Phylogenetics and population genetics of the Eurasian parasitoid Macrocentrus cingulum based on mitochondrial and nuclear loci

Specifying species boundaries is often tricky, because advanced biomolecular analyses can reveal that morphologically similar individuals in fact belong to distinct species. This is frequently the case when populations previously considered as a single polyphagous taxon prove to consist of several genetically distinct taxa using different resources, e.g., among insect parasitoids. Macrocentrus cingulum Brischke (Hymenoptera: Braconidae), a parasitoid of the genus Ostrinia (Lepidoptera: Crambidae) feeding on various host plants across the world, is one of them. In Western Europe, M. cingulum has never been found in Ostrinia nubilalis (Hübner) populations feeding on maize, although it heavily parasitizes sympatric Ostrinia scapulalis Walker populations feeding on mugwort. In contrast, it contributes to pest control of Ostrinia furnacalis Guenée feeding on maize in Asia and O. nubilalis feeding on maize in America, suggesting that European and Asian M. cingulum populations might form two distinct taxa. We tested this hypothesis by conducting phylogenetic and population genetic analyses based on two mitochondrial and two nuclear genes, on 97 M. cingulum individuals sampled in Asia, USA, and Europe. Our analyses not only suggest that all sampled M. cingulum probably belong to the same species, but also show a significant genetic differentiation between individuals originating from Europe on the one hand and Asia/USA on the other, which correlates with infestation patterns. Moreover, they show that American specimens are closely related to Asian ones, consistent with historical records about M. cingulum introductions into the USA in the 1920s and 1930s to control expanding O. nubilalis populations. Combining these results with what is known about the evolutionary history within the genus Ostrinia, we offer a candidate evolutionary scenario that is amenable to future empirical testing. (Résumé d'auteur