Through international cooperation, apiarists achieved a breakthrough in the fight against the Varroa mite: Coordinated by the Arista Bee Research Foundation they bred honey bees, which fight the mite within their hives by themselves. In those specially founded honey bee populations, the worker bees detect the Varroa in the brood cells and kill infested larvae. Doing so, they destroy the mite’s offspring, prevent further infestation and gradually reduce the number of mites within the hive. The Varroa mite is the main cause for the winter losses of honey bee populations and can destroy a whole hive if not controlled.
The sorting behavior against infested offspring shown by some honey bees is called Varroa Sensitive Hygiene, or VSH for short, and is a genetically inheritable trait. The United States Department of Agriculture recognized this as the crucial point for breeding and developed a method to identify VSH-carrying drones within North American hives. These were used to breed a test population. This was the foundation for the European breeding program, which apiarists launched in spring 2014 under the direction of the Arista Bee Research Foundation based in The Netherlands.
Within this setting, more than 100 honey bee colonies were founded: A quarter of the hives originated from the USDA-colonies, the remaining colonies consisted of European honey bees. In order to ensure the VSH-trait becomes active within a colony, the European honey bees and queens had to fulfill two criteria to be selected for the breeding: a low grade of Varroa-infestation within the bee hive and a distinctive general hygienic behavior of the bees. The breeding method ensured that the respective VSH-gene was passed on to the offspring: The bee queen only mated with one drone, a VSH carrier. Normally they mate with ten to fifteen different partners to increase genetic diversity.
The offspring-colonies were then deliberately infested with Varroa mites and left alone to deal with the pest. At the end of the past summer, the apiarists examined the number of adult mites and their offspring within the hives. These numbers indicated the level of VSH-behavior.
The results were very promising: More than twenty colonies showed a very high level of Varroa Sensitive Hygiene (75 percent). The next step in the breeding program will target selection in order to achieve 100 percent VSH in the breeding stock – this is an important step in combating Varroa destructor.
Read the press release of Arista Bee Research: Great step forward in breeding Varroa Resistant Honeybees.
Read more about the work of Arista Foundation in our article “Getting rid of the mites”.