Résumé
Understanding the evolutionary history of biological control agents in their native ranges is crucial for improving their selection, establishment, and performance across environmentally diverse regions. Phytophagous insects that specialize on aquatic plants offer particularly valuable models, as their evolutionary trajectories may be shaped by a combination of climatic variation, host plant availability, and the fragmented nature of aquatic habitats. Megamelus scutellaris is a monophagous planthopper native to South America that has been introduced into the United States and South Africa as part of biological control programs targeting the highly invasive aquatic plant, Pontederia crassipes. In this work, we combined nuclear SNP and mitochondrial sequence data to investigate the genetic structure, demographic history, and environmental drivers of population divergence in M. scutellaris across its native range in Argentina and Paraguay. We identified three main genetic lineages broadly associated with major river basins and ecoregions. Demographic modeling supported an early divergence, likely linked to Pleistocene climatic shifts and hydrological changes, followed by a more recent split dated to the early Holocene. Contemporary gene flow was asymmetric and varied in magnitude among lineages, reflecting differences in connectivity and environmental conditions. Lastly, landscape genomic analyzes revealed a strong association between genetic differentiation and climatic variation, supporting models of isolation by environment and resistance. These findings highlight the role of evolutionary and ecological processes in shaping the genetic landscape of M. scutellaris and provide key insights for selecting source populations better suited to different environments in introduced regions.