Management intensity affects insect pests and natural pest control on Arabica coffee in its native range.
Abstract
Agroforestry systems provide opportunities to reduce the trade-off between agricultural production and biodiversity, for example by enhancing a diverse community of species potentially acting as natural pest control agents. While management of agroforestry systems is intensifying across the globe, we lack insights into the impact of management intensity on pest levels and natural pest control, especially along broad management gradients and as compared with natural forests. We assessed the impact of management intensity on major insect pests (the coffee blotch miner, the serpentine leaf miner, the coffee leaf skeletonizer and damage by other free-feeding herbivores) and natural pest control by parasitoid wasps across sixty sites in the centre of origin of Arabica coffee in southwestern Ethiopia. Within this region, coffee is growing along a broad management gradient ranging from little or no management in the natural forest to intensively managed commercial plantations. In the wet season, pest levels were largely similar in the natural forest, semi-forest and semi-plantation systems, whereas pests reached outbreak densities in the most intensively managed plantation system. In contrast, management intensity did not significantly affect pest levels in the dry season. The insect pests differed in their seasonal dynamics, consistently declined with elevation and were largely unaffected by shade levels. Parasitism rate of the coffee blotch miner was lower, and the parasitoid community was distinct, in the most intensively managed plantation system. Synthesis and applications: Our findings support the hypothesis that the weaker top-down control by parasitoids in the intensively managed plantation sites leads to higher pest levels, and that-at least for some pest species-there is a threshold in the effect of management intensity on pest levels and natural pest control. It is important to consider such non-linear relationships to maintain or enhance the sustainability of agroforestry systems during management intensification. Overall, our findings highlight that ecological knowledge of natural pest control can be used to intensify production to improve the livelihood of smallholder farmers without jeopardizing natural pest control but only up to a certain point where it starts to deteriorate.