The effects of macro- & micro-scale morphology on drag and odor capture around honey bee antennae*

Insects explore environments using chemoreceptors on their antennae. Antennae exhibit diverse morphologies at both the macro-scale (antennal lengths, diameters, and structure) and micro-scale (pore plates and hairs). Presently, we focus on understanding the effect of these morphologies on odor capture efficiency (ratio of odor reaching binding sites to supplied odor) and fluid drag forces for a model organism, the honey bee. We built numerical models of honey bee antennae in representative flows transporting a uniform odor field, resolving three-dimensional flow and odor fields around the antenna. We evaluated effects of Reynolds number (a function of wind speed and antennal diameter) and pore packing density (ratio of pore plate diameter to distance between pores) on capture efficiencies. Increasing Reynolds number increases viscous stresses (predominant contribution to drag) and diminishes the relative strength of diffusive fluxes to the antennal surface (primary mechanism of capture efficiency). Increasing pore packing density does not change viscous stresses but allows more odor to reach binding sites (increasing capture efficiency) asymptotically, driven by competition between adjacent pores. This suggests an optimal spatial configuration of odor binding sites on a given antennal surface area within a uniform odor field. Future efforts will explore unsteadiness in the flow and odor fields and additional macro- and micro-scale effects on drag and odor capture.