Stanislav N. Gorb
Department of Functional Morphology and Biomechanics, Zoological Institute at the University of Kiel, Kiel, Germany, sgorb@zoologie.uni-kiel.de


Most of the one million insect species described so far are associated with plants. Such insects should be able to attach successfully to plant surfaces. Dealing with attachment, we have to consider a contact problem, in which two bodies are involved. Both these parts may have various geometries, mechanical and chemical properties. Moreover, insects produce and deliver a secretory fluid into a contact zone, whereas many plant substrates bear specialised surface coverage. This paper summarises our previous structural and experimental studies on insect attachment and the effect of plant substrates on it.
Contacting surfaces in many insect attachment devices are subdivided into patterns of micro- or nanostructures with a high aspect ratio. This paper provides some explanations of the adhesion enhancement effect in such systems. The attachment abilities of insects depend on the roughness and mechanical stability of the substrate features. Wax bloom found on the surface in many plants is an adaptation against insect attachment. However, the mechanism of adhesion reduction might be different depending on the plant species.
Wax crystals may cause microroughness, which considerably decreases the real contact area between the substrate and setal tips of insect adhesive pads. Wax crystals are easily breakable structures that contaminate insect pads. Insect pad secretion may presumably dissolve wax crystals; and this would result in the appearance of a thick layer of fluid, making the substrate slippery. Finally, structured wax coverage may absorb the fluid from the pad surface.
This paper reports on experimental evidences for some of the four previously proposed hypotheses of anti-adhesion mechanism of plant surfaces covered with epicuticular wax crystals.