What pollinates cacao trees?
You may not BEElieve it, but bees are not the pollinators of cacao trees around the world.
Cacao trees are pollinated by by a small fly called midges, about the size of fruit flies. There are various species of midges which belong to the genus Forcipomyia. You can see some images of them taken here. The larvae images were donated by entomologist Art Borkent, and the other images were taken by me using an electron microscope.
Cacao flowers are very tiny, and many creatures can’t properly pollinate them. However, midges are ideal to get into the little flower and pollinate them.
However, midges are not a specialized pollinator of cacao, and feed on the pollen and nectar from various kinds of plants. It is believed they are more passive, and just happen to pollinate cacao since they grow and live around the trees, as opposed to actively seeking them or having a symbiotic or specialized relationship with cacao as some other pollinators do.
This is one reason why cacao is not very efficient in regards to pollination. Only 1-5% of cacao flowers on a cacao tree are pollinated. Improving the conditions for midges to reproduce, especially during dryer months, may greatly improve pollination rates. However, the solution is not a one-size-fits-all, and local conditions need to be considered when trying to increase midge populations and pollination rates. It is said by some entomologists to be a under-researched topic, usually due to under-funding.
Although the sex ratio of midges at birth is relatively 1:1, it is found that cacao is pollinated predominately by females. It is theorized that perhaps they are out seeking high-protein pollen as nutrition for their egg and reproduction development.
To learn a great deal about midges and the research involved in their relationship to cacao, take a look at The Chocolate Tree by Allen M. Young.