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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Bank Holiday Special – Why insects are so colourful: The complex business of survival

In the desperate struggle to evade predators, many insects have evolved toxic or bad-tasting skin, a camouflaged body (‘crypsis’), or a startle response to scare away predators. In this “evolutionary arms race”, adaptations on one side call forth counter adaptations on the other side. One such defensive adaptation is to appear toxic using brightly coloured (‘conspicuous’) body coloration- this is known as ‘aposematism’ (“Ay-PO-Sematism”). This idea that signals are sent by prey to predators to indicate toxicity was first suggested by Wallace to Darwin in 1861- they theorised that this evolved to stop predators attacking toxic prey to benefit both sides.

Aposematic warning coloration is a widely utilised form of defence used in all the animal kingdom (not just insects) and has evolved separately from many different evolutionary lines (convergent evolution). It can warn predators of defences such as a painful sting, repellent spray (such as a Bombardier beetle’s noxious chemical spray) or a toxic (or unpalatable) taste. Entomological examples of these bright colours include the malevolent yellow and black of wasps, the familiar black-spotted red body of ladybirds and the monarch butterfly’s bright stripes of orange and black with white dots. Even honeybees and bumblebees are striped to warn birds of their painful sting, although the vile taste of their sting must be learned by the predator through repeated encounters.

But why are toxic insects usually conspicuous and not cryptic? A brightly coloured “lone mutant” in a population of cryptic prey would be more easily spotted by predators, seemingly making the genes coding for bright colour less advantageous. However, bright coloration does give a survival advantage- predators will generally only consume similar-looking items and be wary of prey that are novel or conspicuous. For example naïve birds that have not yet encountered toxic prey may have innate colour biases to stop them eating brightly coloured insects. More experienced birds will be able to remember that eating a particular colour pattern will lead to a bad feeling- that is unless some insects cheat however…

Insects that have evolved to mimic another insect’s body pattern, sound or behaviour, usually resemble a dangerous, aposematic species. This is known as batesian mimicry, and can fool predators into thinking it has defences or a bitter taste, when actually it is harmless (this is not to be confused with Müllerian mimicry, where several toxic species resemble each other). These ‘cheats’ gain a survival advantage without having to produce metabolically costly toxins or evolve a ‘weapon’. An example of this is the hornet moth, a mimic of the yellowjacket wasp- it resembles the wasp’s striking body pattern, which deters predators, but it is not capable of stinging. However more mature predators may be able to detect a fake through experience or social learning. So a scarcity of mimics is actually advantageous for both the mimic and the model insect- too many mimics and the predators will stop responding to the warning signals.

Aposematic colouration as an anti-predator strategy is simply an evolutionary alternative to other forms of protective coloration. Other ‘options’ for predator defence include background matching (a form of crypsis) and disruptive coloration, where bold and contrasting colours on an animal’s periphery act to break up its outline and confuse predators. Another intriguing form of protective coloration is known as ‘masquerade’, where the animal resembles an inanimate object (like a leaf) so the predator sees the prey, but mis-classifies it as something inedible. An extreme form of masquerade can be found in the devious pink orchid mantis, which also utilises this technique for hunting- it will wait until an unsuspecting fly lands on it to drink nectar, and instead be grasped and eaten!

AposematismAbove are examples of the different anti-predator defences that insects can achieve using body colour and pattern. (Clockwise from top left: bombardier beetle, green bush cricket, buff-tipped moth and hawk moth.)

Despite the successes of these other forms of defensive coloration, aposematism remains a widespread and successful alternative anti-predator strategy to being camouflaged, which has evolved to protect prey from predators. Predators’ sensory and cognitive abilities have been important in the evolution of warning coloration, and there are ‘cheats’ that take advantage of these otherwise reliable signals of danger.

Author – Chris Mackin (@EntoChris

Further Reading:

Allen, J. A., & Cooper, J. M. (1985). Crypsis and masquerade. Journal of Biological Education, 19(4), 268-270.

Endler, J. A. (2006). Disruptive and cryptic coloration. Proceedings of the Royal Society B: Biological Sciences, 273(1600), 2425-2426.

Endler, J. A., & Greenwood, J. J. D. (1988). Frequency-dependent predation, crypsis and aposematic coloration [and discussion]. Philosophical Transactions of the Royal Society B: Biological Sciences, 319(1196), 505-523.

