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The story of Chocolate
And the unsuspecting secret ingredient
Flies, you see, are the only pollinators of chocolate, or more specifically Theobroma
cacao, the cacao or cocoa tree. This plant species has a complex reproductive
structure, so complex in fact that only one group of very small flies, amusingly known as
No See Ums, can pollinate it.
The pollinating role of flies is hugely important for the general health of a range of
ecosystems, including agricultural ones. Of the 150 families of flies, almost half, 71,
have been shown to feed from flowers and therefore in principle transmit pollen from
one plant to another.
Pollination is a process that allows seeds to be formed in plants. It begins when pollen
grains from the male part of a flower come into contact with the female part of the same
species, and ends when the pollen grain successfully fertilizes the ovule, producing one
or more seeds. Pollination can be manual or mediated by various vectors such as
water, wind, vertebrate animals such as birds and bats, and invertebrates such as
butterflies, bees and flies. Flowers provide food or shelter for their visitors and, in return,
visitors carry pollen from one flower to another resulting in new individuals.
The Theobroma cacao tree produces about 250,000 flowers per year and these are
hermaphrodites; that is, they have both male and female parts. However, a cocoa flower
cannot self-pollinate and needs pollen from another flower – from another flower or from
the same tree – in order to create offspring. Cocoa flowers are strictly entomophilous
pollinated, meaning that they can only be pollinated by insects, particularly tiny flies
belonging to the Ceratopogonidae family.
This limitation is due to several factors:
1) the flower is only two centimeters long; 2) the pollen is protected by the petals, and 3) because of its shape and texture, the pollen cannot be transported by wind or water.
Only a very small, hairy insect (such as ceratopogonids) can enter the cocoa flower and
access the pollen. Only about 10% of flowers are pollinated; and the flowers that are
not, are aborted as the plant’s natural mechanism. Of the total number of pollinated
flowers, less than 5% develop into mature fruit (Groeneveld et al., 2010).
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