Structuring effect of the host plant in the groundnut bruchid, Caryedon serratus (Olivier, 1790) (Coleoptera: Bruchidae). Twenty-six samples of the groundnut seed-beetle which were reared from pods of five different host plants (Arachis hypogaea L., Bauhinia rufescens Lam., Cassia sieberiana DC., Piliostigma reticulatum (DC.) Hochst. and Tamarindus indica L.) in four localities of Senegal were compared using electrophoresis based on six loci of four enzymatic systems. The population structure of Caryedon serratus Olivier was analysed using Weir and Cockerham's estimator of Wright's F-statistics. θ value (0.235) and the dendrogram of Rogers'genetic distances revealed a high degree of genetic differentiation between host plants. Genetic analysis without C. sieberiana samples indicated that populations form host races which are partially isolated according to their host plants (θ = 0.035). Geographical distances between localities are not decisive for genetic structuration of C. serratus populations from a given host plant.