Genetic diversity of the fall armyworm ( Spodoptera frugiperda JE Smith) population invading Ethiopia

Background : The fall armyworm (FAW) ( Spodoptera frugiperda J.E. Smith), a highly invasive pest of maize and other crops, was first reported in Ethiopia in 2017, where it has caused severe yield losses. Two sympatric host-associated strains, corn (C) and rice (R) are recognized. However, the genetic diversity and population structure of Ethiopian FAW remain poorly understood. Methods : We analyzed 250 larvae collected from maize and sorghum fields across four Ethiopian regions via mitochondrial cytochrome oxidase subunit I (COI) and nuclear triose phosphate isomerase (Tpi) markers. Results : COI data revealed 60.6% rice (R) and 39.4% corn (C) strains in Ethiopia. Tpi analysis classified all individuals as the corn strain, indicating a marker discrepancy, likely due to interstrain hybridization. Six COI haplotypes were identified, dominated by two widely distributed haplotypes (Hap1 = 60.8%, Hap3 = 37.1%). Neutrality tests revealed a significantly positive Tajima’s D (D = 4.68, p < 0.001) and Fu and Li’s F*, indicating an excess of intermediate-frequency variants consistent with population structure and lineage admixture rather than recent demographic expansion. AMOVA detected weak but significant genetic differentiation among regions (ΦST = 0.044), while PCoA revealed two major clusters corresponding to mitochondrial lineages rather than geographic origin. Conclusions : These findings provide the first comprehensive genetic characterization of S. frugiperda in Ethiopia and suggest multiple introductions and subsequent lineage mixing. The observed mito-nuclear discordance and strong population structure highlight the importance of genome-wide analyses to better resolve invasion history and inform sustainable management strategies.