Abstract
The pearl millet head miner, Heliocheilus albipunctella, is a major constraint to increasing crop productivity in sub-Saharan Africa. In the absence of any insecticide application by farmers, its control mostly relies on the action of natural enemies. The objective of the present study is to identify crop management and landscape features affecting biocontrol services by natural enemies. A set of 45 millet fields were selected in a 20 ∗ 20 km area in Senegal, from the analysis of high resolution satellite images (Pleiades), and hypotheses on relative abundance of millet fields and semi-natural habitats (mainly trees) in the agricultural landscape. A biocontrol service index (BSI) was computed for each field over two cropping seasons by experimentally excluding natural enemies from naturally egg-infested millet panicles. Information on crop management was collected through farmer's interviews. An information theoretical approach and model averaging were performed to rank the effect of landscape metrics on BSI at eight spatial scales (from 250 to 2000 m). The BSI was generally high (77%) but highly variable among fields (0–100%), and was greater in compound fields compared to bush fields. The BSI also increased with the abundance of tree patches and the diversity of vegetation in a 1750 m-buffer around millet fields. Results support previous studies stressing the importance of semi-natural areas and vegetation diversity to support pest regulation by natural enemies. Further research is needed to better understand relationships between agroforestry systems and biological control, to promote ecologically-intensive solutions for reducing crop losses.