Genetic Diversity and Lineage Distribution of Hypera postica (Gyllenhal) Populations in Xinjiang, China

Hypera postica (Gyllenhal) is a major pest of alfalfa. We combined mitochondrial COI and CytB gene sequences to characterize the genetic diversity of 20 geographic populations of H. postica across Xinjiang, China, and to elucidate their lineage relationships at both regional and global scales. We found that Nucleotide diversity (Pi) was markedly higher in western Xinjiang populations (Pi > 0.016), specifically Wusu (0.023), Tekes (0.023), Jinghe (0.023), Wenquan (0.021), Bole (0.021), Habahe (0.020), Nilka (0.020), Tacheng (0.019), Toli (0.018), Altay (0.017), Emin (0.016), Xinyuan (0.016), and Zhaosu (0.016), whereas central Xinjiang populations exhibited substantially lower diversity (Pi < 0.014), including Shawan (0.014), Qitai (0.011), Jimsar (0.007), Urumqi (0.004), Hutubi (0.003), Fukang (0.001), and Manas (0.001). Pairwise FST analysis revealed pronounced genetic divergence between the western Xinjiang group (Altay, Bole, Wenquan, Tacheng, Emin, Toli, Nilka, Xinyuan, Tekes, Zhaosu) and the central Xinjiang group (Qitai, Urumqi, Fukang, Habahe, Hutubi, Jimsar, Shawan, Manas). At the global level, H. postica can be divided into two major phylogroups: the Western and Eastern lineages. All Xinjiang populations belong to the Eastern lineage. Haplotype network analysis identified two distinct sublineages, western and central Xinjiang, with H2 and H26 as their respective dominant shared haplotypes; both are unique to China. Both maximum likelihood (ML) and Bayesian phylogenetic trees robustly support the central Xinjiang lineage as a distinct clade. Neutrality tests provided strong evidence of recent demographic expansion across the Xinjiang H. postica population as a whole (Fu’s Fs = −21.987, p < 0.05), with particularly pronounced signals in Hutubi (HTB: Tajima’s D = −1.966, Fu’s Fs = −0.781, p < 0.05), Jimsar (JMSE: Tajima’s D = −2.176, Fu’s Fs = −0.962, p < 0.01), and Wenquan (WQ: Fu’s Fs = −11.159, p < 0.01). Our results reveal a clear phylogeographic split within Xinjiang H. postica populations, comprising western and central sub-lineages, with the western sub-lineage likely representing ancestral lineage. The western Xinjiang sub-lineage appears to be shaped primarily by mountainous topography, whereas the central Xinjiang sub-lineage likely results from the combined effects of piedmont plain geography and infection with the endosymbiont Wolbachia strain wHypera4.