Mappes, J., Marples, N., & Endler, J. A. (2005). The complex business of survival by aposematism. Trends in ecology & evolution, 20(11), 598-603.

Schmidt, J. O. (Ed.). (1990). Insect defenses: adaptive mechanisms and strategies of prey and predators. SUNY Press.

Sillen-Tullberg, B., & Bryant, E. H. (1983). The evolution of aposematic coloration in distasteful prey: an individual selection model. Evolution, 993-1000.

Stevens, M., & Merilaita, S. (2009). Animal camouflage: current issues and new perspectives. Philosophical Transactions of the Royal Society B: Biological Sciences, 364(1516), 423-427.

New Feature – Insect Bites: The Sunday Digest

One of the great advantages of the Entomology/IPM course here at Harper Adams Uni is learning from fellow students as well as the staff. The study of Entomology is extremely broad and we all have different interests so to take advantage of this we have a new feature on this blog – Insect Bites: The Sunday Digest.

This is a series of articles written by the EntoMasters students on any aspect of Entomology they choose giving an insight into the diversity of the subject alongside expanding your knowledge, perfect for weekend reading with a cup of tea.

I hope you enjoy

Richard Prew

EntoMasters on Tour – The Royal Entomological Society

Monday the 3rd of November saw the Harper Adams Entomology and IPM students make their way down to The Mansion House situated outside of historic St. Albans for a visit to the hub of Entomology in the UK – The Royal Entomological Society. Coming in from the drizzly November morning we were met with tea, coffee, an array of delicious biscuity treats and friendly faces, much needed after being stuck in M1 traffic for a number of hours.

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Refreshing English Drizzle

Founded in 1833 and granted its royal charter by Queen Victoria in 1885, the principal aim of the society is ‘to promote the dissemination of knowledge in all fields of insect science and to improve communication between entomologists ’. The society, once situated in 41 Queens Gate, London, moved out of the capital in 2008 to the fantastic premises they inhabit in St. Albans today which has enabled a greater amount of funding to be allocated to research, journals and a number of awards for recognising achievement. Many fellows of the society are well renowned and famously include Charles Darwin, Alfred Russell Wallace and Harpers own Professor Simon Leather (Signatures can be found in the obligations book – here is Darwin’s! https://twitter.com/EntoProf/status/529359332157448192/photo/1).

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A Strepsiptera – Twisted Wing Parasite

After dosing up on hot drinks and biscuits we were shown into a small lecture room and listened to talks provided by members of the society. First up was Society’s Director of Science, Professor Jim Hardie, who welcomed us and gave us an insight into the history of the society including what insect is on the logo.

The floor was then handed over to Dr Luke Tilley, director of Outreach and coordinator of National Insect Week, who reinforced the importance of communication and enthusiasm about insects to the wider population and the need to inspire the next generation of potential entomologists. National Insect Week, organised by the Royal Entomological Society, brings together partners and multitude of hardworking volunteers who all share a keen interest in the science, history and conservation of insects to pass on their knowledge to the public and happens every two years across the United Kingdom (For more information on insects and how to get involved in National Insect Week 2016 visit http://www.nationalinsectweek.co.uk/).

As a short interactive exercise for practicing these communications skills we split into small groups and composed short fact files on various insects and tweets on a couple of journal articles. These needed to be eye-catching, interesting and be understandable from the viewpoint of someone who does not necessarily have a scientific background. Even though it was only a bit of fun it got the creative juices flowing and certainly made us think outside of the box.

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Kelleigh and Aidan enjoying the spread

Following this we had a delicious buffet lunch (The miniature yorkshire puddings being my personal favourite) along with a cheeky glass of wine and were given the opportunity to explore the society building. One thing that is noticeable when you first walk in is the fantastic collection of books that is spread throughout the ground floor. These all centre around the Royal Entomological Society library which holds very well preserved, rare books some pre-dating 1850 and all managed by the society’s librarian Val McAtear who bought out some examples and was incredibly trusting enough to let the Harper Students handle and look through them!

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Hundreds of years old and still extraordinarily vibrant

After perusing the RES merchandise and purchasing everything from books to umbrellas it was finally time to brave the M1 and head back up to Shropshire. On behalf of the Harper Adams Entomology and IPM masters I would like to thank the Royal Entomological Society for their hospitality and a great day out.

Richard Prew

Sources and further info: