Pesticidal plants in Miombo woodlands
Plants used to control pests in Southern and Eastern Africa are being studied to enhance their value to resource-poor farmers in the region.
02 Nov 2011
The Miombo woodlands in Malawi are a source of natural pesticides (Image: Phil Stevenson)
The Miombo woodlands of Southern and Eastern Africa are dominated by Colophospermum mopane and Brachystegia species (Leguminosae), and are an important source of non-food plant products, particularly for the rural poor. They provide unique ecosystem services which can generate supplementary income and improve the livelihood of local people.
The EU-funded Southern African Pesticidal Plants Project and the African Dry Land Alliance for Pesticidal Plant Technologies, facilitate collaboration between the University of Greenwich, RBG Kew and numerous African partner institutes and universities to study the sustainable uses of pesticidal plants. These organisations have carried out surveys of famers in Malawi and Zambia concerning the uses of pesticidal plants obtained from Miombo woodlands. The results have recently been published in the International Journal of Pest Management. Although these surveys showed that the majority of farmers were familiar with pesticidal plants, very few actually used them. This highlights the need to foster the actual use of these plants, to maximise the benefits they can bring to resource-poor farmers.
Controlling cattle ticks
One species identified through the surveys was Lippia javanica (Verbencaceae), a woody Miombo shrub which is popular as a healthy green tea. Subsequent research by the project teams, reported in Tropical Animal Health and Production, has shown that this species is effective in controlling cattle ticks that cause morbidity and spread fatal blood diseases in livestock. Tick counts on cattle treated with plant extracts at an application rate of 10% were as low as on cattle treated with the standard amitraz-based commercial product Tickbuster. While some tick parasitism remained on these cows (approximately 10% of that found on untreated cows), peripheral blood samples showed no haemoparasites in the treated cattle, implying that animals did not suffer from clinical tick-borne diseases after treatment with Lippia javanica extracts.
Importance of saponins
Chemical analysis of the mature pods of another pesticidal Miombo tree Bobgunnia madagascariensis (Leguminosae) has identified biologically active saponins, as well as flavonoid glycosides that make up to 20% of the dry pod weight. Some of the flavonoid glycosides proved to be novel, and their structures are reported in Tetrahedron Letters. The saponins are important in the biological activity of the plants, in ways related to their structural features, which can be determined from these analyses. Correctly identifying the active compounds in pesticidal or medicinal plant material is important in selecting elite material containing the most active compounds, and this is discussed in another recent paper in Plant Cell Reports. Identifying the best material for use, or for propagation and replanting programmes, is vital where overharvesting threatens local plant populations.
Item from Dr Phil Stevenson (Natural Product Chemist, RBG Kew/NRI)
Originally published in Kew Scientist, issue 39.
Kamanula, J., Sileshi, G. W., Belmain, S. R., Sola, P., Mvumi, B. M., Nyirenda, G. K. C., Nyirenda, S. P. N. & Stevenson, P. C. (2011) Farmers’ Insect Pest management practices and pesticidal plant use for protection of stored maize and beans in Southern Africa. International Journal of Pest Management 57: 41-49.
Madzimure, J., Nyahangare, E. T., Hamudikuwanda, H., Hove, T., Stevenson, P. C., Belmain, S. R. and Mvumi, B. M. (2011). Acaricidal efficacy against cattle ticks and acute oral toxicity of Lippia javanica (Burm F.) Spreng. Tropical Animal Health and Production 43: 481-489.
Stevenson, P.C., Nyirenda, S.P. and Veitch, N.C. (2010). Highly glycosylated flavonoids from the pods of Bobgunnia madagascariensis. Tetrahedron Letters 51: 4727-4730.
Sarasan, V., Kite G. C., Sileshi, G. W., Stevenson P. C. (2011) The application of phytochemistry and in vitro tools to the sustainable utilisation of medicinal and pesticidal plants for income generation and poverty alleviation. Plant Cell Reports 30:1163–1172.
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