affected by ACMD and resulted in such low yields that local food shortages and starvation occurred. By 1989, a severe epidemic was reported in the West Nile Region of northwestern Uganda. A comprehensive survey of cassava in the area revealed that the disease was spreading rapidly and causing crop failure. By April 1992, most fields were 80-90% infected and cassava production had virtually ceased due to the poor yields of the diseased crops. In some zones the area planted to cassava decreased by 95% because farmers were aware of the futility of planting infected cuttings of the available varieties. This epidemic has now covered 3/4 of Uganda and is moving southwards at a rate of 10 to 20 km per year. It is estimated that over 150,000 ha of cassava growing land is abandoned, equivalent to over 2.2 million metric tones (US $440 million). This has caused food shortages and famine in a number of districts particularly in the eastern and northern regions where the crop has been a major staple. The current epidemic in Uganda is a threat to cassava production in all neighboring counties (Otim-Nape, 1996).

It is necessary to better-characterize the distribution and impact of ACMD in the cassava-growing belt of Africa. In addition, special efforts, such as phytosanitation, introduction of whitefly-resistant cassava clones and disease monitoring, should be continued to both understand and slow down the Uganda ACMD epidemic.

Current knowledge suggests that two cassava mosaic geminiviruses occur in Africa with partially-overlapping distributions (Hong et al., 1993; Swanson & Harrison, 1994). East African cassava mosaic virus (EACMV) has been identified from coastal East Africa, Madagascar, Malawi and Zimbabwe, and African cassava mosaic virus (ACMV) from West, Central Africa and Kenya. Both viruses are transmitted by Bemisia tabaci. Recent evidence, however, suggests that this classification may be an oversimplification. New research suggests that the ACMd epidemic in Uganda may be caused by a geminivirus distinct from both EACMV and ACMV. And, the rate of expansion of the epidemic in Uganda (approx. 20km per year) has also suggested the possible involvement of a novel biotype of B. tabaci.

In summary, in spite of the devastating pest outbreaks and epidemics being caused by WFs and WTVs, our knowledge in the tropics is quite incipient. Without first generating a clearer picture of the nature and extent of the whitefly problem, it will be impossible to develop rational IPM programs.

Project Purpose :: To gather, generate and analyze, through scientific and grower networks, baseline data relevant to the diagnosis and characterization of whitefly and WTV problems in the tropics, in order to propose a sound research agenda for improved understanding of pest and disease dynamics, IPM development and IPM implementation.

Project Outputs ::

  • International network for whiteflies and WTVs in the tropics established
  • Socio-economic and environmental impact assessed
  • Epidemiological characterization initiated
  • Agronomic characterization initiated
  • Preliminary studies for Phase 2 conducted

Project Impact :: The immediate beneficiaries of Phase 1 of the Project will be a) IARC scientists, b) NARS scientists, c) small holder farmers, and d) donor agencies. Additional, indirect, beneficiaries will be the general community of whitefly and WTV scientists and government policy makers.

Project Leader :: Dr. James Legg / International Institute of Tropical Agriculture - IITA
Donor Partner :: Australian Centre for International Agricultural Research - ACIAR
Partner institutions
and collaborating professionals ::


International Institute of Tropical Agriculture IITA - Kampala
Mr. Peter Sseruwagi
Mr. Geoffrey Okao-Okuja

National Agricultural Research Organization - NARO
Dr. William Otim-Nape
Mr. William Sserubombwe

Natural Resources Institute NRI - Uganda
Valentin Aritua

Centro Internacional de la Papa - CIP
Dr. Nicole Smit


International Institute of Tropical Agriculture IITA - Benin
Dr. Braima James
Mr. Brice Gbaguidi

National Agricultural Research Institute of Benin - INRAB
Mr. Norbert G. Maroya

Direction de l'Agriculture/Service Protection des Végétaux - DRAGRI/SPV
Symphorien Saizonou


Plant Protection and Regulatory Services Division - PPRSD
Mr. Anthony Cudjoe
Mr. Joseph Gyamenah


National Root Crop Research Institute - NRCRI
Thank-God N.C. Echendu

J.B. Ojo


University of Buea
Mr. Nelson Ntonifor

Agricultural Research Institute - IRA
J. Ambe Tumanteh


Kenya Agricultural Research Institute - KARI
Dr. Joseph Kamau


Lake Zone Agricultural Research and Development Institute - LZARDI
Mr. Joseph Ndunguru
Mr. Sato Jeremiah
Dr. Regina Kapinga


Chitedze Research Station
M. P. K. J. Theu


Centre National de la Recherche Apliquee au Development - FOFIFA
Sahondramalala Ranomenjanahary
Ms. Jocelyn Ramelison


Mt. Makulu Research Station
Mr. George Kaitisha

United Kingdom

John Innes Centre - JIC
Dr. Peter Markham
Robert Briddon
Gina Banks

Natural Resources Institute - NRI
Dr. Richard Gibson
Dr. Michael Thresh


Biologische Bundesanstalt für Land und Forstwirtschaft - BBA
Dr. H. Josef Vetten

Dissemination Outputs ::  
Keywords :: Ghana; Benin; Nigeria; Cameroon; Uganda; Kenya; Tanzania; Malawi; Zambia; Madagasgar
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