Abstract. Although the honeybee (Apis mellifera L.) is a well-studied species, the functional morphology of its pretarsal structure is still not fully understood. We conducted an in-depth scanning electron microscopic study on these complex structures to contribute to the comprehension of the pretarsal structure-function relationships. As a result, this study has provided valuable information on the ultrastructure of the pretarsus, and in particular on the spines of the unguitractor surface and the small spines and scalloped surface of the claws with longitudinal grooves. Special attention was given to the adhesive contact zone of the arolium with its highly specialized fibrillary cuticle texture. Remarkably, several of the observed pretarsal structures, such as the pyramidal structures on the unguitractor and the thin hairs on both the grooved claws, and the hairs of the manubrium have not been previously described. All observed structures in this study were characterized with respect to their possible physiological and mechanical roles.

Varroa destructor mites and the viruses it vectors are two major factors leading to high losses of honey bees (Apis mellifera) colonies worldwide. However, honey bees in some African countries show resilience to varroa infestation and/or virus infections, although little is known about the mechanisms underlying this resilience. In this study, we investigated the expression profiles of some key molecular markers involved in olfactory sensing and RNA interference, as these processes may contribute to the bees’ resilience to varroa infestation and virus infection, respectively. We found significantly higher gene expression of the odorant binding protein, OBP14, in the antennae of Ethiopian bees compared to Belgian bees. This result suggests the potential of OBP14 as a molecular marker of resilience to mite infestation. Scanning electron microscopy showed no significant differences in the antennal sensilla occurrence and distribution, suggesting that resilience arises from molecular processes rather than morphological adaptations. In addition, seven RNAi genes were upregulated in the Ethiopian honey bees and three of them—Dicer-Drosha, Argonaute 2, and TRBP2—were positively correlated with the viral load. We can conclude that the antiviral immune response was triggered when bees were experiencing severe viral infection and that this might contribute to the bees’ resilience to viruses.