Influence of cell type and mandibular dentition on the ability of captive honey bee workers and drones (Apis cerana indica Fabr. and Apis mellifera L.) to uncap brood cells: biological implications for parasitic mites (Varroa spp.)

Experiments to study the ability of adults (workers and drones) of the eastern honey bee, Apis cerana indica Fabr., and the western honey bee, Apis mellifera L., to uncap brood cells were undertaken in Bangalore, India. Using halved gelatin capsules, individual adults were confined opposite the intact cap that sealed vacant, isolated brood cells. From inside the cell, workers and drones of both species penetrated the drone-cell cap of A. mellifera with regularity. When placed outside the cell, workers of both species were successful in perforating the same cap. Similarly, A. c. indica workers easily perforated the cap of A. c. indica worker cells from inside. However, significant caste-specific differences in success at perforating the cap of A. c. indica drone cells were observed; whereas drones did so regularly, A. c. indica workers usually perished when so challenged. When held facing the cap while inside or outside the drone cell, none or only 10% of workers, respectively, managed to chew a hole in it. Even when two workers faced the same drone-cell cap, one from each side, only 20% of caps were perforated. These results are consistent with the hypothesis that the tough apex of the drone cocoon of A. cerana is typically impervious to uncapping from outside, and hence has provided an opportunity for the uninterrupted reproduction of invading parasitic mites (Varroa spp.). The mandibles of drones of both species possess a diminutive apical tooth along the distal margins that is absent in workers. The lack of mandibular teeth in workers may explain the disparity in ability to penetrate the tough cocoon of A. c. indica drones. The mandibles of both castes suffer wear.