The birds, the bees and everything in between – Part 1

Sarah E J Arnold, Garvin Perry, Puran Bridgemohan, Leroy Grey, Brandon Pierre, Elvis Gerald, Fradian Murray, Christopher Haughton, Opia Dockery, Alan G Buddie, Giovanni Cáfa, Sean T Murphy, Vernon Barrett, Steven R Belmain, Philip C Stevenson, 2015.

Edited by Dr. Marissa Moses and Dr. Lambert Motilal (Cocoa Research Centre, The UWI St. Augustine Campus) of a Paper presented at the International Fine Cocoa Innovation Centre Conference & Symposium, Trinidad and Tobago, March 23-24, 2015.

Cocoa is not often managed specifically for pollination and perhaps this needs to change.

Even if you are not a scientist, you are possibly aware that the ever industrious honey bees are in some sort of trouble. Worldwide, populations of bees are facing a collapse, the reason for which is still not entirely clear. The collapse phenomenon has however caught the attention of researchers and policy makers, because of the threat to food security. Bees are a major pollinator for many crops without which, the yields of food crops would be greatly reduced. Even though the honey bee is is not a pollinator for cocoa, there are common lessons to be drawn from the experience.

Some cocoa varieties are self-compatible, meaning that they do not need another variety to set fruit. However, even if varieties are self compatible or not, they still need the action of pollinators to produce fruit. In the 1940s, two researchers Posnette and MacFie, identified pollinator insects by studying individual flowers (Figure 1). They determined that small midges (Diptera: Ceratopogonidae), especially those in the Forcipomyia genus, and perhaps contributions from other Diptera (e.g. Cecidomyiidae) were the insects responsible for pollination in cocoa. However, the pollination ecology of cocoa is still not completely understood, including whether sufficient pollinators are always present on cocoa estates, and which factors determine midge population size and dynamics. A collaboration with the University of Trinidad and Tobago, University of the West Indies, Mona, and research institutions in the United Kingdom including Natural Resources Institute, University of Greenwich, Centre for Agriculture and Bioscience International (CABI), and the Royal Botanic Kew Gardens, was undertaken to better understand pollination dynamics in cocoa and to plan for their management on cocoa plantations.

Figure 1. Cocoa flowers on the branch of a cocoa tree. The flowers are approximately 1-2 cms long

Figure 1. Cocoa flowers on the branch of a cocoa tree. The flowers are approximately 1-2 cms long

Figure 2. Specially designed suction traps to collect insects in the field.

Figure 2. Specially designed suction traps to collect insects in the field.

The work consisted of:

  1. Invertebrate surveys of cocoa plantations in three islands, Trinidad, Tobago, and Jamaica over a 12 month period.
  2. Analysis of cocoa flower volatiles for major odour components to better understand how pollinators locate flowers.
  3. Meteorological data collection (ie. Rainfall)

At the time of reporting, approximately 62,000 insects from four out of six sites were captured and processed. These insects were captured using specially designed suction traps (Figure 2). Interestingly, only 1.9% of the insects were midges (Diptera: Ceratopogonidae), however there were almost ten times the number of Cecidomyiidae, earlier identified as secondary pollinators. Ceratopogonid midges are therefore generally present in cocoa estates, but not always abundant.

Analysis of cocoa flower volatiles also revealed the major odour components are different to those previously claimed. Work is ongoing to develop synthetic lures using these components for insect sampling and attraction in the field.

Finally, strong correlations were found between the previous month’s rainfall and the numbers of Ceratopogonidae caught, indicating that soil moisture, key for midge larval development, may be an important determinant of midge populations. These findings highlight the need to plan management strategies to take into account future unpredictable rainfall patterns, in order to safeguard sustainable pollination services in years to come. Further investigations will enable development of more detailed management guidelines to support sustainable pollinator populations on Caribbean cocoa estates.

To read more on these studies we recommend:

  1. Forbes, Samantha J., and Tobin D. Northfield. (2016) “Increased pollinator habitat enhances cacao fruit set and predator conservation.” Ecological Applications, 27(3): 887-899.
  2. Frimpong, E. A., I. Gordon, P. K. Kwapong, and B. Gemmill-Herren (2009) “Dynamics of cocoa pollination: tools and applications for surveying and monitoring cocoa pollinators.” International Journal of Tropical Insect Science 29, no. 02: 62-69.
  3. Winder, J. A. (1978) “Cocoa flower Diptera; their identity, pollinating activity and breeding sites.” Pans 24, no. 1 :5-18