Résumé
Phytophagous insects are models of choice to study adaptive divergence since they often display clear feeding preferences, along with life history traits linked to their host plants. Characterizing the evolutionary mechanisms contributing to their divergence would help us better understand host shift and speciation events. In Western Europe, two sympatric, sibling species have been characterized within the Ostrinia genus (Lepidoptera, Crambidae): the European corn borer O. nubilalis, which larvae feed on this crop, and O. scapulalis, which exploit different dicots. As corn was introduced in Europe 500 years ago, O. nubilalis could have arisen through a host shift from O. scapulalis (which would be ancestral), followed by host specialization on corn and the evolution of incomplete reproductive isolation barriers. To test this hypothesis and better assess the divergence history between the two species, we collected and genotyped more than 500 individuals across Europe on the different host plants. Population structure analyses using 200 000 SNPs genome-wide suggest a longitudinal isolation by distance pattern in O. scapulalis and intermediate populations in Southern Europe, possibly because of secondary contacts. Our analyses also uncover a putative chromosomal inversion encompassing half of the sex chromosome, and which contribution to the divergence varies across both species ranges. These preliminary results should help clarifying the evolutionary history of O. nubilalis and they will be discussed in the context of the recent introduction of corn in Europe.