Insects are facing a worldwide decline caused by various anthropogenic factors such as land-use change, contamination, and climate warming. In Switzerland, butterfly population reduction has been observed in several species, but the lack of long-term population monitoring makes it challenging to reconstruct their historical trajectories.

Museum collections house billions of historical specimens, a high-value record of entomological data. The genomic information carried by those individuals has recently been made available by advances in museomics. Here, we investigate the temporal dynamics of three butterfly species (Polyommatus icarus, Pieris napi, Vanessa atalanta) since the early 20th century in Switzerland. To finely track temporal genetic changes, we performed an extensive sampling comprising 663 historical specimens collected in museums and spanning more than a century, alongside with 360 fresh samples for comparison with current populations, totaling 1023 individuals. Using cutting-edge methods allowing to recover thousands of genomic loci from historical (leveraging the HyRAD protocol) and fresh (applying a ddRAD approach) specimens, we aim at comparing population genetic parameters across multiple space and time points, including present-day.

Establishing population dynamics using estimates such as genetic diversity, effective size and inbreeding along the last century and all over Switzerland offers a retrospective view on the human impact on butterfly population through decades, providing valuable guidelines for future environmental management strategies.