From my swarm collecting activities it was apparent that wild bee colonies had not suffered, also one of my own colonies survived in a home made hive, which developed into the 'Hollow Tree' experiment. To investigate this situation further I wrote to local newspapers in England and Wales requesting information regarding wild bee colonies and received over 100 reports. This led me to believe that the breed of bee was unimportant and perhaps the habitat and environment were deciding factors.
Bees naturally groom themselves free of the varroa mite.
Periods where there is a reduction of brood resulting in excessive numbers of mites. If a colony of 10,000 bees in a nest site of 1 cubic foot breeds 1000 varroa per year, a colony of 20,000 bees with a nest site of 2 cubic feet would breed 4000 varroa per year. Similarly a colony of 30,000 bees in a nest site of 3 cubic feet would breed 9000 varroa per year. This is due to large colonies breeding more drones allowing a more rapid varroa build up. Where the depth of comb increases in proportion with the hive capacity, and the distances travelled by the mite to reach drone brood increases accordingly, the bees have a proportional increase in grooming opportunity, and this compensation is sufficient to ensure the survival of larger colonies.