Department of Zoology, University of Cambridge, , Downing Street, Cambridge CB2 3EJ, UK.
J R Soc Interface. 2011 Jul 6;8(60):952-60. doi: 10.1098/rsif.2010.0575. Epub 2011 Jan 5.
Insect adhesion is mediated by thin fluid films secreted into the contact zone. As the amount of fluid affects adhesive forces, a control of secretion appears probable. Here, we quantify for the first time the rate of fluid secretion in adhesive pads of cockroaches and stick insects. The volume of footprints deposited during consecutive press-downs decreased exponentially and approached a non-zero steady state, demonstrating the presence of a storage volume. We estimated its size and the influx rate into it from a simple compartmental model. Influx was independent of step frequency. Fluid-depleted pads recovered maximal footprint volumes within 15 min. Pads in stationary contact accumulated fluid along the perimeter of the contact zone. The initial fluid build-up slowed down, suggesting that flow is driven by negative Laplace pressure. Freely climbing stick insects left hardly any traceable footprints, suggesting that they save secretion by minimizing contact area or by recovering fluid during detachment. However, even the highest fluid production rates observed incur only small biosynthesis costs, representing less than 1 per cent of the resting metabolic rate. Our results show that fluid secretion in insect wet adhesive systems relies on simple physical principles, allowing for passive control of fluid volume within the contact zone.
昆虫的附着是通过分泌到接触区域的薄液膜来介导的。由于液体的量会影响附着的力，因此分泌的控制似乎是可能的。在这里，我们首次定量了蟑螂和竹节虫的附肢垫中液体的分泌速率。连续按压过程中留下的足迹体积呈指数衰减并接近非零的稳定状态，这表明存在存储体积。我们从一个简单的隔室模型估计了它的大小和流入量。流入量与步频无关。排空的附肢垫在 15 分钟内恢复了最大的足迹体积。处于静止接触状态的附肢垫会在接触区域的周边积聚液体。初始的液体积累速度会减慢，这表明流动是由负的拉普拉斯压力驱动的。自由攀爬的竹节虫几乎没有留下可追踪的足迹，这表明它们通过最小化接触面积或在脱离时回收液体来节省分泌。然而，即使观察到的最高分泌速率也只产生很小的生物合成成本，不到静息代谢率的 1%。我们的结果表明，昆虫湿粘性系统中的液体分泌依赖于简单的物理原理，允许在接触区域内被动控制液体量。
