A series of case studies highlighting Taxonomy's Value to Society
Implementing the Global Taxonomy Initiative of the CBD
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.