High genetic diversity and strong genetic structure of Strongyllodes variegatus populations in oilseed rape production areas of China.

Background: Strongyllodes variegatus (Fairmaire) is a major insect pest of oilseed rape in China. Despite its economic importance, the contribution of its population genetics in the development of any suitable protection control strategy for the management of oilseed rape crops is poorly studied. It is a much urgent need to prevent its spread to the rest of the world.

Results: Using the sequences of mitochondrial DNA cytochrome c oxidase subunit I (COI) and cytochrome b (Cytb) as genetic markers, we analyzed the population genetic diversity and structure of 437 individuals collected from 15 S. variegatus populations located in different oilseed rape production areas in China. In addition, we estimated the demographic history using neutrality test and mismatch distribution analysis. The high level of genetic diversity was detected among the COI and Cytb sequences of S. variegatus. The population structure analyses strongly suggested three distinct genetic and geographical regions in China with limited gene flow. The Mantel test showed that the genetic distance was greatly influenced by the geographical distance. The demographic analyses showed that S. variegatus had experienced population fluctuation during the Pleistocene Epoch, which was likely to be related to the climatic changes.

Conclusion: Overall, these results demonstrate that the strong genetic structure of S. variegatus populations in China, which is attributed by the isolation through the geographical distance among populations, their weak flight capacity and subsequent adaptation to the regional ecological conditions.