The ectoparasitic mite, Varroa destructor, together with its associated honeybee viruses that it vectors, in particular Deformed wing virus (DWV), remains unarguably the leading cause of honeybee colony mortality world-wide and the main cause of the near complete eradication of wild honeybees in Europe and North America. In almost all parts of the world, survival of managed honeybee colonies is completely dependent on control treatments applied by beekeepers, to reduce mite levels in the colony and thus avoid the establishment of a virus epidemic. Without treatment, colonies commonly die within 1-2 years. These treatments are chemical based and therefore are harmful to bees, leave residues in hive products, and are increasingly ineffective as the mite develops resistance.
The natural host of varroa mites, the Asian hive bee (Apis cerana), rarely experiences damage by the mite since a stable host-parasite relationship has been established over a long evolutionary scale. Such a relationship is clearly missing with the new host, the Western honeybee (Apis mellifera). In the 1970s and 1980s, the mite made a host jump to the Western honeybee and has since then successfully spread throughout the world, only leaving Australia and a few isolated locations mite-free. At present, treatments are necessary for honeybee colony survival, but with the unwanted side-effect that they also remove the selective pressure necessary to establish a stable host-parasite relationship. Hence, the current rationale for beekeeping to treat and remove the parasite both hampers the evolution of resistance and obstructs fundamental research on natural selection host‒parasite coevolution in this new host‒parasite system, which is now only possible in a few rare honeybee populations surviving long-term without varroa control. These honeybee populations offer exclusive insight into the natural adaptive capacity of honeybees, yet little is understood about their mechanisms of resistance or tolerance.
The goal of BEE NATURAL is to comprehensively describe resistant and tolerant phenotypes in rare and valuable naturally adapted varroa-resistant honeybee population existing in Gotland, Sweden, Avignon France and Oslo, Norway, in order to deeper our fundamental understanding of host-parasite interaction and to identify candidate genes for marker assisted selection. Genomic regions or target genes associated with resistant and tolerant traits will be identified through the efforts of the BEE NATURAL project, using Next Generation Sequencing (NGS) technologies such as RNA-seq and whole genome sequencing (WGS), providing valuable information that can be applied towards developing marker-assisted selection: a powerful new approach for disease resistant breeding that can facilitate major advances in breeding efforts and genetic stock improvement.This will be achieved through a set of complementary approaches presented in four work plans (WP).
WP1 – Reveal the phenotypic and genetic mechanisms of naturally adapted mite resistance by identifying host chemical signals that inhibit the reproduction of mites and identify host genomic regions or causative genes associated with this adaptation through a transcriptomic analysis.
WP2 – Characterise the molecular adaptations of naturally adapted tolerance and resistance to virus infections by analysing the transcriptome of both the host and viruses in laboratory virus inoculation time course experiments.
WP3 – Identify potential virus adaptations over 20 years of natural selection by analysing historical host samples from the long-term surviving, mite-resistant honeybee population on Gotland, Sweden.
WP4 – Identify genomic regions and causative genes associated with disease resistance to develop marker-assisted selection by performing a Genome-wide association study using whole genome sequencing (WGS) of honeybee DNA from samples provided by a network of volunteer beekeepers recruited to facilitate large-scale phenotyping and sampling in different geographical environments.
The knowledge gained from this project can be used to improve honeybee health through disease resistance/tolerance breeding and remove the dependency on chemical treatments currently necessarily used in beekeeping today to reduce virus epidemics. This will lead to improved sustainability of pollination services provided by honeybees for both crop production and wild plant biodiversity. Therefore, the project is in-line with the European sustainable development goals for zero hunger, good health and well-being and life on land.
