Using Genomic Data to Infer Evolutionary Processes in the Asexual Parasitoid Microctonus aethiopoides

Biological control offers a sustainable alternative to pesticides, with asexual parasitoids favoured for their ability to reproduce without males and produce all-female offspring. However, asexuality may limit the parasitoid's long-term adaptability to parameters, such as climate changes or physiological or behavioural changes in the host, reducing the potential effectiveness of the biocontrol. In this study, we performed whole-genome resequencing on 43 individuals of the Irish strain of the asexual (thelytokous) endoparasitoid Microctonus aethiopoides, which was introduced to New Zealand in 2006 to control clover root weevil (Sitona obsoletus). We sampled from five parasitoid populations, one from the original collection location in Ireland and four release locations in New Zealand, to assess spatial and temporal genetic variation and investigate the genetic basis for its reproductive mechanism. Population structure analyses revealed two distinct genetic clusters, likely reflecting the differential establishment of haplotypes introduced from Ireland rather than geographic isolation. Though one haplotype appeared more widespread, particularly in the South Island, further sampling is needed to confirm this. All populations exhibited uniformly low genetic diversity, with Tajima's D values decreased in contemporary populations, indicating population expansion since introduction. Patterns of high heterozygosity and short homozygous segments support automictic thelytoky, likely via central fusion, as the primary mode of asexual reproduction. However, linkage disequilibrium rates resembled those of sexual populations, suggesting possible facultative sexual reproduction in this species. Overall, our genomic data provide new insights into how asexual biocontrol agents persist and evolve post-release and shed light on this species' long-term viability and reproductive strategy.