The Afrotropical breeding grounds of the Palearctic-African migratory painted lady butterflies (Vanessa cardui)

Migratory insects are key players in ecosystem functioning and services, but their spatiotemporal distributions are typically poorly known. Ecological niche modeling (ENM) may be used to predict species seasonal distributions, but the resulting hypotheses should eventually be validated by field data. The painted lady butterfly (Vanessa cardui) performs multigenerational migrations between Europe and Africa and has become a model species for insect movement ecology. While the annual migration cycle of this species is well understood for Europe and northernmost Africa, it is still unknown where most individuals spend the winter. Through ENM, we previously predicted suitable breeding grounds in the subhumid regions near the tropics between November and February. In this work, we assess the suitability of these predictions through i) extensive field surveys and ii) two-year monitoring in six countries: a large-scale monitoring scheme to study butterfly migration in Africa. We document new breeding locations, year-round phenological information, and host plant use. Field observations were nearly always predicted with high probability by the previous ENM, and monitoring demonstrated the influence of the precipitation seasonality regime on migratory phenology. Using the updated dataset, we built a refined ENM for the Palearctic-African range of V. cardui. We confirm the relevance of the Afrotropical region and document the missing natural history pieces of the longest migratory cycle described in butterflies.

Automated summary

Migratory insects play important roles in ecosystem functioning and services, but knowledge about their distributions is often limited. Ecological niche modeling (ENM) can be used to predict seasonal distributions, but field data is needed for validation. In this study, we assessed the predictions made by ENM for the painted lady butterfly migration between Europe and Africa using extensive field surveys and two-year monitoring in six countries. The field observations matched the ENM predictions and we discovered new breeding locations, phenological information, and host plant use. With the updated data, we built a refined ENM for the Palearctic-African range of the butterfly. This study confirms the importance of the Afrotropical region and provides missing natural history information for the longest migratory cycle described in butterflies.