Cacao tree pollination remains a mystery

It’s strange that cacao, the main ingredient in chocolate, is central to a great mystery. For centuries, humans have grown and eaten cacao but somehow, we never understood one of the central processes that gave us such delicious food – its pollination.

Cacao flowers are tiny and the insects that gather on the tree are also miniscule and diverse, so it may be excusable that no one’s looked close enough at the right time to find a pollinator for cacao. Now, new research published in the journal Ecological Solutions and Evidence examines the pollination of cacao.   

In northern Peruvian dry agroforests – that is, cacao plantations grown in the shade of other trees – glue was applied to the flowers of the plant to see what insect visited. A variety of insects were caught, with 38% being aphids, 13% were ants and 10% were thrips. In wet agroforests of southern Peru, thrips made up 65% of the insects caught, midges were 14%, and parasitic wasps were 10% of visitors. 

There was also a difference in the behavior of insects in these different habitats. In dry agroforests, more insects were found in the shade. In the wetter agroforests, however, insects preferred to be in the sun – at least during the rainy season when the research was carried out. 

Interestingly, the cacao set fruit at a rate of just 2%, hand pollination was only able to raise this number to 7%. This baffled the scientists who could only hypothesize. Perhaps there are no good pollinators for cacao in Peru. The scientists also noted that only an average of 30 pollen grains were found on cacao flowers, much less than expected for successful pollination. 

There is still much to investigate in the pollination of cacao. “Among other things, it would be important to identify the main pollinators,” said Justine Vansynghel, lead researcher and PhD student.

This information could help improve the yields of cacao in native regions like Peru, which lags behind the pollination rates of plantations in Asia and Africa, probably because these plants are high yielding clones. More research may finally discover the pollinator but for now, cacao remains a delicious mystery. 

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By Zach Fitzner, Earth.com Staff Writer