Cell size and Varroa destructor mite infestations in susceptible and naturally-surviving honeybee (Apis mellifera) colonies

The ectoparasitic mite Varroa destructor is a key threat for European honeybee subspecies (Apis mellifera) globally. However, some A. mellifera populations are known to survive mite infestations by means of natural selection (naturally surviving), likely due to reduced mite reproductive success. The effect of small brood cell size on mite reproductive success has not been investigated in these surviving populations and we have little knowledge of its relationship with mite-surviving traits. Here we tested the impact of smaller worker brood cell size on mite reproductive success in susceptible and naturally surviving colonies in Norway. The data show that mite reproductive success was significantly reduced in smaller cells in susceptible colonies (higher rates of non-reproduction, delayed reproduction, and male absence), but not in the surviving colonies. The results support the claim that smaller cell size can have an impact on V. destructor reproductive success, but this seems not to work in tandem with mite-surviving mechanisms favored by natural selection.