Spatial distribution of Sahlbergella singularis Hagl. (Hemiptera: Miridae) populations and their damage in unshaded young cacao-based agroforestry systems

The population dynamics of African cacao mirids have been widely studied in shaded cacao systems, which are predominant in most of the cocoa producing countries. The current establishment of new cacao systems in Cameroon enables us to study mirids and the spatial distribution of their damage in six unshaded cacao plantations that are down on savannah and forest regions. We assessed mirids density through visual counts of individuals and damage by scoring dry leaves on branches and cankers on branches and trunks. Our results showed that the mirid populations were low and aggregated on few cacao trees. Mirid spatial distribution was structured in half of the plots and trees with mirids were grouped in distinct areas and/or scattered throughout the plots. Dry leaves damage was low but more widely spread with a spatial distribution less structured than mirid populations. Canker damage was high and their spatial distribution was structured, with some areas more infested. Since cankers accumulated on branches during the 4-years period following plot establishment, our results provide information about the history of mirid infestation in the plots. Despite the aggregation of mirid populations in the plots, infestation areas vary over space and time. However, the presence of higher infestations in some areas in the plots could indicate that there are zones that offer better ecological conditions to mirids. Our study contributed to a better knowledge of population dynamics for cacao mirids in sunny habitats as well as their damage; and these should be taken into consideration for integrated pest management strategies against S. singularis. (Résumé d'auteur