This page will continue to be updated as our research develops.
Why are cocoa midges important?
From past research on cocoa pollination carried out many decades ago in different parts of the world, we can say that cocoa flowers are largely pollinated by midges (scientifically, Diptera: Ceratopogonidae). The importance of other insects for this process is not fully known. Cocoa midges carry pollen between cocoa flowers. Many clones of cocoa are self-incompatible, which means they depend upon receiving pollen from a different tree, and therefore it is important that insects are present to do this. Cocoa midges are the most efficient insects for this task because they are the perfect size to enter flowers, and their bodies are covered in tiny hairs which allow pollen grains to stick to them.
There is good evidence that hand or manual pollination increases yields of cocoa, so creating conditions that improve midge survival, resulting in more natural pollinators, should result in higher quality and quantity of cocoa yield.
What do midges need to live?
Cocoa midges are not strong flyers so it is important that conditions are good for their survival throughout the cocoa plantation. Exisiting research has found that the immature midges (microscopic, bristly yellow worm-like larvae) develop in rotting material such as leaves, banana stem and empty cocoa pods. Because they can not fly very far, such litter should be present through the cocoa farm. Good moisture and humidity are very important; we are finding that extended drought limits the number of midges around, particularly if the soil and leaf litter become very dry.
Adult midges are short-lived and feed at cocoa flowers. There is good evidence that something in the cocoa flowers is important to increase their lifespan and productivity.
How can a cocoa farm be managed to support pollinators?
Factors that likely to inhibit midge survival are:
- frequent use of pesticides, particularly when flowers are around - remember that midges breed in the ground, so treatments that soak the soil can also affect them
- prolonged dry spells or dry ground conditions
- too much or too little shade - presence of some shade trees and intercropping is good, but some open areas also help
- limited amounts of rotting vegetation on the ground
In particular, our early evidence suggests that moisture in soil, and presence of rotting food material for midges are key - long, dry periods may reduce midge numbers if there are few moist refuges for them to persist in, and when wetter weather returns, it may take longer for midge numbers to increase than for the cocoa to recover and flower again. Therefore, management to keep the soil layer moist (but not waterlogged) will support midges - but be aware that under some conditions this can also contribute to cocoa disease issues.
Our research and previous work by other scientists suggests that laying out breeding material for the midge larvae to develop in can support cocoa midges very effectively. The best breeding materials that have been tested so far are cocoa pods - but only this year's cocoa pods - and banana trash (especially sliced into thick discs). Old cocoa pods that are dried out and are no longer "slimy" inside are less useful as the moist "slime" is good for midges. It is fine to remove the pulp from inside the cocoa pods, however.
The CocoaPOP project will be investigating practical ways in which the pollination of cocoa can be improved and confirm what are the best ways to improve pollination services. We will share these results here as the project progresses.
You may also find this information document produced by CATIE useful and interesting: Sexual Reproduction of Cacao [pdf, 6.5MB] produced as part of their Central American Cacao Project.
What about biodiversity generally?
There is increasing evidence that in agriculture generally, a healthy ecosystem can support sustainable good yields. A diversity of pollinating species is often more effective than large populations of just a single pollinating species. Similarly, supporting a range of natural enemies - insects and other invertebrates that either prey on, or parasitise, pests - will help to minimise pest outbreaks. Natural enemies are often affected by pesticide use just as much as the pests are, so the decision to use pesticides in agriculture can be a complex one, depending on the level of pest damage being seen on the crop, and also whether the pests are vectors of crop disease (such as CSSV).
Recent research from other cocoa ecologists* has indicated that a healthy ant population on cocoa farms can raise yields. This is because ants serve as important predators of many pests of cocoa. (There is also some debate overn whether they play a pollination role in some places, but this is still very uncertain.)
The research also found positive effects of a good bird population, under certain management systems. Controlling levels of hunting carefully in cocoa plantations can form part of this.
Moderate shade is good for pollinators, and also supports predator populations.
*Gras, P., Tscharntke, T., Maas, B., Tjoa, A., Hafsah, A., & Clough, Y. (2016) How ants, birds and bats affect crop yield along shade gradients in tropical cacao agroforestry. Journal of Applied Ecology.
Which areas still need more research?
There are still many questions about cocoa pollination needing further research:
- Is banana pseudostem as good as cocoa pod litter for supporting midges? Is this the case in all countries?
- Which species of cocoa midge are the most important in different countries, and how do their needs differ?
- Does biochar affect cocoa midge numbers?
- What intercrops are best for cocoa midges? Are there other plants that can be grown to support them?
- How do cocoa midges find flowers...and is there any way we can breed cocoa clones to be more attractive to them?