Genetic structure at national and regional scale in a long-distance dispersing pest organism, the bird cherry-oat aphid Rhopalosiphum padi

Genetic diversity is determinant for pest species success and vector competence. Understanding the ecological and evolutionary processes that determine the genetic diversity is fundamental to help identify the spatial scale at which pest populations are best managed. In the present study, we present the first comprehensive analysis of the genetic diversity and evolution of Rhopalosiphum padi, a major pest of cereals and a main vector of the barley yellow dwarf virus (BYDV), in Great Britain. We have used a genotype by sequencing approach to study whether i) there is any underlying population genetic structure in this long distant disperser pest at a national and regional scale; ii) the populations evolve as a response to environmental change and selective pressures, and; iii) the populations comprise anholocyclic lineages. Individual R. padi were collected using the Rothamsted Insect Surveys suction-trap network at several sites across England between 2004 and 2016 as part of the RIS long-term nationwide surveillance. Results identified two genetic clusters in Great Britain that mostly paralleled a North - South division, although gene flow is ongoing between the two subpopulations. These different groups do not correspond to sexual and asexual types, sexual reproduction being predominant in Great Britain, and could correspond to ecotypes. Results also show that there is migration with gene flow across Great Britain, although there is a reduction between the northern and southern sites with the Southwestern population being the most genetically differentiated. There is no evidence for isolation-by-distance and other factors like primary host distribution could influence the migration patterns. Finally, results also show no evidence for the evolution of the R. padi population, and it is demographically stable despite the ongoing environmental change. These results are discussed in view of their relevance to pest management and the transmission of BYDV.