I spent the last week in Kumasi, Ghana, one of the major cocoa-growing regions in the country. My mission there was to train and lead a team in the collection of environmental DNA in different cocoa-growing systems. Undoubtedly, the results of that work, when published, will be featured in this newsletter. I thought it would be fitting that this week’s article is about Cocoa. Cocoa farming is vital to Africa’s economy, especially in the West and parts of Central Africa, where its cultivation provides livelihoods for millions of small-scale farmers. Recent shifts from traditional shaded agroforestry systems to more intensive “full-sun” monocultures raise questions about long-term sustainability. This article summarises the findings of a study conducted in Cameroon, which explores the connection between shade management and insect communities in cocoa farms. The study compares these monocultures with traditional agroforestry systems and investigates the subsequent effects on insect communities.
The Shade Dilemma: Sunny vs. Shady Farms
Traditionally, Cocoa is cultivated under a canopy of shade trees. This agroforestry method offers numerous benefits, such as preserving biodiversity, enhancing soil health, and providing crucial ecosystem services. However, the recent trend of intensified farming dubbed ‘full sun’, which involves clearing land and planting cocoa trees in open areas, has raised concerns about long-term consequences. Sunny farms initially produce more Cocoa, but they face several challenges in the long term. These include higher pest burdens, loss of beneficial insects, shorter productive lifespans, and greater vulnerability to climate change.
The Study Approach: Field Surveys and Modelling
The study was conducted across 28 cocoa farms in the Centre, East, and South regions of Cameroon. These farms were selected based on their shade cover, size, and logistical feasibility, and they were ensured to be located at least 500 meters apart.
Shade cover was measured using an extensible pole-mounted camera to capture pictures of the canopy above cocoa tree crowns. The percentage of vegetation cover was calculated for each picture, and the mean shade cover was derived from ten pictures taken along transects within the farms, ranging from 20% to 98%.
Three sampling methods were used to survey arthropod populations: sweep netting, malaise traps, and visual surveys. Sweep netting involved two sessions per visit, one at dawn and one at dusk. Each session consisted of walking a 240-meter transect through the farm, sweeping vegetation at chest height every 6 meters, alternating between left and right. This resulted in a total of 40 sweeps per session. The contents of the sweep net were transferred to plastic bags containing cotton wool soaked in 50% ethanol. After the arthropods ceased moving, they were identified to order level and counted.
For malaise traps, two traps were set up at each farm the evening before the dawn sweep netting session. Traps were positioned at least 20 meters from farm boundaries and separated by a minimum of 50 meters. They were unbaited, with collection jars containing 50% ethanol, left for 24 hours to collect arthropods. Collected specimens were identified and counted to order level upon retrieval.
Visual surveys were conducted in two forms: full tree visual surveys and pest counts. A sub-sample of eight farms was selected for tree visual surveys, involving 25-minute observations of all arthropods in a specific cocoa tree. Each survey was divided into five 5-minute periods focusing on different parts of the tree. For pest counts, the methodology was similar, but only pests damaging the cocoa trees were recorded. These surveys were carried out at dawn, and the observer recorded arthropods found on trunks or branches below eye level during a 40-minute walk through the site, inspecting about 50 trees per site.
The study focused on 11 arthropod taxa, including various orders and the brown capsid, which is considered the primary pest of Cocoa in Africa. Data analysis involved a Bayesian hierarchical model to integrate data from the three sampling methods, capturing the community composition and estimating population size for each arthropod order.
Four Key Findings
More Shade, Fewer Pests: Farms with more shade cover had significantly lower populations of pest insects, including brown capsids and mealybugs.
Beneficial Insects Thrive in Shade: Insects that provide valuable ecosystem services, such as spiders and flies, were more abundant in shady farms.
Shifting Community Composition: Overall, shady farms had more beneficial insects and fewer pests, leading to a more balanced ecosystem.
Seasonal Effects: Researchers discovered variations in insect population seasonally, with brown capsids being more abundant during the wet season.
A Bit About The Brown Capsid- a Major Pest of Cocoa
Brown capsids, scientifically known as Sahlbergella singularis, are the primary pests affecting cocoa crops in Africa. These small, sap-sucking insects belong to the Hemiptera order and are notorious for causing significant damage to cocoa plants, resulting in annual crop losses estimated between 25% and 40%.
Notably, the research revealed that brown capsid populations are significantly affected by shade cover. Their abundance was four times higher in sunny farms compared to shady farms. Additionally, brown capsid populations showed seasonal variation, doubling from the dry season to the wet season. These findings have important implications for cocoa farming practices, suggesting that maintaining shade trees in cocoa farms could be an effective strategy for controlling this major pest.
Implications for Cocoa Farming
This research emphasises the importance of shaded cocoa farming practices in maintaining insect biodiversity and ensuring sustainable crop production. Shaded farms, with their lower pest burdens and more balanced ecosystems, offer a viable and resilient approach to cocoa cultivation. Farmers, policymakers, and stakeholders in the chocolate industry should acknowledge these findings and promote biodiversity-friendly farming practices. Future research should continue exploring the detailed interactions between shade cover, insect communities, and the ecosystem services they provide to optimise sustainable cocoa farming in Africa.
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