Résumé
Worldwide, crop monocultures have proven to be particularly susceptible to pests and diseases. In Africa, unshaded "pure" cocoa plantations are often highly damaged by mirids and consequently require intensive phytosanitary protection. The aim of this study was to assess the impact of an alternative agronomic practice, a cocoa-fruit intercropping system, on infestation by Sahlbergella singularis, the main pest of cocoa in Cameroon. We focused our study on the potential effect of fruit trees as physical barriers, limiting mirid infestation during the first years of plantation, when fruit trees are not yet developed enough to provide cocoa with shade. Over two consecutive years, we assessed mirid infestations in seven four-year-old plantations located in the Centre region of Cameroon. Plantations were about one-third ha and included lines with fruit trees (avocado, safou and citrus) replacing cocoa on a regular basis. Mirid infestation was assessed at the population peak through observation of individuals or recent damage on cocoa pods and shoots. Spatial pattern analysis was done with presence-absence data through join count analysis and permutation tests. Our results showed that 1) mirids were strongly aggregated at small distance and 2) the cocoa-fruit intercropping system presented here did not impact mirid distribution on cocoa. These studies contribute to the improvement of IPM strategies for cocoa mirids through a better knowledge of population dynamics of these pests in plantations with reasoned patterns. (Résumé d'auteur)