Intraspecific Hybridization Improves Performance of the Biological Control Agent Hypena opulenta

Introduced species often undergo genetic drift and natural selection, which can reduce genetic diversity and drive differentiation among populations. Intraspecific hybridization, outcrossing among individuals from genetically distinct groups, may counteract these effects by increasing heterozygosity, potentially improving performance. However, in classical biological control agents, genetic diversity is typically low due to small founding sizes, long-term quarantine rearing, and single-source collections from the native range. As a result, opportunities for beneficial hybridization may be limited. We evaluated whether intraspecific hybridization could enhance genetic diversity and performance of Hypena opulenta (Lepidoptera: Erebidae), a biological control agent of invasive swallow-wort vines (Vincetoxicum spp.) in North America. We used two populations: one reared under laboratory conditions for 28 generations, and another established in the field in Canada, separated from the lab population for 14 generations. We created a third population by crossing individuals from the two source populations. We conducted Whole Genome Sequencing (WGS) on 15-20 individuals per population to assess genetic divergence and heterozygosity and compared performance of the three populations under both laboratory and field conditions. Despite relatively recent separation, clear genetic structure had developed between the lab and field populations. Both exhibited low genome-wide heterozygosity, while the outbred population showed significantly higher heterozygosity. Hybridization also led to improved performance: outbred females produced more pupae in the laboratory, caused greater defoliation of host plants, and yielded the most second-generation adults in the field. These results demonstrate that even short-term isolation can lead to meaningful divergence and that intentional intraspecific hybridization can boost both genetic diversity and performance. Our findings suggest that outcrossing among recently separated populations could be a practical approach to improve performance of biological control agents prior to field release, with broader implications for managing genetic diversity in applied ecology and conservation contexts.