Genetic Diversity of mtCO1 in Different Geographical Populations of Megalurothrips usitatus

Megalurothrips usitatus is a significant vegetable pest in China, causing substantial damage to legume crops as economic plants. The purpose of this study is to compare the genetic diversity of M. usitatus in different geographical populations and ascertain the genetic differentiation of M. usitatus, and to provide a theoretical basis for the precise control of M. usitatus.

A total of 18 geographical populations of M. usitatus were collected from 6 prefecture-level cities in Guangdong Province and 9 prefecture-level cities outside Guangdong Province. The mitochondrial DNA (mtDNA) cytochrome c oxidase subunit 1 (CO1) gene sequence was obtained based on PCR. The haplotype diversity (Hd), nucleotide diversity (π) of different geographical populations were analyzed, and Tajima's D neutrality test based on the mtCO1 was performed to evaluate the genetic structure of M. usitatus populations across different geographical regions. The fixation index (F_ST) and gene flow (Nm) were calculated to evaluate the degree of genetic differentiation among populations.

A total of 111 mtCO1 gene sequences were detected in 18 geographical populations of M. usitatus. A total of 617 conserved sites and 24 variable sites were detected, accounting for 3.68% of the total sequence length. A total of 20 haplotypes (H1-H20) were detected, of which H4 was the dominant haplotype, accounting for 48.6% of the total sequence and distributed in 17 populations. The overall population of M. usitatus exhibited relatively high haplotype diversity (Hd=0.677) and nucleotide diversity (π=0.00425), but nucleotide sequence divergence among different genetic types was not pronounced. The nonsignificant Tajima's D neutrality test indicated stable population size without marked expansion. Furthermore, the population fixation coefficient (F_ST=0.04973<0.05) and gene flow (Nm=9.55>1) suggested sufficient genetic exchange and low genetic differentiation among geographically distinct populations. The results of molecular variance analysis showed that the main factor causing the overall population variation was intra-population variation.

The geographically distinct populations of M. usitatus exhibited relatively high genetic diversity, with frequent gene flow and minimal genetic differentiation among populations, suggesting a stable overall population size. These findings provide a theoretical basis for the integrated management of M. usitatus field populations in diverse regions.