Discovery of mass migration and breeding of the paintedlady butterfly Vanessa cardui in the Sub-Sahara: the Europe-Africa migration revisited

Migratory behaviour has repeatedly evolved across taxa as an adaptation to heterogeneity in space and time.However, insect migration is still poorly understood, partly because of the lack of field data. The painted ladybutterfly Vanessa cardui undertakes a long-distance annual migration between Europe and Africa. While springflights from the Maghreb to Europe are well characterized, it is not known how far the European autumnmigrants travel into Africa and whether they massively cross the Sahara Desert. We conducted fieldwork in fourAfrican countries (Chad, Benin, Senegal, and Ethiopia) in autumn and documented southward migrants incentral Chad and abundant breeding sites across the tropical savannah as far south as the Niger River in thewest and the Ethiopian highlands in the east. Given directionality and timing, these migrants probablyoriginated in Europe and crossed the Mediterranean, the Sahara and the Sahel, a hypothesis that implies thelongest (>4000 km) migratory flight recorded for a butterfly in a single generation. In the light of the newevidence, we revise the prevailing spatiotemporal model for the annual migration of V. cardui to incorporatetropical Africa, which could potentially be regarded as the missing geographic link between autumn (southwards)and spring (northwards) movements. © 2016 The Linnean Society of London, Biological Journal of the LinneanSociety, 2016.Funding was provided by the Committee for Research and Exploration of National Geographic (grant number 9528-14) and by the Spanish MINECO (project CGL2013-48277-P). G.T. is supported by the Marie Curie Actions FP7-PEOPLE-2013-IOF (project 622716) and by grant BP-A00275 (AGAUR-Generalitat de Catalunya).Peer Reviewe