Choice in Varroa jacobsoni Oud. between honey bee drone or workerbrood cells for reproduction

Abstract

The parasitic mite Varroa jacobsoni Oud. reproduces in brood cells of Apis mellifera. Reproductive success (RS) is higher in drone cells than in worker cells. Although the mites are capable of discriminating between the cell types, the less favorable worker cells are also parasitized. A model is proposed that explains the acceptance of worker cells by density-dependent reduction of RS if more than one Varroa enters a brood cell. Calculations were based on simulated distributions of Varroa on brood combs. Assuming that mites infesting brood cells would always accept drone cells, but would only sometimes accept worker cells, the optimal rate of worker cell acceptance was determined. While at low infestation levels and high fractions of drone cells selection would favor the parasitization of drone brood cells only, mixed strategies would result if infestation is high and/or drone cells are scarce. The model calculations were applied to data on brood cell availability in European colonies during one annual season, including seasonal shifts of selection intensity and direction. On average, accepting worker cells would be advantageous when there are approximately 300 or more mites within a colony, which would be within the natural range of worker cell acceptance at densities of approximately 1000 Varroa mites per colony.