The single largest culprit of colony losses is the parasitic mite Varroa destructor. Sometimes compared to a ‘dirty needle’, Varroa mites make a hole and feed on honey bees, vectoring viruses and bacteria as they feed. The mite was introduced from Asia, and the Western honey bee (Apis meliffera) is very vulnerable to this pest. Left unchecked, Varroa mites will kill most honey bee colonies.
Most beekeepers use chemical treatments to control Varroa mites and keep colonies alive. This is not ideal because chemical treatments are costly and laborious, have variable results, can leave residues, and may have sublethal effects on the bees themselves. Mites have also repeatedly developed resistance to chemical treatments.
Beekeepers desperately need more tools to control Varroa mites. Unfortunately, the market for these tools is quite small in comparison to other markets for new pest control research and development. Another, more sustainable approach to managing Varroa is through the development and use of mite-resistant bees. A variety of mechanisms such as grooming and brood removal are known. The best-characterized mechanism of resistance is the behavioral trait called Varroa sensitive hygiene (VSH). Bees that express VSH can detect reproducing Varroa in capped brood and remove the infested larvae, ensuring that Varroa do not successfully reproduce, keeping mite populations low.