The marvels of chocolate

Have you ever wondered where chocolate comes from and if it is possible that there will be a chocolate shortage in the future? Have you ever wondered if chocolate has anything to do with entomology? According to the Telegraph newspaper the average person In the UK spends a minimum of £57 on chocolate per year. It is therefore no surprise that the Theobroma cacao tree, from which we get most of our chocolate, is the second most important tropical cash crop, being worth $5 billion, providing employment for approximately 40-50 million farmers in Africa and Asia. (Schawe et al. 2013). Chocolate is processed from cocoa beans which grow on the 5-8 metre tall T. cacao tree (Young, 1982). As well as chocolate the cocoa beans are also processed into many well-known products such as cocoa powder and cosmetics (Schawe et al. 2013). Chocolate is not only delicious, but it has actually played a major role in human society by representing power and celebration and was even historically used as a currency.

The red/ brown egg shaped cocoa pods containing the cocoa beans are only produced if the flower is successfully pollinated by a particular insect. For once we are not talking about bees. Although you probably will not believe me, the pollinator is actually a fly, well, two species of the biting midge. Their Latin names are Forcipomyia quasiingrami and Lasiohela nana and they both belong to the Ceratopogonidae family (Young,1982). Can you believe it! Chocolate production is solely reliant on a biting midge!

The biting midge is 2-3mm long, about the size of a grain of rice (Young, 1982). Considering how important the midge is it lives quite a secretive life, the larvae (maggot) feed on dead organic matter and fungus and the adults require pollen and blood for egg production (Leston, 1970). The midge larvae click and jump so maybe that has made you rethink your opinion of maggots (Frimpong, 2009). Well when you think of flies you may automatically think of their larvae the maggot. I am writing this to show you wonder of chocolate, I certainly don’t want to put you off it. But without the midge larvae there would be no chocolate! Therefore if we destroy this annoying midge we would have no chocolate. Which would be worse?

So when you think of chocolate what do you imagine the flowers would be like? Well actually they are 5 pink sepals, holding 5 pouch like yellow petals. The petals conceal a ring of 5 staminodes, infertile stamens which enclose a central ring of 5 stamens covered in pollen. The flower’s ovaries are in the centre. The midges hover and weave around the aromatic flowers before crawling into the petal. The red nectar lines guide the midge towards the central narrow nectaries, where it feeds on nectar. The pollen from the previous flower visited is transferred to the ovary, fertilising the seed. When the midge crawls out of the flower it consumes some of the stamens pollen, but a large majority of pollen sticks to the midges long caudal hairs (Young, 1985). The midge then flies up to 6m away or is blown 100m-3km away from the flower, to another flower (Frimpong, 2009; Klein et al. 2008; Groneveld, 2010) and so it continues.

So far so good, but what if I was to tell you this midge is becoming rare, then what would you say? And what should we do about this? What if I was also to tell you that these midges also depend on rotting bananas and fungus growth on them for larvae growth (Leston, 1970) would you change your mind about fungus? The main reason for the midges decline appears to be loss of its microhabitat of dead leaves and discarded cocoa pods. The farmers are keeping their plantations too clean, banana peel may be the answer.

There is an additional problem. This particular tree (T. cacao ) is inefficient at producing fruit. Flowers must be pollinated on their first day of bloom. Otherwise, after 2 days, the flowers drop to the ground. As a result less than 5% of the 10% of flowers that are successfully pollinated develop into fruit (Groneveld, 2010). So next time you open a 100g chocolate bar remember it took 1 pod with 30-40 seeds to produce it. In a year alone the cocoa industry uses about 35 trillion cocoa pods. And so perhaps it is no wonder chocolate can be loosely translated to “the food of the gods”. So, next when you hear someone talking about the importance of bees just stop for a minute and consider the midges and how without them there would be no chocolate. And, next time a midge bites you think of their cousins the insect pollinators.

By Ruth Carter


References

Encyclopedia of Life. 2015. Theobroma cacao. [On-line]. Encyclopedia of Life. Available from: http://eol.org/pages/484592/overview [01/11/2015].

Frimponga, E., Gordona, I., Kwaponga, P. and Gemmill-Herrena, B. 2009. Dynamics of cocoa pollination: Tools and applications for surveying and monitoring cocoa pollinators. International Journal of Tropical Insect Science, 29 (2), pp. 62-69.

Groeneveld, J., Tscharntke, T., Moser, G. and Clough, Y. 2010. Experimental evidence for stronger cacao yield limitation by pollination than by plant resources. Perspectives in Plant Ecology, Evolution and Systematics, 12 pp. 183-191.

Kew. 2015. Theobroma cacao (cocoa tree). [On-line]. Home Science & Conservation, Discover plants and fungi. Available from: http://www.kew.org/science-conservation/plants-fungi/theobroma-cacao-cocoa-tree[01/11/2015].

Klein, A., Cunningham, S., Bos, M. and , S., I. 2008. Advances in pollination ecology from tropical plantation crops. Ecological Society of America, 89 (4), pp. 935-943.

Schawe, C., Durka, W., Tscharntke, T., Hensen, I. and Kessler, M. 2013. Gene flow and genetic diversity in cultivated and wild cacao (Theobroma cacao) in Bolivia1. American Journal of Botany, 100 (11), pp. 2271-2279.

Young, A. 1985. Studies of cecidomyiid midges (Diptera: Cecidomyiidae) as cocoa pollinators (Theobroma cacao L.) in Central America. Proceedings of the Entomological Society of Washington, 87 (1), pp. 49-79.

Young, A. 1982. Effects of shade cover and availability of midge breeding sites on pollinating midge populations and fruit set in two cocoa farms. Journal of Applied Ecology, 19 (1), pp. 47-63.

Young, A., Severson D. 1994. Comparative analysis of steam distilled floral oils of cacao cultivars (Theobroma cacao L., sterculiaceae) and attraction of flying insects: Implications for a Theobroma pollination syndrome. Journal of Chemical Ecology, 20 (10), pp. 2687-2703.

 

 

 

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