Pathogens and parasites may facilitate their transmission by manipulating host behavior.
Honeybee pathogens and pests need to be transferred from one colony to another if they
are to maintain themselves in a host population. Inter-colony transmission occurs typically
through honeybee workers not returning to their home colony but entering a foreign colony
(“drifting”). Pathogens might enhance drifting to enhance transmission to new colonies.We
here report on the effects infection by ten honeybee viruses and Nosema spp., and Varroa
mite infestation on honeybee drifting. Genotyping of workers collected from colonies
allowed us to identify genuine drifted workers as well as source colonies sending out drifters
in addition to sink colonies accepting them. We then used network analysis to determine
patterns of drifting. Distance between colonies in the apiary was the major factor explaining
79% of drifting. None of the tested viruses or Nosema spp. were associated with the frequency
of drifting. Only colony infestation with Varroa was associated with significantly
enhanced drifting. More specifically, colonies with high Varroa infestation had a significantly
enhanced acceptance of drifters, although they did not send out more drifting workers.
Since Varroa-infested colonies show an enhanced attraction of drifting workers, and not
only those infected with Varroa and its associated pathogens, infestation by Varroa may
also facilitate the uptake of other pests and parasites.