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Contribution to cocoa mirid control in Africa

adult and nymphs on a cocoa pod. R. Babin © CIRAD" class="colorbox">adult and nymphs on a cocoa pod. R. Babin © CIRAD" border="0" width="200px" align="left"> Cocoa cropping is one of the main income sources of rural families in the forest region of Cameroon. However, this crop is hampered by pests such as mirids. Sahlbergella singularis and Distantiella theobroma are the most damaging cocoa crop pests in Africa. In some countries, they are responsible for cocoa production losses of 30-40%.

Pest control requires a good overall understanding of agroecological mechanisms and factors involved in the pest’s natural population dynamics. The biology of Sahlbergella singularis was therefore studied using laboratory reared mirids. A study of the demographic parameters of the reared population revealed that S. singularis is a slow growing species. This explains its low population densities in plantations. Fertility is also a key parameter explaining seasonal variations in natural populations. The growth of natural populations is thus associated with the presence of young cocoa pods, which provide females with a food source favourable for reproduction. A study on the impact of agroecological factors on S. singularis population densities in plantations revealed that densities depend on the cocoa crop plot conditions. Pesticide treatment, shading and the use of hybrid varieties are key cropping factors. Populations of this pest are also highly aggregated in plantation areas benefitting from maximum sunshin. Forest tree shade was found to be more uniform than fruit tree shade and therefore less conducive to the development of heavily infested areas, which are commonly called mirid pockets.

Mirid control recommendations of agricultural researchers are seldom applied by cocoa growers. The results have also been discussed with the aim of tailoring them to the cocoa cropping conditions that currently prevail in Cameroon.