Hi all

Two studies support the concept of inter-colony transmission of mites and pathogens being linked to colony density. One studies landscape density by genotyping drones at drone congregation areas, and the other looks at drifting in apiaries by genotyping bees in hives, looking for strays. 

High colony density (hives per square kilometer) correlated to increased pathogen load, as Bailey stated for years. One of the side effects of honey bee mortality is the lowering of colony density. Fewer colonies = healthier colonies.

Drifting among hives correlated to varroa levels. Interestingly, they did not show varroa infested bees to be more prone to drift, but rather, the varroa infested colonies allowed other bees entry. 

Evidently, the infested hives had more drifted bees than the uninfested ones. They state: "Varroa-infested colonies show an enhanced attraction of drifting workers."

Citations

Forfert, N., Natsopoulou, M. E., Frey, E., Rosenkranz, P., Paxton, R. J., & Moritz, R. F. (2015). Parasites and pathogens of the honeybee (Apis mellifera) and their influence on inter-colonial transmission. PloS one, 10(10), e0140337.

Forfert, N., Natsopoulou, M. E., Paxton, R. J., & Moritz, R. F. (2016). Viral prevalence increases with regional colony abundance in honey bee drones (Apis mellifera L). Infection, Genetics and Evolution.

PLB

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