LAUSR

BACKGROUND The small brown planthopper, Laodelphax striatellus (Fallén), is an important pest of rice. It is suspected of migrating over the sea from China to Japan. However, where in China they come from and how they affect Japanese populations remain unclear. RESULTS Here, we studied the genetic structure of 15 L. striatellus populations sampled from Japan and China using SNPs generated by the RADseq technique. We found weak genetic differentiation between the Chinese and Japanese populations. Our data revealed migration signals of L. striatellus from China to southern and northern Japan. However, the source regions of the immigrants remain unclear due to the low genetic differentiation between populations. Our results also pointed to the possibility of backward gene flow from Japanese to Chinese populations. We suspect that the southeastern wind associated with East Asian summer monsoon may facilitate the reverse migration of L. striatellus from Japan to China. Interestingly, we found that the X-chromosome displayed relatively higher genetic differentiation among populations and suffered more intensive selection pressure than autosomes. CONCLUSION We provide genetic evidence of transoceanic migration of L. striatellus from China to Japan and found that the X-chromosome can aid the deciphering of the migration trajectories of species with low genetic differentiation. These findings have implications for forecasting the outbreak of this pest and also provide insights into how to improve the tracking of the migration routes of small insects via population genomics. This article is protected by copyright. All rights reserved.