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

Abstract

17Genetic diversity is determinant for pest species' success and vector competence. Understanding the 18 ecological and evolutionary processes that determine the genetic diversity is fundamental to help 19 identify the spatial scale at which pest populations are best managed. In the present study, we 20 present the first comprehensive analysis of the genetic diversity and evolution of Rhopalosiphum 21 padi, a major pest of cereals and a main vector of the barley yellow dwarf virus (BYDV), in Great 22Britain. We have used a genotype by sequencing approach to study whether i) there is any 23 underlying population genetic structure in this long distant disperser pest at a national and regional 24 scale; ii) the populations evolve as a response to environmental change and selective pressures, and; 25 iii) the populations comprise anholocyclic lineages. Individual R. padi were collected using the 26Rothamsted Insect Survey's suction-trap network at several sites across England between 2004 and 27 2016 as part of the RIS long-term nationwide surveillance. Results identified two genetic clusters in 28Great Britain that mostly paralleled a North -South division, although gene flow is ongoing between 29 the two subpopulations. These different groups do not correspond to sexual and asexual types, 30 sexual reproduction being predominant in Great Britain, and could correspond to ecotypes. Results 31 also show that there is migration with gene flow across Great Britain, although there is a reduction 32 between the northern and southern sites with the Southwestern population being the most 33 genetically differentiated. There is no evidence for isolation-by-distance and other factors like 34 primary host distribution could influence the migration patterns. Finally, results also show no 35 evidence for the evolution of the R. padi population, and it is demographically stable despite the 36 ongoing environmental change. These results are discussed in view of their relevance to pest 37 management and the transmission of BYDV. 38

Contrasting population structure and demographic history of cereal aphids in different environmental and agricultural landscapes

“…Of these loci, approximately 4% deviated from the Hardy–Weinberg equilibrium (HWE) after Bonferroni correction. The levels of gene diversity ( H e ) observed across all populations are lower than in previous studies of S. miscanthi in China, but similar to that of the UK population of S. avenae and other cereal aphids like Rhopalosiphum padi (Morales‐Hojas et al., 2019) (Table 2). Overall, the Chinese population is not in HWE, and the inbreeding coefficient is positive (Table 2).…”

“…The study demonstrates that the populations of S. miscanthi and S. avenae in China and England have evolved in the last 5 to 20 years, which could be as a result of environmental and human‐induced changes such as insecticide use, and the genetic structure and diversity have changed in comparison with that observed in earlier studies. This contrasts with what it has been observed previously in another cereal aphid in England, Rhopalosiphum padi , whose population has not shown any change in genetic diversity or structure at least since 2003 (Morales‐Hojas et al., 2019).…”

“…We discuss the results in view of the differences in life‐history types and the evolution of insecticide resistance, which may be limited by the reproductive type. These genomics approaches have identified genetic variation at a national and regional scale for other aphids in regions where they disperse long distances (Morales‐Hojas et al., 2019).…”