Résumé
Adaptation to host-plant defences through key innovations is a driving force of evolution in phytophagous insects. Species of the neotropicalbruchid genusAcanthoscelidesSchilsky are known to be associated with specific host plants. The speciation processes involved in suchspecialization pattern that have produced these specific associations may reflect radiations linked to particular kinds of host plants. By studyinghost-plant associations in closely related bruchid species, we have shown that adaptation to a particular host-plant (e.g. with a certain type ofsecondary compounds) could generally lead to a radiation of bruchid species at the level of terminal branches. However, in some cases of recenthost shifts, there is no congruence between genetic proximity of bruchid species, and taxonomic similarity of host plants. At deeper branches inthe phylogeny, vicariance or long-distance colonization events seem to be responsible for genetic divergence between well-marked clades ratherthan adaptation to host plants. Our study also suggests that the few species ofAcanthoscelidesdescribed from the Old World, as well asNeotropical species feeding on Mimosoideae, are misclassified, and are more closely related to the sister genusBruchidius.