How pollination affects chocolate production

A world without chocolate is hard to imagine. But cacao trees, which are the source of chocolate, are vulnerable.

I am a passionate chocolate lover and an entomologist studying cocoa pollination. The sustainability of the harvest currently seems to depend on several species of tiny fly pollinators that are frankly struggling to do their job.

thousands of flowers

Chocolate is made from the seeds of the cacao tree, Theobroma cacao L., which literally means “food of the gods.” The plant is native to the western Amazon region of South America and has been cultivated in many parts of Central and South America for more than 3,000 years. Today it is grown in equatorial regions around the world, including West Africa and several tropical regions in Asia.

These flowers are tiny, only about half an inch in diameter (1-2 cm). The flowers usually grow in clusters directly from the trunk of the tree or from large branches.

Each flower must be pollinated to successfully produce an almost football-sized fruit – a pod containing 30-60 seeds that can be made into chocolate.

It sounds simple, but successful cocoa pollination is actually problematic in many regions. Only about 10-20% of the flowers produced by a cacao tree are successfully pollinated. The rest, up to 90%, never get pollen – or not enough pollen to form fruit.

Scientists don’t fully understand cocoa pollination, which is surprising given that over 50 million people worldwide currently depend on chocolate for their livelihood.

A big task for a small fly

The insects responsible for pollinating the tiny cacao buds are themselves also tiny in order to gain access to the bud’s reproductive structures. Midges from the Ceratopogonidae family and gall midges from the Cecidomyiidae family are among the most important known cocoa pollinators worldwide.

Most cacao trees are so-called self-incompatible, meaning they cannot pollinate themselves. Successful pollinators must ingest pollen from the male parts of a flower on one tree and deposit it on the female parts of a flower on another tree.

Cacao blossoms are also short-lived and are usually only receptive to pollen for a day or two. Flowers that do not receive sufficient pollen will die and fall off within 36 hours of opening.

There is evidence that improving mosquito habitat can increase fruit yield. Therefore, in some cocoa-growing areas, current agricultural practices include the development and maintenance of appropriate soil habitats within and near cocoa plantations to increase the numbers of midges capable of pollen transmission.

Lasting Secrets

The success of artificial or manual pollination, which can more than double yields, shows that cocoa trees are capable of producing many more pods than they currently do.

Hand pollination is a technique used to increase cocoa yields. Credit: William Borney/Getty Images

It’s hard not to wonder: why don’t mosquitoes do a better job of pollinating cacao blossoms? Scientists think part of the answer may lie in the fact that mosquitoes don’t just depend on cacao blossoms for their life cycle. Since they can obtain sugars from other plant sources, they are likely to be passive rather than active pollinators of cacao. Scientists also wonder if they are up to the task of crossing the considerable distances between wild trees.

All of this begs the question: are there any insects better suited for this job? And if so, where did they go?

Most studies linking mosquitoes to cocoa pollination have been conducted in orchards, while the biology of wild cocoa pollination is almost completely unexplored.

One exception is a study that looked at both cultivated and wild cacao in Bolivia. It turned out that mosquitoes accounted for only 2% of all insect visitors to wild trees. Other flies and small wasps were more common there.

These results are intriguing and raise the possibility that one or more unknown insects are the primary pollinators of cocoa in the wild. Whether this is the case can only be shown by additional study of wild cacao. Such information could have far-reaching implications for the chocolate industry.