Contrasting patterns of genetic structure and population demography in two Dicraeus species feeding on bamboo flowers in Japan

Population outbreaks of insects provide an excellent opportunity to elucidate their evolutionary history. In this study, we uncovered the phylogenetic relationships of Dicraeus spp. in Japan and compared the population genetic structure of two bamboo-feeding Dicraeus spp., Dicraeus phyllostachyus and Dicraeus nartshukae, by leveraging a recent nationwide mass flowering event of several bamboo species in Japan. We performed analysis using mitochondrial COI gene sequencing and genome-wide single-nucleotide polymorphisms detected by multiplexed inter-simple sequence repeat genotyping by sequencing (MIG-seq). We found genetic similarity in COI haplotypes over a large geographical range in the two Dicraeus spp., but, for both species, no concordance was detected between the collected host plants and genetic structures. In the genome-wide single-nucleotide polymorphism data, no clear genetic clusters were detected for D. phyllostachyus populations, whereas D. nartshukae populations were divided into two groups, in the north and south of Japan. Demographic analysis indicated that D. phyllostachyus had greatly expanded its population recently compared with D. nartshukae. These contrasting patterns between the two species might reflect the differences in the demographic history between the species. Our study suggested that the mass flowering event might cascade to the genetic structure of the florivorous insects through trophic interactions.