Abstract
Genetic diversity is the 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 England. We have used a genotyping‐by‐sequencing approach to study whether (a) there is any underlying population genetic structure at a national and regional scale in this pest that can disperse long distances; (b) the populations evolve as a response to environmental change and selective pressures; and (c) the populations comprise anholocyclic lineages. Individual R. padi were collected using the Rothamsted Insect Survey's 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 England that mostly corresponded to a North–South division, although gene flow is ongoing between the two subpopulations. These genetic clusters do not correspond to different life cycle types, and cyclical parthenogenesis is predominant in England. Results also show that there is dispersal with gene flow across England, although there is a reduction between the northern and southern sites with the south‐western population being the most genetically differentiated. There is no evidence for isolation by distance and other factors such as primary host distribution, uncommon in the south and absent in the south‐west, could influence the dispersal 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.
Highlights
Insect pests are responsible for the loss of up to 20% of the major grain crops in the world with some models predicting that this yield loss will increase to 19 – 46% driven by a 2oC rise of the average global surface temperature (Deutsch et al, 2018)
This study shows that reduced genome sequencing approaches can detect population genetic structure in species like R. padi in regions where they disperse long distances (Delmotte et al, 2002; Loxdale & Brookes, 1988), which a priori should result in a weak signature of genetic differentiation, and help identify predominant mode of reproduction in the population by estimating the inbreeding coefficient and test for Hardy-Weinberg equilibrium (HWE), which is essential to understand plant virus transmission
The results of the present study suggest that the two genetic clusters identified in R. padi do not correspond to different reproductive forms
Summary
Insect pests are responsible for the loss of up to 20% of the major grain crops in the world with some models predicting that this yield loss will increase to 19 – 46% driven by a 2oC rise of the average global surface temperature (Deutsch et al, 2018). Aphids show great plasticity in terms of reproductive type at the intraspecific level; lineages in some species range from cyclical parthenogenesis with one sexual generation in autumnwinter (holocycly) to obligate parthenogenetic (Blackman, 1974; Leather, 1993) This variation results in a great capacity to adapt to different environmental conditions. As a result of this climatic induced response, a correlation between the proportion of obligate parthenogenetic and latitude has been shown (Blackman, 1974; Llewellyn et al, 2003; Simon et al, 1999) This variation in life-cycle drives abundance and plays a central role in the transmission of viruses to crops. This study will be relevant to improve the management and control of cereal viruses vectored by this pest species, such as BYDV
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