Molecular tools to study historic and recent pathways of entry and spread for the invasive Japanese beetle Popillia japonica and development of control strategy

Popillia japonica, commonly known as the Japanese beetle, represents a significant threat to agricultural and natural ecosystems outside its native range in Japan. This study analyses the genetic structure and invasive capabilities of P. japonica using advanced sequencing and genomic analysis methods. The first chapter details the creation of a new reference genome for P. japonica, emphasising the importance of a solid genetic basis for evolutionary and control studies. Despite the success in constructing the genome, some technical limitations raise questions about the complete representation of the genetic variability of the species. The second chapter focuses on the population genetics of P. japonica, tracing the beetle's migratory routes and analysing the structure of invasive populations. Using complete mitochondrial genomes, the study reconstructs range expansion from a phylogeographical perspective, identifying links between North American populations and those recently established in Europe. The third chapter examines the cytochrome P450 gene family, which has been shown to play a role in environmental stress response and insecticide resistance. The analysis reveals a significant expansion of some P450 gene clades, suggesting a potential link to the polyphagous ecology and great adaptability of P. japonica. Overall, the results outline a detailed understanding of the genetic adaptability of P. japonica and provide important foundations for more effective and targeted management and control strategies. This study emphasises the importance of an integrated approach combining genomic and ecological information to address the challenges posed by invasive species.