Population genetics of the meadow spittlebug Philaenus spumarius, the main insect vector of Xylella fastidiosa in Europe

Sap-feeding insects are known vectors of plant viruses and groups of economically important bacterial plant pathogens, such as Xylella fastidiosa . The bacterium X. fastidiosa was recently detected in Europe and is responsible for the destruction of entire ancient olive groves in Italy. X. fastidiosa is transmitted by xylem-feeding insects, including the meadow spittlebug Philaenus spumarius (Linnaeus, 1758) (Hemiptera: Aphrophoridae), which is the main vector of X. fastidiosa in Europe. P. spumarius is prevalent across Europe, including the United Kingdom, and the insect has a broad plant host range that enables it to vector X. fastidiosa to a diverse range of plant species. However, P. spumarius has been predominantly studied at the species level. To investigate the genetic structure of UK populations and assess migration patterns of this species, we first assembled its 2.7 Gb genome. In addition, we sampled P. spumarius populations at six localities in the UK (Norfolk, Kent, Sussex, Yorkshire, Wales and Scotland) and re-sequenced the genomes of 116 individuals. Across Europe, P. spumarius is split into three divergent mitochondrial lineages (haplogroups), of which two are found in the UK – one in the north and one in the south – whereas the third is predominantly found in southern Europe (e.g., Italy). SNP data from whole-genome sequencing showed a weak genetic structure among the UK populations in support of isolation by geographical distance and evidence of admixture between the two mitochondrial lineages. Furthermore, we did not find a clear clustering of insect genotype by host plant species, indicating that P. spumarius is probably a true generalist. We are exploring this further by generating a chromosome-level assembly of P. spumarius and using this assembly to reassess the UK P. spumarius population structure. Furthermore, we are collaborating with colleagues globally to examine the P. spumarius populations by re-sequencing genomes of ±200 individuals from populations across Europe, the USA and New ...