Description of a new mealybug species saves US$ billions across Africa
Problem Statement: Cassava (manioc or tapioca; Manihot esculenta) is a drought resistant, staple food crop for over 200 million people in sub-saharan Africa. In 1973 a new mealybug species, since described as Phenacoccus manihoti, was found seriously damaging the cassava crop in the Republic of Congo. Initial attempts to control the pest using natural enemies from South America failed. By the early 1980s, the infestation was causing production losses of over 80 per cent throughout tropical sub-Saharan Africa, severely impacting the livelihoods of tens of millions of people.
Methods: Finding natural enemies of a pest requires finding its place of origin. Initial taxonomic work suggested that similar mealybug material had been collected earlier from Brazil, so searches for natural enemies were focused on Central and Northern South America. A natural enemy was identified and introduced to Africa as a biological control agent but failed to have an impact. Further taxonomic work revealed that the mealybug material initially collected in South America had been mis-identified; though similar, it was not the same as the pest species devastating cassava in Africa, P. manihoti. As a result of this mis-identification,an ineffective natural enemy had been introduced as a biological control agent. Once this was recognised, a hymenopteran parasitoid (Anagyrus lopezi) of P. manihoti was located and introduced to Africa.
Outcomes and Impacts: The initial lack of taxonomic knowledge resulted in a misidentification, and misdirected pest eradication efforts resulted in wasted effort and hundreds of millions of dollars in further crop losses. Following further taxonomic studies, A. lopezi proved to be a highly effective biological control agent; by 1990 it had successfully established itself in 25 African countries. P. manihoti, the cassava mealybug (CMB), is now considered to be under control throughout its range in Africa. As a result of this problem, it was recognised that another such introduction could easily occur, and funding was made available for a taxonomic revision of the mealybugs of the Neotropics so that any future introductions could be quickly and accurately identified and, hopefully, controlled. While the total project costs reached over $30 mil (in 1994 $ values), revenues to African farmers (depreciated over 40 years), are estimated at between $8 billion and $20 billion, implying a cost / benefit ratio between 1:200 to over 1:600.
Lessons: The use of natural enemies to control pests is highly cost effective but requires sound taxonomic expertise. Through the project’s success on the ground across all of sub-Saharan Africa and the vast training and public awareness effort, it became the starting point for a series of biological control successes involving the same partners, thus contributing to widespread poverty alleviation.
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1 . Marta S. Loiácono, División Entomología, Facultad de Ciencias Naturales y Museo, Paseo del Bosque, 1900 La Plata, Buenos Aires, Argentina. Email: firstname.lastname@example.org 2. Peter Neuenschwander, Biological Center for Africa, International Institute of Tropical Agriculture, 08 P.B. 0932, Cotonou, Bénin. E-mail: P.Neuenschwander@cgiar.org 3. Dr Gillian W. Watson, Department of Entomology, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK. Tel: (+) (0) 20 7942 5741. Fax: (+) 7942 5229. E-mail: G.Watson@nhm.ac.uk
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