Global FAW population genomic signature supports complex introduction events across the Old World

Native to the Americas, the invasive Spodoptera frugiperda (fall armyworm; FAW) was reported in West Africa in 2016, followed by chronological order of detections across the Old World and the hypothesis of an eastward Asia expansion. We explored population genomic signatures of American and Old World FAW and identified 12 maternal mitochondrial DNA genome lineages across the invasive range, while from 870 high-quality nuclear single nucleotide polymorphic DNA markers five distinct New World population clusters were identified, broadly reflected their native geographical ranges and absence of host-plant preferences. We identified unique admixed Old World populations, and admixed and non-admixed Asian FAW individuals, all of which suggested multiple introductions underpinned the pest’s global spread. Directional gene flow from the East into eastern Africa was also detected, in contrast to the west-to-east spread hypothesis. Our study demonstrated population genomic approaches via international partnership to address global emerging pest threats and biosecurity challenges.