Institut de Recherche sur la Biologie de l'Insecte, UMR 7261, CNRS, Université de Tours, Tours, France.
Robotics and Mechatronics, Technical Medical Centre, University of Twente, Enschede, The Netherlands.
J R Soc Interface. 2020 Jun;17(167):20190779. doi: 10.1098/rsif.2019.0779. Epub 2020 Jun 3.
The assumption that insect pectinate antennae, which are multi-scale organs spanning over four orders of magnitude in size among their different elements, are efficient at capturing sexual pheromones is commonly made but rarely thoroughly tested. Leakiness, i.e. the proportion of air that flows within the antenna and not around it, is a key parameter which depends on both the macro- and the microstructure of the antenna as well as on the flow velocity. The effectiveness of a structure to capture flow and hence molecules is a trade-off between promoting large leakiness in order to have a large portion of the flow going through it and a large effective surface area to capture as much from the flow as possible, therefore leading to reduced leakiness. The aim of this work is to measure leakiness in 3D-printed structures representing the higher order structure of an antenna, i.e. the flagellum and the rami, with varying densities of rami and under different flow conditions. The male antennae of the moth (Lepidoptera: Saturniidae) were used as templates. Particle image velocimetry in water and oil using 3D-printed scaled-up surrogates enabled us to measure leakiness over a wide range of equivalent air velocities, from 0.01 m s to 5 m s, corresponding to those experienced by the moth. We observed the presence of a separated vortex ring behind our surrogate structures at some velocities. Variations in the densities of rami enabled us to explore the role of the effective surface area, which we assume to permit equivalent changes in the number of sensilla that host the chemical sensors. Leakiness increased with flow velocity in a sigmoidal fashion and decreased with rami density. The flow capture ratio, i.e. the leakiness multiplied by the effective surface area divided by the total surface area, embodies the above trade-off. For each velocity, a specific structure leads to a maximum flow capture ratio. There is thus not a single pectinate architecture which is optimal at all flow velocities. By contrast, the natural design seems to be robustly functioning for the velocity range likely to be encountered in nature.
多尺度昆虫栉状触角跨越四个数量级，不同元素之间的大小差异很大，人们普遍认为这种触角在捕捉性信息素方面是高效的，但很少有研究对其进行全面测试。泄漏率，即空气在触角内流动而不是在其周围流动的比例，是一个关键参数，它取决于触角的宏观和微观结构以及流速。结构捕捉流动（进而捕捉分子）的有效性是一个权衡，既要促进大的泄漏率以确保大部分流动通过，又要保持较大的有效表面积以尽可能多地从流动中捕获分子，因此泄漏率会降低。本工作的目的是测量代表触角更高阶结构的 3D 打印结构（即鞭节和分支）的泄漏率，这些结构的分支密度不同，在不同的流动条件下进行测量。使用蛾类（鳞翅目：Saturniidae）的雄性触角作为模板。在水和油中使用 3D 打印的比例模型进行粒子图像测速，使我们能够在广泛的等效空气速度范围内（从 0.01 m s 到 5 m s）测量泄漏率，这些速度对应于蛾类所经历的速度。我们观察到在某些速度下，我们的替代结构后面存在分离的涡环。分支密度的变化使我们能够探索有效表面积的作用，我们假设这允许容纳化学传感器的感觉器官数量等效变化。泄漏率随流速呈类“S”型增加，并随分支密度降低而降低。流量捕获比，即泄漏率乘以有效表面积除以总表面积，体现了上述权衡。对于每个速度，特定的结构都会导致最大的流量捕获比。因此，并非存在一种在所有流速下都最优的栉状结构。相比之下，自然设计似乎在自然环境中可能遇到的速度范围内稳健运行。
