Zéphirin Tadu

Ant mosaics in cocoa agroforestry systems of Southern Cameroon: influence of shade on the occurrence and spatial distribution of dominant ants

In African cocoa agroforestry systems, ants represent the most important part of arboreal arthropod biomass and play a crucial role in ecosystem functioning. The more abundant are supposed to be involved in crop pest regulation. However, the lack of knowledge about ecological interactions between ants and their habitat, including other ant species of the community, leaded to contradictory views on their efficiency as potential biological control agents. In the present study, we studied the impact of shade trees on the occurrence and spatial distribution of the most abundant ants of cocoa agroforestry systems of Southern Cameroon. We characterized shade of four traditional cocoa farms and described distribution patterns of numerically dominant ants through spatial analysis. Our results showed that the populations of the most abundant arboreal species, in our study Oecophylla longinoda, Tetramorium aculeatum, Crematogaster spp., Camponotus spp. were generally aggregated in plantations. However, the distribution structure of ant populations was variable between samples, suggesting that the normal development of ant colonies may interfere with ecological constraints like interspecific competition and abiotic factors. Distribution mapping as well as statistical analysis showed that highest densities of O. longinoda were sheltered by cocoa trees in the sunniest areas of plots. On the other hand, Crematogaster species were usually strongly aggregated in the most shaded areas. Mechanisms involved in ant/shade relationships were discussed and we suggested that a good management of shade may take into account ant communities, which could play a significant role in conservation biological control against cocoa pests.

Ant Diversity in Different Cocoa Agroforest Habitats in the Centre Region of Cameroon

Agroforestry systems may represent refugia for native fauna in highly disturbed environments. In the context of ongoing intensive destruction of tropical rainforest by agricultural activities, there is a wealth of information on the influence of agricultural practices on arthropod diversity on southern Cameroon cocoa farms. The present study examined the diversity and the composition of ant communities on traditional cocoa farms in relation to agricultural practices along a south—north latitudinal gradient in the Centre Region of Cameroon. Ants were sampled in 21 plots using the chemical knock-down technique, along a latitudinal gradient from Ngomedzap (forest) in the south through Obala (forest-savanna) to Bokito (savanna) in the north. Species richness, Shannon diversity index and Bray-Curtis distance were used to characterize diversity of ant communities and their dissimilarity between habitats. A total of 66 ant species, belonging to 24 genera and seven subfamilies were identified from a sample of 114 843 workers. The ant diversity of Obala is higher than that of Ngomedzap and Bokito. Estimation of Bray-Curtis distances demonstrated that the ant communities of Ngomedzap and Obala were similar to each other, but very different from that of Bokito. The ant communities of Centre Cameroonian cocoa farms appeared relatively diversified. These communities varied in species composition and diversity in relation to agricultural practices along south—north latitudinal gradients.

Identifying ant-mirid spatial interactions to improve biological control in cacao-based agroforestry system

Abstract The use of ants for biological control of insect pests was the first reported case of conservation biological control. Direct and indirect community interactions between ants and pests lead to differential spatial pattern. We investigated spatial interactions between mirids, the major cocoa pest in West Africa and numerically dominant ant species, using bivariate point pattern analysis to identify potential biological control agents. We assume that potential biological control agents should display negative spatial interactions with mirids considering their niche overlap. The mirid/ ant data were collected in complex cacao-based agroforestry systems sampled in three agroecological areas over a forest-savannah gradient in Cameroon. Three species, Crematogaster striatula Emery (Hymenoptera: Formicidae), Crematogaster clariventris Mayr (Hymenoptera: Formicidae), and Oecophylla longinoda Latreille (Hymenoptera: Formicidae) with high predator and aggressive behaviors were identified as dominant and showed negative spatial relationships with mirids. The weaver ant, O. longinoda was identified as the only potential biological control agent, considering its ubiquity in the plots, the similarity in niche requirements, and the spatial segregation with mirids resulting probably from exclusion mechanisms. Combining bivariate point pattern analysis to good knowledge of insect ecology was an effective method to identify a potentially good biological control agent.