Population structure and gene flow in the global pest, Helicoverpa armigera

Abstract

Helicoverpa armigerais a major agricultural pest that is distributed across Europe, Asia, Africa and Australasia. This species is hypothesized to have spread to the Americas 1.5million years ago, founding a population that is at present, a distinct species,Helicoverpa zea. In 2013,H.armigerawas confirmed to have re-entered South America via Brazil and subsequently spread. The source of the recent incursion is unknown and population structure inH.armigerais poorly resolved, but a basic understanding would highlight potential biosecurity failures and determine the recent evolutionary history of region-specific lineages. Here, we integrate several end points derived from high-throughput sequencing to assess gene flow inH.armigeraandH.zeafrom populations across six continents. We first assemble mitochondrial genomes to demonstrate the phylogenetic relationship ofH.armigerawith other Heliothine species and the lack of distinction between populations. We subsequently usede novogenotyping-by-sequencing and whole-genome sequences aligned to bacterial artificial chromosomes, to assess levels of admixture. Primarily, we find that BrazilianH.armigeraare derived from diverse source populations, with strong signals of gene flow from European populations, as well as prevalent signals of Asian and African ancestry. We also demonstrate a potential field-caught hybrid betweenH.armigeraandH.zea,and are able to provide genomic support for the presence of theH.armigera confertasubspecies in Australasia. While structure among the bulk of populations remains unresolved, we present distinctions that are pertinent to future investigations as well as to the biosecurity threat posed byH.armigera.