The yield of a cocoa tree depends much more on how many blossoms are pollinated by mosquitos than its supply of water, light, and nitrogen.
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Nr. 109/2010 – 01.06.2010
Mosquitos provide better cocoa harvest
(pug) The yield of a cocoa tree depends much more on how many blossoms are pollinated by mosquitos than its supply of water, light, and nitrogen. This is what agricultural ecologists of the University Göttingen recently found out in Indonesia. The stagnation of world-wide cocoa production is driving up prices for cocoa beans and is leading to bottlenecks in the industry: so far, efforts to raise the agricultural output concentrated either on the cultivation of more productive and more resistant varieties or an increase of the yield through greater use of fertilizers and light. “So far, the role of pollination has remained largely unnoticed,“ states the Göttingen agricultural ecologist Dr. Yann Clough, who conducted the investigations. The scientists published the results of their research in the online edition of the journal “Perspectives in Plant Ecology, Evolution and Systematics”.
On the Indonesian island of Sulawesi, the Göttingen researchers investigated the conditions under which cocoa trees can benefit from increased pollination. In their experiment, they manually pollinated 10, 40, 70, or 100 percent of a cocoa plant’s blossoms. At the same time, they altered the respective avalability of water, light, and nitrogen. Just an increase from 10 to 40 percent in the pollination intensity of the blossoms was sufficient to double the yield of the tree. “In nature, pollination rates of at most 10 percent are assumed. The potential for an increase of yield is therefore enormous,” explains Dr. Clough.
The cocoa tree, which grows to between 3 and 20 meters, is unique as an agricultural crop in many ways: the fruit with the beans used for the production of cocoa is located directly on the trunk and the blossoms are – unlike, for example, coffee – not pollinated by bees but tiny mosquitos. ” In order to increase the pollination intensity, and therefore the yield of a cocoa tree, the mosquito population in the plantations has to be deliberately promoted,“ says Dr. Clough.
Original publication: Groeneveld, J.H., Tscharntke, T., Moser, G., Clough, Y. Experimental evidence for stronger cacao yield limitation by pollination than by plant resources. Perspectives in Plant Ecology, Evolution and Systematics. DOI:10.1016/j.ppees.2010.02.005
Dr. Yann Clough
Faculty of Agricultural Sciences
Department of Crop Sciences
Waldweg 26, 37073 Göttingen
Telefon (0551) 39-22358