Gestion intégrée des ravageurs de céréales et de légumineuses stockées au Sénégal par l’utilisation de substances issues de plantes

This thesis used an integrated approach to develop options for the control of cereal and legumes insect pests in Senegal combining laboratory and field tests. A diagnostic survey was conducted to fully understand current storage practices and control methods in foods and seeds. The study focused on traditional practices from the eastern parts of Senegal to develop options in harmony with the populations concerns. Boscia senegalensis is a plant known for its medicinal properties and its food use was the first plant to be tested for the control of Caryedon serratus, the groundnut weevil. We observed that fruits (3% w/w) and crushed leaves (6% w/w) of this species protected groundnuts. B. senegalensis was subsequently used for protection of cowpea, millet and maize against Callosobruchus maculatus, Tribolium castaneum, Sitophilus zeamais and Prostephanus truncatus. Only T. castaneum was insensitive to this plant at low concentrations. Methylisothiocyanate (MITC) is the main active ingredient of this plant liberated from glucocapparin. This molecule can reach C. maculatus and C. serratus larvae and eggs which develop inside grains but concentrations need to be two to four times higher than adults. Ripe fruits still proved to be effective but immature fruits had a higher efficacy. Residues of MITC were detected in the stored grains after treatment, but the treatment had no effect on germination of stored grains. During the study a reliable and effective method to analyze glucocapparin in leaves and fruits of B. senegalensis was developed, during two years in four localities showing an apparently very marked “soil effect”. Highest glucocapparin concentrations were recorded in January at the beginning of dry season and the lowest during the rainy season from August to November, independent of locality. Powdered maize cobs were effective in maintaining maize grain quality in laboratory studies. Observed damage and losses were respectively 5 and 1% at 2.4% (w/w). At higher doses, mixing of powdered maize cobs with grains offered equal protection as Actellic (pyrimiphos-methyl). The efficacy of this control method was tested during two years in farmer’s granaries confirmed the validity of the laboratory tests. The traditional practice of incorporating insecticidal plants within the storage structure did not impact development of pests already established in the granaries. By contrast, storage of maize cobs using a sandwich method with Hyptis spicigera proved to be effective against storage pests. In addition, the storage of non-winnowed maize grains offered a substantial degree of protection against insect infestations. Their composition was carried out by GC-MS/GC-FID analyses.