WHY DO VARROA MITES INVADE WORKER BROOD CELLS OF THE HONEY-BEE DESPITE LOWER REPRODUCTIVE SUCCESS

Varroa jacobsoni reproduces both in drone and worker brood cells of ho ney bees, but in drone cells reproductive success is higher than in wo rker cells. A simple model using clonal population growth as a fitness measure has been developed to study the circumstances under which spe cialization on drone brood would be a better strategy than reproductio n in both types of cell. For European Apis mellifera, the model sugges ts that if mites have to wait less than 7 days on average before they can invade a drone cell, specialization on drone brood would be a bett er strategy. This is close to the estimated waiting time of 6 days. He nce, small differences in reproductive success in drone and worker cel ls and in the rate of mortality may determine whether specialization o n drone brood will be promoted or not. In European A. mellifera coloni es, Varroa mites invade both drone and worker cells, but specializatio n on drone brood cells seems to occur to some extent because drone cel ls are more frequently invaded than worker cells. In the parasite-host association of V. jacobsoni with African or Africanized A. mellifera or with A. cerana, the mites also invade both drone and worker cells, but the mites specialize on drone brood for reproduction since a large percentage of the mites in worker brood do not reproduce. Only in the parasite-host association of Euvarroa sinhai, a mite closely resembli ng V. jacobsoni, and A. florea is because these mites only specializat ion complete, invade drone brood.