Abstract: 【Aim】 This study aims to identify the genetic differentiation and gene flow among geographic populations of Spodoptera exigua in China and clarify its population demographic history. 【Methods】 In the present study, the genetic diversity, genetic differentiation, gene flow and molecular variance were analyzed using DnaSP 5.0 and Arlequin 3.11 based on the partial sequences of mtDNA COI gene in 20 geographic populations of S. exigua in China. Phylogenetic trees and the haplotype network of COI haplotypes were also constructed. 【Results】 The results showed that a total of 10 haplotypes were defined among 529 sequences, including Hap_1 shared by all populations. Low level of genetic diversity (Hd=0.257±0.025, Pi=0.0007±0.0001, Kxy=0.323) in the total populations was detected. There was little genetic differentiation (F_ST=0.211) and a high level of gene flow (N_m=1.870) among different geographic populations. The analysis of molecular variance (AMOVA) showed that the percentage of variation within a population was greater than that among populations. There was no significant correlation between the pairwise genetic distances for mtDNA COI sequences and the natural logarithm of geographical distance. The phylogenetic trees and haplotype network showed that haplotypes were distributed in different clades and had no obvious geographical structure. Finally, the neutral test (Tajima’s D=-2.177, P<0.05; Fu’s F_S=-8.629, P<0.05) and unimodal mismatch distribution indicated that S. exigua experienced recent population expansion in China. 【Conclusion】 The results suggest that the gene flow among S. exigua populations is not affected by the geographical distance, further confirming that the moth has a high ability of migration.

Key words: Spodoptera exigua, COI gene, genetic differentiation, genetic structure, gene flow, Medianjoining network