Meeting Abstract
While the pectinate antennae of silk moths and other insect groups are considered as the paragon of sensitivity to sexual pheromones since centuries, we still lack a mechanistic understanding of odor capture by such structures. 3D printing cannot currently fabricate multiscale structures spanning the antennal four orders of magnitude. We therefore focus on the functional, two-scales sub-structure of an antenna of Samia cynthia (Lepidoptera, Saturniidae): a brush of sensory filliform sensilla attached to one rami, the supporting tubular structure. A semi-analytical model to compute mass transfer, originally developed for heat transfer in pipes, is adapted to the specific geometry of longitudinal sensilla facing the flow. Particle Image velocimetry (PIV) is used with scaled-up physical models for estimating the leakiness of the structure, i.e. the proportion of flow passing through the structure rather than around. The combination of these experimental and modeling approaches delivers the capture efficiency over a biologically relevant range of air speed. We found that two distinct processes are setting pheromone capture efficiency. At low Re numbers, leakiness at the higher organizational scale, i.e. the entire substructure, determines the efficiency of odor capture. At higher Re numbers, advection at the lower organizational scale of a single sensillum is determining efficiency. We study how this trade-off results into capture efficiency of the entire sub-structure and observe that the multiscale architecture of the pectinate antenna of insects is highly adapted for odor capture over a large range of flow speeds. We end by discussing the embedding of this sub-structure in an entire antenna, using cylinders as proxy for the sub-structures. Their diameter is determined such that the cylinders have the same drag as the sub-structures.
