Evaluation of 10-Year Selection for Virus Resistance in a Mass Breeding Program

Viral infections pose a major threat to honey bee health. While viruses are typically controlled indirectly through efforts of attaining Varroa resistance, the heritable trait suppressed in ovo virus infection (SOV) provides a direct avenue for selecting virus resistance. This study evaluated the potential of this trait using data collected within an established mass breeding selection program. Drone egg samples collected from honey bee colonies in Flanders (2015-2024) were screened for four viruses to determine the queen's SOV status. Queens are classified as SOV-positive if no viral particles are detected in their sample, and as SOV-negative if genomic material from at least one of these viruses is present. The proportion of SOV-positive queens significantly increased over time, regardless of maternal background, and targeted breeding from SOV-positive maternal lines enhanced the likelihood of producing SOV-positive offspring. Simultaneously, the prevalence and viral load values of several viruses decreased over time. These findings demonstrate that selective breeding for SOV-positivity can improve virus resistance in managed honey bee populations. There is even a potential to raise the SOV trait occurrence by incorporating targeted mating within selection programs. Therefore, future research should focus on the combined selection for SOV through targeted breeding and mating, alongside Varroa-resistant traits.