Varroa mites (Varroa destructor) and common apiary practices are examined in an article posted in Nature on 15 May 2017.
Natural swarming suppressed in domesticated bees and hives placed close together enable infected forager bees to spread the mites more quickly. In an 11-month study of 120 commercial colonies, Gloria DeGrandi-Hoffman at the US Department of Agriculture in Tucson, Arizona, and her colleagues found that, although hives had been treated with chemicals to control the mites, 55% of treated hives were still lost.
A model that simulated varroa populations and bee interactions showed that natural swarming, which is suppressed in domesticated bees, keeps varroa populations down. Swarming bees carry the mites away from hives, thus depleting their food supply, and the infected forager bees that raid other hives can quickly spread the mites when hives are placed close together.
Find the article at Gloria DeGrandi-Hoffman, Fabiana Ahumada, Henry Graham; Are Dispersal Mechanisms Changing the Host–Parasite Relationship and Increasing the Virulence of Varroa destructor (Mesostigmata: Varroidae) in Managed Honey Bee (Hymenoptera: Apidae) Colonies?. Environ Entomol 2017 nvx077. doi: 10.1093/ee/nvx077