Given the relatively large number of colonies that can be produced and monitored (only a few samples of bee washing are needed for phoretic mite level assessments per year), a both strong and still broad selection can be made based on high resistance as well as good honey collectors, gentleness and with low swarming tendency. We have experienced in our Hawaii program and now also in our EU program that using this step is actually very powerful. They just represent the genes of their mother, they have no direct biological father! Indeed, the best colonies can then deliver well selected drones, because drones are coming from unfertilized eggs. So from these land mated station queens/colonies we do not produce further queen offspring (they could have low resistant genes from the not-pure drones), but we can definitely use the (pure!) drones for our selection program. However, the queens mated on these stations can be used in production colonies in which they will be assessed for our selection program. This means that the mated queens will not produce 100% “pure” colonies. As this is a land mating station, we assume that a certain, hopefully low, percentage of the drones comes from colonies from other beekeepers. On such a mating station, ideally somewhat isolated from other apiaries, we place colonies that will deliver drones carrying varroa resistance genes.
Therefor we are more and more making use of land mating stations. The amount of work involved makes it less suitable to do large scale production of mated queens in the broader beekeeper community. The disadvantage of the MDI colonies is that it requires special insemination skills. We can use a large variety of different drone lines compared to a mating station that usually has only one or two different lines per year. The advantage of using Multi Drone Inseminations is that we can keep the biodiversity as high as possible. This is a method that can be used at large number of colonies without too much labor involved. We also monitor the varroa population growth in these colonies by taking samples (300 bees per colony) to determine the number of mites on these bees (instead of in the brood), called the “phoretic” mite count. These colonies can be kept much longer (2 to 4 years) and can be tested for the described traits. As we are now later in the selection process, most of the drones will carry the resistant genes. For this reason, we inseminate a larger number of queens with the semen of at least 10 drones.
As they are small, the colonies cannot be easily selected for the other important traits as honey production and low tendency to swarm. SDI colonies can only be small and are relatively short lived (because of the limited amount of sperm stored by the queen). The SDI colonies are very well suited starting from a population with limited VSH genes. Multi Drone Insemination (MDI) at Beers, NL
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