This blog entry is brought to you, somewhat belatedly, from the lovely island of Trinidad in the Caribbean.
Trinidad and Tobago, while having a big strength in industry, engineering and particularly oil and gas, is mindblowingly biodiverse when you get out of the cities and into the rural areas. The cocoa agroforestry systems are particularly lovely, with new wonders almost around every corner!
And it’s cocoa that’s brought me here. It’s an amazing tree, with flowers that come straight out of the trunk, and eventually develop (if pollinated) into vividly coloured pods about eight inches long. Like a lot of crops, it’s dependent on insect pollination – but while we’ve got a reasonable grasp of the pollination systems of crops like strawberry and oilseed rape in Europe and North America, with cocoa there are still big questions that we can only begin to answer with existing knowledge.
Starting with “What pollinates cocoa?”
Accepted wisdom is that cocoa is pollinated by 2mm long Ceratopogonid midges, particularly in the genus Forcipomyia1 – and, indeed, they seem to be the most effective insects for the job on a per-visit basis – lots of evidence suggests that they interact with flowers in the perfect way to pick up and deposit pollen, and that often one midge visit may be suffient to get a cocoa pod 9-odd months later2. However, they’re also relatively infrequent on a lot of cocoa fields, which raises the question of whether there’s really enough of them to account for the number of pods observed. How important are other small flies like Chironomids or Cecidomyiids? Do ants and thrips play a role, particularly in self-compatible cultivars of cocoa where pollen from another tree isn’t necessary for fruit-set? We don’t know nearly as much as we’d like to about the answers to these questions.
Similarly, how the midges find the flower is a bit of an unknown: do they see it, and if so…what are they looking for? Do they smell it – and if so, what are the important chemicals, and how much do they vary? What do they get from cocoa flowers that other flowers don’t (or do they?) provide?
And it seems that the cocoa needs them more than they need the cocoa. Everywhere cocoa has been planted in the world, be it Trinidad, Jamaica, Mexico, Hawaii, Ghana, Indonesia, Australia…, a species of Forcipomyia has shown up to pollinate it3. So clearly they were doing just fine long before the cocoa arrived, but once the cocoa is there they seem to derive some sort of benefit from it.
So…cocoa midges. While getting people interested in anything to do with chocolate is relatively easy, the midges themselves are somewhat less charismatic than other pollinators such as bees, hummingbirds or butterflies. Small, hairy, and closely related to various biting species – oh, and their larval stage is a 2mm long hairy maggoty thing that lives in rotting vegetation such as cocoa pods, rotting banana stem and leaf litter4.
Actually, understanding the larva is pretty important – while it’s the adults we need, we won’t get any if the larvae aren’t happy. That’s what we’ve ended up primarily focusing on this year in my current project out here. CocoaPOP (Cocoa Pollination for Optimised Production, or, formally, Optimizing Cocoa Production For Increased Yield and Income Generation) is a project co-funded by the EU via the ACP group of states, lead by the University of Trinidad and Tobago with partners from Trinidad, Jamaica and the UK. We’re looking at what’s going on with cocoa pollinators in the Caribbean – how healthy are the populations, what species are present, is the management supporting them, and how can we help? We’ve spent the last couple of years doing some fairly intensive insect sampling on 6 sites across 3 islands, to get an idea of what the pollinators do over the course of a year. We’re learning quite a lot and looking forward to publishing papers soon.
Now we’re on to the next phase – trying interventions to see how they affect pollinator numbers and eventual cocoa yield, and trying to understand the midges better. There’s evidence that this should work5, so fingers crossed! Rearing the little creatures in the lab is keeping us challenged, but we’re giving it our best shot! So I’ve spent the last couple of weeks busy in the lab and the field, helping to get the new experiments rolling and seeing what can be done to give us live midges in the lab to study.
I also had the opportunity to attend the first International Fine Cocoa Innovation Centre conference on the Ortinola Estate (formerly a cocoa estate owned by the Cadbury family, apparently). It was a great opportunity to learn about all stages of cocoa, from the genetics underpinning the important traits, through agronomy and then flavour profiles, marketing, small businesses and cooperatives. While the Caribbean is only producing a small amount of cocoa at the moment on a global scale, I think there is some real enthusiasm for increasing the region’s importance as a cocoa producer. I met some fantastic people from all sorts of areas of cocoa: academia, industry, SMEs and cooperatives. There was a pollination meeting/workshop afterwards too, which was an amazing opportunity to talk with lots of equally enthusiastic people about the next few big questions in cocoa production and discuss directions in future research.
1Billes, D.J. (1941) Pollination of Theobroma cacao L. in Trinidad, B.W.I. Tropical Agriculture (Trinidad), 18(8):151-156; . Posnette, A.F. (1944) Pollination of cacao in Trinidad. Tropical Agriculture (Trinidad), 21(6):115-118.
2Falque, M., Vincent, A., Vaissiere, B.E. & Eskes, A.B. (1995) Effect of pollination intensity on fruit and seed set in cacao (Theobroma cacao L.). Sexual Plant Reproduction, 8(6):354-360.
3Winder, J.A., & Silva, P. (1972). Cacao pollination: Microdiptera of cacao plantations and some of their breeding places. Bulletin of Entomological Research, 61(04):651-655.
4Besemer, H.A. & Soria, S. de J. (1978) Laboratory rearing of Forcipomyia spp. midges (Diptera, Ceratopogonidae): 1. Adult feeding, larval feeding and copulation trials; a revision of Saunders method of rearing. Revista Theobroma (Brazil), 8(2):43-59; Winder, J.A. & Silva, P. (1972) Cacao pollination: Microdiptera of cacao plantations and some of their breeding places. Bulletin of Entomological Research, 61(4):651-655.
5Groeneveld, J.H., Tscharntke, T., Moser, G., & Clough, Y. (2010) Experimental evidence for stronger cacao yield limitation by pollination than by plant resources. Perspectives in Plant Ecology, Evolution and Systematics, 12(3):183-191; Adjaloo, M., Banful, B.K.B., & Oduro, W. (2013) Evaluation of breeding substrates for cocoa pollinator, Forcipomyia spp. and subsequent implications for yield in a tropical cocoa production system. American Journal of Plant Sciences. 4(2):204-211.