Genetic diversity and genetic differentiation pattern of an endoparasitoid parasitizing the invasive gall midge across China.

Platygaster robiniae Buhl & Duso (Hymenoptera: Platygastridae) is an important parasitoid of the black locust gall midge Obolodiplosis robiniae (Haldeman) (Diptera: Cecidomyiidae), an invasive pest that has spread from its native range in North America to Europe and Asia in recent decades. As the dominant natural enemy of O. robiniae in both its native and introduced regions, P. robiniae plays a notable role in the biocontrol of the invasive pest. Understanding the population genetic structure and historical dynamics of P. robiniae is important for gaining valuable insights into the interactions between the parasitoid and invasive species of O. robiniae. However, these aspects remain poorly understood. In this study, we analyzed the genetic variation and historical dynamics of 22 P. robiniae populations across China using mitochondrial cytochrome oxidase subunit I (COI) gene sequences. Our results revealed a high level of genetic diversity and significant genetic differentiation. P. robiniae populations represented relatively abundant haplotypes (59 haplotypes) and phylogenic relationships showed that all populations clustered into 2 clades. Demographic analyses suggested that P. robiniae populations in China have undergone a recent population expansion. These findings provided valuable genetic insights into P. robiniae and contributed to a better understanding of the evolutionary dynamics of an endoparasitoid associated with an invasive gall midge in newly colonized regions.