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BioNET-INTERNATIONAL

Why taxonomy matters
A series of case studies highlighting Taxonomy's Value to Society
www.bionet-intl.org/case_studies

Implementing the Global Taxonomy Initiative of the CBD
CASE STUDY 2
The description of a new mealybug species enables implementation of a successful biological control programme across Africa, saving billions of US$


Relevant Sector: Agriculture (cassava crop production industry)

Geographic Location: Sub-Saharan Africa; South America

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% 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. (This led to the description of a second new species, P. herreni, from Paraguay and Bolivia but not found in Africa). As a result of this mis-identification, the wrong (and hence ineffective) natural enemy had been introduced as a biological control agent. Once this misidentification was recognised and corrected, 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 (discounted by 6%) reached over $30 mil (in 1994 $ values), revenues to African farmers (depreciated over 40 years), are estimated at between $8 billion and $20 billion, with benefit:cost ratios ranged from 200 to over 700. Once the taxonomic confusions of both the host and the parasitoid had been cleared, the project, which became one of the best-researched biological control programmes, was ready to mass-produce and release an efficient parasitoid within 3 years.

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.

References:
1. Cox, J.M. & Williams, D.J. (1981) An account of cassava mealybugs (Hemiptera: Pseudococcidae) with a description of a new species. Bulletin of Entomological Research 71: 247-258. 2. De Santis, L. y N.P.Ras 1988. Control biológico de la cochinilla Phenacoccus manihoti en Africa (Insecta). Academia Nacional de Agronomía y Veterinaria 62 (7): 5-11.S. 3. Herren, H.R. & Neuenschwander, P. (1991) Biological control of cassava pests in Africa. Annual Review of Entomology 36: 257-283. 4. Neuenschwander, P. 2001. Biological control of the cassava mealybug in Africa: a review. Biological Control 21, 214-229. 5. Norgaard, R.B. (1988) The biological control of cassava mealybug in Africa. American Journal of Agricultural Economics 70: 366-371. 6. Watson, G.W. (1999) The role of taxonomy in biological control. Pp. 1-6 in: Pros. Kongres Perhimpunan Entomologi Indonesia V dan Simposium Entomologi: Pengelolaan Serangga Secara Berkelanjutan [Proceedings of the Fifth Congress of the Indonesian Entomological Society: Sustainable Insect Management], Bandung, 24-26 Juni 1997 (plenary paper). 7. Zeddies, J., Schaab, R.P., Neuenschwander, P. & Herren, H.R. 2001. Economics of biological control of cassava mealybug in Africa. Agricultural Economics 24, 209-219.

Contact Information:
1 . Dra. Marta S. Loiácono, División Entomología, Facultad de Ciencias Naturales y Museo, Paseo del Bosque, 1900 La Plata, Buenos Aires, Argentina. Email: mloiacono@sinectis.com.ar
2. Dr. 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