Protecting Ghana's precious bean

Cracking open a healthy green cocoa pod, research entomologist Joseph Sarfo reveals the thick white flesh which conceals the cocoa bean and the mainstay of the Ghanaian economy. The purple-coloured and bitter tasting bean is Ghana's largest cash crop. But not every cocoa pod looks as healthy at harvest. Between 30 and 40 per cent of the cocoa produced globally is lost to pests and diseases. For Ghana, the world's second largest cocoa producer at 600,000 tonnes annually, this represents a huge and avoidable loss.

Striking a natural balance

With over 60 per cent of Ghana's population directly or indirectly dependent on cocoa production, the Cocoa Research Institute of Ghana (CRIG) takes its work of seeking ways to manage pests and diseases very seriously. There is one pest in particular which poses a major threat to Ghana's cocoa. Mirids, or capsids, feed on the cocoa pod or shoot, sucking the juice from the pod and eventually turning it black. Sarfo reports that the pests can reduce yield by 30 per cent or more: "That's drastic! In fact, if you don't control them the whole farm will be destroyed, so we are looking at up to 100 per cent damage, particularly where control or management practices are poor." Mirids attack cocoa trees in pockets, but can be prevented from spreading if caught early. Chemical pesticides have been the traditional method of control, but alternative techniques developed by CRIG are proving promising.

"We want to shift away from the use of chemicals because of the problems that are associated with it. Our consumers are very much aware about the health implications," says Sarfo. Chemicals are expensive and often inaccessible to Ghanaian farmers. They also pollute the environment and kill other insects, including beneficial insects such as natural enemies. Looking for ways to maintain the natural balance, Sarfo and his CRIG colleagues have developed a cheap and easy way to target and control the mirid pests.

Pheromone traps

Mirids, like other insects, produce pheromones which influence behaviour. Different pheromones affect different behaviour processes, and CRIG's research focused on pheromones that mirids use in reproduction. After the female sex pheromone had been identified and isolated, it was synthesised in the laboratory and then tested for its effectiveness in attracting male mirids. The synthetic compounds showed identical properties to the natural chemicals produced by females.

The next stage is to use these synthetic pheromones to develop traps, and this stage is still in progress. The most promising model has a sticky substance on the inside of the trap, so that the males, attracted by the pheromones, get stuck inside. If enough males are trapped, this will break the reproductive cycle and control the pest.

Sarfo says that farmers involved in trials have welcomed the new technology. However, sustainability is an issue as it is difficult to make the traps from locally sourced materials. Further research is also required to determine whether the numbers of insects trapped is sufficient to control the pest, or whether the traps would be better utilised as a monitoring tool. "Let's say we find out that a certain number of the traps can control the damage by attracting the males, fine. But even if it cannot control the insect directly, the numbers trapped provides an indication of their presence on the farm, and that can be used for monitoring," says Sarfo. Chemical usage can then be reduced by only applying when mirid populations are likely to cause substantial damage to the cocoa pods.

Developing new models

At the experimental cocoa plots of the research institute, a thick carpet of brown and yellow leaves indicates the mirid-infested trees. They are a reminder of what every cocoa farmer in Ghana fears. The exact direction of the new trap technology - to monitor or control mirids - is yet to be decided, but there is no doubt that new, environmentally friendly pest control methods are needed.

Cocoa is important throughout West Africa, and this was highlighted during the African Cocoa Summit in Nigeria in May 2006. The CRIG is looking for ways to work with other countries in the region, to share ideas and successes. Researchers from CRIG have visited Cameroon, for example, where research is currently focusing on hydraulic compression sprayers for mirid pest control. Cocoa farmers in Ghana and throughout the region will be hoping that these and other pest control methods fulfil their promise.

For further information see project details on Research for Development