The Distribution of Ants in a Rwandan Coffee Plantation and Their Potential to Control Pests

Native ants are the oldest example of biological control agents used in tropical tree crops. Unfortunately, intensification of agricultural practices has led to a simplification of habitat and subsequent loss of native ant biodiversity. This paper describes an evaluation of the ants present in a Rwandan coffee plantation. The plantation was unshaded, intensively managed and regularly treated with pesticides. No herbicides or fertilisers were used, although the area had been mulched. Only five ant species were found in the plantation (Pheidole megacephala, Lepisiota depressa, Nesomyrmex angulatus and Camponotus (Myrmosericus) spp. (2 spp.). Pheidole megacephala dominated the plantation and occurred on 94 % of trees, while L. depressa, C. (Myrmosericus) spp. and N. angulatus each occurred on 13 % or less of trees. Pheidole megacephala and L. depressa were negatively associated, whereas C. (Myrmosericus) spp. were positively associated with L. depressa. Association between the coffee pests and ant species was not significant. We conclude that intensification of coffee production in this plantation and domination by P. megacephala has contributed to the low diversity of ants present and that those species that do occur there are not particularly efficient at reducing pest densities.