The honeybee seems to be able to fight Varroa mites. It is not clear whether this behaviour is used specifically to combat Varroa mites or whether it is rather an accidental component of normal grooming behaviour. It is a fact that in some colonies Varroa mites with massive injuries are found on the screen bottom board. Since the screen bottom boards are protected from the bees by a grid and no other known inhabitants in the hives are eligible for the injuries, the injuries can only have been inflicted by bees outside the control board.
The effectiveness of the behaviour is not clarified. Every Varroa killed reduces the Varroa infestation of the bees. This applies to both the Varroa mites, eleminated by Grooming and the Varroa mites, eleminated by book scorpions. Each mite that is removed in spring, for example, means 60 mites less in autumn. Of course, it does not matter where in the beehive these mites are removed. It is only important that they are withdrawn from the circulation.
In the videos you can see that social grooming is usually triggered by cleaning and shaking movements of a bee that wants to free itself from pollen rests. Individual bees in the surrounding area then support the action.
But there are also real grooming bees. At least in some phases, they have made grooming their job. They check one bee after another and clean them.
Grooming appears more often at certain times of the day. At this time I often check the control board hourly. In this way I can be sure that the bees have injured the mites. The mites sometimes live on for a short time.
Due to the many video recordings, I think that the bees do not systematically remove mites. I think they stumble over them by accident during social grooming and then bite their legs off.
It is evident that acid-treated bees do not show notable grooming. To engage in grooming they need their highly sensitive sensors (as you see in the videos below). These sensors are probably damaged by acids.
Another reason for the lack of grooming in modern beekeeping could be the breeding of bees with properties such as increased honey production. This extreme attachment to individual tasks causes bees to neglect other important tasks.
The following IR video was made in a tree hive:
See more videos here.